Columbia University Lectures

 THE DOCTRINE OF EVOLUTION

 THE HEWITT LECTURES

 1906-1907

 COLUMBIA UNIVERSITY PRESS SALES AGENTS

 NEW YORK: LEMCKE & BUECHNER 30-32 WEST 27TH STREET

 LONDON: HUMPHREY MILFORD AMEN CORNER, E. C. 

 _COLUMBIA UNIVERSITY LECTURES_

 THE DOCTRINE OF EVOLUTION

 ITS BASIS AND ITS SCOPE

 BY

 HENRY EDWARD CRAMPTON, PH. D. 

 PROFESSOR OF ZOÖLOGY, COLUMBIA UNIVERSITY

 New York

 COLUMBIA UNIVERSITY PRESS

 1916

 _All rights reserved_

 COPYRIGHT, 1911, By THE COLUMBIA UNIVERSITY PRESS

 Set up and electrotyped. Published June, 1911. Reprinted December, 1912; September, 1916. 

 Norwood Press J. S. Cushing Co. --Berwick & Smith Co. Norwood, Mass. , U. S. A. 

PREFACE

The present volume consists of a series of eight addresses delivered asthe Hewitt Lectures of Columbia University at Cooper Union in New YorkCity during the months of February and March, 1907. The purpose of theselectures was to describe in concise outline the Doctrine of Evolution, itsbasis in the facts of natural history, and its wide and universal scope. They fall naturally into two groups. Those of the first part deal withmatters of definition, with the essential characteristics of livingthings, and, at greater length, with the evidences of organic evolution. The lectures of the second group take up the various aspects of humanevolution as a special instance of the general organic process. In thislatter part of the series, the subject of physical evolution is firstconsidered, and this is followed by an analysis of human mental evolution;the chapter on social evolution extends the fundamental principles to afield which is not usually considered by biologists, and its purpose is todemonstrate the efficiency of the genetic method in this department as inall others; finally, the principles are extended to what is called "thehigher human life, " the realm, namely, of ethical, religious, andtheological ideas and ideals. 

Naturally, so broad a survey of knowledge could not include any extensivearray of specific details in any one of its divisions; it was possibleonly to set forth some of the more striking and significant facts whichwould demonstrate the nature and meaning of that department from whichthey were selected. The illustrations were usually made concrete throughthe use of photographs, which must naturally be lacking in the presentvolume. In preparing the addresses for publication, the verbal form ofeach evening's discussion has been somewhat changed, but there has been nosubstantial alteration of the subjects actually discussed. 

The choice of materials and the mode of their presentations weredetermined by the general purpose of the whole course. The audiences weremade up almost exclusively of mature persons of cultivated minds, but whowere on the whole quite unfamiliar with the technical facts of naturalhistory. It was necessary to disregard most of the problematical elementsof the doctrine so as to bring out only the basic and thoroughlysubstantiated principles of evolution. The course was, in a word, a simplemessage to the unscientific; and while it may seem at first that thediscussions of the latter chapters lead to somewhat insecure positions, itshould be remembered that their purpose was to bring forward the proofthat even the so-called higher elements of human life are subject toclassification and analysis, like the facts of the lower organic world. 

It may seem that the biologist is straying beyond his subject when heundertakes to extend the principles of organic evolution to thosepossessions of mankind that seem to be unique. The task was undertaken inthe Hewitt Lectures because the writer holds the deeply groundedconviction that evolution has been continuous throughout, and that thestudy of lower organic forms where laws reveal themselves in morefundamental simplicity must lead the investigator to employ and applythose laws in the study of the highest natural phenomena that can befound. Another motive was equally strong. Too frequently men of scienceare accused of restricting the application of their results to their ownparticular fields of inquiry. As individuals they use their knowledge forthe development of world conceptions, which they are usually reluctant todisplay before the world. It is because I believe that the accusation isoften only too well merited that I have endeavored to show as well ascircumstances permit how universal is the scope of the doctrine based uponthe facts of biology, and how supreme are its practical and dynamicvalues. 

It remains only to state that the present volume contains nothing new, either in fact or in principle; the particular form and mode of presentingthe evolutionary history of nature may be considered as the author'spersonal contribution to the subject. Nothing has been stated that has notthe sanction of high authority as well as of the writer's own conviction;but it will be clear that the believers in the truth of the analysis asmade in the later chapters may become progressively fewer, as the variousaspects of human life and of human nature are severally treated. Nevertheless, I believe that this volume presents a consistent reasonableview that will not be essentially different from the conceptions of allmen of science who believe in evolution. 

CONTENTS

CHAPTER PAGE

 I. EVOLUTION. THE LIVING ORGANISM AND ITS NATURAL HISTORY 1

 II. THE STRUCTURE AND DEVELOPMENT OF ANIMALS AS EVIDENCE OF EVOLUTION 35

 III. THE EVIDENCE OF FOSSIL REMAINS 73

 IV. EVOLUTION AS A NATURAL PROCESS 106

 V. THE PHYSICAL EVOLUTION OF THE HUMAN SPECIES AND OF HUMAN RACES 150

 VI. THE MENTAL EVOLUTION OF MAN 197

 VII. SOCIAL EVOLUTION AS A BIOLOGICAL PROCESS 241

VIII. EVOLUTION AND THE HIGHER HUMAN LIFE 278

INDEX 313

I

EVOLUTION. THE LIVING ORGANISM AND ITS NATURAL HISTORY

The Doctrine of Evolution is a body of principles and facts concerning thepresent condition and past history of the living and lifeless things thatmake up the universe. It teaches that natural processes have gone on inthe earlier ages of the world as they do to-day, and that natural forceshave ordered the production of all things about which we know. 

It is difficult to find the right words with which to begin the discussionof so vast a subject. As a general statement the doctrine is perhaps thesimplest formula of natural science, although the facts and processeswhich it summarizes are the most complex that the human intellect cancontemplate. Nothing in natural history seems to be surer than evolution, and yet the final solution of evolutionary problems defies the most subtleskill of the trained analyst of nature's order. No single human mind cancontain all the facts of a single small department of natural science, norcan one mind comprehend fully the relations of all the various departmentsof knowledge, but nevertheless evolution seems to describe the history ofall facts and their relations throughout the entire field of knowledge. Were it possible for a man to live a hundred years, he could only beginthe exploration of the vast domains of science, and were his lifeprolonged indefinitely, his task would remain forever unaccomplished, forprogress in any direction would bring him inevitably to newer and stillunexplored regions of thought. 

Therefore it would seem that we are attempting an impossible task when weundertake in the brief time before us the study of this universalprinciple and its fundamental concepts and applications. But are thedifficulties insuperable? Truly our efforts would be foredoomed to failurewere it not that the materials of knowledge are grouped in classes anddepartments which may be illustrated by a few representative data. And itis also true that every one has thought more or less widely and deeplyabout human nature, about the living world to which we belong, and aboutthe circumstances that control our own lives and those of our fellowcreatures. Many times we withdraw from the world of strenuous endeavor tothink about the "meaning of things, " and upon the "why" and "wherefore" ofexistence itself. Every one possesses already a fund of information thatcan be directly utilized during the coming discussions; for if evolutionis true as a universal principle, then it is as natural and everyday amatter as nature and existence themselves, and its materials must includethe facts of daily life and observation. 

Although the doctrine of evolution was stated in very nearly its presentform more than a century ago, much misunderstanding still exists as to itsexact meaning and nature and value; and it is one of the primary objectsof these discussions to do away with certain current errors of judgmentabout it. It is often supposed to be a remote and recondite subject, intelligible only to the technical expert in knowledge, and apart from theeveryday world of life. It is more often conceived as a metaphysical andphilosophical system, something antagonistic to the deep-rooted religiousinstincts and the theological beliefs of mankind. Truly all the facts ofknowledge are the materials of science, but science is not metaphysics orphilosophy or belief, even though the student who employs scientificmethod is inevitably brought to consider problems belonging to thesediverse fields of thought. A study of nervous mechanism and organicstructure leads to the philosophical problem of the freedom of the will;questions as to the evolution of mind and the way mind and matter arerelated force the investigator to consider the problem of immortality. Butthese and similar subjects in the field of extra-science are beyond itssphere for the very good reason that scientific method, which we are todefine shortly, cannot be employed for their solution. Evolution is ascience; it is a description of nature's order, and its materials arefacts only. In method and content it is the very science of sciences, describing all and holding true throughout each one. 

The overwhelming importance of knowing about natural laws and universalprinciples is not often realized. What have we to do with evolution andscience? Are we not too busy with the ordering of our immediate affairs toconcern ourselves with such remote matters? So it may appear to many, whothink that the study of life and its origin, and of the vital facts aboutplants and animals may be interesting and may possess a certainintellectual value, but nothing more. The investigation of man and of menand of human life is regarded by the majority as a mere cultural exercisewhich has no further result than the recording of present facts and pasthistories; but it is far otherwise. Science and evolution must deal withmere details about the world at large, and with human ideals and with lifeand conduct; and while their purpose is to describe how nature works nowand how it has progressed in the past, their fullest value is realized inthe sure guidance they provide for our lives. This cannot be clear untilwe reach the later portions of our subject, but even at the outset we mustrecognize that knowledge of the great rules of nature's game, in which wemust play our parts, is the most valuable intellectual possession we canobtain. If man and his place in nature, his mind and social obligations, become intelligible, if right and wrong, good and evil, and duty come tohave more definite and assignable values through an understanding of theresults of science, then life may be fuller and richer, better and moreeffective, in direct proportion to this understanding of the harmony ofthe universe. 

And so we must approach the study of the several divisions of our subjectin this frame of mind. We must meet many difficulties, of which the chiefone is perhaps our own human nature. For we as men are involved, and it ishard indeed to take an impersonal point of view, --to put aside allthoughts of the consequences to us of evolution, if it is true. Yetemotion and purely human interest are disturbing elements in intellectualdevelopment which hamper the efforts of reason to form assuredconceptions. We must disregard for the time those insistent questions asto higher human nature, even though we must inevitably consider them atthe last. Indeed, all the human problems must be put aside until we haveprepared the way for their study by learning what evolution means, what aliving organism is, and how sure is the evidence of organictransformation. When we know what nature is like and what naturalprocesses are, then we may take up the questions of supreme and deepconcern about our own human lives. 

 * * * * *

Human curiosity has ever demanded answers to questions about the world andits make-up. The primitive savage was concerned primarily with theeveryday work of seeking food and building huts and carrying on warfare, and yet even he found time to classify the objects of his world and toconstruct some theory about the powers that made them. His attainments mayseem crude and childish to-day, but they were the beginnings of classifiedknowledge, which advanced or stood still as men found more or less timefor observation and thought. Freed from the strife of primeval andmedieval life, more and more observers and thinkers have enlarged theboundaries and developed the territory of the known. The history of humanthought itself demonstrates an evolution which began with the savages'vague interpretation of the "what" and the "why" of the universe, andculminates in the science of to-day. 

What, now, is a science? To many people the word denotes something coldand unfeeling and rigid, or something that is somehow apart from dailylife and antagonistic to freedom of thought. But this is far from beingtrue. Karl Pearson defines science as _organized knowledge_, and Huxleycalls it _organized common sense_. These definitions mean the same thing. They mean that in order to know anything that deserves confidence, inorder to obtain a real result, it is necessary in the first place toestablish the reality of facts and to discriminate between the true, thenot so sure, the merely possible, and the false. Having accurate andverified data, scientific method then proceeds to classify them, and thisis the _organizing_ of knowledge. The final process involves a summary ofthe facts and their relations by some simple expression or formula. A goodillustration of a scientific principle is the natural law of gravitation. It states simply that two bodies of matter attract one another directly inproportion to their mass, and inversely in proportion to the square of thedistance between them. In this concise rule are described the relationswhich have been actually determined for masses of varying sizes and atdifferent distances apart, --for snowflakes falling to the earth, for theavalanche on the mountain slope, and for the planets of the solar system, moving in celestial coördination. 

Such a principle as the law of gravitation, like evolution, is true if thebasic facts are true, if they are reasonably related, and if theconclusion is drawn reasonably from them. It is true for all persons whopossess normal minds, and this is why Huxley speaks of science as "commonsense, "--that is, something which is a reasonable and sensible part of themental make-up of thinking persons that they can hold in common. The formand method of science are fully set forth by these definitions, and thepurpose also is clearly revealed. For the results of investigation are notmerely formulæ which summarize experience as so much "conceptualshorthand, " as Karl Pearson puts it, but they must serve also to describewhat will probably be the orderly workings of nature as future experienceunfolds. Human endeavor based upon a knowledge of scientific principlesmust be far more reliable than where it is guided by mere intuition orunreasoned belief, which may or may not harmonize with the everyday worldlaws. Just as the law of gravitation based upon past experience providesthe bridge builder and the architect with a statement of conditions to bemet, so we shall find that the principles of evolution demonstrate thebest means of meeting the circumstances of life. 

Evolution has developed, like all sciences, as the method we havedescribed has been employed. Alchemy became chemistry when the so-calledfacts of the medievalist were scrutinized and the false were discarded. Astrology was reorganized into astronomy when real facts about the planetsand stars were separated from the belief that human lives were influencedby the heavenly bodies. Likewise the science of life has undergonefar-reaching changes in coming down to its present form. All the principlesof these sciences are complete only in so far as they sum up in the bestway the whole range of facts that they describe. They cannot be final untilall that can be known is known, --until the end of all knowledge and oftime. It is because he feels so sure of what has been gained that the manof science seems to the unscientific to claim finality for his results. Hehimself is the first to point out that dogmatism is unjustified when itsassertions are not so thoroughly grounded in reasonable fact as to rendertheir contrary unthinkable. He seeks only for truth, realizing that newdiscoveries must oblige him to amend his statement of the laws of naturewith every decade. But the great bulk of knowledge concerning life andliving forms is so sure that science asserts, with a decision oftenmistaken for dogmatism, that evolution is a real natural process. 

 * * * * *

The conception of evolution in its turn now demands a definitedescription. How are we to regard the material things of the earth? Arethey permanent and unchanged since the beginning of time, unchanging andunchangeable at the present? We do not need Herbert Spencer's elaboratedemonstration that this is unthinkable, for we all know from dailyexperience that things do change and that nothing is immutable. Did thingshave a finite beginning, and have they been "made" by some _supernatural_force or forces, personified or impersonal, different from those agencieswhich we may see in operation at the present time? So says the doctrine ofspecial creation. Finally, we may ask if things have changed as they nowchange under the influence of what we call the natural laws of thepresent, and which if they operated in the past would bring the world andall that is therein to be just what we find now. This is the teaching ofthe doctrine of evolution. It is a simple brief statement of naturalorder. And because it has followed the method of common sense, scienceasserts that changes have taken place, that they are now taking place, andfurthermore that it is unnecessary to appeal to other than everydayprocesses for an explanation of the present order of things. 

Wherever we look we see evidence of nature's change; every rain that fallswashes the earth from the hills and mountains into the valleys and intothe streams to be transported somewhere else; every wind that blowsproduces its small or greater effect upon the face of the earth; thebeating of the ocean's waves upon the shore, the sweep of the greattides, --these, too, have their transforming power. The geologists tell usthat such natural forces have remodeled and recast the various areas ofthe earth and that they account for the present structure of its surface. These men of science and the astronomers and the physicists tell us thatin some early age the world was not a solid globe, with continents andoceans on its surface, as now; that it was so very hot as to be semi-fluidor semi-solid in consistency. They tell us that before this time it wasstill more fluid, and even a mass of fiery vapors. The earth's molten bulkwas part of a mass which was still more vast, and which included portionswhich have since condensed to form the other bodies of the solarsystem, --Mars and Jupiter and Venus and the rest, --while the sun remains asthe still fiery central core of the former nebulous materials, which haveundergone a natural history of change to become the solar system. Thewhole sweep of events included in this long history is called cosmicevolution; it is the greater and more inclusive process comprising all thetransformations which can be observed now and which have occurred in thepast. 

At a certain time in the earth's history, after the hard outer crust hadbeen formed, it became possible for living materials to arise and forsimple primitive creatures to exist. Thus began the process of organicevolution--_the natural history of living things_--with which we areconcerned in this and later addresses. Organic evolution is thus a part ofthe greater cosmic process. As such it does not deal with the origin oflife, but it begins with life, and concerns itself with the evolution ofliving things. And while the investigator is inevitably brought toconsider the fundamental question as to the way the first life began, as astudent of organic forms he takes life for granted and studies only therelationships and characteristics of animals and plants, and theirorigins. 

But even as a preliminary definition, the statement that organic evolutionmeans _natural change_ does not satisfy us. We need a fuller statement ofwhat it is and what it involves, and I think that it would be best tobegin, not with the human being in which we are so directly interested, nor even with one of the lower creatures, but with something, as ananalogy, which will make it possible for us to understand immediately whatis meant by the evolution of a man, or of a horse, or of an oak tree. Thefirst steam locomotive that we know about, like that of Stephenson, was acrude mechanism with a primitive boiler and steam-chest and drive-wheels, and as a whole it had but a low degree of efficiency measured by ourmodern standard; but as time went on inventive genius changed one littlepart after another until greater and greater efficiency was obtained, andat the present time we find many varied products of locomotive evolution. The great freight locomotive of the transcontinental lines, the swiftengine of the express trains, the little coughing switch engine of therailroad yards, and the now extinct type that used to run so recently onthe elevated railroads, are all in a true sense the descendants of acommon ancestor, namely the locomotive of Stephenson. Each one has evolvedby transformations of its various parts, and in its evolution it hasbecome adapted or fitted to peculiar circumstances. We do not expect thefreight locomotive with its eight or ten powerful drive-wheels to carrythe light loads of suburban traffic, nor do we expect to see a littleswitch engine attempt to draw "the Twentieth Century Limited" to Chicago. In the evolution, then, of modern locomotives, differences have comeabout, even though the common ancestor is one single type; and thesedifferences have an adaptive value to certain specific conditions. Asecond illustration will be useful. Fulton's steamboat of just a centuryago was in a certain true sense the ancestor of the "Lusitania, " with itsdeep keel and screw propellers, of the side-wheel steamship for river andharbor traffic like the "Priscilla, " of the stern-wheel flat-bottom boatsof the Mississippi, and of the battleship, and the tug boat. As in thefirst instance, we know that each modern type has developed through theaccumulation of changes, which changes are likewise adjustments todifferent conditions. The diversity of modern types of steamships may beattributed therefore to adaptation. 

The several kinds are no more interchangeable than are the different formsof locomotives that we have mentioned. The flat-bottom boat of theMississippi would not venture to cross the Atlantic Ocean in winter, norwould the "Lusitania" attempt to plow a way up the shallow mud-bankedMississippi. These products of mechanical development are not efficientunless they run under the circumstances which have controlled theirconstruction, unless they are fitted or adapted to the conditions underwhich they must operate. 

Evolution, then, means _descent with adaptive modification_. We mustexamine the various kinds of living creatures everywhere to see if they, like the machines, exhibit in their make-up similar elements whichindicate their common ancestry in an earlier age, and if we can interprettheir differences as the results of modifications which fit them to occupydifferent place in nature. 

Two objections to the employment of these analogies will presentthemselves at once. The definition may be all very well as far as themachines are concerned, but, it may be asked, should a living thing like ahorse or a dog be compared with the steamship or the locomotive? Can welook upon the living thing as a mechanism in the proper sense of the word?A second objection will be that human invention and ingenuity havecontrolled the evolution of the steamship and engine by the perfection ofnewer and more efficient parts. It is certainly true that organicevolution cannot be controlled in the same way by men, and that sciencehas not yet found out what all the factors are. And yet we are going tolearn in a later discussion that nature's method of transforming organismsin the course of evolution is strikingly similar to the human process oftrial and error which has brought the diverse modern mechanisms to theirpresent conditions of efficiency. This matter, however, must remain forthe time just as it stands. The first objection, namely, that an organismought not to be viewed as a machine, is one that we must meet immediately, because it is necessary at the very outset to gain a clear idea of theessentially mechanical nature of living things and of their relations tothe conditions under which they live. It is only when we have such a clearunderstanding that we can profitably pursue the further inquiries into theevidence of evolution. Our first real task, therefore, is an inquiry intocertain fundamental questions about life and living things, upon which weshall build as we proceed. 

 * * * * *

All living things possess three general properties which seem to beunique; these are a peculiar chemical constitution, the power of repairingthemselves as their tissues wear out, and the ability to grow andmultiply. The third property is so familiar that we fail to see howsharply it distinguishes the creatures of the organic world. To realizethis we have only to imagine how strange it would seem if locomotives andsteamships detached small portions of themselves which could grow into thefull forms of the parent mechanisms. Equally distinctive is the marvelousnatural power which enables an animal to re-build its tissues as they arecontinually used up in the processes of living; for no man-made, self-sustaining mechanism has ever been perfected. The property of chemicalcomposition is believed by science to be the basis of the second and thethird; but this matter of chemical constitution must take its proper placein the series of structural characters, which we shall discuss further onas we develop the conception of organic mechanism. 

Whatever definition we may employ for a machine or an engine, we cannotexclude the living organism from its scope. As a "device for transformingand utilizing energy" the living organism differs not at all from any"dead" machine, however complex or simple. The greatest lesson ofphysiological science is that the operations of the different parts of theliving thing, as well as of the whole organism itself, are mechanical;that is, they are the same under similar circumstances. The livingcreature secures fresh supplies of matter and energy from the environmentoutside of itself; these provide the fuel and power for the performance ofthe various tasks demanded of an efficient living thing, and they are thesources upon which the organism draws when it rebuilds its wasted tissuesand replenishes its energies. The vital tasks of all organisms must beconsidered in due course, but at first it is necessary to justify ouranalogies by analyzing the structural characteristics of animals andplants, just as we might study locomotives in a mechanical museum beforewe should see how they work upon the rails. 

Among the familiar facts which science reveals in a new light are thepeculiarly definite qualities of living things as regards size and form. There is no general agreement in these matters among the things of theinorganic world. Water is water, whether it is a drop or the PacificOcean; stone is stone, whether it is a pebble, a granite block, or a solidpeak of the Rocky Mountains. It is true that there is a considerable rangein size between the microscopic bacterium at one extreme and the elephantor whale at the other, but this is far less extensive than in the case oflifeless things like water and stone. In physical respects, water may be afluid, or a gas in the form of steam, or a solid, as a crystal of snow ora block of ice. But the essential materials of living things agreethroughout the entire range of plant and animal forms in having ajellylike consistency. 

But by far the most striking and important characteristic of living thingsis their definite and restricted chemical composition. Out of the eightyand more chemical elements known to science, the essential substance ofliving creatures is formed by only six to twelve. These are the simple andobvious characteristics of living things which are denoted by the word"organic. " Everyone has a general idea of what this expression signifies, but it is important to realize that it means, in exact scientificterms, --_constituted in definite and peculiar ways_. 

The living thing, then, possesses a definite constitution, which is amechanical characteristic, while furthermore it is related to itssurroundings in a hard and fast way. Just as locomotives are different instructure so that they may operate successfully under differentconditions, so the definite characteristics of living things are exactlywhat they should be in order that organisms may be adjusted or fitted intothe places in nature which they occupy. This universal relation to theenvironment is called _adaptation_. It is only too obvious when ourattention is directed to it, but it is something which may have escapedour notice because it is so natural and universal. The trunk of a treebears the limbs and branches and leaves above the ground, while the rootsrun out into the surrounding soil from the foot of the trunk; they do notgrow up into the air. An animal walks upon its legs, the wings of a birdare just where they should be in order that they may be useful as organsof flight. And these mechanical adjustments in the case of livingcreatures occur for the same reason as in mechanisms like the steamship, which has the propeller at its hinder end and not elsewhere, and whichbears its masts erect instead of in any other way. 

The next step in the analysis of organisms reveals the same wonderfulthough familiar characteristics. The living organism is composed of partswhich are called _organs_, and these differ from one another in structuraland functional respects. Each of them performs a special task which theothers do not, and each differentiated organ does its part to make thewhole creature an efficient mechanism. The leg of the frog is an organ oflocomotion, the heart is a device for pumping blood, the stomachaccomplishes digestion, while the brain and nerves keep the parts workingin harmony and also provide for the proper relation of the whole creatureto its environment. So rigidly are these organs specialized in structureand in function that they cannot replace one another, any more than thedrive wheels of the locomotive could replace the smokestack, or the boilerbe interchanged with either of these. All of the organs are thus fitted oradjusted to a particular place in the body where they may most efficientlyperform their duties. Each organ therefore occupies a particular place inan organic environment, so to speak. Thus the principle of adaptationholds true for the organs which constitute an organism, as well as fororganisms themselves in their relations to their surroundings. 

The various organs of living things are grouped so as to form the severalorganic systems. There are eight of these, and each performs a group ofrelated tasks which are necessary for complete life. The alimentary systemconcerns itself with three things: it gets food into the body, or ingests;it transforms the insoluble foods by the intricate chemical processes ofdigestion; and it absorbs or takes into itself the transformed foodsubstances, which are then passed on to the other parts of the body. It ishardly necessary to point out that the ingestive structures for takingfood and preparing it mechanically lie at and near the mouth, while thedigesting parts, like the stomach, come next, because chemicaltransformation is the next thing to be done; while finally the absorbingportions of the tract, or the intestines, come last. The second group oforgans, like gills and lungs, supplies the oxygen, which is as necessaryfor life as food itself; this respiratory system also provides for thepassage from the body of certain of the waste gases, like carbonic acidgas and water vapor. The excretory system of kidneys and similarstructures collects the ash-waste produced by the burning tissues, anddischarges this from the whole mechanism, like the ash hoist of asteamship. The circulatory system, made up of smaller and larger vessels, with or without a heart, transports and propels the blood through thebody, carrying the absorbed foods, the supplies of oxygen, and the wastesubstances of various kinds. All of these four systems are concerned with"commissary" problems, so to speak, which every individual must solve forand by itself. 

Another group of systems is concerned with wider relations of theindividual and its activities. For example, the motor system accomplishesthe movements of the various organs within the body, and it also enablesthe organism to move about; thus it provides for motion and locomotion. Systems of support, comprising bones or shells, occur in many animalswhere the other organs are soft or weak. Perhaps the most interesting ofthe individual systems of relation is the nervous system. The strands ofits nerve fibers and its groups of cells keep the various organs of thebody properly coördinated, whereas in the second place, through thesensitive structures at the surface of the body, they receive theimpressions from the outside world and so enable the organism to relateitself properly to its environment. The last organic system differs fromthe other seven in that the performance of its task is of far lessimportance to the individual than it is to the race as a whole. It is thereproductive system, with a function that must be always biologicallysupreme. We can very readily see why this must be so; it is because naturehas no place for a species which permits the performance of any individualfunction to gain ascendency over the necessary task of perpetuating thekind. Nature does not tolerate race suicide. 

All organisms must perform these eight functions in one way or another. The bacterium, the simplest animal, the lowest plant, the higher plantsand animals, --all of these have a biological problem to solve whichcomprises eight terms or parts, no more and no less. This is surely anastonishing agreement when we consider the varied forms of livingcreatures. And perhaps when we see that this is true we may understand whyadaptation is a characteristic of all organisms, for they all have similarbiological problems to solve, and their lives must necessarily be adjustedin somewhat similar ways to their surroundings. 

Carrying the analysis of organic structure one step further, it is foundthat the various organisms are themselves complex, being composed of_tissues_. A frog's leg as an organ of locomotion is composed of theprotecting skin on the outside, the muscles, blood vessels, and nervesbelow, and in the center the bony supports of the whole limb. Like theorgans, these tissues are differentiated, structurally and functionally, and they also are so placed and related as to exhibit the kind ofmechanical adjustment which we call adaptation. The tissues, then, intheir relations to the organs are like the organs in their relations tothe whole creature, i. E. Adapted to specific situations where they maymost satisfactorily perform their tasks. 

Finally, in the last analysis, all organisms and organs and tissues can beresolved into elements which are called _cells_. They are not littlehollow cases, it is true, although for historical reasons we employ a wordthat implies such a condition. They are unitary masses of living matterwith a peculiar central body or nucleus, and every tissue of every livingthing is composed of them. 

The cells of bone differ from those of cartilage mainly in the differentconsistency of the substances secreted by the cells to lie between them;skin cells are soft-walled masses lying close together; even blood is atissue, although it is fluid and its cells are the corpuscles which floatfreely in a liquid serum. Thus an organism proves to be a complexmechanism composed of cells as structural units, just as a building isultimately a collection of bricks and girders and bolts, related to oneanother in definite ways. 

Our analysis reveals the living creature in an entirely new light, notonly as a machinelike structure whose parts are marvelously formed andcoordinated in material respects, but also as one whose activities orworkings are ultimately cellular in origin. Structure and function areinseparable, and if an animal or a plant is an aggregate of cells, thenits whole varied life must be the sum total of the lives of itsconstituent cells. Should these units be subtracted from an animal, one byone, there would be no material organism left when the last cells had beendisassociated, and there would be no organic activity remaining when thelast individual cell-life was destroyed. All the various things we do inthe performance of our daily tasks are done by the combined action of ourmuscle and nerve and other tissue cells; our life is all of their lives, and nothing more. The cell, then, is the physiological or functional unit, as truly as it is the material element of the organic world. Beingcombined with countless others, specialized in various ways, relations areestablished which are like those exhibited by the human beingsconstituting a nation. In this case the life of the community consists ofthe activities of the diverse human units that make it up. The farmer, themanufacturer, the soldier, clerk, and artisan do not all work in the sameway; they undertake one or another of the economic tasks which they may bebest fitted by circumstances to perform. Their differentiation anddivision of labor are identical with the diversity in structure and infunction as well, exhibited by the cells of a living creature. We mightspeak of the several states as so many organs of our own nation; thecommercial or farming or manufacturing communities of a state would belike the tissues forming an organ, made up ultimately of human units, which, like cells, are engaged in similar activities. As the individualhuman lives and the activities of differentiated economic groupsconstitute the life of a nation and national existence, so cell-lives makethe living of an organism, and the expressions "division of labor" and"differentiation" come to have a biological meaning and application. 

 * * * * *

The cell, then, is in all respects the very unit of the organic world. Notonly is it the ultimate structural element of all the more familiaranimals and plants that we know, as the foregoing analysis demonstrates, but, in the second place, the microscope reveals simple little organisms, like _Amoeba_, the yeast plant and bacteria, which consist throughouttheir lives of just one cell and nothing more. Still more wonderful is thefact that the larger complex organisms actually begin existence as singlecells. In three ways, therefore, --the analytic, the comparative, and thedevelopmental, --the cell proves to be the "organic individual of the firstorder. " As the ultimate biological unit, its essential nature must possessa profound interest, for in its substance resides the secret of life. 

This wonderful physical basis of life is called _protoplasm_. It containsthree kinds of chemical compounds known as the proteins, carbohydrates, and hydrocarbons. Proteins are invariably present in living cells, and aremade up of carbon, hydrogen, nitrogen, sulphur, and usually a littlephosphorus. The elements are also combined in a very complex chemical way. For example, the substance called hæmoglobin is the protein which existsin the red blood cells and which causes those cells to appear light red oryellow when seen singly. Its chemical formula states the precise number ofatoms which enter into the constitution of a single molecule as:C_{600}H_{960}N_{154}FeO_{179}. This is truly a marvelously complexsubstance when compared with the materials of the inorganic world, likewater, for example, which has the formula H_{2}O. And just as the peculiarproperties of H_{2}O are given to it by the properties of the hydrogen andthe oxygen which combine to form it, just so, the scientist believes, themarvelous properties of protein are due to the assemblage of theproperties of the carbon and hydrogen and other elements which enter intoits composition. 

It would be interesting to see how each one of these elements contributessome particular characteristic to the whole compound. The carbon atom, forexample, is prone to combine with other atoms in definite varied ways, andthe high degree of complexity which the protein molecule possesses maydepend in greater part upon the combining power of its carbon elements. The nitrogen atom makes the protein an extremely volatile compound, sothat the latter burns readily in the tissue cells; and the hydrogen andoxygen bring their specific characteristics to the total molecule. Andfurthermore, it is evident that the great complexity of this constituent, protein, gives to protoplasm its power of doing work, or, in a word, itspower of living. In constructing it, much energy has been absorbed andstored up as potential energy, and so, like the stored-up energy in awatch spring or in gunpowder, this may be converted, under properconditions, into the kinetic energy and the work of actual operation. Onaccount of its peculiar and complex nature, it possesses great capacityfor burning or oxidization, thus serving as a source of vital power. Itburns in the living tissue just as coal oxidizes in the boiler of anengine; its atoms fly apart and unite with oxygen so as to satisfy theirchemical affinities for this substance. If we could only see what happensto the protein molecule when it undergoes oxidization, we would witness aviolent explosion, like that of a mass of gunpowder. And the astonishingfact is that this process is actually the same for the living molecule, for exploding gunpowder, and for the fuel which burns in the locomotiveboiler. Does this mean that the essential process of what we call life isa chemical one? So it would seem on the basis of this fact alone, but aconclusion must be deferred until we reach a later point. 

The second kind of substance which we find in protoplasm is thecarbohydrate. A typical member of this group is common sugar, C_{6}H_{12}O_{6}; another sugar has the formula C_{12}H_{22}O_{11}. Starchis again a typical carbohydrate, and its formula is C_{6}H_{10}O_{5}, orsome multiple of this. One sees at a glance that these substances agree inhaving twice as many hydrogen atoms as there are oxygen atoms, the sameproportion that the hydrogen bears to the oxygen in the compound water, --acharacteristic which makes it easy to remember the general constitution ofcarbohydrate as compared with the protein. The substances of this secondclass are obviously much less complex, both as regards the different kindsof atoms and in respect to the numbers of each kind that enter into theformation of a single molecule. Therefore the carbohydrates do not possessso much power or energy as the protein molecule; in short, they are notsuch good fuels for the living mechanism. 

Finally, we find almost always in protoplasm other substances composed ofcarbon and hydrogen and oxygen which are called hydrocarbons, distinguished from carbohydrates by the fact that the number of oxygenatoms is less than half the number of hydrogen atoms. These substances arethe fats and oils of various kinds, less powerful sources of energy thanthe proteins, but they contain more potential energy than thecarbohydrates because they are more oxidizable. 

Besides the characteristic substances of these three classes, protoplasmcontains certain other chemical compounds, like the various salts ofsodium, chlorine, magnesium and potassium, and a few others, which bringthe list of chemical elements to the number twelve. We have already notedhow strikingly small and restricted is the list of elements composingliving matter as compared with the long array of eighty-odd differentkinds of chemical atoms existing in the world as a whole. 

But an astonishing result is reached through the brief analysis we havejust made. It is this: we do not find _peculiar_ kinds of atoms whichoccur exclusively in living matter; the materials are exactly the same asthose of the outer world. In short, the elements of both the organic andinorganic divisions of the universe prove to be the same. Carbon iscarbon, whether it is part of the substance of a living brain cell, orblack inert coal, or the glistening diamond, or an incandescent part ofthe fiery sun. Hydrogen is the same, whether it be a constituent of theocean, of the air, or of the living muscle fiber. And so it is with all ofthe other elements of the living mechanism. This starts us upon a line ofthought which leads to a significant conclusion, namely, that a livingthing which seems so distinct and permanent is after all only a temporaryaggregate of elements which come to it from the not-living world; existingfor a time in peculiar combinations which render life possible, they passincessantly away from the living thing and return to the inorganic world. Every breath we draw sends out particles which were at one time livingportions of ourselves; every movement we make involves the destruction ofliving muscle cells, whose protoplasm breaks down into the ash and gas andfluid wastes which eventually return to the world of dead things. A treeloses its living leaves with each recurring season, and the antlers of thestag are lost annually, to be replaced anew. Indeed the major part of someorganisms is itself actually dead. The bones and hair and nails of such ananimal as a cat are almost entirely lifeless, even though they areintegral and necessary portions of the organism as a whole. They areconstructed by living protoplasm which has died in their making. Thuswithout going beyond the boundaries of the individual body, thesesubstances have passed from the sphere of life, and are dead. The apparentgap on the other side between the lifeless and living world is equallyimaginary, for our living substance is continually replenished and rebuiltfrom the elements of our dead foods. So, as Huxley says, a living organismis like a flame or a whirlpool, which is an ever changing though seeminglyconstant individuality. We look at a gas flame, and we see in the flameitself those particles of gas which have come through the pipe to beagitated violently in the higher temperature of the flame as they areoxidized or burnt. These particles immediately pass off as carbonic acidgas and water vapor which are no longer parts of the flame. A fountain iscontinually replenished by the water which is not-fountain, but whichbecomes for the time a part of the graceful jet, falling out and away asit leaves the fountain itself. Just so a living organism is an everchanging, ever renewed, and ever destroyed mass of little particles--theatoms of the inorganic world which combine and come to life for a time, but which return inevitably to the world of lifeless things. This is oneof the most fundamental facts of biology. The independence of a livingthing like a human being or a crustacean is a product of the imagination. How can we be independent of the environment when we are interlocked in somany ways with inorganic nature? Our very substance with its energies hasbeen wrested from the environment; and as we, like all other livingthings, must replenish our tissues as we wear out in the very act ofliving, we cannot cease to maintain the closest possible relations withthe environment without surrendering our existence in the battle of life. 

From the foregoing discussion, it will be evident, I am sure, that thereis ample justification for the biological dictum that a living individualis a mechanism. Not only is the organism composed always of cell unitsgrouped mechanically in tissues and organs and organic systems; not onlyare the operations which make up its life constant and regular undersimilar conditions; not only is the whole creature mechanically connectedwith the inorganic world; but above all the whole activity of a biologicalindividual is concerned necessarily and again mechanically with theacquisition of materials endowed with energy, which materials and energyare mechanically transformed into living matter and its life. Even thoughan organism is so much more complex than a locomotive, and so plastic, nevertheless, in so far as both are mechanisms, the conception of theevolution of the former may be much more readily understood through aknowledge of the historical transformation of the latter. 

 * * * * *

What, now, is life? To most people "life seems to be something whichenters into a combination of carbon and hydrogen and the other elements, and makes this complex substance, the protoplasm, perform its variousactivities. " Nearly every one finds it difficult to regard life andvitality as anything but actuating principles that exist apart from thematerials into which they enter, and which they seem to make alive. According to this general conception, "life is something like an engineerwho climbs into the cab of the locomotive and pulls the levers which makeit go, " as health might supposedly be regarded as something that does notinhere in well-being, but gets into the body to alter it. But is thisconception really justified by the facts of animal structure andphysiology? Let us recall the steps of our analysis. The living organismis a collection of differentiated parts, the organs; the life of anorganism is a series of activities of the several organic systems andorgans. If we could take away one organ after another, there would benothing left after the last part had been subtracted. In a similar manner, the activities of organs prove to be the combined activities of thetissue-cells, and again the truth of this statement will be clear when weimagine the result of taking away one cell after another from organismslike the frog or tree. When the last cell had been withdrawn, there wouldbe nothing left of the frog's structure, and there would be no element ofthe frog's life. It is true that the particular way the tissue-cells arecombined is of primary importance, but it is none the less true that thelife of a cell is the kind of element out of which the life of even themost complex organism is built. And we have seen that the essentialsubstance of a cell is a complex chemical compound we call protoplasm, whose elements are identical with chemical substances outside the livingworld. Is there any ground for supposing that the properties of protoplasmare due to any other causes than those which may be found in the chemicaland physical constitution of protoplasm? In brief, is life physics andchemistry? Nowadays the majority of biologists believe that it is. Just asthe properties of water are contributed by the elements hydrogen andoxygen which unite to form it, just so the marvelous properties ofprotoplasm are regarded as the inevitable derivatives of the combinedproperties of the various chemical elements which constitute protoplasm. Biologists have known for more than a century, since the work of Lavoisierand Laplace in 1780, that the fundamental process of the living mechanismis oxidation, and that this process is the same, as they said, for theburning candle and the guinea pig. Beginning with Woehler, in 1828, scoresof students of physiological chemistry have duplicated the chemicalprocesses of living matter, which were regarded as so peculiar to theliving organism that they seemed to be due to the operation of anon-mechanical and vital cause. The investigator mentioned was the first toconstruct artificially from inorganic substances the nitrogen-containingash product of the living organism called urea. Now hundreds of so-calledorganic compounds have been made synthetically and their number is addedto week after week. Therefore, the biologist who finds that a physical andchemical analysis of some vital processes is possible, and that theanalysis is being extended with astonishing rapidity, finds himself unableto regard protoplasmic activity as anything different in kind or categoryfrom the processes of physics and chemistry which go on in the world ofdead things. 

It is true that even at the present time some biologists are reluctant toaccept the thoroughgoing mechanical interpretation of organic phenomena, partly because these are so complex that their ultimate constituentscannot be discerned, but more often on account of the apparentlypurposeful nature of biological processes. Some, indeed, have gone so faras to postulate something like consciousness which controls and directsthe formation of protoplasm, and the exercise of its distinctiveproperties in the way of growth, reproduction, and embryonic developmentinto the adapted adult. But the fact remains that wherever analysis hasbeen possible the constituent elements of an organic process prove to bephysical and chemical. Protoplasm differs from inorganic materials only inits complexity and in the properties which seem to owe their existence tothis complexity. As Huxley points out, it is no more justifiable topostulate the existence of a vitalistic principle in protoplasm than itwould be to set up an "aquosity" to account for the properties of water, or a "saltness" for the qualities of a certain combination of sodium andchlorine. We may not know how the elements produce the properties of thecompound, but we do know that such properties are the invariable productsof their respective constituents in combination. As far as the evidencegoes, it tells strongly and invariably in favor of the mechanisticinterpretation. 

Under the present limitations, it is impossible to give this subject thefurther discussion it deserves. It is not our purpose to review the originof life in times past, and the origin of living matter from inorganicconstituents, though the subject is one of the most important in the fieldof cosmic evolution. We must begin with the living organism; and how thefirst one arose must be of less importance to us than the knowledge of itsmechanical constitution and of its mechanical operation. Of far greatervalue is the realization that a living creature is not an independentthing, but that, on the contrary, it must hold the closest possiblerelations with the world of materials and energies constituting itsenvironment. We must again insist upon the importance of that mechanicaladjustment to the conditions of life which is the universal characteristicof plants and animals. It is the history of these creatures and the originof their adapted conditions that we are called upon to study. We mustscrutinize the nature of to-day to see if we can find evidence thatevolution is true, and if we can discern the forces which, acting upon theliving mechanism as man has dealt with machines, might bring the variousspecies of the present day to their modern forms. 

 * * * * *

We have now learned that evolution means a common ancestry of living formsthat have come to differ in the course of time; our common reason hasshown us also that organisms are in a true sense complicated chemicalmechanisms adapted to meet the conditions under which they must operate. We come now to the evidences offered by the organic world that evolutionis true and that natural forces control its workings. Clearly theexamination of the matter of _fact_ is independent of the question of_method_. For just as the chemist may experiment with various substancesto see if they will dissolve in water and not in alcohol before it isnecessary or desirable for him to take up the further studies of the lawsof solution, so reasonable grounds must be found for regarding evolutionas true before passing to its method of accomplishment. And in thefollowing discussions, the animals will be used almost exclusively, notbecause the study of plants fails to discover the same relations andprinciples, but because the better known animal series is more varied andextensive, and above all for the reason that the human organism arraysitself as the highest term of the animal series. 

In the complete scheme adopted by most naturalists, five categoriesinclude the evidences bearing upon the fact of evolution. These are_Classification_; Comparative Anatomy, or _Morphology_; ComparativeDevelopment, or _Embryology; _Palæontology_, which comprises the factsprovided by fossil relics of animals and plants of earlier geologicalages; and _Geographical Distribution_. Each of these divisions includes adescriptive and analytical series of facts, whose characteristics are"explained" or summarized in the form of the general principles of therespective divisions. Such principles, taken singly and collectively, constitute the evidences of evolution. 

The particular nature of any one of these categories, evolved in thedevelopment of science practically in the order stated, depends upon thespecial quality of an animal which it selects for comparison andorganization in connection with other similar facts, and also in its ownmode of viewing its facts. One and the same organism may present materialsfor two, three, or even all five of these divisions, for they are by nomeans mutually exclusive. For example, a common cat possesses certaindefinite characteristics which give it a particular place when animalsmore or less like it are grouped or classified according to their degreesof resemblance and difference, in small _genera_ of very similar forms, inlarger _tribes_ or _orders_ of similar genera, and in more and moreinclusive groups of these lesser divisions, such as the _classes_ and_phyla_, or main branches of the animal tree. The common cat and itsrelatives are even earlier to be regarded as anatomical subjects, andtheir thorough analysis belongs to comparative anatomy, --a name whichexplains itself. The purpose of this department of natural history is toexplore the entire range of animal forms and animal structures, and todetermine the degree of resemblance and difference exhibited by thegeneral characters of entire organisms and by the special qualities oftheir several systems of organs. It provides the data from whichclassification selects those which indicate mutual affinities withgreatest precision and surety. But its materials are _all_ the facts ofanimal structure, and because each and every known organism can be andmust be studied, the investigator engaged in formulating the evidence ofevolution has at his disposal all the data referring to the entire realmof animals. The data of embryology are likewise coextensive with theterritory of the animal world, for we do not know of any form which doesnot change in the course of its life history. An adult cat is the productof a kitten which is itself the result of a long series of changes fromearlier and simpler conditions. In so far as it deals with structures inthe making, embryology is a study of anatomy, but as it is concernedprimarily with all of the plastic remodeling which animals undergo duringthe production of their final forms, it is an independent study. Nevertheless we shall learn how intimate are the relations of these twodivisions of zoölogy and how the evolutionary teachings of each body offact support and supplement those of the other. 

Palæontology searches everywhere among the deposits of earlier ages forlinks to be fitted into their proper sequence of time, from which itconstructs the chain of diverse types leading down to the species of thepresent. A cat of to-day is therefore viewed in an entirely differentconnection, as the last term in a consecutive series of species. Formingalliances with geology, and even with physics and chemistry, thisdepartment of zoölogy endeavors to reconstruct the past from what itlearns to-day about organisms and the conditions under which they live. Finally the observations that cats of various kinds do not occureverywhere in the world, but only in certain more or less restrictedlocalities, belong to the subject of geographical distribution, andillustrate its nature. 

Our task is to learn the teachings of these several divisions by recallingand putting together what we know already about the commonest animals, ornoting what can be observed in a visit to a zoölogical garden andaquarium. On account of the present limitations of time, the subject ofclassification will be combined with comparative anatomy; embryology willbe taken up together with these subjects; palæontology will be the mainsubject of the next discussion, which will include also a brief statementof the meaning of distribution. Then we will be prepared to study natureto see how evolution works. 

II

THE STRUCTURE AND DEVELOPMENT OF ANIMALS AS EVIDENCE OF EVOLUTION

In order to become acquainted with the way the structures of animalsprovide evidences of evolution, it is by no means necessary to review theentire range of their forms, because research has discovered that theprinciples of relationship are universal among animals, and that any groupof examples will demonstrate what is taught by comparative anatomy as awhole. The commonest creatures may serve us best in order that we may cometo view evolution as a process that involves each and every living thingthat we know, and not as something which belongs only to the remote andunknown past. 

Let us begin with the common cat and the group of carnivora orflesh-eating animals to which it belongs. As we pass along the streets ofthe city, we will see many cats which differ in some details, though theyresemble one another closely. While they vary somewhat in form, the rangein this quality is not so noticeable as in the matter of color; some ofthem will be gray, some maltese, while others will be yellowish or black, and they will differ in the striped or spotted character of theircoloration. We readily classify them all as "cats" in spite of theirdifferences, because they are alike in so many ways that we have learnedto associate as the distinguishing characteristics of these animals, andto label--"cat. " The animals which we might see in a walk of severalblocks may reasonably be regarded as offspring of the same pair ofancestors of a few years back, even though they are dissimilar. We allknow that the kittens of one and the same litter vary: no two of them areever exactly alike in color or disposition or voice or size, nor is anyone identical with either of its parents, although it may be necessary toemploy exact means of measuring them in order to demonstrate theirvariation. The fact of difference, then, is surely not inconsistent witheven the closest ties of blood, and we do not need to go beyond the scopeof daily observation to find that this is true in nature wherever we look. 

Should we extend our observations so as to include the cats of Boston andPhiladelphia and San Francisco, the animals would probably vary over awider range, but they would be so similar to New York cats in theirmake-up that we would have no difficulty in regarding them and all theothers of the United States as the descendants of a single pairs ofancestors, perhaps brought over in the "Mayflower. " But why does this viewseem justified? Because experience has taught us that the living thingswhich resemble each other most closely are those which are most intimatelybound by ties of blood and common heritage. It is "natural" for relativesto resemble one another more than persons not related, and for brothers andsisters to be more alike than cousins. Science does not refer to somethingoutside everyday observation when it states that _the possession by twoanimals of a great body of similar characters beneath their minordifferences is an indication of their common ancestry_. 

Thus at the very outset our simple illustration establishes the mostfundamental principle of comparative anatomy. Let us see how it worksfurther. The Manx cat possesses an abbreviated tail, although in otherrespects it is practically the same as the familiar long-tailed form; theAngora and the Persian differ in having long hair. All of these animalsare so much alike in so many respects, and so closely resemble the wildcats, that it is not unreasonable to regard them all as the descendants ofthe same original wild ancestors, and as the varying products of lineswhich branched out from the same stock in different directions and atdifferent times. It is, in a word, their "cat-_ness_" which demonstratestheir relationships. But common sense need not stop here. Guided by thefacts of anatomical similarity, it convinces us that the dun-colored lionand puma, the striped tiger and the spotted leopard are simply cats of alarger growth whose remoter ancestry is one with that of the previouslycited forms. Not until we explore and compare their several systems do wesee how thoroughgoing is their uniformity in structural plan. And becausereason justifies the view regarding the origin of domestic cats from wildancestors, the evolution of all the various members of the cat tribe mustbe acknowledged. These animals exhibit a fundamental likeness, which, toemploy a musical analogy, is the "theme" of "cat-_ness_, " and they are somany variations of this theme. 

The members of another tribe of the familiar carnivora display in theirown way the same kind of evidences of relationship. The varieties ofdomesticated dogs differ far more widely among themselves than do commoncats, yet their community of ancestry is demonstrated not only bystructural resemblances, but also by the striking fact that forms asdiverse as the greyhound and the fox terrier can be crossed. Here againthere are wild forms, like the wolf and fox and jackal, so like thedomesticated members of the dog tribe that we cannot fail to recognize acommon "dog-_ness_" and its significance as evidence of the relationshipin ancestry of all these animals. 

Extending our survey so as to include the other tribes of flesh-eaters, identical principles come to light. One is compelled to regard the polarand grizzly bears as obvious blood relatives of the brown bear, and evenof the raccoon of our own territory. Instead of walking upon their toeslike cats and dogs, these animals plant their feet flat upon the ground;and they agree in many other details of structure that place themtogether, but somewhat apart from the other tribes. The many kinds ofseals and walruses and sea elephants form still another group displayingsimilar bodily characters, but differing more widely from the "cat theme"in these differences. They are all true carnivora, but in the course oftheir evolution they have progressively changed so as to be adapted tolife in the water where they find their prey. The bones of the limbs arethe same in number and arrangement as in the cat's limb, but the seal'santerior appendage or "arm" has altered in numerous ways so as to becomean efficient flexible paddle, while the hind limbs have shiftedposteriorly, very much as screw propellers have evolved in the history ofsteam vessels. How the members of the seal tribe have changed in theirdescent from purely terrestrial ancestors is partly explained by suchintermediate animals as the otter. This form is adapted by its slenderbody and partly webbed feet to a semi-aquatic life; it seems to havehalted at a point beyond which all of the seals have passed in theirevolution. 

Each one of these tribes by itself provides conclusive evidence ofevolution, for it is most reasonable to regard the "theme" in every caseas a product of common inheritance, while the variations of any theme arebest understood as the results of adaptive changes in various directions. But the examples have disclosed a larger relation and a principle of widerscope, as indeed the assignment of all these tribes to the single naturalgroup of the _carnivora_ implies. These tribes are put together becausecomparative anatomy finds that the common characters of all cats arefundamentally like those of all dogs and bears and seals, and in thesecommon qualities the carnivora differ from all other mammalia. Does thismean that the branches which bear respectively the various members of theseveral tribes are outgrowths of a single limb of the evolving animaltree? Science does not hesitate to give an affirmative answer, because, asin the case of the similar but varying domestic cats, no other explanationof tribal resemblance in structure seems so reasonable and natural. 

So far the examples have been taken from one order of the highest class ofbackboned animals, called mammalia. When our survey is extended to otherdivisions of this class, additional laws of organic relationship arediscovered. If in a series of evolving generations the line ofmodification proceeding from a terrestrial animal like a cat tosemi-aquatic and marine types substantially like an otter and a seal shouldbe carried further, it will inevitably lead to forms possessing characterssuch as those displayed by whales and the related porpoises, dolphins, andnarwhals of the order cetacea. In their make-up all of these animalsclearly possess the general characteristics of mammals, and theyconstitute collectively another limb which has sprung from the same stockas the carnivora, although at an earlier time. This we believe because oftheir plan of body and because their peculiar organization fits them evenmore perfectly than the seals for aquatic existence that is their onlypossible mode of life. In the case of the whales the bony framework of thefore limb is again like that of the cat's leg, although the wholestructure is a flexible finlike paddle. The hind limb has disappeared asan efficient organ, but the significant fact is that small rudiments ofhind limbs are present just where corresponding structures are placed inthe seal. These vestiges cannot be reasonably accounted for, unless theyare the degenerate hinder limbs of a remote four-footed ancestor. Furthermore the unborn whale possesses a complete coat of hair, which isafterwards replaced by blubber; but hair is a thatchlike coat to shedrain, as the way the hairs lie on a terrestrial mammal indicates. We aretherefore forced to conclude that whales have originated from four-footedanimals walking about on land, because no opposed explanation gives soreasonable an interpretation of the observed facts. 

Another group of familiar animals materially reinforces the resultsalready established. After what has been said, it will not be difficult toperceive the meaning of the resemblances among mice of the house andfield, and of rats and rabbits and squirrels. All of them possess heavycurved gnawing teeth, or incisors, and lack the flesh-tearing or canineteeth. They agree in many other respects which distinguish them as aseparate natural order of the mammals called the rodentia. Again we find ahighly aberrant form in the flying squirrel, which leads toward an orderwith another plan of body. This animal is a true rodent, which lengthensits leap from branch to branch by means of a fold of skin stretchingbetween its fore and its hind limbs. It is an animated aeroplane, and itshows in part how bats have originated. The wing of a bat is an elasticmembrane stretching not only between the two legs of one side, but alsobetween the greatly lengthened "fingers" of the fore limb. But the bonesof arm, wrist, and fingers are almost precisely the same in number andrelation as in walking forms. The fact that this peculiar wing adheres toa plan belonging to the anterior legs of walking or climbing types has noreasonable explanation save that of evolution. 

The well-known group of hoofed animals, including horses and cattle, isalso valuable for our present purposes, as well as in a later connectionwhen the evidence of fossils is described. The elephant possesses fivetoes armed with well-developed nails or hoofs. A tapir has four or threetoes, and it would seem that its ancestor had had five toes, of which oneor two had been lost. A rhinoceros possesses three toes, and its foot isconstructed internally like the elephant's with the outer elements absent. The horse comes last with one large toe and hoof, but on either side ofthe main bones of this digit are vestiges of what must have been toes inits ancestors. Among the even-toed forms the hippopotamus has four whichreach the ground, with a vestige of a fifth, so this animal has apparentlydescended from a typical mammal with the full number along a differentline from that taken by the odd-toed forms. A pig has a cloven hoof, madeup of what we may call the third and fourth members of a series of fivedigits, but the second and fifth fingers and toes are present, though theyare withdrawn from the ground so as to be no longer functional; thisanimal seems to have proceeded further along the same line taken by thehippopotamus. A deer, with still smaller rudiments at the sides of itsdouble foot, leads in the comparative series to the camel with a clovenhoof devoid of any such relics. 

We must pass with only brief mention the lower orders of mammalia, likethe insect-eating forms to which armadillos and ant-bears belong. Ofgreater interest are the pouched mammals like the kangaroo and opossums, which live almost exclusively in the Australian realm. The kangaroo isendowed with a head somewhat like that of a goat, and well-developed hindlegs that enable it to make leaps of astonishing length. Some of itsrelatives, such as the bandicoot, are like rats, or like bears, as in thecase of the wombat. The Tasmanian wolf is another true marsupial, eventhough divergent adaptation has brought it to resemble the carnivora ofthe dog tribe in general appearance and in special structures like theteeth. Finally at the very bottom of the mammalian scale are two smallforms living in the Australian faunal region. The duckbill or_Ornithorhynchus_ is the better known animal, with its close fur, webbedfeet, and flattened ducklike beak, while its only other near relative, the_Echidna_, is somewhat similar to the spiny hedgehog in externalappearance. A unique peculiarity of these two forms is that they produceeggs much like those of reptiles and birds, and this fact, together withothers of a structural nature, brings the whole group of mammals near tothe lower classes of the Vertebrata. 

Looking back on the several orders of mammals, it will be seen that thelast mentioned are much less differentiated or specialized in theirgeneral organization. Above the level of the egg-layers and the pouchedmammals, the higher orders branch out in different directions and reach upto various levels of the scale of animal organization. 

The foregoing structural evidences of organic transformation in the pasthistories of cats and seals and whales insistently recall the analogies ofthe locomotive and the ship employed at the outset. All these animals, like the mechanical examples, have come to differ in their derivation fromthe same original parents, and their lines of descent have diverged so asto fit the products of evolutionary modification to diverse circumstances. Even the vestigial organs of animals have their counterparts in themachines. The cowcatcher was a large and important structure in the earlydays of railroading, but it has become relatively useless with thedecrease of grade crossings and the construction of more complete lines offence. The structure still persists, sometimes in a greatly reduced form. Even more obvious is the change of structure in the case of masts ofvessels, which originally bore the sails for propelling the ship. Whensteam engines were employed to give motive power, masts did not disappear. They now provide the derrick supports of trading steamers; in battleshipstheir function is changed to that of fighting tops and signal yards. Eventhe poles carried by canal boats to bear windmills must be regarded as thereduced vestiges of masts originally constructed to carry sails; and theiradaptive evolution, like that of countless structures in animals, has beenaccomplished by degeneration. 

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The birds are another class of backboned animals which exhibit identicalprinciples of relationship. A heron has long legs and wide-spreading toes, which keep its body out of the water as it stalks about the marshes whereit seeks its food; its bill is a long slender pincers. Compare it with aneagle; the latter has a short and heavily hooked beak to tear flesh, whileits stout legs bear strongly curved talons to hold its struggling prey. Swimming birds like the swan and duck and loon possess feet which areconstructed in general like those of the former examples, but they arewebbed and shortened to serve as paddles. In the penguin we find acounterpart of the seal among mammals; its feathers are much reduced andits fore limbs are no longer wings enabling the animal to fly, but theyare paddles which it uses when it swims in pursuit of fish. Finally theostrich and wingless bird of New Zealand--the _Apteryx_--have wings thatare useless vestiges, which, in the latter case, are hidden under thebrushlike feathers covering the body. It is unnecessary to add moreexamples, for even these few illustrations establish exactly the sameprinciples of relationship and evidences of evolution that are to be foundin the series of mammalia. 

Reptiles also are grouped, like the mammals and birds, as variations abouta central theme. An ordinary lizard is perhaps the nearest in form to theremote ancestor from which all have sprung. Some lizards are long and veryslender, with all four limbs of greatly reduced size. Others, which arestill true lizards, have lost the hind limbs, or even all the legs, as inthe "blind worms" of England. One step more, and an animal which hasprogressed further along a similar line of descent would be a snake. Justas whales as a group are derivable from forms which resemble typesbelonging to another order, so snakes as an order are to be regarded asmore radically altered derivatives of some four-footed lizardlikecreature. Alligators are very much like lizards in general form, and theirorder is a diverging branch from the same limb. Finally the evolution ofturtles from the same ancestors is intelligible if we begin with a shortstout animal like the so-called "horned toad" of Arizona, and proceed tothe soft-shelled tortoise of the Mississippi River system; theestablishment of a bony armor completes the evolution of the familiar andmore characteristic turtle. 

Frogs and salamanders constitute another lower class, called the amphibia, whose members are gilled during the earlier stages of development. Anadult frog is essentially a salamander without a tail and with highlydeveloped hinder limbs. The salamanders differ as regards the number offishlike gill clefts that they all possess in their young stages, butwhich disappear entirely or in part during later life. In comparison withthe lizard as a typical reptile, a salamander is more primitive in all ofits inner organic systems, while in its nearly continuous body, with headand tail gradually merging into the trunk, it also displays a somewhatsimpler form of body. 

The fishes are the lowest among the common vertebrates, and they offer anabundance of independent testimony as to the truth of the principles ofcomparative anatomy. The common shark is perhaps the most fundamentalform, with a hull-like body undivided into head, trunk, and tail, and fromit have originated such peculiar variations as the hammerhead and skate. Among fishes with true bones, a cod or trout is the most typical ingeneral features. Without ceasing to be true bony fishes, the trunk-fishand cow-fish are adapted by their peculiar characters of spine and armorplate to repel many enemies. The puff fish can take in a great amount ofwater, when disturbed, so as to become too large to be swallowed by someof its foes, illustrating another adaptive modification for self-defense. The wonderful colors and color patterns of the tropical fish of the reef, or of the open water forms like the mouse-fish of the Sargossa Sea, oftenrender them more or less completely hidden from the foraging enemy. Aflounder looks like a fish which was originally symmetrical, but which hadcome to lie flat on its side upon the bottom, whereupon the eye underneathhad left its original place to appear on the upper surface. The difficultand unusual conditions of deep-sea existence have been met by fishes intwo ways; some forms possess luminous frilled and weedlike fins, whichlure their prey to within easy reach of their jaws, while others haveenormous eyes, so as to make use of all possible rays of light in theirpursuit of food organisms. But all of these diverse forms are true_fishes_, possessing a common heritage of structure which demonstratestheir unity of origin. 

The brief review of backboned animals has shown how comprehensive are theprinciples of relationship. The families and tribes of each order, such asthe carnivora, are like branches arising from a single limb; the orders intheir turn exhibit common qualities of structure which mean that they havegrown from the same antecedents, while even the larger divisions orclasses of mammals, birds, reptiles, amphibia, and fishes, possess a deepunderlying theme whose dominant motif is the backbone, which proves theirultimate unity in ancestry. The greater and lesser branches have reacheddifferent levels, for the fish is clearly simpler in its make-up than thehighly specialized bird. But the great fact is that structural evidencesdemonstrating the reality of genealogical affinities are displayed by theentire series of vertebrates; although they differ much or little in manyor fewer respects they have one and the same ground-plan. 

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The lower animals devoid of backbones, and therefore called invertebrates, are not so well-known except to the student of comparative anatomy, because they are not so often met with, and because they are usually verysmall or microscopic; but in many respects their importance to theevolutionist surpasses that of the vertebrates. Their structural plans arefar more varied, and they range more widely from higher and relativelycomplicated organisms to the unitary one-celled animals. A knowledge ofsome of them is essential for our present purpose, which is to learn howsure is the basis for the principles of relationship and how complete isthe structural evidence of evolution. 

Worms are represented in the minds of most people by the common earthwormor sandworm. The body in either case is made up of a series of segments orjoints which agree closely throughout the animal in external appearanceand in internal constitution. A section of the digestive tract, a pair ofnerve centers, two funnel-like tubes for excretion, and similar bloodvessels occur in each portion. 

Precisely similar features are displayed by the crustacea, which seem tobe so different. Every one is familiar with the appearance of lobsters andcrabs. Even in these animals the body is composed of segments, but theseare not like one another, nor are they freely movable throughout the body. Five are fused in all crustacea to make a head; in lower members of theorder the eight succeeding segments are free, but in the lobster they arejoined together and united with the head. The hinder part of this animalis a long abdomen whose segments remain more primitive and independent. But in a crab, the whole plan has been modified by the shortening andbroadening of the head-thorax, and by the reduction of the abdomen, whichis also turned under the anterior part of the body. The internal organicsystems are constructed upon a worm plan with modifications. Nearly everyone of the segments bears one pair of appendages, which can be referred bytheir forked nature to the two-parted, oarlike flaps of sandworms, but theappendages of crustacea have departed from their prototypes in functionalrespects and in details of structure. They are variously feelers, jaws, legs, pincers, and swimming paddles, evolved to serve different purposes, just as the limbs of the vertebrates we have described have becomevariously arms, wings, flippers and paddles in apes, bats, seals, andwhales. 

Butterflies, beetles, bees, and grasshoppers seem at first sight to beentirely different, even though they agree in being more or lesssegmented. But all of them have heads with four pairs of appendages of thesame essential plan, middle thoracic regions of three segments more orless united, bearing three pairs of legs and usually two pairs of wings, while the hinder part is a freely jointed abdomen without real limbs. Inthese respects the countless varieties of insects agree so that they alsolike crustacea of various kinds seem to have been derived from wormlikeanimals with more simply segmented bodies. Indeed spiders and scorpionsand their relatives of the group arachnida prove for similar reasons to bederivatives of the same original stock, and own cousins of the insects. 

In nearly every one of the invertebrate branches we find representativeswhich interest us chiefly because they appear to have reached theirpresent condition by retrograde evolution. Barnacles are really crustacea, but they have lost their eyes as well as some other structures that aremost useful in animals with a free existence, because they have adopted afixed mode of life, which has also brought about the loss of the originalfreely jointed character of the body. A tapeworm as an example of internalparasites is an extremely degenerate form which lacks a digestive tract, because this is superfluous in an animal which lives bathed in thenutrient fluids of its host. Comparing it in other respects with other lowwormlike creatures, it appears to be a relative of peculiar simple wormswith complete organization and independence of life. All these degenerateforms enlarge our conception of adaptation by adding the essential pointthat progress is not always the result of evolution. Indeed we havelearned this in the case of vestigial and rudimentary structures of higherforms like whales, and now we find that entire animals may degenerate as aresult of changes no less adaptive than progressive modifications. 

Passing by other invertebrate groups made up of species arranged likehigher animals in smaller and larger branches according to their degree offundamental similarity, we arrive at a place in the scale occupied bytwo-layer animals without the highly developed and clearly differentiatedorganic systems of the forms above. The fresh-water animal _Hydra_exemplifies the creatures of this level, where also we find sea-anemonesand the soft polyps which form corals and coral reefs by their combinedskeletons. _Hydra_ is an animal to which we must return again and again aswe study one or another aspect of organic evolution. In general form it isa hollow cylinder closed at one end, by which it attaches itself, while atthe upper end, surrounded by a group of tentacles, is the mouth whichleads to the central cavity. The wall of this simple body is composed oftwo layers of cells, between which there is a gelatinous layer rarelyinvaded by cells. The inner layer lines the central space into which foodorganisms are thrust by the tentacles, and it is concerned primarily withdigestion. The outer layer comprises cells for protection and sensationprimarily. Cells of both layers have muscular prolongations which by theiroperation enable the whole animal to change its form and to move from oneplace to another. 

It may seem that such an animal is totally unlike any of the higher andmore complex types. In certain respects, however, it is identical with theother forms inasmuch as it performs all of the eight biological tasksdemanded by nature. It is also similar in so far as its inner layer, likethe innermost sheet of cells in higher forms, is concerned with problemsof taking and preparing food, while the protective outer layer resemblesin function the outermost covering of all animals higher in the scale. Beyond these a still more fundamental agreement is found in its cellularcomposition. 

At the lower end of the animal scale are organisms which consist of onecell and nothing more. _Amoeba_, to which we must refer again and again, is an example of this group which possesses an overwhelming importance tothe comparative student because the origins of all the characteristics ofanimals higher in the scale are to be found within it. _Amoeba_ itselfis a naked mass of protoplasm, about 1/100 of an inch in diameter, enclosing a nucleus. Its form is not constant during activity, forfingerlike processes called pseudopodia are pushed out tentatively in manydirections to be followed as circumstances direct by the materials of thewhole cell body. Other protozoa differ in possessing constant forms, or inhaving constant vibratile processes, or shells of some kind, while instill other cases like individuals combine to make colonies which are moreor less definite and permanent. Here at the very foot of the organic scaleare found animals which seem to be entirely different from those above. Upon examination they, like _Hydra_, prove to be the same as regards thenumber and kind of functions they perform, but in structural regards theirevolutionary relation to all higher animals is indicated solely by thefact that they are cells composed of protoplasm. Nevertheless theprinciple which states that resemblance means consanguinity still holdstrue, for cellular constitution is a unique possession of things of theliving world, --something which demonstrates the common origin of allliving things just as truly as the "cat-_ness_" of our first series ofexamples reveals for a smaller group the significance of likeness and thenature of the basic law of comparative anatomy. 

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Employing a figure of speech, we have climbed down the animal tree fromthe higher regions where the mammals belong. Having reached the very footof the trunk we are in a position to review and summarize the evidenceswhich we have discovered all about us as we have descended. The variousexamples we have mentioned and the groups to which they belong clearlyoccupy different places in the scale which begins with the protozoa andextends upward to the most complicated and differentiated animals. _Hydra_takes its place above the protozoa for obvious structural reasons; wormsbelong to a still higher zone, surpassed by the more complex jointedanimals like crustacea and insects. Far above these are the vertebrates, among which we have already demonstrated the occurrence of differentgrades of organization, from the fish up to the higher amphibia andreptiles, and beyond in two directions to the diverging birds and mammals. The basic characteristics of every group in a high position may be tracedback to some one or another of the divisions at a lower level, so that thegeneral sequence of the structural levels from low to high becomesintelligible as the order of their evolution. 

To my mind the rudimentary and vestigial structures of animals are inthemselves proof positive of a natural history of change. The fewillustrations can be reinforced by countless examples offered by everygroup of living animals. If such structures have not evolved naturally bydegenerating from more efficient counterparts in ancestors of earliertimes, and if they have been specially created, they are utterlymeaningless and their very existence is unreasonable. If common sense isto be employed, they demonstrate evolution. 

Everywhere throughout the whole series animals place themselves in atreelike arrangement, for in their respective levels they occur likeleaves at the ends of the lines of descent which have led up to them andwhich are comparable to the branches and limbs arising from the trunk of atree. Thus the major and minor divisions of animals do not follow in theorder of the rungs of a ladder, even though they must be assigned todifferent levels according to the complexity of their construction. Thesummary given above, namely, that the occurrence of lower and higherlevels reveals an order of evolution, is amplified and not contradicted bythe statement that the species of animals are group in a treelikearrangement. It is the task of the evolutionist, provided with all thefacts of comparative anatomy and dealing only with the various species asseparate leaves, so to speak, to reconstruct the now invisible but notunreal twigs and branches and limbs of the animal tree, and to show howthey have diverged at one time or another as they have grown and spread toproduce the species of the present day. This he may do in so far as he mayfind sufficient materials to enable him to employ the methods ofcomparative anatomy and the great natural principle established by thismethod--that essential likeness means consanguinity. 

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 No evidence of evolution could be more significant and interesting thanthe results provided by the comparative study of development. In the firstplace it is an obvious fact that every living thing changes in the courseof its life-history, and if as an adult it occupies a high place in theanimal scale, its embryological transformation is more elaborate andintricate than in the case of a lower form. Every one knows that organismsdo develop, and yet I believe that few appreciate the tremendoussignificance of the mere fact that this is true, while still fewer areaware that the peculiar and characteristic early stages through which ananimal passes in becoming an adult are even more striking than the fact ofdevelopment itself. We shall learn something of these earlier conditionsin the development of some of our most familiar animals, but at the outsetnothing can be more important than an appreciation of the first greatlesson of this department of natural history--namely that organictransformation is real and natural. We do not need to employ the methodsof formal logic to know that in growing up a human infant undergoes thechanges of childhood and adolescence, that kittens become cats, and thatan oak tree is produced by an acorn, for we know these things directly byobserving them. It is natural for development to take place under normalconditions, and if it does not, then something has interfered with nature. Inasmuch as "growing up" is accomplished by the alteration of an organicmechanism with one structure into an individual with a changed plan ofbody, it is in essence the actual process of evolution which thecomparative study of grown animals of to-day demonstrates in the way wehave learned. The study of animal structure discovers the process ofevolution because the most reasonable interpretation of the similaritiesand minor differences exhibited everywhere by the various groups ofanimals is that descent with adaptive and divergent modification has takenplace; the result is reached by inference, it is true, but by scientificand logical inference. With development it is otherwise. No reasoning isnecessary to tell us that organic transformation is a real and a naturalprocess. We see it everywhere about us and we ourselves have come to bewhat we are by a natural history of change. Can we consistently deny thatit is possible for a species to alter in the long course of time when afew brief weeks are sufficient for the new-laid egg of the fowl to developinto a fledgling? Many indeed strain at the gnat of the longer process inthe past when without hesitation they recognize the real and obvious factof individual development in a brief period. 

I have said that development is a "natural" process. We employ this wordfor the familiar and everyday occurrence or thing; it does not imply thateverything is known about the object or phenomenon, because science knowsthat complete and final knowledge is impossible. We say that it is naturalfor rain to fall to the earth, and we speak of the law of gravitationaccording to which this takes place as a natural principle, but it may nothave occurred to many to inquire _what_ makes rain fall and _why_ domasses of matter everywhere behave toward one another in the consistentmanner described by the law in question. Sunshine is natural, but we donot know _why_ light travels as it does from the sun to the earth, andthis is another question which, like the inquiry into the ultimate causeof the familiar and natural phenomenon of gravitation, has not yet beenanswered. But it is still regarded as natural for the rain to fall and forthe sun to shine. In the same way does science view development, denotingit natural because it is an ordinary everyday matter. And we are under nomore obligation to postulate supernatural control for the changing formsin the life-history of a chick or a cat than we need to assume thatgravitation and the radiation of light demand immediate supernaturaldirection. The embryology of no form is fully understood or described orexplained, but no intelligent person would be willing to assert thatbecause complete knowledge is lacking, it is unnatural for organictransformation to take place during growth. Whatever may be the ultimateorigin and nature of the directing powers behind gravitation anddevelopment and other phenomena, we have no concern with such mattersbecause they cannot be handled by scientific methods and one belief aboutthem is on the same plane with any other. Our task is to deal with theeveryday phenomena of life and the production of living species. 

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It is not necessary to go far afield to find an animal which willintroduce us to the general principles of embryology. In the presentinstance as in the case of comparative anatomy almost any form willdisclose the meaning of development, for animate nature is uniform andconsistent in its methods of operation throughout its wide range. We shallbegin with the familiar frog which every one knows is a product of atadpole; passing on to the chick we will learn more facts that will enableus to formulate the main principle of comparative embryology in definiteterms; we will then be prepared to extend our survey so as to includesomewhat less familiar facts and animals that are even more significantthan the first illustrations. 

If we should visit a woodland pond in early spring, we would findsomewhere among the leaves and sticks in the water large masses of a clearjellylike consistency enclosing hundreds of little black spheres about aneighth of an inch in diameter. These are the egg masses and eggs of acommon frog. Watching them day by day we see the small one-celled eggspheres divide into more and more numerous portions which are thedaughter-cells, destined to form by their products the many varied tissuesand organs of the developing larva and adult frog. After three or fourdays the egg changes from its globular form into an oval or ellipticalmass, and from one end of this a small knob projects to become a flattenedwaving tail a few days later. On the sides of the larger anterior portionshallow grooves make their appearance and soon break through from thethroat or pharynx to the exterior as gill-slits. Shortly afterwards thelittle embryo wriggles out of its encasing coat of jelly, develops amouth, and begins its independent existence as a small tadpole, with eyes, nasal and auditory organs, and all other parts that are necessary for afree life. Thus the one-celled egg has transformed into something that itwas not at first, and in doing this it has proved the possibility and thereality of organic reconstruction. 

The tadpole breathes by means of its gills, and it is at first entirelydevoid of the lungs which the adult frog possesses and uses. When we speakof the larval respiratory organs as gills we imply that they are like theorgans of a fish which have the same name; they are truly like those offishes, for the blood-vessels which go to them are essentially the same asin the lower types and they are supported by simple skeletal rods like thegill-bars of the fish. In a word, they are the same things. 

The animal feeds and grows during the months of its first summer, andhibernates the following winter; with the warmth of spring it revives andproceeds further along the course of its development. Near the base of thetail two minute legs grow out from the hinder part of the body, and whilethese are enlarging two front legs make their appearance a little behindthe gills. The tadpole now rises more frequently to the surface where ittakes small mouthfuls of air. Meanwhile great changes are effected insidethe body where the various systems of fishlike organs become remodeledinto amphibian structures. A sac is formed from the wall of the esophagus, and this enlarges and divides to form the two simple lungs. The legsincrease in size, the tail dwindles more and more, the gills close up, andsoon the animal hops out on land as a complete young frog. From this timeon it breathes by means of its lungs instead of gills, even though itreturns to the water to escape its foes, to seek its prey, and tohibernate in the mud of the lake bed during the winter months. 

All these changes are familiar and natural, but until science places themand similar facts in their proper relations their significance is lost tous. The tadpole is essentially a fish in its general structure and mode oflife, even though its heritage is such that it can develop into a higheranimal. When it does become a frog it proves beyond a doubt that there isno impassable barrier between fishes and amphibia. Our earlier comparisonof the structures of these two classes of vertebrates led to theconclusion that the latter had evolved from antecedents like the former, and had thus followed them upon the earth; now that sequence seems to havesome connection with the method by which a tadpole, obviously not a fishbut nevertheless actually fishlike, changes into a frog, a member of ahigher class of vertebrates. This method is employed by developing frogsapparently because it follows the ancestral order of events, and because, so to speak, the only way a frog knows how to become a frog is to developfrom an egg first into a fishlike tadpole and then to alter itself as itsancestors did during their evolution in the past. We begin to see, then, that in addition to the impressive fact of development itself, the mode oforganic transformation is far more conclusive evidence of evolution, because it reveals an order of events which parallels the orderestablished by comparative anatomy as the evolutionary sequence. 

However it is well to review some of the changes by which a chick comesinto existence before attempting to comprehend fully the fundamentalprinciple of development that the tadpole's history discloses to us. Theegg of a common fowl is certainly not a chick. Within the calcareous shellare two delicate membranes that enclose the white or albumen; within this, swung by two thickened cords of the albumen, is the yellow yolk ballenclosed by a proper membrane of its own. In the earliest condition, evenbefore the albumen and the shell are added and before the egg is laid, onone side of the yolk-mass there is a tiny protoplasmic spot which is atfirst a single cell and nothing more. The hen's egg is relativelyenormous, but nevertheless, like that of the frog, it starts upon itscourse of development as a single unitary biological element--a cell. During the earliest subsequent hours the first cell divides again andagain to form a small disk upon the surface of the yolk. Soon the cellsalong the middle line of this small sheet become rearranged to make anobvious streak or band, and about this line a simple tube is constructedwhich is destined to become the future brain and spinal cord. The wholedisk continues to enlarge by further division of its constituent elementsso that it encloses more and more of the yolk mass, but the little chickitself is made out of the cells along the central line of the originalplate, from which it folds at the sides and in front and behind so as tolie somewhat above and apart from the flatter enclosing cell layers whichpartly surround the yolk. 

At the sides of the primitive nerve-tube small blocks of cells arise todevelop into primitive muscles and other structures. As nourishment isbrought to the embryo from the surrounding layers enclosing the nutrientyolk, one system after another takes its shape and builds its severalparts into organs which can be recognized as elementary structures of achick. Among the more interesting ones are small clefts or slits formed inthe side walls of the rudimentary throat or pharynx. Blood-vessels goforward from the simple heart to run up through the intervening barsexactly as in the tadpole and the fish. In brief, the young chickpossesses a series of gill-slits, for these structures are the same inessential plan and relations as the clefts of tadpoles and fishes. Doesthis mean that even birds have descended from gill-breathing ancestors?Science answers in the affirmative, because evolution gives the onlyreasonable explanation of such facts as these. The case seems differentfrom that of the frog, because gills are used by the tadpole, butgill-slits and gill-bars can have no conceivable value for the chick asorgans concerned with the purification of the blood. None the less, if thetransition from a gilled tadpole to the adult with lungs means anevolution of amphibia from fishlike ancestors, then the change of a chickembryo with gill-clefts into the fledgling without them is most reasonablyinterpreted as proof that birds as well as amphibia have had ancestors assimple as fishes. 

As development progresses four small pads make their appearance; two ofthese lie on either side of the body back of the head and the other twoarise near the posterior end. They are far from being wings and legs, butas day follows day they become molded into somewhat similar limbs, as muchalike in general plan as the four legs of a lizard; subsequently the onesat the front change into real wings and the hinder ones become legs. Meanwhile the internal organs slowly transform from fishlike structuresinto things that display the characteristics of reptilian counterparts, and only later do they become truly avian. Last of all the finishingtouches are made, and the whole creature becomes a particular kind of abird which picks its way out of the shell and shifts for itself as achick. 

Only a few of the countless details have been mentioned which demonstratethe resemblance of the successive stages first to fishes, and later toamphibia and reptiles. We have a wide choice of materials, but even theforegoing brief list of illustrations shows that the order in which thestages follow is the one which comparative anatomy independently proves tobe the order of the evolution of fishes, amphibia, reptiles, and birds. Why, now, should it be necessary for a developing bird to follow thisorder? The answer has been found in the immense array of embryologicalfacts that investigators have verified and classified, that all tell thesame story. It is, that birds have arisen by evolution from ancestorswhich were really as simple as the members of these lower classes. Itseems then that the only way a bird of to-day can become itself is totraverse the path along which its progenitors had progressed in evolution. Stating its conclusions precisely, science formulates the principle in thefollowing words: _individual development is a brief résumé of the historyof the species in past times_, or, more technically, _ontogenyrecapitulates phylogeny_. To be sure, the full history is not reviewed indetail, for the chick embryo does not actually swim in water and breatheby means of gills. Only a condensed account of evolution of its kind ispresented by an embryo during its development; as Huxley and Haeckel haveput it, whole lines and paragraphs and even pages are left out; many falsepassages of a later date are inserted as the result of peculiar larval andembryonic needs and adjustments. But in its major statements and as ageneral outline, the account is a trustworthy natural document submittedas evidence that higher species of to-day have evolved from ancestorswhich must have been like some of the present lower animals. 

Coming now to the mammalia, it might seem that we have reached forms sohighly developed that they would not exhibit the same kind ofdevelopmental history, but would have their own mode of growing up. Thisis not so, for like the adult fish, the larval tadpole, and the embryochick, an embryo of a cat or a man is at one time constructed with aseries of gill-clefts and with blood-vessels and skeletal supports offishlike nature that are everywhere associated with gills. The embryos ofwildcats and dogs, rabbits and rats, pigs, deer, and sheep, and of allother mammalia, possess similar structures. Thus they all pass through astage which is found also in the development of reptiles, birds, andamphibia, --a stage which corresponds to the fish throughout its life. Unless these facts mean that the great classes of vertebrates haveoriginated together from the same or closely similar ancestors, they areunintelligible; for we cannot see why a cat or a chick should have to beessentially fishlike at any time unless this is so. Comparative anatomystates as we have learned that the amphibia as a class have evolved fromand have out-developed the fishes, that reptiles have progressed stillhigher, and that birds and mammals have originated from reptilianancestors along roads that have diverged beyond the immediate parentclass. Because the members of each class have to pass along the same pathtrodden by their many varied ancestors, although at express speed, as itwere, the similarity of the earliest stages in their development isexplained, for during these periods they are traversing a path over whichtheir ancestors passed together. 

The places where the developing embryos depart from the common mode showwhere the several divisions took leave of one another in theirevolution, --a point that comes out with great clearness when the facts ofmammalian development are broadly compared. The embryos of carnivora androdents and hoofed animals are alike in their earlier development, andtheir agreement means a community of origin. At a certain point the cat anddog depart from the common mode, but they remain alike up to a far laterstage than the one in which they are similar to the embryos of rats andsheep. The rat and squirrel and rabbit, on their part, remain togetheruntil long after they take leave of the carnivora and ungulates; while thesheep and cattle and pigs have their own branch line, which they follow incompany after leaving the embryos of the other orders. The reasons forthese facts seem to be that the members of the three orders exemplifiedhave evolved from the same stock, which accounts for their embryonicsimilarity for a long time after they collectively come to differ fromamphibia and reptiles, while the members in each order becamedifferentiated only later, wherefore their embryonic paths coincide for alonger period. Thus the degree of adult resemblance which indicates thecloseness of relationship corresponds with the degree of embryonicagreement; that is, the cat and dog are much alike and their modes ofdevelopment are essentially the same to the latest stages, while the catand horse agree only during the earliest and middle stages, and their linesdiverge before those of the cat and dog on the one hand, or those of thehorse and pig on the other. 

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Like the fundamental principle of comparative anatomy in its sphere, theLaw of Recapitulation, formulated as a summary description of theforegoing and similar facts, is one that holds true throughout the entirerange of embryology and for every division of the animal series, howeverlarge or small. We have discussed its broader application, and now we maytake up some of the more or less special cases mentioned in the earliersection of the present chapter, to see how it may work in detail. 

The flounder was noted as a variant of the fish theme which seemed to be adescendant of a symmetrical ancestor because its structural plan was likethat of other bony fishes. If this be true, and if in its development aflounder must review its mode of evolution as a species, the young fishought to be symmetrical; and it actually is. The grotesque skate andhammerhead shark were demonstrated to be derivatives of a simpler type ofshark; their embryos are practically indistinguishable from those ofordinary dogfish and sharks. 

Among the jointed animals a wealth of interesting material is found by theembryologist. All crabs seemed to be modified lobsterlike creatures; toconfirm this interpretation, based solely upon details of adult structure, young crabs pass through a stage when to all intents and purposes they arecounterparts of lobsters. Even the twisted hermit crab, which has asoft-skinned hinder part coiled to fit the curve of the snail shell used asa protection, is symmetrical and lobster-like when it is a larva. 

Among the insects many examples occur that are already familiar to everyone. The egg of a common house-fly hatches into a larva called a maggot;in this condition the body destined to become the vastly different fly iscomposed of soft-skinned segments very much alike and also similar to thejoints of a worm. Comparative anatomy demonstrates that the fly and allother insects have arisen from wormlike ancestors, whose originallysimilar segments later differentiated in various ways to become thediverse segments of adult insects; the embryonic history of flies ofto-day corroborates these assertions, in so far as every individual flyactually does become a wormlike larva before it changes into the final andcomplete adult insect. The other kinds of insects are equally striking intheir life-histories. All beetles, such as the potato bug and June bug, develop from grubs which, like the maggots of flies, are similar to wormsin numerous respects. Butterflies and moths pass through a caterpillarstage having even more striking resemblances to worms. All the larvæ ofinsects are therefore like one another, and like worms also, in certainfundamental characters of internal and external structure; so theconclusion that the whole group of insects has arisen by evolution frommore primitive ancestors resembling the worms of to-day is based uponmutually explanatory details of comparative anatomy and embryology. 

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Let us now turn back to some of the earlier pages of the embryologicalrecord which we passed over in order that we might translate the laterportions dealing with more familiar and intelligible structures likegills. Before the egg of the frog becomes an elliptical mass of cells, itis at one time a double-walled sac enclosing a central cavity; in thisstage it is called a _gastrula_. Tracing back the mode of its formation, we find that it is produced from a hollow sphere of fewer cells that areessentially alike; this stage also is so important that the special term_blastula_ is applied to it. Still earlier, there are fewer cells--128 orthereabouts, 64, 32, 16, 8, 4, 2, and 1. In other words, the startingpoint in the development of the frog is a _single biological unit_; thisdivides and its products redivide to constitute the many-celled blastulaand the double-walled gastrula. All the other animals we have mentionedbegin like the frog, as eggs which are single cells and nothing more; theytoo pass on to become blastulæ and gastrulæ, similar to those of the frogin all essential respects, particularly as regards the nature of theorgans produced by each of the two primary layers, and the mode of theirformation. Does the occurrence of blastulæ and gastrulæ and one-celledbeginnings mean that the higher animals composed of numerous and muchdifferentiated cells have evolved in company from two-layered saccularancestors which were themselves the descendants of spherical colonies oflike cells, and ultimately of one-celled animals?

Comparative anatomy has asserted that this is so, as we have alreadylearned, for it finds that adult animals array themselves at differentlevels of a scale beginning at the bottom with the protozoa, continuing onto the two-layered animals like _Hydra_ and jellyfish and sea-anemones, and then extending upwards to the region of the more complicatedinvertebrates and vertebrates. It was difficult perhaps to believe thatthese successive grades of organic structure indicated an order ofevolution, because it seemed impossible that an animal so simple as aprotozoan could produce offspring with the complex organization of a frogor a cat, even in long ages. But development delivers its evidencerelating to this matter with telling and impressive force. How can wedoubt the possibility of an evolution of higher animals from ancestors assimple as _Hydra_ and _Amoeba_ when a frog and a cat, like all othercomplicated organisms, begin individual existence as single cells, andpass through gastrula stages? If we deny it, we contradict the evidence ofour senses, for the development is actually accomplished by thetransformation of a single cell into a double-walled sac, and of this intodifferent and more intricate organic mechanisms. The process _can_ takeplace, for it _does_ take place. Not until the investigator becomesfamiliar with a wide range of diverse animals and the peculiar qualitiesof their similar early stages, can he estimate the tremendous weight ofthe facts of comparative embryology. Were the statement iterated andreiterated on every page and in every paragraph, there would be no undueemphasis put upon the astounding fact that the apparently impassable gapbetween a one-celled animal like _Amoeba_ and a mammal like a cat isactually compassed during the development of the last-named organisms fromsingle cells. The occurrence of gill-slits in the embryos of lizards, birds, and mammals now seems a small thing when compared with thecorrespondences disclosed by the earliest stages of development. But inspite of their complexity, all the changes of "growing up" are explainedand understood by the simple formula that the mode of individualdevelopment owes its nature primarily to the hereditary influence ofearlier ancestors back to the original animals which were protozoa. 

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Embryology as a distinct division of zoölogy has grown out of studies ofclassification and comparative anatomy. Its beginnings may be found inmedieval natural history, for as far back as 1651 Harvey had pointed outthat all living things originate from somewhat similar germs, the tersedictum being "Ex ovo omnia. " By the end of the eighteenth century many hadturned to the study of developing organisms, though their views by nomeans agreed as to the way an adult was related to the egg. Some, likeBonnet, held that the germ was a minute and complete replica of itsparent, which simply unfolded and enlarged like a bud to produce a similarorganism. Even if this were true, little would be gained, for it wouldstill remain unknown how the germinal miniature originated to be just whatit was conceived and assumed to be. Wolff was the originator of the viewthat is now practically universal among naturalists, namely, thatdevelopment is a real process of transformation from simpler to morecomplex conditions. 

The subject of comparative embryology grew rapidly during the nineteenthcentury as the field of comparative anatomy became better known, and whennaturalists became interested in animals, not only as specific types, butalso as the finished products of an intricate series of transformations. When life-histories were more closely compared, the meaning of theresemblances between early stages of diverse adult organisms was read bythe same method which in comparative anatomy finds that consanguinity isexpressed by resemblance. The great law of recapitulation, stated in oneform by Von Baer and more definitely by Haeckel in the terms employed inthe foregoing sections, was for a time too freely used and too rigidlyapplied by naturalists whose enthusiasm clouded their judgment. A strongreaction set in during the latter part of the nineteenth century, whenattention was directed to the anachronisms of the embryonic record and tothe alterations that are the results of larval or embryonic adaptation asshort cuts in development. Nevertheless, it is not seriously questioned, Ibelieve, that the main facts of a single life-history owe their nature tothe past evolution of the species to which a given animal belongs. 

Nowadays the problems in this well-organized department are concerned notonly with more accurate accounts of the development of animals, but alsowith the mechanics of development, with the relative value of external andinternal influences, and above all with the physical basis of inheritance. It is clear that the factors that direct the development of a wood frog'segg so that it becomes a wood-frog and not a tree-toad must lie in the eggitself, as derivatives from the two parent organisms. Weismann and hisfollowers have proved that a peculiar substance in the nuclei of the eggand its daughter-products contains the essential factors of development, whatever these may be. Experiments dealing with the phenomena of heredityin pure and mixed breeds have largely confirmed Weismann's doctrine, andthey have prepared the way for a deeper investigation of the marvelousprocess of biological inheritance. 

However much he may be interested in the details of embryological science, the general student of natural history is more concerned with the bearingof its primary laws upon the great problem of evolution. In the foregoingbrief review of the fundamental facts and principles of this subject, thepurpose has been to show how the phenomena of development are viewed bymen of science, and how they take their place in the doctrine of organicevolution. And it has also been made plain that comparative anatomy andcomparative embryology support and supplement one another in countlessways and places, although each in itself is a complete demonstration thatevolution is a real and a natural process. 

III

THE EVIDENCE OF FOSSIL REMAINS

Few natural objects appeal to the interest and imagination of the studentwith more force than the fragments of animals and plants released from therocks where they have been entombed for ages. Our lives are so brief thatit is impossible for us to comprehend the full duration of the slowprocess which constructed the burial shrouds of these creatures of longago. We try to picture the earth and its inhabitants as they were whenlizards were the highest forms of animals, and we wonder how life waslived in the dense forests of the coal age. Science can never learn allabout the ancient history of the earth and of the organisms of bygonetimes; yet it has been able to accomplish much through its endeavors toreconstruct the past, for its method is one by which sure results canalways be obtained whenever there are definite facts with which it canwork. In our present study of evolution we reach the point when we mustexamine the testimony of the rocks, and the results and methods of thatdepartment of knowledge called palæontology, which is concerned withfossils and their interpretation. 

The word "palæontology" means literally the "science of living things oflong ago. " It deals directly with the remains of animals and plants foundas fossils, and it interprets them through its knowledge of the way modernanimals are constructed and of the changes the earth's crust hasundergone. A skull-like object may be found in a coal field and may comeinto the hands of the palæontologist: from his acquaintance with the headskeletons of recent types he will be able to assign the extinct creaturewhich possessed the skull to a definite place in the animal scale and tounderstand its nearer or wider affinities with other animals of latertimes and of earlier epochs. In doing these things palæontology employsthe methods of comparative anatomy with which we have now become familiar. In the performance of its other tasks, however, palæontology must workindependently. It is necessary to know when a fossilized animal lived, notthat its time need be measured by an absolute number of a few thousands ormillions of years antedating our own era, for that is impossible. But theimportant thing is to know its relative age, and whether it preceded orfollowed other similar animals of its own group or of different divisions. The rocks themselves must be understood, how they have been formed and howthey are related in mineralogical nature and in historical succession. Palæontology also deals with a number of subjects that are not inthemselves biological, such as the combination of circumstances necessaryfor the adequate preservation of fossil relics. In so far as it isconcerned with physical matters, as contrasted with strictly biologicaldata, it is one with geology. Indeed, the investigators in these twodepartments must always work side by side and render mutual assistance toone another in countless ways, for each division needs the results of theother in order to accomplish its own distinct purposes. It must be evidentto every one that it is impossible to understand the meaning of fossilsand the place of the testimony of the rocks in the doctrine of evolutionwithout knowing much about the geological history of the earth and theinfluences at work in the past. For these reasons palæontology differssomewhat from the other divisions of zoölogy where direct observationgives the materials for arrangement and study; in this case the individualdata, that is, the fossil fragments themselves, can be made available onlythrough a knowledge of their exact situations, of the reasons for theiroccurrence in particular places in the rock series and of the way rocksthemselves are constructed and worked over by natural agencies. Our taskis therefore twofold: certain physical matters of a geological nature mustfirst be investigated before the biological facts can be described. 

No doubt most people feel justified in believing that the whole doctrineof evolution must stand or fall according to the cogency of thepalæontological evidences. Plain common sense says that the owners ofshelly or bony fragments found in the deeply-laid strata of the earth musthave lived countless years ago, and if the evolutionist asserts thatprimitive organic forms of ancient times have produced changed descendantsof later times, it would seem that fossil evidence would be supremely andoverwhelmingly important. It is true, of course, that this evidence ispeculiarly significant, because in some ways it is more direct than thatof the other categories already outlined. But it must not be forgottenthat the doctrine is already securely founded upon the basic principles ofanatomy and embryology. Science must treat the data of this category bydifferent methods and must view them in different ways. Therefore we areinterested in palæontology because of the way it tells the story ofevolution in its own words, and because we are justified in expecting thatits account should include a description of some such order of events asthat revealed by the developing embryos of modern organisms and thatdemonstrated by the comparative anatomy of the varied species of adultanimals. 

It is true that palæontology gives direct testimony about the evolutionarysuccession of animals in geologic time. But we now know that embryology iseven more direct in its proof that organic transformation is natural andreal; while at the same time there is a completeness in the full series ofdevelopmental stages connecting the one-celled egg with the adult creaturethat must be forever lacking in the case of the fossil sequence ofspecies. If paragraphs and pages are missing from the brief embryonicrecapitulation, whole chapters and volumes of the fossil series have beenlost for all time. The investigators whose task it has been to decipherthe story of the earth's evolution have had to meet numerous andexasperating difficulties which do not confront the embryologist andanatomist who study living materials. Nevertheless the library ofpalæontological documents is one which has been founded for over acentury, and it has grown fast during recent decades, so that consistentaccounts may now be read of the great changes in organic life as the earthhas altered and grown older. And in all this record, there is not a singleline or word of fact that contradicts evolution. What definite evidencethere is tells uniformly in favor of the doctrine, for it is possible, inthe first place, to work out the order of succession of many of the greatgroups of animals, and this order is found to be the same as thatestablished by the other bodies of evidence. Secondly, some fossil groupsare astonishingly complete, so that the ancient history of a form like thehorse can be written with something approaching fullness. Finally, theremains of certain animals have been found so situated in geological ways, and so constructed anatomically, that the zoölogist is justified indenoting them "missing links, " because they seem to have been intermediatebetween groups that have diverged so widely during recent epochs as torender their common ancestry scarcely credible. 

With these general results in mind, we must now become acquainted withsuch subjects as the interpretation of fossils, the causes for theincompleteness of the series, the conditions for fossilization, the forcesof geological nature, and other matters that make the fossils themselvesintelligible as scientific evidence. 

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Many views have been entertained regarding the actual nature of the relicsof antiquity exhumed from the rocks or exposed upon the surface by thewear and tear of natural agencies. In earliest times such things werevariously considered as curious freaks of geological formation, as sportsof nature, or as the remains of the slain left upon the battle-ground ofmythical Titans. Some of the Greeks supposed that fossils were parts ofanimals formed in the bowels of the earth by a process of spontaneousgeneration, which had died before they could make their way to thesurface. They were sometimes described as the bones of creatures strandedupon the dry land by tidal waves, or by some such catastrophe as thetraditional flood of the scriptures. In medieval times, and even in ourown day, some people who have been opposed to the acceptance of anyportion of the doctrine of evolution have actually defended the view thatthe things called fossils were never the shells or bones of animals livingin bygone times, but that they only simulate such things and have beencreated as such together with the layers of rock from which they may havebeen taken. If we employed the same arguments in dealing with the brokenfragments of vases and jewelry taken from the Egyptian tombs or from theburied ruins of Pompeii, we would have to believe that such pieces werecreated as fragments and that they were never portions of completeobjects, just because no one alive to-day has ever seen the perfect vesselor bracelet fashioned so long ago. Common sense directs us to discard sucha fantastic interpretation in favor of the view that fossils are what theyseem to be--simply relics of creatures that lived when the earth wasyounger. 

Until this common sense view was adopted there was no science ofpalæontology. Cuvier was the first great naturalist to devote particularattention to the mainly unrelated and unverified facts that had beendiscovered before his time. He was truly the originator of this branch ofzoölogy, for he brought together the observations of earlier men andextended his own studies widely and surely, emphasizing particularly thenecessity for noting carefully the geological situation of a fossil inrocks of an older or later period of formation. His great result was thedemonstration that many groups of animals existed in earlier ages thatseem to have no descendants of the same nature to-day, and also that manyor most of our modern groups are not represented in the earliest formedsedimentary rocks, although these recent forms possess hard parts whichwould surely be present somewhere in these levels if the animals actuallyexisted in those times. But the meaning of these facts escaped Cuvier'smind. He was a believer in special creation, like Linnæus and all but afew among his predecessors, and he explained the diversity of the faunasof different geological times in what seems to us a very simple and naïveway. In the beginning, he held, when the world was created, it wasfurnished with a complete set of animals and plants. Then some greatupheaval of nature occurred which overwhelmed and destroyed all livingcreatures. The Creator then, in Cuvier's view, proceeded to construct anew series of animals and plants, which were not identical with those ofthe former time, but were created according to the same general workingplans or architectural schemes employed before. Another cataclysm wassupposed to have occurred, which destroyed the second series of organismsand laid a new covering of rocks over the earth's surface for a subsequentperiod of relative quiet; and so the process was continued. By thisaccount, Cuvier endeavored to reconcile the doctrine of supernaturalcreation and intervention with the obvious facts that organisms havediffered at various times in the earth's history. Although he saw thatanimals of successive periods displayed similar structures, like theskeleton of vertebrates, which testified to some connection, Cuvier couldnot bring himself to believe that this connection was a genealogical one. 

Mainly through the influence of the renowned English man of science, Charles Lyell, the students of the earth came to the conclusion that itsmanifold structures had developed by a slow and orderly process that wasentirely natural; for they found no evidence of any sudden and drasticworld-wide remodeling such as that postulated by the Cuvierian hypothesisof catastrophe. The battle waged for many years; but now naturalistsbelieve that the forces, of nature, whose workings may be seen on allsides at the present time, have reconstructed the continents and oceanbeds in the past in the same way that they work to-day. The long name of"uniformitarianism" is given to Lyell's doctrine, which has exerted aninfluence upon knowledge far outside the department of geology. Darwintells us how much he himself was impressed by it, and how it led him tostudy the factors at work upon organic things to see if he could discernevidence of a biological uniformitarianism, according to which the pasthistory of living things might be interpreted through an understanding oftheir present lives. 

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What, now, are the reasons why the palæontological evidence is notcomplete and why it cannot be? In the first place the seeker after fossilremains finds about three fifths of the earth's surface under water sothat he cannot explore vast areas of the present ocean beds which wereformerly dry land and the homes of now extinct animals. Thus the field ofinvestigation is seriously restricted at the outset, but the naturalistfinds his work still more limited, in so far as much of the dry landitself is not accessible. The perennial snows of the Arctic region renderit impossible to make a thorough search in the frigid zone, and there aremany portions of the temperate and torrid zones that are equallyunapproachable for other reasons. But even where exploration is possible, the surface rocks are the only ones from which remains can be readilyobtained, for the layers formed in earlier ages are buried so deeply thattheir contents must remain forever unknown in their entirety. Only a fewscratches upon the earth's hard crust have been made here and there, so itis small wonder that the complete series of extinct organisms has not beenproduced by the palæontologist. 

A brief survey of the varied groups of animals themselves is sufficient tobring to light many biological reasons which account for still more of thevacant spaces in the palæontological record. We would hardly expect tofind remains of ancient microscopic animals like the protozoa, unless theypossessed shells or other skeletal structures which in their aggregatemight form masses like the chalk beds of Europe. Jellyfish and worms andnaked mollusks are examples of the numerous orders of lower animals havingno hard parts to be preserved, and so all or nearly all of the extinctspecies belonging to these groups can never be known. But when an animallike a clam dies its shell can resist the disintegrating effects ofbacteria and other organic and inorganic agencies which destroy the softparts, and when a form like a lobster or a crab, possessing a bodyprotected by closely joined shell segments, falls to the bottom of thesea, the chances are that much of the animal's skeleton will be preserved. Thus it is that corals, crustacea, insects, mollusks, and a few otherkinds of lower forms constitute the greater mass of invertebratepalæontological materials because of their supporting structures of onekind or another. Perhaps the skeletal remains of the vertebrates of thepast provide the student of fossils with his best facts, on account of theresistant nature of the bones themselves, and because the backbonedanimals are relatively modern; then, too, the rocks in which their remainsoccur have not been so much altered by geological agencies, or buried sodeeply under the strata formed later. Of course only the hardest kinds ofshells would remain as such after their burial in materials destined toturn into rock; in the majority of cases, an entombed bone is infiltratedor replaced by various mineral substances so that in time little ornothing of the original thing would remain, though a mold or a cast wouldpersist. 

But even if an animal of the past possessed hard structures, it must havesatisfied certain limited conditions to have its remains prove serviceableto students of to-day. A dead mammal must fall upon ground that has justthe right consistency to receive it; if the soil is too soft, its severalparts will be separated and scattered as readily as though it had fallenupon hard ground where it would be torn to pieces by carnivorous animals. The dead body must then be covered up by a blanket of silt or sand likethat which would be deposited as the result of a freshet. If a skeleton istoo greatly broken up or scattered, it may be difficult or even impossiblefor its discoverer to piece together the various fragments and assemblethem in their original relations. Very few individuals have been so buriedand preserved as to meet the conditions for the formation of an idealfossil. To realize how little may be left of even the most abundant ofhigher organisms, we have only to recall that less than a century agoimmense herds of bison and wild horses roamed the Western plains, but veryfew of their skulls or other bones remain to be enclosed and fossilized infuture strata of rocks. When we appreciate all these difficulties, bothgeological and biological, we begin to see clearly why the ancient linesof descent cannot be known as we know the path and mode of embryonictransformation. The wonder is not that the palæontological record isincomplete, but that there is any coherent and decipherable record at all. Yet in view of the many and varied obstacles that must be surmounted bythe investigator, and the adverse factors which reduce the availableevidence, the rapidly growing body of palæontological facts is amplysufficient for the naturalist to use in formulating definite andconclusive principles of evolution. 

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For the purposes of palæontology, the most essential data of geology arethose which indicate the relative ages of the strata that make up the hardouter crust of the earth, for only through them can the order of animalsuccession be ascertained. It does not matter exactly how old the earthmay be. While it is possible to determine the approximate length of timerequired for the construction of sedimentary rocks like those whichnatural agencies are producing to-day, there are few definite facts toguide speculation as to the mode or duration of the process by which thefirst hard crystalline surface of the earth was formed. But palæontologydoes not care so much about the earliest geological happenings, for it isconcerned with the manifold animal forms that arose and evolved after lifeappeared on the globe. Questions as to the way life arose, and as to theearliest transformations of the materials by which the earth was firstformed are not within the scope of organic evolution, although they relateto intensely interesting problems for the student of the process of cosmicevolution. 

According to the account now generally accepted, the original material ofthe earth seems to have been a semi-solid or semi-fluid mass formed by thecondensation of the still more fluid or even gaseous nebula out of whichall the planets of the solar system have been formed and of which the sunis the still fiery core. As soon as the earth had cooled sufficiently itssubstances crystallized and wrinkled to form the first mountains andridges; between and among these were the basins which soon filled with thecondensing waters to become the earliest lakes and oceans. The wear andtear of rains and snows and winds so worked upon the surfaces of thehigher regions that sediments of a finer or coarser character like sandand mud and gravel were washed down into the lower levels. These sedimentswere afterwards converted into the first rocks of the so-called stratifiedor sedimentary series, as contrasted with the crystalline or plutonicrocks like the original mass of the earth and the kinds forced to thesurface by volcanic eruptions. Later the earth wrinkled again in variousways and places so that new ridges and mountains were formed with newsystems of lakes and oceans and rivers; and again the elements continuedto erode and partially destroy the higher masses and to lay down new andlater series of sedimentary rocks upon the old. 

It seems scarcely credible that the apparently weak forces of nature likethose we have mentioned are sufficiently powerful to work over the massivecrust of the earth as geology says they have. Our attention is caught, asa rule, only by the greater things, like the earthquakes at San Franciscoand Valparaiso, and the tidal waves and cyclones of the South Seas; butthe results of these sporadic and local cataclysms are far less than theeffects of the persistent everyday forces of erosion, each one of whichseems so small and futile. When we look at the Rocky Mountains with theirhigh and rugged peaks, it seems almost impossible that rain and frost andsnow could ever break them up and wear them down so that they would becomelike the rounded hills of the Appalachian Mountain chain, yet this is whatwill happen unless nature's ways suddenly change to something which theyare not now. A visitor to the Grand Cañon of the Colorado sees amagnificent chasm over a mile in depth and two hundred miles long whichhas actually been carved through layer after layer of solid rock by therushing torrents of the river. Perhaps it is easier to estimate thegeological effects of a river in such a case as Niagara. Here we find adeep gorge below the famous falls, which runs for twenty miles or so toopen out into Lake Ontario. The water passing over the brim of the fallswears away the edge at a rate which varies somewhat according to theharder or softer consistency of the rocks, but which, since 1843, hasaveraged about 104 inches a year. Knowing this rate, the length of thegorge, and the character of the rocky walls already carved out, the lengthof time necessary for its production can be safely estimated. It is about30, 000 to 40, 000 years, not a long period when the whole history of theearth is taken into account. A similar length of time is indicated for therecession of the Falls of St. Anthony, of the Mississippi River, anagreement that is of much interest, for it proves that the two riversbegan to make their respective cuttings when the great ice-sheet recededto the north at the end of the Glacial epoch. 

What has become of the masses washed away during the formation of thesegorges? As gravel and mud and silt the detritus has been carried to thestill waters of the lower levels, to be laid down and later solidifiedinto sandstone and slate and shale. All over the continents these thingsare going on, and indefatigable forces are at work that slowly but surelyshear from the surface almost immeasurable quantities of earth and rock tobe transported far away. In some instances it is possible to find out justhow much effect is produced in a given period of time, especially in thecase of the great river systems. For example, the mass of the fineparticles of mud and silt carried in a given quantity of the water of theMississippi as it passes New Orleans can be accurately measured, and asatisfactory determination can also be made of the total amount of watercarried by in a year. From these figures the amount of materials insuspension discharged into the Gulf of Mexico becomes known. It issufficient to cover one square mile to the depth of 269 feet; in twentyyears it is one cubic mile, or five cubic miles in a century. Turning nowto the other aspect of this process, and the antecedent causes whichproduce these effects, it appears that the area of the Mississippi Riverbasin is 1, 147, 000 square miles--about one third of the total area of theUnited States. Knowing this, and the annual waste from its surface, it iseasy to demonstrate that it will take 6000 years to plane off an averageof one foot of soil and rock from the whole of this immense area. Ofcourse only an inch or a few inches will be taken from some regions wherethe ground is harder or rockier, or where little rain falls, while manyfeet will be washed away from other places. The waters of the Hoang-hocome from about 700, 000 square miles of country, from which one foot ofsoil is washed away in 1464 years. The Ganges River, draining about143, 000 square miles, carries off a similar depth of eroded materials fromits basin in 823 years! Should we add to the above figures those thatspecify the bulk of the chemical substances in solution carried by thesewaters, the total would be even greater. We know that in the case of theThames River, calcareous substances to the amount of 10, 000 tons a yearare carried past London, and all this mineral has been dissolved byrain-water from the chalky cliffs and uplands of England, so that the landhas become less by this amount. Thus we learn that vast alterations arebeing made in the structure of great continents by rain and rivers, as wellas by glaciers and other geological agencies. And at the same time that oldstrata are undergoing destruction new ones are in process of constructionat other places, where animal remains can be embedded and preserved asfossils. The forces at work seem weak, but they continue their operationsthrough ages that are beyond our comprehension and they accomplish resultsof world-building magnitude. 

Thus the whole process of geological construction is such that olderexposed strata continually undergo disintegration, but this involves thedestruction of any fossils that they might contain. The very forces thatpreserve the relics of extinct animals at one time undo their work at alater period. There are many other influences besides that destroy theregularity of rock layers or change their mineralogical characters bymetamorphosis. It is easier to see how volcanic outbursts alter theirneighboring territory. The intense subterranean heat and imprisoned steammelt the deeper substances of the earth's crust, so that these materialsboil out, as it were, where the pressure is greatest, and where lines offracture and lesser resistance can be found. Because so much detritus isannually added to the ocean floors--enough to raise the levels of theoceans by inches in a century--it is natural that greater pressures shouldbe exerted in these areas than in the slowly thinning continental regions. These are some of the reasons why volcanoes arise almost invariably alongthe shores or from the floors of great ocean beds. The chain that extendsfrom Alaska to Chili within the eastern shore of the Pacific Ocean, andthe many hundreds of volcanoes of the Pacific Islands bring to the surfacevast quantities of eruptive rocks which break up and overlie thesedimentary strata formed regularly in other ways and at other times. Thevolcanoes of the Java region alone have thrown out at least 100 cubicmiles of lava, cinders, and ashes during the last 100 years--twenty timesthe bulk of the materials discharged into the Gulf of Mexico by theMississippi River in the same period of time. 

From these and similar facts, the naturalist finds how agencies of thepresent construct new rocks and alter the old; and so in the light of thisknowledge, he proceeds with his task of analyzing the remote past, confident that the same natural forces have done the work of constructingthe lower geological levels because these earlier products are similar tothose being formed to-day. After learning this much, he must immediatelyundertake to arrange the strata according to their ages. This might seem adifficult or even an impossible task, but the rocks themselves provide himwith sure guidance. 

Wherever a river has graven its deep way through an area of hard rocks, asin the case of Niagara, the walls display on their cut surfaces a seriesof lines and planes showing that they are superimposed layers formedserially by deposits that have differed some or much at different timesaccording to the circumstances controlling the erosion of theirconstituent particles. A layer of several feet in thickness may becomposed of compact shale, while above it will be a zone of limestone, andagain above this another layer of shale. Successive strata like these, where they are parallel and obviously undisturbed, are evidently arrangedin the order of their formation and age. But by far the most impressivedemonstration of the basic principle of geology employed for thedetermination of the relative ages of rocks is the mighty Cañon of theColorado. As the traveler stands on the winding rim of this vast chasm, his eye ranges across 13 miles of space to the opposite walls, whichstretch for scores of miles to the right and left; upon this serried facehe will see zone after zone of yellow and red and gray rock arranged withmathematical precision and level in the same order as on the steep slopesbeneath him. Plain common sense tells him that the great sheets of rockstretched continuously at one time between the now separate walls, andthat the various strata of sandstone and limestone were deposited insuccessive ages from below upwards in the order of their exposure. Whennow he extends his explorations to another state like Utah or Wyoming, hemay find some but not all of the series exhibited in the Grand Cañon, overlaid or underlaid by other strata which in their turn can be assignedto definite places in the sequence. By the same method, the geologistcorrelates and arranges the rocks not only of different parts of the samestate, or of neighboring states, but even those of widely separated partsof North America and of different continents. But he learns that he mustrefrain from over-hasty conclusions, for he soon finds that thesedimentary rocks have not been constructed at the same rate in differentplaces during one and the same epoch, and that rocks formed even at oneperiod are not always identical in nature. But his guiding principle issensible and reasonable, and by employing it with due caution he providesthe palæontologist with the requisite knowledge for his special task, which is to arrange the extinct animals whose remains are found as fossilsof various earth ages in the order of their succession in time. 

CONDENSED TABLE OF PALAEONTOLOGICAL FACTS

__________________________________________________________________________ | | | | YEARS | NUMBER OF | | | ORDER OFNECESSARY FOR | FEET IN | GEOLOGICAL | GEOLOGICAL | APPEARANCE OF FORMATION | THICKNESS | AGE | EPOCH | CHARACTERISTIC | | | | GROUPS______________|___________|______________|_______________|________________ | | | | | | | | M B R A F I | | | | a i e m i n b | | | | m r p p s v r | | Recent | | m d t h h e a | | or | | a s i i e r t | | Quaternary | | l l b s t e | | | | s e i e s | | | | s a -______________|___________|______________|_______________|_|_|_|_|_|_|____ | | | | | | | | | | | | | Pleistocene | | | | | | | | | Cenozoic | Pliocene | | | | | | | 5, 000, 000 | 25, 000 | or | Miocene | | | | | | | | | Tertiary | Oligocene | | | | | | | | | | Eocene | | | | | | |______________|___________|______________|_______________|_|_|_|_|_|_|____ | | | | | | | | | | | | Mesozoic | Cretaceous | | | | | | | 4, 000, 000 | 23, 000 | or | Jurassic | | | | | | | | | Secondary | Triassic | | | | | |______________|___________|______________|_______________|_____|_|_|_|____ | | | | | | | | | | | Permian | | | | | | | Palæozoic | Carboniferous | | | | 21, 000, 000 | 106, 000 | or | Devonian | | | | | Primary | Silurian | | | | | | Cambrian | | |______________|___________|______________|_______________|________________ | | | | 20, 000, 000 | 30, 000 | Azoic | Archæn |______________|___________|______________|_______________|________________

After what seems an unduly long preparation, we now come to the actualbiological evidence of evolution provided by the results of this divisionof zoölogical science. But all of the foregoing is fundamentally part ofthis department of knowledge and it is absolutely essential for any onewho desires to understand what the fossils themselves demonstrate. 

The oldest sedimentary rocks are devoid of fossil remains and so they arecalled the Azoic or Archæan. They comprise about 30, 000 feet of stratawhich seem to have required at least 20, 000, 000 years for their formation. This period is roughly two-fifths of the whole time necessary for theformation of _all_ the sedimentary rocks, and this proportion holds trueeven if the entire period of years should be taken as 100, 000, 000 insteadof 50, 000, 000 or less. The earth during this early age was slowlyorganizing in chemical and physical respects so that living matter couldbe and indeed was formed out of antecedent substances--but this processdoes not concern us here. The important fact is that the second majorperiod, called the Palæozoic, or "age of ancient animals, " saw theevolution of the lowest members of the series, --the invertebrates, --andthe most primitive of the backboned animals, like fishes and amphibia. Therocks of this long age include about 106, 000 feet of strata, demandingsome 21, 000, 000 or 22, 000, 000 years for their deposition. Thus it isproved that the invertebrate animals were succeeded in time by the highervertebrates, which is exactly what the evidences of the previouscategories have shown. When we remember that the lower animals are devoidas a rule of skeletal structures that might be fossilized, and when werecall the fact that the strata of the palæozoic provided the materialsout of which the upper layers were formed afterwards, we can understandwhy the ancient members of the invertebrate groups are not known as wellas the later and higher forms like vertebrates. Yet all the fossils ofthese relatively unfamiliar creatures clearly prove that no complex animalappears upon a geological horizon until after some simple type belongingto a class from which it may have taken its origin; in brief, there are noanachronisms in the record, which always corresponds with the recordwritten by comparative anatomy, wherever the facts enable a comparison tobe made. 

But the extinct animals of the third and fourth ages are more interestingto us, because there are more of them and because they are more like thewell-known organisms of our present era. These two ages are called theMesozoic or Secondary, and the Cenozoic or Tertiary. The former is sonamed because it was a transitional age of animals that are intermediatein a general way between the primitive forms of the preceding age andthose of the next period; the latter name means the "recent-animal" age, when evolution produced not only the larger groups of our present animalseries, but also many of the smaller branches of the genealogical treelike orders and families to which the species of to-day belong. 

Confining our attention to the large vertebrate classes, the testimony ofthe rocks proves, as we have said, that fishes appeared first in what arecalled the Silurian and Devonian epochs, where they developed into a richand varied array of types unequaled in modern times. At that period, theywere the highest existing animals--the "lords of creation, " as it were. Tochange the figure, their branch constituted the top of the animal tree ofthe time, but as other branches grew upwards to bear their twigs andleaves, as the counterparts of species, the species of the branch offishes decreased in number and variety, as do the leaves of a lower partof a tree when higher limbs grow to overshadow them. 

Following the fishes, the amphibia arose during the coal age orCarboniferous, usurping the proud position of the lower vertebrate class. The reptiles then appeared and gained ascendancy over the amphibia, tobecome in the Mesozoic age the highest and most varied of the existingvertebrates. At that time there were the great land dinosaurs with alength of 80 feet, like _Brontosaurus_; aquatic forms like _Ichthyosaurus_and _Plesiosaurus_, whose mode of evolution from terrestrial to swimminghabits was like that of seals and penguins of far later eras. Flyingreptiles also evolved, to set an example for the bats of the mammalianclass, for both kinds of flying organisms converted their anterior limbsinto wings, although in different ways. 

During the Triassic and Jurassic periods of the Mesozoic age, the firstbirds and mammals appeared to follow out their diverging and independentlines of descent. Palæontology makes it possible to trace the origin anddevelopment of many of the different branches that grew out of themammalian limb from different places and at different times during theMesozoic and the following age, called the Cenozoic, or age of recentanimals. It is unnecessary, however, for us to review more of the details:the main result is obvious; namely, that the appearance of the greatclasses of vertebrates is in the order of comparative anatomy andembryology. Not only, then, is the fact of evolution rendered trebly sure, but the general order of events is thrice and independently demonstratedto be one and the same. Surely we must see that no reasonable explanationother than evolution can be given for these basic facts and principles. 

Turning now to the second division of palæontological evidence, we come tothose groups where abundant materials make it possible to arrange theanimals of successive epochs in series that may be remarkably complete. For the reasons specified, the backboned animals provide the richestarrays of these series, and such histories as those of horses andelephants have taken their places in zoölogical science as classics. Buteven among the invertebrates significant cases may be found. For example, in one restricted locality in Germany the shells of snails belonging tothe genus _Paludina_ have been found in superimposed strata in the orderof their geological sequence. The ample material shows how the severalspecies altered from age to age by the addition of knobs and ridges to thesurface of the shell, until the fossils in the latest rocks are fardifferent from their ancestors in the lowermost levels. Yet theintervening shells fill in the gaps in such a way as to show almostperfectly how the animals worked out their evolutionary history. Thisexample illustrates the nature of many other known series of mollusks andof brachiopods, extending over longer intervals and connecting more widelyseparated ages like the Secondary and the present period. 

Since the doctrine of evolution and its evidences began to occupy thethoughts of the intellectual world at large, no fossil forms have receivedmore attention than the ancient members of the horse tribe. As we havelearned, a modern horse is described by comparative anatomy as a one-toeddescendant of remote five-toed ancestors. When the hoofed animals ofmodern times were reviewed as subjects for comparative anatomical study, the odd-toed forms arranged themselves in a series beginning with ananimal like an elephant with the full number of five digits on each footand ending at the opposite extreme with the horse. A reasonableinterpretation of these facts was that the animals with fewer toes hadevolved from ancestors with five digits, of which the outer ones hadprogressively disappeared during successive geological periods, while themiddle one enlarged correspondingly. The facts provided by palæontologysustain this contention with absolutely independent testimony. Disregarding some problematical five-toed forms like _Phenacodus_, thefirst type of undoubted relationship to modern horses is _Hyracotherium_, a little animal about three feet long that lived during the Eocene periodof the Cenozoic epoch. Its forefeet had four toes each, and its hinderlimbs ended with three toes armed with small hoofs, but one of itsrelatives of the same time has a vestige of another digit on the hindfoot. By the geological time mentioned, therefore, the earliest truehorses had already lost some of the toes that their progenitors possessed. In the Miocene the extinct species, obviously descended from the Eoceneforms, had lost more of their toes; still higher, that is, in the rocksformed during succeeding periods of time, the animals of this division aremuch larger and each of their feet has only three toes, of which themiddle one is the largest while the ones on the sides are small andwithdrawn from the ground so as to appear as useless vestiges. To producemodern horses and zebras from these nearer ancestors, few additionalchanges in the structure of the feet are necessary, for the lateral toesneed only to become a little more reduced and the middle one to enlargeslightly to give the one-toed limb of modern types, with its splint-likevestiges still in evidence to show that the ancestor's foot comprised moreof these terminal elements. Comparing the animals of successive periods, these and other skeletal structures demonstrate that the ancestry of eachgroup of species is to be found in the animals of the preceding epoch, andthat the whole history of horses is one of natural transformation, --in aword, of evolution. 

No less interesting in their own way are the remains of other hoofed formsthat lead down to the elephants of to-day and to the mammoth and mastodonof relatively recent geologic times. Common sense would lead to theconclusion that a form like a modern tapir was the prototype from whichthese creatures have arisen, and common sense would lead us to expect thatif any fossils of the ancestors of the modern group of elephants occurredat all they would be like tapirs. Thus a fossil of much significance inthis connection is _Moeritherium_, whose remains have been found in therocks exposed in the Libyan desert, for this creature was practically atapir, while at the same time its characters of muzzle and tusk mark it asvery close to the ancestors of the larger woolly elephants of latergeological times, when the trunk had grown considerably and the tusks hadbecome greatly prolonged. Again the fossil sequence confirms theconclusions of comparative anatomy, regarding the mode by which certainmodern animals have evolved. 

The fossil deer of North America, as well as many other even-toed membersof the group of mammalia possessing hoofs, provide the same kind ofconclusive evidence. The feature of particular interest in the case oftheir horns, is a correspondence between the fossil sequence and the orderof events in the life-history of existing species, --that is, between theresults of palæontology and of embryology. Horns of the earliest knownfossil deer have only two prongs; in the rocks above are remains of deerwith additional prongs, and point after point is added as the ancienthistory of deer is traced upwards through the rocks to modern species. Weknow that the life-history of a modern species of animals reviews theancestral record of the species, and what happens during the developmentof deer can be directly compared with the fossil series. It is a matter ofcommon knowledge that the year-old stag has simple spikes as horns, andthat these are shed to be replaced the following year by larger forkedhorns. Every year the horns are lost and new ones grow out, and becomemore and more elaborately branched as time goes on, thus giving a seriesof developmental stages that faithfully repeats the general order offossil horns. Even Agassiz, who was a believer in special creation and anopponent of evolution, was constrained to point out many other instances, mainly among the invertebrata, where there was a like correspondencebetween the ontogeny of existing species and their phylogenetic history asrevealed by the fossil remains of their ancestors. 

 * * * * *

In the last place, we must give more than a passing consideration to someof the extinct types of animals that occupy the position of "links"between groups now widely separated by their divergence in evolution fromthe same ancestors. Perhaps the most famous example is _Archæopteryx_found in a series of slates in Germany. This animal is at once afeathered, flying reptile, and a primitive bird with countless reptilianstructures. Its short head possesses lizard-like jaws, all of which bearteeth; its wings comprise five clawed digits; its tail is composed of along series of joints or vertebræ, bearing large feathers in pairs; itsbreastbone is flat and like a plate, thus resembling that of reptiles anddiffering markedly from the great keeled breastbone of modern flyingbirds, whose large muscles have necessitated the development of the keelfor purposes of firm attachment. In brief, this animal was close to thepoint where reptiles and birds parted company in evolution, and althoughit was a primitive bird, it is in a true sense a "missing link" betweenreptiles and the group of modern birds. Other fossil forms like_Hesperornis_ and _Ichthyornis_, whose remains occur in the strata of alater date, fill in the gap between _Archæopteryx_ and the birds at thepresent time, for among other things they possess teeth which indicatetheir origin from forms like _Archæopteryx_, while in other respects theyare far nearer the birds of later epochs. That these links are not uniqueis proved by numerous other examples known to science, such as those whichconnect amphibia and reptiles, ancient reptiles and primitive mammals, aswell as those which come between the different orders of certainvertebrate classes. 

In summarizing the foregoing facts, and the larger bodies of evidence thatthey exemplify, we learn how surely the testimony of the rocks establishesevolution in its own way, how it confirms the law of recapitulationdemonstrated by comparative embryology, and how it proves that the greaterand smaller divisions of animals have followed the identical order intheir evolution that the comparative study of the present day animals hasindependently described. 

 * * * * *

The facts of geographical distribution constitute the fifth division ofzoölogy, and an independent class of evidences proving the occurrence ofevolution. This department of zoölogy assumed its rightful status onlyafter the other divisions had attained considerable growth. Manynaturalists before Darwin and Wallace and Wagner had noticed that animalsand plants were by no means evenly distributed over the surface of theglobe, but until the doctrine of evolution cleared their vision they didnot see the meaning of these facts. As in the case of all the otherdepartments of zoölogy the immediate data themselves are familiar, butbecause they are so obvious the mind does not look for theirinterpretation but accepts the facts at their face value. While thephenomena of distribution are no less fascinating to the naturalist, andno less effective in their demonstration of evolution, their comprehensivetreatment would demand more space than the whole purpose of the presentdescription of organic evolution would justify. Thus a brief outline onlycan be given of the salient principles of this subject in order that theirbearing upon the problem of species may be indicated. 

Even as children we learn many facts of animal distribution; every oneknows that lions occur in Africa and not in America, that tigers live inAsia and Malaysia, that the jaguar is an inhabitant of the Brazilianforests, and that the American puma or mountain lion spreads from north tosouth and from east to west throughout the American continents. Theoccurrence of differing human races in widely separated localities is noless familiar and striking, for the red man in America, the Zulu inAfrica, the Mongol and Malay in their own territories, display the samediscontinuity in distribution that is characteristic of all other groupsof animals and of plants as well. As our sphere of knowledge increases, weare impressed more and more forcibly by the diversity and unequal extentof the ranges occupied by the members of every one of the varied divisionsof the organic world. Another fact which becomes significant only whenscience calls our attention to it is the absence from a land likeAustralia of higher mammals such as the rabbit of Europe. The hypothesisof special creation cannot explain this absence on the assumption that therabbit is unsuited to the conditions obtaining in the country named, forwhen the species was introduced into Australia by man, it developed andspread with marvelous rapidity and destructive effect. It may seemimpossible that facts like these could possess an evolutionarysignificance, but they are actual examples of the great mass of databrought together by the naturalists who have seen in them something to beinterpreted, and who have sought and found an explanation in theformularies of science. 

The general principles of distribution appear with greatest clearness whenan examination is made of the animals and plants of isolated regions likeislands. The Galapagos Islands constitute a group that has figured largelyin the literature of the subject, partly because Darwin himself was soimpressed by what he found there in the course of his famous voyage aroundthe world in the "Beagle. " They form a cluster on the Equator about sixhundred miles west of the nearest point of the neighboring coast of SouthAmerica. Although the lizards and birds that live in the group differsomewhat among themselves as one passes from island to island, on thewhole they are most like the species of the corresponding classesinhabiting South America. Why should this be so? On the hypothesis ofspecial creation there is no reason why they should not be more like thespecies of Africa or Australia than like those of the nearest body of themainland. The explanation given by evolution is clear, simple, andreasonable. It is that the characteristic island forms are the descendantsof immigrants which in greatest probability would be wanderers from theneighboring continent and not from far distant lands. Reaching theisolated area in question the natural factors of evolution would leadtheir offspring of later generations to vary from the original parentaltypes, and so the peculiar Galapagos species would come into being. Thefact that the organisms living on the various islands of this group differsomewhat in lesser details adds further justification for the evolutionaryinterpretation, because it is not probable that all the islands would bepopulated at the same time by similar stragglers from the mainland. Thefirst settlers in one place would send out colonies to others, whereindependent evolution would result in the appearance of minor differencespeculiar to the single island. In this manner science interprets thegeneral agreement between the animals of the Azores Islands and the faunaof the northwestern part of Africa, the nearest body of land, from whichit would be most natural for the ancestors of the island fauna to come. 

The land-snails inhabiting the various groups of islands scatteredthroughout the vast extent of the Pacific Ocean provide the richest andmost ideal material for the demonstration of the principles ofgeographical distribution. In the Hawaiian Islands snails of the family ofAchatinellidæ occur in great abundance, and like the lizards of theGalapagos Islands different species occur on the different members of thegroup. Within the confines of one and the same island, they vary fromvalley to valley, and the correlation between their isolation ingeographical respects and specific differences on the other hand, firstpointed out by Gulick, makes this tribe of animals classical material. InPolynesia and Melanesia are found close relatives of the Achatinellidæ, namely, the Partulæ, which are thus in relative proximity to theAchatinellidæ and not on the other side of the world. Furthermore, thePartulæ are not alike in all of the groups of Polynesia where they occur;the species of the Society Islands are absolutely distinct from those ofthe Marquesas, Tonga, Samoan, and Solomon Islands, although they agreeclosely in the basic characters that justify their reference to a singlegenus. The geological evidence tells us that these islands were once thepeaks of mountain ranges rising from a Pacific continent which has sincesubsided to such an extent that the mountain tops have become separateislands. Thus the resemblances between Hawaiian and Polynesian snails, andthe closer similarities exhibited by the species of the various groups ofPolynesia, are intelligible as the marks of a common ancestry in awidespread continental stock, while the observed differences show theextent of subsequent evolution along independent lines followed out afterthe isolation of the now separated islands. The principle may be workedout in even greater detail, for it appears that within the limits of onegroup diverse forms occupy different islands, evolved in different ways intheir own neighborhoods; while in one and the same island, the populationsof the different valleys show marked effects of divergence in laterevolution, precisely as in the case of the classic Achatinellidæ of theHawaiian Islands. 

The broad and consistent principle underlying these and related facts isthis: _there is a general correspondence between the differences displayedby the organisms of two regions and the degree of isolation or proximityof these two areas_. Thus the disconnected but neighboring areas of theGalapagos Islands and South America support species that resemble eachother closely, for the reasons given before; long isolated areas likeAustralia and its surroundings possess peculiar creatures like theegg-laying mammals, and all of the pouched animals or marsupials with onlyone or two exceptions like our own American opossum, --a correlationbetween a geological and geographical discontinuity on the one hand and apeculiarity on the other that reinforces our confidence in thefaunal evolutionary interpretation of the facts of distribution. 

It is true that the various classes of animals do not always appear withcoextensive ranges. The barriers between two groups of related specieswill not be the same in all cases. A range like the Rocky Mountains willkeep fresh-water fish apart, while birds and mammals can get acrosssomewhere at some time. All these things must be taken into account inanalyzing the phenomena of distribution, and many factors must be givendue attention; but in all cases the reasons for the particular state ofaffairs in geographical and biological respects possess an evolutionarysignificance. 

Having then all the facts of animal natural history at his disposal, andthe uniform principles in each body of fact that demonstrate evolution, itis small wonder that the evolutionist seems to dogmatize when he assertsthat descent with adaptive and divergent modification is true for allspecies of living things. The case is complete as it stands to-day, whileit is even more significant that every new discovery falls into line withwhat is already known, and takes its natural place in the all-inclusivedoctrine of organic evolution. Because this explanation of thecharacteristics of the living world is more reasonable than any other, science teaches that it is true. 

IV

EVOLUTION AS A NATURAL PROCESS

The purpose of the discussions up to this point has been to present thereasons drawn from the principal classes of zoölogical facts for believingthat living things have transformed naturally to become what they now are. Even if it were possible to make an exhaustive analysis of all of theknown phenomena of animal structure, development, and fossil succession, the complete bodies of knowledge could not make the evolutionaryexplanation more real and evident than it is shown to be by the simplefacts and principles selected to constitute the foregoing outline. We havedealt solely with the evidences as to the fact of evolution; and now, having assured ourselves that it is worth while to so do, we may turn tothe intelligible and reasonable evidence found by science which provesthat the familiar and everyday "forces" of nature are competent to bringabout evolution if they have operated in the past as they do to-day. Investigation has brought to light many of the subsidiary elements of thewhole process, and these are so real and obvious that they are simplytaken for granted without a suspicion on our part of their power untilscience directs our attention to them. 

For one reason or another, those who take up this subject for the firsttime find it difficult to banish from their minds the idea that evolution, even if it ever took place, has been ended. They think it futile to expectthat a scrutiny of to-day's order can possibly find influences powerfulenough to have any share in the marvelous process of past evolutiondemonstrated by science. The naturalists of a century ago held a similaropinion regarding the earth, viewing it as an immutable and unchangedproduct of supernatural creation, until Lyell led them to see that theworld is a plastic mass slowly altering in countless ways. It is no moretrue that living things have ceased to evolve than that mountains andrivers and glaciers are fixed in their final forms; they may seemeverlasting and permanent only because a human life is so brief incomparison with their full histories. Like the development of a continentas science describes it, the origin of a new species by evolution, itsrise, culmination, and final extinction may demand thousands of years; sothat an onlooker who is himself only a conscious atom of the turbulentstream of evolving organic life does not live long enough to observe morethan a small fraction of the whole process. Therefore living species seemunchanged and unchangeable until a conviction that evolution is true, anda knowledge of the method of science by which this conviction is borneupon one, guide the student onwards in the further search for theefficient causes of the process. 

The biologist employs the identical methods used by the geologist inworking out the past history of the earth's crust. The latter observes theforces at work to-day, and compares the new layers of rock now beingformed with the strata of deeper levels; these are so much alike that heis led to regard the constructive influences of the past as identical withthose he can now watch at work. Similarly the biologist must first learn, as we have done, the principles of animal construction and development, and of other classes of zoölogical facts, and then he must turn hisattention from the dead object of laboratory analysis to the workings oforganic machines. The way an organism lives its life in dynamic relationsto the varied conditions of existence, as well as the mutual physiologicalrelations of the manifold parts of a single organism, reveal certaindefinite natural forces at work. Therefore his next task is to compare theresults accomplished by these factors in the brief time they may be seenin operation with the products of the whole process of organic evolution, to learn, like the geologist in his sphere, that the present-day naturalforces are able to do what reason says they have done in the past. 

When the subject of inquiry was the reality of evolution, it was perhapssurprising to find that even the most familiar animals like cats and frogsprovided adequate data for science to use in formulating its principles. So it is with the matter of method; it is unnecessary to go beyond theobservations of a day or a week of human life to find forces at work, asreal and vital as animal existence and organic life themselves. This istrue, because evolution is true, and because the lives of all creaturesfollow one consistent law. Our task is therefore much more simple thanmost people suppose it to be; let us look about us and classify what wemay observe, increasing our knowledge from the wide array of equallynatural facts supplied by the biologist. 

The analogies of the steamship and the locomotive proved useful at manytimes during the discussion of the fact of evolution, and even in thepresent connection they will still be of service. The evolution of thesedead machines has been brought about by man, who, as an element of theirenvironment, has been their creator as well as the director of theirhistorical transformations. The result of their changes has been greaterefficiency and better adjustment or adaptation to certain requirementsfixed by man himself. The whole process of improvement has been one, inbrief, of trial and error; new inventions have often been worthless, andthey have been relegated to the scrap-heap, while the better part has beenfinally incorporated in the type machine. In brief, then, the importantelements in the evolution of these examples have been three; first, _adaptation_, second, the _origination of new parts_, and third, the_retention of the better invention_. 

Are the creatures of the living world so constituted that biologicalequivalents of these three essential elements of mechanical evolution canbe found? Are organisms adapted to the circumstances controlling theirlives, and are they capable of changing naturally from generation togeneration, and of transmitting their qualities to their offspring? Theseare definite questions that bring us face to face with the fundamentalproblems relating to the dynamics or workings of evolution. We need notask for or expect to find complete answers, for we know that it isimpossible to obtain them. But we may expect to accomplish our immediateobject, which is to see that evolution is natural. Our attention must beconcentrated upon the three biological subjects of _adaptation_, _variation, _ and _inheritance_, and we must learn why science describesthem as real organic phenomena and the results of natural causes. 

 * * * * *

At the very outset, when the general characteristics of living things wereconsidered, much was said on the subject of adaptation as a universalphenomenon of nature. It was not contended that perfection is attained byany living mechanism, but it was held that no place exists in nature foran organism that is incapable of adjusting itself to the manifoldconditions of life. A _modus vivendi_ must be established and somesatisfactory degree of adaptation must be attained, or else an animal or aspecies must perish. With this fundamental point as a basis, we look tonature for two kinds of natural processes or factors, first, those whichmay originate variations as _primary factors_, --the counterparts of humaningenuity and invention in the case of locomotive evolution, --and the_secondary factors_ of a preservative nature which will perpetuate themore adaptive organic changes produced by the first influences; it isclear that the latter are no less essential for evolution than the firstcauses for the appearance of variations. 

The term "variation" is employed for the natural phenomenon of being orbecoming different. It is an obvious fact that no child is ever exactlylike either of its parents or like any one of its earlier ancestors; whilefurthermore in no case does an individual resemble perfectly another ofits own generation or family. This departure from the parental condition, and the lack of agreement with others even of its closest blood-relatives, are two familiar forms of variation. As a rule, the degree to which agiven organism is said to vary in a given character is most convenientlymeasured by the difference between its actual condition and the generalaverage of its species, even though there is no such thing as a specimenof average nature in all of its qualities. In brief, then, variation meansthe existence of some differences between an individual and its parents, its fraternity, and, in a wider sense, all others of its species. 

Passing now to the causes of variation, all of the countless deviations ofliving things can be referred to three kinds of primary factors; namely, the _environmental_, _functional_, and _congenital_ influences that workupon the organism in different ways and at different times during itslife. We shall learn that the evolutionary values of these three classesare by no means equal, but we take a long step forward when we realizethat among the things we see every day are facts demonstrating the realityof three kinds of natural powers quite able to change the characters oforganic mechanisms. 

The "environment" of an organism is everything outside the creatureitself. In the case of an animal it therefore includes other members ofits own kind, and other organisms which prey upon its species or whichserve it as food, as well as the whole series of inorganic influenceswhich first come to mind when the term is used. For example, theenvironment of a lion includes other lions which are either members of itsown family, or else, if they live in the same region, they are its more orless active rivals and competitors. In the next place, other kinds ofanimals exist whose lives are intimately related to the lion's life, suchas the antelopes or zebras that are preyed upon, and the human hunter towhom the lion itself may fall a victim. In addition, there are thecontrasted influences of inorganic nature which demand certain adjustmentsof the lion's activities. Light and darkness, heat and cold, and otherfactors have their direct and larger or smaller effects upon the life of alion, although these effects are less obvious in this instance than in thecase of lower organisms. 

The reality of variations due to the inorganic elements of the environmentis everywhere evident. Those who have spent much time in the sun are awarethat sunburn may result as a product of a factor of this class. The amountof sunlight falling upon a forest will filter through the tree-tops so asto cause some of the plants beneath to grow better than others, thusbringing about variations among individuals that may have sprung from themyriad seeds of a single parent plant. In times of prolonged drought, plants cannot grow at the rate which is usual and normal for theirspecies, and so many variations in the way of inhibited development mayarise. 

Then there are the variations of a second class, more complex in naturethan the direct effects of environment, --namely, the functional results ofuse and disuse. A blacksmith uses his arm muscles more constantly than domost other men, and his prolonged exercise leads to an increase of hismuscular capacity. All of the several organic systems are capable ofconsiderable development by judicious exercise, as every one knows. If thefunctional modifications through use were unreal, then the routine of thegymnasium and the schoolroom would leave the body and the mind as theywere before. Furthermore, we are all familiar with the opposite effects ofdisuse. Paralysis of an arm results in the cessation of its growth. When afall has injured the muscles and nerves of a child's limb, that structuremay fail to keep pace with the growth of the other parts of the body as aresult of its disuse. These are simple examples of a wide range ofphenomena exhibited everywhere by animals and even by the human organism, demonstrating the plasticity of the organic mechanism and its modificationby functional primary factors of variation. 

But by far the greater number of variations seem to be due to theso-called congenital causes, which are sharply contrasted with theinfluences of the first and second classes. It is quite true that theinfluences of the third class cannot be surely and directly demonstratedlike the others, but however remote and vague they themselves may appear tobe, their effects are obvious and real, while at the same time theireffects are to be clearly distinguished from the products of the other twokinds. Congenital factors reside in the physical heritage of an organism, and their results are often evident before an individual is subjected toenvironmental influences and before it begins to use its various organs. For example, it is a matter of common observation that a child with lighthair and blue eyes may have dark-eyed and brown-haired parents. The factof difference is a phenomenon of variation; the causes for this factcannot be found in any other category than that comprising the hereditaryand congenital influences of parent upon offspring. _How_ the effect isproduced by such causes is less important in the present connection thanthe natural _fact_ of congenital variation. Science, however, has learnedmuch about the causes in question, as we shall see at a later point. 

Thus the first step which is necessary for an evolution and transformationof organic mechanisms proves to be entirely natural when we give onlypassing attention to certain obvious phenomena of life. The fact of"becoming different" cannot be questioned without indicting our powers ofobservation, and we must believe in it on account of its reality, eventhough the ultimate analysis of the way variations of different kinds areproduced remains for the future. 

Having learned that animals are able to change in various ways, the nextquestion is whether variations can be transmitted to future generationsthrough the operation of secondary factors. Long ago Buffon held that thedirect effects of the environment are immediately heritable, although themode of this inheritance was not described; it was simply assumed andtaken for granted. Thus the darker color of the skin of tropical humanraces would be viewed by Buffon as the cumulative result of the sun'sdirect effects. Lamarck laid greater stress upon the indirect orfunctional variations due to the factors of use and disuse, and he alsoassumed as self-evident that such effects were transmissible as "acquiredcharacters. " This expression has a technical significance, for it refersto variations that are added during individual life to the whole group ofhereditary qualities that make any animal a particular kind of organism. If evolution takes place at all, any new kind of organism originating froma different parental type must truly acquire its new characteristics, butfew indeed of the variations appearing during the lifetime of an animalowe their origin to the functional and environmental influences, whoseeffects only deserve the name of "acquired characters" in the specialbiological sense. 

In sharp contrast to Lamarckianism, so called, --although it did notoriginate in the mind of the noted man of science whose name it bears, --isthe doctrine of natural selection, first proposed in its full form byCharles Darwin. This doctrine presents a wholly natural description of themethod by which organisms evolve, putting all of the emphasis upon thecongenital causes of variation, although the reality of other kinds ofchange is not questioned. But the contrast between Darwinism and the otherdescriptions of secondary factors can best be made after a somewhatdetailed discussion of the former, which has gained the adherence of themajority of the naturalists of to-day. However, we must not pass onwithout pointing out that however much the explanations given by variousmen of science may differ, they all agree in expressly recognizing thecomplete naturalness of the secondary as well as of the primary factors ofevolution. 

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The doctrine of natural selection forms the best basis for the detaileddiscussion of the way evolution has come about in the past and how it isgoing on to-day. This is true because it was the first description ofnature's program to carry conviction to the scientific world, and becauseits major elements have stood the test of time as no other doctrine hasdone. Much has been added to our knowledge of natural processes duringpost-Darwinian times, and new discoveries have supplemented andstrengthened the original doctrine in numerous ways, although they havecorrected certain of the minor details on the basis of fullerinvestigation. 

At the outset it must be clearly understood that Darwin's doctrine isconcerned primarily with the _method_ and not with the evidences as to theactual _fact_ of evolution. Most of those who are not familiar with theprinciples of science believe that Darwin discovered this process; buttheir opinion is not correct. The reality of natural change as a universalattribute of living things had been clearly demonstrated long beforeDarwin wrote the remarkable series of books whose influence has been feltoutside the domains of biology and to the very confines of organizedknowledge everywhere. The "Origin of Species" was published in 1859, andonly the last of its fourteen chapters is devoted to a statement of theevidence that evolution is true. In this volume Darwin presented theresults of more than twenty-five years of patient study of the phenomenaof nature, utilizing the observations of wild life in many regions visitedby him when he was the naturalist of the "Beagle" during its famous voyagearound the world. He also considered at length the results of thebreeder's work with domesticated animals, and he showed for the first timethat the latter have an evolutionary significance. Because his logicalassembly of wide series of facts in this and later volumes did so much toconvince the intellectual world of the reasonableness of evolution, Darwinis usually and wrongly hailed as the founder of the doctrine. It isinteresting to note in passing that Alfred Russel Wallace presented aprecisely similar outline of nature's workings at about the same time asthe statement by Darwin of his theory of natural selection. But Wallacehimself has said that the greater credit belongs to the latterinvestigator who had worked out a more complete analysis on the basis offar more extensive observation and research. 

The fundamental point from which the doctrine of natural selectionproceeds is the fact that all creatures are more or less perfectly adaptedto the circumstances which they must meet in carrying on their lives; thisis the reason why so much has been said in earlier connections regardingthe universal occurrence of organic adaptation. An animal is not anindependent thing; its life is intertwined with the lives of countlessother creatures, and its very living substance has been built up out ofmaterials which with their endowments of energy have been wrested from theenvironment. Every animal, therefore is engaged in an unceasing struggleto gain fresh food and new energy, while at the same time it is involvedin a many-sided conflict with hordes of lesser and greater foes. It mustprevail over all of them, or it must surrender unconditionally and die. There is no compromise, for the vast totality we individualize as theenvironment is stern and unyielding, and it never relents for even amoment's truce. 

To live, then, is to be adapted for successful warfare; and the questionas to the mode of origin of species may be restated as an inquiry into theorigin of the manifold adaptations by which species are enabled to meetthe conditions of life. Why is adaptation a universal phenomenon oforganic nature?

The answer to this query given by Darwinism may be stated so simply as toseem almost an absurdity. It is, that if there ever were any unadaptedorganisms, they have disappeared, leaving the world to their moreefficient kin. Natural selection proves to be a continuous process oftrial and error on a gigantic scale, for all of living nature is involved. Its elements are clear and real; indeed, they are so obvious when ourattention is called to them that we wonder why their effects were notunderstood ages ago. These elements are (1) the universal occurrence ofvariation, (2) an excessive natural rate of multiplication, (3) thestruggle for existence entailed by the foregoing, (4) the consequentelimination of the unfit and the survival of only those that aresatisfactorily adapted, and (5) the inheritance of the congenitalvariations that make for success in the struggle for existence. It is truethat these elements are by no means the ultimate causes of evolution, buttheir complexity does not lessen their validity and efficiency as theimmediate factors of the process. 

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Taking up the first proposition, we return to the subject of variationthat has been discussed previously for the purpose of demonstrating itsreality. The observations of every day are enough to convince us that notwo living things are ever exactly alike in all respects. The reason isthat the many details of organic structure are themselves variable, sothat an entire organism cannot be similar to another either in material orin functional regards, while furthermore it would be impossible for ananimal to be related to environmental circumstances in the same way asanother member of its species unless it was possible for two things tooccupy the same space at the same time! Individual differences in physicalconstitution are displayed by any litter of kittens, with identicalparents; it needs only a careful examination to find the variations in theshape of the heads, the length of their tails, and in every othercharacter. Sometimes the differences are less evident in physicalqualities than in disposition and mental make-up, for such variations canbe found among related kittens just as surely as among the childrenbelonging to a single human family. 

Not only do all organisms vary, but they seem to vary in somewhat similarways. While modern investigations have thrown much light upon therelations between variations and their causes, of particular value in thecase of the congenital phenomena, the greatest advance since Darwin's timeconsists in the demonstration by the naturalists who have employed thelaborious methods of statistical analysis that the laws according to whichdifferences occur are the same where-ever the facts have been examined. Asingle illustration will suffice to indicate the general nature of thisresult. If the men of a large assemblage should group themselves accordingto their different heights in inches, we would find that perhaps one halfof them would agree in being between five feet eight inches and five feetnine inches tall. The next largest groups would be those just below andabove this average class, --namely, the classes of five feet seven to eightinches and five feet nine to ten inches. Fewer individuals would be in thegroups of five feet five to six inches and five feet ten to eleven inches, and still smaller numbers would constitute the more extreme groups onopposite sides of these. If the whole assemblage comprised a sufficientnumber of men, it would be found that a class with a given deviation fromthe average in one direction would contain about the same number ofindividuals as the class at the same distance from the average in theopposite direction. Taking into account the relative numbers in theseveral classes and the various degrees to which they depart from theaverage, the mathematician describes the whole phenomenon of variation inhuman stature by a concise formula which outlines the so-called "curve oferror. " From his study of a thousand men, he can tell how many there wouldbe in the various classes if he had the measurements of ten thousandindividuals, and how many there would be in the still more extreme classesof very short and very tall men which might not be represented among onethousand people. 

It is not possible to explain why variation should follow this or anyother mathematical law without entering into an unduly extensivediscussion of the laws of error. The mathematicians themselves tell us ingeneral terms that the observations they describe so simply by theirformulæ follow as the result of so-called chance, by which they mean thatthe combined operation of numerous, diverse, and uncorrelated factorsbrings about this result, and not, of course, that there is such a thingas an uncaused event or phenomenon. 

Whenever any extensive series of like organisms has been studied withreference to the variations of a particular character, the variationsgroup themselves so as to be described by identical or similar curves oferror. It is certainly significant that this is true for such diversecharacters, cited at random from the lists of the literature, as thenumber of ray-flowers of white daisies, the number of ribs of beechleaves, and of the bands upon the capsules of poppies, for the shades ofcolor of human eyes, for the number of spines on the backs of shrimps, andfor the number of days that caterpillars feed before they turn into pupæ. 

To summarize the foregoing facts, we have learned that variation isuniversal throughout the living world, and that the primary factorscausing organic difference--the counterparts of human ingenuity in thecase of dead mechanisms--are the natural influences of the environment, oforganic physiological activity, and of congenital inheritance. Thesefactors are accorded different values in the evolution of new species, aswe may see more clearly at a later juncture, but the essential point hereis that they are not unreal, although they may not as yet be described byscience in final analytical terms. 

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We come now to the second element of the whole process of evolution, namely, what we may call overproduction or excessive multiplication. Likevariation and so many other phenomena of nature, this is so real andnatural that it escapes our attention until science places it before us ina new light. The normal rate of reproduction _in all species of animals_is such that if it were unchecked, any kind of organism would cumber theearth or fill the sea in a relatively short time. That this is universallytrue is apparent from any illustration that might be selected. Let us takethe case of a plant that lives for a single year, and that produces twoseeds before it withers and dies; let us suppose that each of these seedsproduces an adult plant which in its turn lives one year and forms twoseeds. If this process should continue without any interference, thetwentieth generation after as many years would consist of more than onemillion descendants of the original two-seeded annual plant, provided onlythat each individual of the intervening years should live a normal lifeand should multiply at the natural rate. But such a result as this isrendered impossible by the very nature which makes annual plants multiplyin the way they do. Let us take the case of a pair of birds which producefour young in each of four seasons. Few would be prepared for the figuresenumerating the offspring of a single pair of birds at the end of fifteenyears, if again all individuals lived complete and normal lives: at theend of the time specified there would be more than two thousand millionsof descendants. The English sparrow has been on this continent little morethan fifty years; it has found the conditions in this country favorablebecause few natural enemies like those of its original home have been met, and as a consequence it has multiplied at an astounding rate so as toinvade nearly all parts of North America, driving out many species of songbirds before it. About twenty years ago David Starr Jordan wrote that ifthe English sparrow continued to multiply at the natural rate of thattime, in twenty years more there would be one sparrow to every square inchof the state of Indiana; but of course nature has seen to it that thisresult has not come about. A single conger-eel may produce fifteen millioneggs in a single season, and if this natural rate of increase wereunchecked, the ocean would be filled solid with conger-eels in a fewyears. Sometimes a single tapeworm, parasitic in the human body, willproduce three hundred million embryos; the fact that this animal isrelatively rare diverts our attention from the alarming fertility of thespecies and the excessive rate of its natural increase. Perhaps the mostamazing figures are those established by the students of bacteria andother micro-organisms. Many kinds of these primitive creatures are knownwhere the descendants of a single individual will number sixteen toseventeen millions after twenty-four hours of development under ordinarilyfavorable conditions. Though a single rodlike individual taken as astarting-point may be less than one five-thousandth of an inch in length, under natural circumstances it multiplies at a rate which _within fivedays_ would cause its descendants _to fill all the oceans to the depth ofone mile_. This is a fact, not a conjecture; the size of one organism isknown, and the rate of its natural increase is known, so that it is merelya matter of simple arithmetic to find out what the result would be in agiven time. 

Even in the case of those animals that reproduce more slowly, anovercrowding of the earth would follow in a very short time. Darwin wrotethat even the slow-breeding human species had doubled in the precedingquarter century. An elephant normally lives to the age of one hundredyears; it begins to breed at the age of thirty, and usually produces sixyoung by the time it is ninety. Beginning with a single pair of elephantsand assuming that each individual born should live a complete life, onlyeight hundred years would be requisite to produce nineteen millionelephants; a century or two more and there would be no standing room forthe latest generation of elephants. It is only too obvious that such aresult is not realized in nature, but it is on account of other naturalchecks, and not because the natural rate of reproductive increase isanything but excessive. 

The third element of the process of natural selection is the struggle forexistence which is to a large extent the direct consequence ofover-multiplication. Because nature brings more individuals into existencethan it can support, every animal is involved in many-sided battles withcountless foes, and the victory is sometimes with one and sometimes withanother participant in the conflict. A survivor turns from one vanquishedenemy only to find itself engaged in mortal combat with other attackingforces. Wherever we look, we find evidence of an unceasing struggle forlife, and an apparently peaceful meadow or pond is often the scene offierce battles and tragic death that escape our notice only because thecontending armies are dumb. 

A community of ants, often comprising more individuals than an entireEuropean state, depends for its national existence upon its ability toprevail over other communities with which it may engage in sanguinary warswhere the losses of a single battle may exceed those of Gettysburg. Thedeveloping conger-eels find a host of enemies which greatly deplete theirnumbers before they can grow even into infancy. An annual plant does notproduce a million living offspring in twenty years because seeds do notalways fall upon favorable soil, nor do they always receive the properamount of sunlight and moisture, or escape the eye of birds and otherseed-eating animals. These three illustrations bring out the fact thatthere are three classes of natural conditions which must be met by everyliving creature if it is to succeed in life. In detail, the struggle forexistence is _intra-specific_, involving some form of competition orrivalry among the members of a single species; it is _inter-specific_, asa conflict is waged by every species with other kinds of living things;and finally it involves an adjustment of life to _inorganic environmental_influences. While it may seem unjustifiable to speak of heat and cold andsunlight as enemies, the direct effects produced by these forces are to bereckoned with no less certainty than the attacks of living foes. 

The three divisions of the struggle for existence are so important notonly in purely scientific respects, but also in connection with theanalysis of human biology, that we may look a little further into theirdetails, taking them up in the reverse order. Regarding the environmentalinfluences, the way that unfavorable surroundings decimate the numbers ofthe plants of any one generation has already been noted, and it is typicalof the vital situation everywhere. English sparrows are killed byprolonged cold and snow as surely as by the hawk. The pond in whichbacteria and protozoa are living may dry up, and these organisms may bekilled by the billion. Even the human species cannot be regarded as exemptfrom the necessity of carrying on this kind of natural strife, for scoresand hundreds die every year from freezing and sunstroke and the thirsts ofthe desert. Unknown thousands perish at sea from storm and shipwreck, while the recorded casualties from earthquakes and volcanic eruptions andtidal waves have numbered nearly one hundred and fifty thousand in thepast twenty-eight years. The effects of inorganic influences upon allforms of organic life must not be underestimated in view of such facts asthese. 

In the second place, the vital struggle includes the battles of everyspecies with other kinds of living things whose interests are inopposition. The relations of protozoa and bacteria, conger-eels and otherfish, English sparrows and hawks, plants and herbivorous animals, aretypical examples of the universal conflict in which all organisms areinvolved in some way. Again it is only too evident that human beings mustparticipate every day in some form of warfare with other species. In orderthat food may be provided for mankind the lives of countless wildorganisms must be sacrificed in addition to the great numbers ofdomesticated animals reared by man only that they may be destroyed. Thewolf and the wildcat and the panther have disappeared from many of ourEastern states where they formerly lived, while no longer do vast herds ofbison and wild horses roam the Western prairies. Because one or anotherhuman interest was incompatible with the welfare of these animals theyhave been driven out by the stronger invaders. 

That the victory does not always fall to the human contestant istragically demonstrated by the effects of the incessant assaults upon manmade by just one kind of living enemy, --the bacillus of tuberculosis. Every year more than one hundred and twenty-five thousand people of theUnited States die because they are unable to withstand its persistentattacks; five million Americans now living are doomed to death at thehands of these executioners, and the figures must be more than doubled tocover the casualties on the human side in the battles with the regimentsof all the species of bacteria causing disease. 

The competition between and among the individuals of one and the samespecies is the third part of the struggle for existence, and it is oftenunsurpassed in its ferocity. When two lion cubs of the same litter beginto shift for themselves, they must naturally compete in the sameterritory, and their contest is keener than that which involves either ofthem and a young lion born ten or fifteen miles away. The seeds of oneparent plant falling in a restricted area will be engaged in a competitivestruggle for existence that is much more intense than many other parts ofnature's warfare. In brief, the intensity of the competition will bedirectly proportional to the similarity of two organisms in constitutionand situation, and to the consequent similarity of vital welfare. Theinterests of the white man and the Indian ran counter to each other a fewhundred years ago, and the more powerful colonists won. The assumption ofthe white man's burden too often demonstrates the natural effect ofdiversity of interest, and the domination of the stronger over the weaker. In any civilized community the manufacturer, farmer, financier, lawyer, and doctor must struggle to maintain themselves under the conditions oftheir total inorganic and social environments; and in so far as the objectof each is to make a living for himself, they are competitors. But thecontest becomes more absorbing when it involves broker and broker, lawyerand lawyer, financier and magnate, because in each case the contestantsare striving for an identical need of success. 

Although the severity of the conflict imposed by nature is somewhatmodified in the case of social organisms, where community competes withcommunity and nation with nation, no form of social organization has yetbeen developed where the individual contest carried on by the members ofone community has been done away with. It is an inexorable law of naturethat all living things must fight daily and hourly for their very lives, because so many are brought into the world with each new generation thatthere is not sufficient room for all. No organism can escape the strugglefor existence except by an unconditional surrender that results in death. Everywhere we turn to examine the happenings of organic life we can findnothing but a wearisome warfare in which it is the ultimate and cruel lotof every contestant to admit defeat. 

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What now are the results of variation, over-multiplication, andcompetition? Since some must die because nature cannot support all thatshe produces, since only a small proportion of those that enter upon lifecan find a foothold or successfully meet the hordes of their enemies, which will be the ones to survive? Surely those that have even theslightest advantage over their fellows will live when their companionsperish. It is impossible that the result could be otherwise; it mustfollow inevitably from what has been described before. The whole processhas its positive and its negative aspects: the survival of the fittest andthe elimination of the unfit. Perhaps it would be more correct to say themore real element is the negative one, for those which are least capableof meeting their living foes and the decimating conditions of inorganicnature are the first to die, while the others will be able to prolong thestruggle for a longer or shorter period before they too succumb. Thus thedestruction of the unfit leaves the field to the better adapted, that is, to those that vary in such a way as to be completely or at least partiallyadapted to carry on an efficient life. In this way Darwinism explains theuniversal condition of organic adjustment, showing that it exists becausethere is no place in nature for the incompetent. 

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Finally we come to the process of inheritance as viewed by Darwin, and itspart in the production and perfection of new species. In every case, Darwin said, the efficiency or inefficiency of an animal depends upon itscharacteristics of an inherited or congenital nature. Variations in thesequalities provide the array of more or less different individuals fromwhich impersonal nature selects the better by throwing out first theinferior ones. An organism can certainly change in direct response toenvironmental influence or by the indirect results of use and disuse, butnot unless it is so constituted by heredity as to be able to changeadaptively. Therefore the final basis of success in life must be sought inthe inherited constitutions of organic forms. 

For the reason that the qualities which preserve an animal's existence arealready congenital, they are already transmissible, as Darwin contended. Since his time much has been learned about the course of inheritance andits physical basis, and the new discoveries have confirmed the essentialtruth of Darwin's statement that the congenital characters only possess areal power in the evolution of species. 

We must devote some time to the subject of inheritance at a laterjuncture, but before leaving the matter an additional point must beestablished here; the selective process deals immediately with congenitalresults, as the heritable characters that make for success or failure inlife, but by doing this it really selects the group of congenital factorsbehind and antecedent to their effects. For example, an ape that survivesbecause of its superior cunning, does so because it varies congenitally inan improved direction; and the factors that have made it superior areindirectly but no less certainly preserved through the survival of theirresults in the way of efficiency. Hereditary strains are thus the ultimatethings selected through the organic constitutions that they determine andproduce. 

Natural selection, as the whole of this intricate process, is simply trialand error on a gigantic scale. Nature is such that thousands of varyingindividuals are produced in order that a mere handful or only one survivormay be chosen to bear the burden of carrying on the species for anothergeneration. The effect of nature's process is judicial, as it were. We mayliken the many and varied conditions of life to as many jurymen, beforewhich every living thing must appear for judgment as to its fitness orlack of it. A unanimous verdict of complete or partial approval must berendered, or an animal dies, for the failure to meet a single vitalcondition results in sure destruction. Of course, we cannot regardselection as involving anything like a primitive conscious choice. It isbecause we individualize all of the complex totality of the world as"Nature" with a capital N that so many people unconsciously come to thinkof it as a human-like personality. He who would go further and hold thatall of nature is actually conscious and the dwelling-place of thesupernatural ultimate, must beware of the logical results of such a view. What must we think of the ethical status of such a conscious power whocauses countless millions of creatures to come into the world andruthlessly compels them to battle with one another until a cruel andtragic death ends their existence?

But that is a metaphysical matter, with which we need not concernourselves in this discussion; the important point is that among theeveryday happenings of life are processes that are quite competent toaccount for the condition of adaptation exhibited by various animal forms. These processes are real and natural, not imaginative or artificial, andso they will remain even though it will become clear that much is still tobe learned about the causes of variation and the course of biologicalinheritance. Darwin was the first to contend that natural selection is buta part of nature's method of accomplishing evolution. As such it iscontent to recognize variations and does not concern itself with theorigin of modifications; it accepts the obvious fact that congenitalvariations are inherited, although it leaves the question as to how theyare inherited for further examination. Because the doctrine of naturalselection does not profess to answer all the questions propounded byscientific inquisitiveness, it must not be supposed that it fails in itsimmediate purpose of giving a natural explanation of how evolution may bepartly accounted for. 

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Before proceeding to the post-Darwinian investigations that have done somuch to amplify the account of natural evolution, let us consider thecontrasted explanation given by Lamarck and his followers. As we havestated earlier, Lamarckianism is the name given to the doctrine thatmodifications other than those due to congenital factors may enter intothe heritage of a species, and may add themselves to those alreadycombined as the peculiar characteristics of a particular species. Let ustake the giraffe and its long neck as a concrete example. The great lengthof this part is obviously an adaptive character, enabling the animal tobrowse upon the softer leafy shoots of shrubs and trees. The vertebralcolumn of the neck comprises just the same number of bones that arepresent in the short-necked relatives of this form, so that we arejustified in accepting as a fact the evolution of the giraffe's long neckby the lengthening of each one of originally shorter vertebræ. TheLamarckian explanation of this fact would be that the earliest forms inthe ancestry of the giraffe as such stretched their necks as they fed, andthat this peculiar function with its correlated structural modificationbecame habitual. The slight increase brought about by any singleindividual would be inherited and transmitted to the giraffes of the nextgeneration; in other words, an individually acquired character would beinherited. The young giraffes of this next generation would then begin, not where their parents did, but from an advanced condition. Thus, bycontinued stretching of the neck and by continued transmission of theelongated condition, the great length of this part of the body in themodern giraffe would be attained. 

The explanation of natural selection would be quite different. TheDarwinian would say that all the young giraffes of any one generationwould vary with respect to the length of the neck. Those with longer neckswould have a slight advantage over their fellows in the extended sphere oftheir grazing territory. Being better nourished than the others, theywould be stronger and so they would be more able to escape from theirflesh-eating foes, like the lion. For the reason that their variationwould be congenital and therefore already transmissible, their offspringwould vary about the advanced condition, and further selection of thelonger necked individuals would lead to the modern result. 

The Lamarckian explanation encounters one grave difficulty which is notmet by the second one, in so far as it demands some method by which abodily change may be introduced into the stream of inheritance. So far, this difficulty has not been overcome, and the present verdict of scienceis that the transmission of characters acquired as the result of otherthan congenital factors is not proved. It would be unscientific to saythat it cannot be proved in the future, but there are good _a priori_grounds for disbelief in the principle, while furthermore the results ofexperiments that have been undertaken to test its truth have been entirelynegative. Rats and mice have had their tails cut off to see if thismutilation would have its effect upon their young, and though this hasbeen done for more than one hundred successive generations the length ofthe tail has not been altered. Quite unconscious of the scientificproblem, many human races have performed precisely similar experimentsthrough centuries of time. In some classes of Chinese, the feet of younggirls have been bound in such a way as to produce a small, malformed foot, but this has not resulted in any hereditary diminution in the size of thefeet of Chinese females. Many other similar mutilations have beenpractised, as for example, the flattening of the skull of some NorthAmerican Indians, but the deformity must be produced again with eachrecurring generation. One after another, the cases that were supposed togive positive evidence have been reinvestigated, with the result that hasbeen stated above. It would seem, therefore, that heredity and congenitalmodification must play by far the greater part in the evolution ofspecies. 

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The doctrine of natural selection took form in the mind of Darwin mainlyon account of three potent influences; these were, first, the geologicaldoctrine of uniformitarianism proposed by Lyell, second, his ownobservations of wild life in many lands and his analysis of the breeder'sresults with domesticated animals, and third, the writings of Malthusdealing with overpopulation. As Darwin had read the works of Buffon, Lamarck, and Erasmus Darwin, his grandfather, who had written a famoustreatise under the title of "Zoonomia, " he was familiar with the evidencesknown in his student days tending to prove that organic evolution was areal natural process. Lyell's doctrine of uniform geological history madean early and deep impression upon his mind, and it led him to ask himselfwhether the efficient causes of past evolution might not be revealed by ananalysis of the present workings of nature. As naturalist of the "Beagle"during its four years' cruise around the world, Darwin saw many new landsand observed varied circumstances under which the organisms of the tropicsand other regions lived their lives. The fierce struggle for existencewaged by the denizens of the jungle recalled to him the views of Malthusregarding overpopulation and its results. These and other influences ledhim to begin the remarkable series of note-books, from which it isinteresting indeed to learn how the doctrine of natural selection began toassume a definite and permanent form in his mind, as year followed year, and evidence was added to evidence. And it is a valuable lesson to thestudent of science that for twenty-five years Darwin devoted all his timeto the acquisition of facts before he gave his doctrine to the world inthe famous "Origin of Species. "

Darwin was particularly impressed by the way mankind has dealt with thevarious species of domesticated animals, and he was the first naturalistto point out the correspondence between the breeder's method of"artificial selection, " and the world-wide process of natural selection. As every one knows, the breeder of race horses finds that colts vary muchin their speed; discarding the slower animals, he uses only the swifterfor breeding purposes, and so he perfects one type of horse. With otherobjects in view, the heavy draught horse, the spirited hackney, and theagile polo pony have been severally bred by exactly the same method. Amongcattle many kinds occur, again the products of an artificial or humanselection; hornless breeds have been originated, as well as others withwide-spreading or sharply curved horns; the Holstein has been bred for anabundant supply of milk as an object, while Jerseys and Alderneys excel inthe rich quality of their milk. Various kinds of domesticated sheep andrabbits and cats also owe their existence to the employment of theselfsame method, unconsciously copied by man from nature; for men havefound variations arising naturally among their domesticated animals, andthey have simply substituted their practical purposes or their fancy fornature's criterion of adaptive fitness, preserving those that they wish toperfect and eliminating those unfitted to their requirements or ideas. 

In the case of many of these and other examples, wild forms still occurwhich seem to be like the ancestral stock from which the domesticatedforms have been produced. All the varied forms of dogs--from mastiff totoy-terrier, and from greyhound to dachshund and bulldog--find theirprototypes in wild carnivora like the wolf and jackal. In Asia andMalaysia the jungle fowl still lives, while its domesticated descendantshave altered under human direction to become the diverse strains of thebarnyard, and even the peculiar Japanese product with tail featherssometimes as long as twenty feet. That far-reaching changes can be broughtabout in a relatively short time is proved by the history of the gamecock, which has nearly doubled in height since 1850, while at the sametime its slender legs, long spurs, and other qualities have been perfectedfor the cruel sport for which it has been bred. Again, the wild rockpigeon seems to be the ancestral form from which the fantail and pouterand carrier-pigeon with their diverse characters have taken their origin. 

It is true that some biologists have urged certain technical objections tothe employment of domesticated animals and their history as analogies tothe processes and results in wild nature. To my mind, however, artificialselection is truly a part of the whole process of natural selection. Manis but one element of the environment of tame forms, and his fancy or needis therefore one of the varied series of external criteria that must bemet if survival is to be the result; failing this, elimination follows assurely as under the conditions of an area uninhabited or uninfluenced bymankind. Congenital variation is real, selection is real and the heredityof the more fit modification is equally real. Surely Darwin was right incontending that the facts of this class amplify the conception of naturalselection developed on the basis of an analysis of wild life. 

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Knowing the elements of the selective process, it is possible to analyzeand to understand many significant phenomena of nature, and to gain aclearer conception of the results of the struggle for existence, especially when the human factor is involved. Let us see how much isrevealed when the foregoing results are employed in a further study ofsome of nature's vital situations. 

As a consequence of the many-sided struggle for existence, theinterrelations of a series of species will approach a condition ofequilibrium in an area where the natural circumstances remain relativelyundisturbed for a long time. For example, among the field-mice of onegeneration, just as many individuals will survive as will be able to findfood and to escape hereditary foes such as cats and snakes and owls. Thenumber of owls, in their turn, will be determined by the number ofavailable mice and other food organisms, as well as by the severity of theadverse circumstances that cause elimination of the less fit among thefledglings brought into the world. The vital chain of connections issometimes astonishingly long and intricate. One remarkable illustration isgiven by Fiske, as an elaboration of an example cited by Darwin. He pointsout that the fine quality of the traditional roast beef of England isdirectly determined by the number of elderly spinsters in that country. The chain of circumstances is as follows: the quality of the cloverfields, furnishing the best food for cattle, depends largely upon thevisits to the clover-blossoms by wild bees, that accomplish thefertilization of the flowers by carrying pollen upon their bodies from oneplant to another. Field-mice devour the young in the nests of these bees, so if there are few field-mice there will be many bees, and consequentlybetter grazing for the cattle. The number of field-mice will varyaccording to the abundance of cats, and so the number of these domesticanimals will exert an influence upon the whole foregoing chain of forms. But, as Fiske points out, cats are the favorite companions of elderlyspinsters; therefore, if there are many of the latter, there will be morecats, fewer field-mice, more bees, richer clover fields, and finer cattle!Each link is real and the whole chain is a characteristic example of thecountless ways that the natural destinies of living things areinterrelated and intertwined. 

The reality of such organic interrelationships is revealed with wonderfulclearness in the numerous instances where some disturbing factor hasaltered one or another element of the balanced system. The invasion of thenew world by Europeans has directly led to the partial or completeextinction of the tribes of Indians to whom the land formerly belonged;they have disappeared almost entirely from our state of New York, togetherwith the bear and wolf and many other species of animals that formerlyexisted here. Wild horses and bison have also vanished before the advancesof civilization and the alteration of their homes. Sometimes theextermination of one pest has resulted in an increase in the number ofanother through human interference with nature's equilibrium. In some ofour Western states, a bounty was offered for the scalps of wolves, so asto lessen the number of these predatory foes of sheep. But when the wolveswere diminished in number, their wild food-animals, the prairie dogs, found their lot much bettered, and they have multiplied so rapidly that insome places they have become even more destructive than the wolves. 

One of the most remarkable illustrations is that of the rabbits introducedinto Australia. This island continent was cut off from the surroundinglands long before the higher mammals evolved in far distant regions, sothat the balance of nature was worked out without reference to animalslike the rabbit. When the first of these were introduced they found aterritory without natural enemies where everything was favorable. Theypromptly multiplied so rapidly that within a few years their descendantswere numerous enough to eat up practically every green thing they couldreach. Two decades ago, the single province of Queensland was forced toexpend $85, 000, 000 in a vain effort to put down the rabbit plague. Theremarkable statement has been made that in some places nature has taken ahand in causing a new type of rabbit to evolve. Finding the situationdesperate, some of the animals have begun to develop into tree-climbingcreatures. The animals exist in such numbers that the available food uponthe ground is insufficient for all, and so some elimination results. Butthe young rabbits with longer claws, varying in this way on account ofcongenital factors, have an advantage over their fellows because they canclimb some of the trees and so obtain food inaccessible to the others. Ifthe facts are correctly reported, and if the process of selection on thebasis of longer claws and the climbing habit is continued, the originaltype of animal is splitting up into a form that will remain the same andlive upon the ground, and another that will be to all intents and purposesa counterpart of our familiar squirrel. All the evidence goes to show thatsquirrels have evolved from terrestrial rodents; if the data relating toAustralian rabbits are correct, nature is again producing a squirrel-likeanimal by evolution in a region where the former natural situation hasbeen interfered with by man. 

The laws of biological inheritance have received close and deep study bynumerous investigators of Darwinian and post-Darwinian times, because fromthe first it was clearly recognized that a complete description ofnature's method of accomplishing evolution must show how species maintainthe same general characteristics from generation to generation, and alsohow new qualities may be fixed in heredity as species transform in thecourse of time. Before our modern era in biology, the fact of inheritancewas accepted as self-sufficient; now much is known that supplements andextends the incomplete account given by natural selection of the wayevolution takes place. 

It is not possible in the present brief outline to describe all theresults of recent investigations, but some of them are too important to bepassed over. Perhaps the most interesting one is that the laws of heredityseem to be the same for man and other kinds of living creatures, as provedby Galton and Pearson and many others who have dealt with such charactersas human stature, human eye color, and an extensive series of thepeculiarities of lower animals and even of plants. 

The researches dealing with the physical basis of inheritance and itslocation in the organism have yielded the most striking and brilliantresults. Darwin himself realized that the doctrine of natural selectionwas incomplete, as it accepted at its face value the inheritance ofcongenital racial qualities without attempting to describe the way an eggor any other germ bears them, and he endeavored to round out his doctrineof selection by adding the theory of pangenesis. According to this, everycell of every tissue and organ of the body produces minute particlescalled gemmules, which partake of the characters of the cells that producethem. The gemmules were supposed to be transported throughout the entirebody, and to congregate in the germ-cells, which in a sense would beminute editions of the body which bears them, and would then be capable ofproducing the same kind of a body. If true, this view would lead to theacceptance of Lamarck's or even Buffon's doctrine, for changes induced inany organ by other than congenital factors could be impressed upon thegerm-cell, and would then be transported together with the originalspecific characters to future generations. Darwin was indeed a goodLamarckian. 

But the researches of post-Darwinians, and especially those of thestudents of cellular phenomena, have demonstrated that such a view has noreal basis in fact. Many naturalists, like Naegeli and Wiesner, wereconvinced that there was a specific substance concerned with hereditaryqualities as in a larger way protoplasm is the physical basis of life. Itremained for Weismann to identify this theoretical substance with aspecific part of the cell, namely, the deeply staining substance, orchromatin, contained in the nucleus of every cell. Bringing together theaccumulating observations of the numerous cytologists of his time, andutilizing them for the development of his somewhat speculative theories, Weismann published in 1882 a volume called "The Germ Plasm, " which is animmortal foundation for all later work on inheritance. The essentialprinciples of the germ-plasm theory are somewhat as follows. The chromatinof the nucleus contains the determinants of hereditary qualities. Inreproduction, the male sex-cell, which is scarcely more than a minute massof chromatin provided with a thin coat of protoplasm and a motile organ, fuses with the egg, and the nuclei of the two cells unite to form a doublebody, which contains equal contributions of chromatin from the twoparental organisms. This gives the physical basis for paternal inheritanceas well as for maternal inheritance, and it shows why they may be of thesame or equivalent degree. When, now, the egg divides, at the first andlater cleavages, the chromatin masses or chromosomes contained in thedouble nucleus are split lengthwise and the twin portions separate to gointo the nuclei of the daughter-cells. As the same process seems to holdfor all the later divisions of the cleavage-cells whose products aredestined to be the various tissue elements of the adult body, it followsthat all tissue-cells would contain chromatin determinants derived equallyfrom the male and female parents. As of course only the germ-cells of anadult organism pass on to form later generations, and as their content ofchromatin is derived not from the sister organs of the body, but from theoriginal fertilized egg, there is a direct stream of the germ plasm whichflows continuously from the germ-cell to germ-cell through succeedinggenerations. It would seem, therefore, that the various organic systemsare, so to speak, sister products in embryonic origin. The reproductiveorgans are not produced by the other parts of the body, but their cellsare the direct descendants of the common starting-point namely, the egg. As the cells of the reproductive organs are the only ones that pass overand into the next and later generations, it will be evident, in the firstplace, that the germ plasm of their nuclei is the only essential substancethat connects parent and offspring. This stream of germ plasm passes on indirect continuity through successive generations--from egg to the completeadult, including its own germ-cells, through these to the next adult, withits germ-cells, and so on and on as long as the species exists. It doesnot flow circuitously from egg to adult and then to new germ-cells, but itis direct and continuous, and apparently it cannot pick up any of thebody-changes of an acquired nature. Now we see why individual acquisitionsare not transmitted. The hereditary stream of germ plasm is alreadyconstituted before an animal uses its parts in adult life; we cannot seehow alterations in the structure of mature body parts through use andadjustment to the environment can be introduced into it to become newqualities of the species. 

It must be clear, I am sure, that this theory supplements naturalselection, for it describes the physical basis of inheritance, itdemonstrates the efficiency of congenital or germ-plasmal factors ofvariation in contrast with the Lamarckian factors, and finally in the waythat in the view of Weismann it accounts for the origin of variations asthe result of the commingling of two differing parental streams of germplasm. 

At first, for many reasons, Weismann's theories did not meet with generalacceptance, but during recent years there has been a marked return to manyof his positions, mainly as the result of further cytological discoveries, and of the formulation of Mendel's Law and of De Vries's mutation theory. The first-named law was propounded by Gregor Mendel on the basis ofextensive experiments upon plants conducted during many years, 1860 andlater, in the obscurity of his monastery garden at Altbrünn, in Austria. It was rescued from oblivion by De Vries, who found it buried in a mass ofliterature and brought it to light when he published his renowned MutationTheory in 1901. Mendelian phenomena of inheritance, confirmed and extendedby numerous workers with plants and animals, prove that in many casesportions of the streams of germ plasm that combine to form the hereditarycontent of organisms may retain their individuality during embryonic andlater development, and that they may emerge in their original purity whenthe germ-cells destined to form a later generation undergo the preparatoryprocesses of maturation. They demonstrate also the apparent chance natureof the phenomena of inheritance. To my mind the most striking andsignificant result in this field is the demonstration that a particularchromosome or chromatin mass determines a particular character of an adultorganism, which is quite a different matter from the reference of all thehereditary characters to the chromatin as a whole. Wilson and others havebrought forward convincing proof that the complex character of sex ininsects actually resides in or is determined by particular and definitemasses of this wonderful physical basis of inheritance. 

Mendel's principles also account in the most remarkable way for manypreviously obscure phenomena, like reversion, or a case where a childresembles its grandparent more than it does either of its parents; suchphenomena are due, so to speak, to the rise to the surface of a hiddenstream of germ plasm that had flowed for one or many generations beneathits accompanying currents. I believe that the law is replacing more andmore the laws of Galton and Pearson, formulated as statistical summariesof certain phenomena of human inheritance taken _en masse_. According toGalton's celebrated law of ancestral inheritance, the qualities of anyorganism are determined to the extent of a certain fraction by its twoparents taken together as a "mid-parent, " that a smaller definite fractionis contributed by the grandparents taken together as a mid-grandparent, and so on to earlier generations. But Mendel's Law has far greaterdefiniteness, it explains more accurately the cases of alternativeinheritance, and it may be shown to hold for blended and mosaicinheritance as well. 

De Vries's new "mutation theory" is clearly not an alternative but acomplementary theory to natural selection, the Weismannian and Mendeliantheories. Like these last, it emphasizes the importance of the congenitalhereditary qualities contained in the germ plasm, though unlike theDarwinian doctrine it shows that sometimes new forms may arise by suddenleaps and not necessarily by the slow and gradual accumulation of slightmodifications or fluctuations. The mutants like any other variants mustpresent themselves before the jury of environmental circumstances, whichpasses judgment upon their condition of adaptation, and they, too, mustabide by the verdict that means life or death. 

From what has been said of these post-Darwinian discoveries, theLamarckian doctrine, which teaches that acquired non-congenital charactersare transmitted, seems to be ruled out. I would not lead you to believethat the matter is settled. I would say only that the non-transmission ofracial mutilations, negative breeding experiments upon mutilated rats andmice, the results of further study of supposedly transmitted immunity topoisons--that all these have led zoölogists to render the verdict of "notproved. " The future may bring to light positive evidence, and cases likeBrown-Séquard's guinea-pigs, and results like those of MacDougal withplants, and of Tower with beetles, may lead us to alter the opinionstated. But as it stands now most investigators hold that there are stronggeneral grounds for disbelief in the principle, and also that it lacksexperimental proof. 

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The explanation of natural evolution given by Darwinism and the principlesof Weismann, Mendel, and De Vries, still fails to solve the mysterycompletely, and appeal has been made to other agencies, even to teleologyand to "unknown" and "unknowable" causes as well as to circumstantialfactors. A combination of Lamarckian and Darwinian factors has beenproposed by Osborn, Baldwin, and Lloyd Morgan, in the theory of organicselection. The theory of orthogenesis propounded by Naegeli and Eimer, nowgaining much ground, holds that evolution takes place in direct lines ofprogressive modification, and is not the result of apparent chance. Ofthese and similar theories, all we can say is that if they are true, theyare not so well substantiated as the ones we have reviewed at greaterlength. 

The task of experimental zoölogy is to work more extensively and deeplyupon inheritance and variation, combining the methods and results ofcellular biology, biometrics, and experimental breeding. We may safelypredict that great advances will be made during the next few years inanalyzing the method of evolution; and that a few decades hence men willlook back to the present time as a period of transition like the era ofreawakened interest and renewed investigation that followed the appearanceof the "Origin of Species. " For the present, we can justly say "thatevolution, so far as it is understood, is a real and natural process. "

V

THE PHYSICAL EVOLUTION OF THE HUMAN SPECIES AND OF HUMAN RACES

The teachings of science that relate to the origin and history of thehuman species constitute for us the most important part of the wholedoctrine of organic evolution and now, having completely outlined thisdoctrine as a general one, we are brought to the point where we must dealfrankly and squarely with the insistent questions arising on all sides asto the way that mankind is involved in the vast mechanism of nature'sorder. These questions have been ignored heretofore, in order that thenatural history of animals in general might be discussed without anyinterference on the part of purely human interest and concern. It nowbecomes our privilege, and our duty as well, to employ and apply theprinciples we have learned in order to understand more completely theorigin of the human body as an organic type, the history of human races, the development of human faculty and of social institutions, and theevolution finally of even the highest elements of human life. These arescientific problems, and if we are to solve them we must employ the nowfamiliar methods of science which only yield sure results. 

We must not underestimate the many difficulties to be encountered, for thefield before us is a vast territory of complex human life and of manifoldhuman relations. Without prolonged exercise in scientific methods, it isimpossible to view our own kind impersonally, as we do the creatures oflower nature. Furthermore it seems to many that an analysis of human lifeand biological history, even if it is possible, must alter or degrademankind in some degree; this is no more true than that a knowledge of theprinciples of engineering according to which the Brooklyn Bridge has beenconstructed renders that structure any different or unsafe for travel. Manremains man, whether we are in utter ignorance of his mode of origin, orwhether we know all about his ancestry and about the factors that havemade him human. It is because our species appears to occupy a superior andisolated position above the rest of nature that the mind seems reluctantto follow the guidance of science when it conducts its investigations intothe history of seemingly privileged human nature. And it is feared also, that if evolution is proven for man as well as for all other kinds ofanimals, our cherished ideas and our outlook upon many departments ofhuman life must be profoundly affected. This may be so, but scienceendeavors only to find out the truth; it cannot alter truth, nor does itseek to do so. We might well wish that the world were different in manyrespects and that we were free from the control of many natural lawsbesides that of evolution, but if the real is what it is, then our duty isplain before us; as we think more widely and deeply on the basis ofripened experience, it becomes ever clearer that a knowledge of humanhistory gives the only sure guidance for human life. 

To the zoölogist it seems strange that so many are opposed to a scientificinquiry into the facts of human evolution, and to the conclusionsestablished by such an inquiry, --though, to be sure, this opposition isdirectly proportional to ignorance or misunderstanding of the nature andpurpose of scientific investigation and of human evolution. The naturalistcomes to view our species as a kind of animal, and as a single one of thehundreds of thousands of known forms of life; thus the question of humanorigin is but a small part of organic evolution, which is itself only anepisode in the great sweep of cosmic evolution, endless in past time andin the future. Were we some other order of beings, and not men, humanevolution would appear to us in its proper scientific proportions, namely, as a minute fraction of the whole progress of the world. 

While the foregoing statements are true, it is nevertheless right that aclose study should be made of the particular case of mankind. No doubtmuch of the naturalist's interest in nature at large is due to hisconviction that the laws revealed by the organisms of a lower sphere musthold true for man, and may explain many things that cannot be so clearlydiscerned when only the highest type is the subject of investigation. Itis only too evident that little more than a general outline can be givenof the wide subject or group of subjects included under the head of humanevolution. We must divide the subject logically into parts, so that eachone may be taken up without being complicated by questions relating totopics of another category, although the findings in any one departmentmust surely be of importance for comparison with the results establishedin another section; for if evolution is universally true, the mainconclusion in any case must assist the investigation of another, just ascomparative anatomy and embryology supplement and corroborate each otherin the larger survey of organic evolution. As before, the illustrations ofeach department of the subject must be selected from the stock of everydayobservation and information that we already possess, for we gain much whenwe realize that evolution includes all the happenings of everyday life andthought, as well as the occurrences of the remote past. 

For the present, then, the questions relating to the higher aspects ofhuman life must be put aside, only that they may be taken up at the last. Social evolution likewise finds its place in a later section, after thephenomena of mind and mental evolution receive due attention anddescription. At the present juncture, the human species presents itself asa subject for organic analysis and classification, merely as a physicalorganism. Just as the study of locomotives must begin with the detailedstructure of machines in the workshop before they can be profitablyunderstood as working mechanisms, so the physical evolution of mankindmust first be made intelligible before it is possible to prosecutesuccessfully the studies dealing with the psychology, social relations, and higher conceptions that seem at first to be the exclusive propertiesof our species. 

The problems of physical evolution of man and of men fall into two groups. Those of the first deal with the origin of the human species as a unit, and its comparative relation to lower organisms, while those of the secondpart are concerned with the further evolution of human races that havecome to be different in certain details of structure since the human typeas such arose. In the first part, all men will be assumed to be alike andthe members of a homogeneous species whose fundamental attributes are tobe compared with those of other animals; only afterwards will attention bedirected to the differences, previously ignored, that divide human beingsinto well-marked varieties. It must be evident even at this point that themode of evolution demonstrated by the first investigation will be likelyto bear some close relation to the methods by which human races haveevolved to their present diverse anatomical situations. 

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The foregoing classification of the problems concerned with the nature andorigin of the human species renders it possible to restrict the immediateinquiry to a definite and precise question. It is this: does the evidencerelating to the physical characteristics of our species prove that man isthe product of a supernatural act of creation, or does it show that man'splace in nature has been reached by a gradual process of naturalevolution? In order to obtain an equally precise and definite answer tothis question, referring to the particular case of most concern to us, itis obvious that the method to be employed is the one which has given us anunderstanding of organic evolution as an all-inclusive natural process. The data must be verified, related, and classified, so that their meaningmay be concisely stated in the form of scientific principles. What are thefacts of human structure, comparatively treated? How does the human bodydevelop? Does palæontology throw any light on the antiquity of man? Do therules of nature's order control the lives of men? Our course is now clear;we shall take up serially the anatomy, embryology, and fossil history ofthe human species, in order to see that there is ample proof of the actualoccurrence of evolution, and then, as before, we may look about for thecauses which have produced this result by natural methods. 

While it is necessary to treat the subject directly, namely, by examiningthe actual evidences relating to the particular case in question, it isworthwhile before doing so to point out that, as the whole includes apart, human evolution has already been proved beyond question. Thisconclusion must be accepted, unless reasons can be given for excludingmankind from the rest of the living world as an absolutely unique type, supreme and isolated because of some peculiar endowments not shared withthe rest of animate nature. If these reasons are lacking, and the unity oforganic nature be recognized, human evolution cannot be denied unless someinterpretation more reasonable and logical than evolution can be given forthe whole mass of facts exemplified and discussed in the foregoingchapters. We may accordingly approach the main questions by asking ifthere are any reasons for regarding the human species as a unique andisolated type of organism. 

At the outset, we must recognize that in so far as the human body ismaterial, its movements and mass relations are controlled by physicalprinciples, like all other masses of matter. It is well, indeed, that thisis so, for if gravitation and the laws of inertia were not consistent andreliable principles holding true at all times and not intermittently, itwould be difficult to order our lives with confidence. In the next place, the general principles of biology hold true for the structure andphysiology of the human species as they do for all other living things. Ahuman body is composed of eight systems of organs, whose functions areidentical with the eight vital tasks of every other animal. All theseorgans are made up of cells as ultimate vital units, and the materials ofwhich human cells are composed belong to the class of substances calledprotoplasm. Human protoplasm, like all other living materials, mustreplenish itself, and respire and oxidize in obedience to biological lawsthat have been found to be uniform everywhere. Thus the human organism isno more unique in fundamental organic respects than it is apart from theworld of physical processes and laws. 

How does the matter stand when the general structural plan of a humanbeing is examined? Is it entirely different from everything else? It is afact of common knowledge that the human body is supported by a bony axis, the vertebral column, to which the skull is articulated and to which alsothe skeletal framework of the limbs is attached. These characteristicsplace man inevitably among the so-called vertebrata; he is certainly notan invertebrate, nor is the basic structure of his body such that a thirdgroup, outside the invertebrata and vertebrata, can be made to includeonly the single type--man. 

Passing now to the classes that make up the group of vertebrates, we meetfirst the lampreys or cyclostomes without jaws, and the others with jaws, such as the fishes, amphibia, reptiles, birds, and mammals, each classdistinguished by certain definite characters in addition to the vertebralcolumn. The fishes have gills and scales; amphibia of to-day arescaleless, and they are provided with gills when they are young and lungsas adults; reptiles have scales and lungs; birds are warm-blooded andfeathered; while mammals are warm-blooded and haired. Is the human speciesa unique kind of vertebrate, or does it find a place in one of theseclasses? The occurrence of hair, of a four-chambered heart which propelswarm blood, of mammary glands, and of other systematic characters marksthis species as a kind of mammal and not as a vertebrate in a section byitself. 

The members of the class mammalia differ much among themselves; and nowthat we recognize clearly that man is a mammalian vertebrate, the nextquestion is whether an order exists to which our type must be assigned, orwhether we have at last reached a point where it is justifiable toestablish an isolated division to contain the human species alone. We arefamiliar with many representatives of different mammalian orders and withthe kind of structural characteristics that serve as convenientdistinctions in denoting their relationships. Horses and cattle, sheep, and goats and pigs resemble one another in many respects besides theirhoofs, and they form one natural order; the well-developed gnawing teethof rats and rabbits and squirrels place these forms together in the orderrodentia; the structures adapting their possessors for a flesh-eating andpredatory life unite the tribes of the lion, wolf, bear, and seal, in theorder carnivora. Among these and other orders of mammalia is one to whichthe lemurs, monkeys, and apes are assigned, because all these forms agreein certain structural respects that place them apart from the othermammalia, in the same way, for example, that the races of white men may berecognized as a group distinct from the black and red races. Butcomparative studies, prosecuted not only by those who have been forced toadopt the evolutionary interpretation, but also by believers in specialcreation like Linnæus and Cuvier and other more modern opponents ofevolution, have shown that the peculiar qualities of this order are sharedby the human species. Indeed, the name of primates was given to thissection by Linnæus himself, because the human body found a place in thearray which begins at the lower extreme with the lemurs and the monkeysand ends with man at the other end. Again it is found that no separateorder of mammals exists to include only the genus _Homo_. 

To one unacquainted with the facts of vertebrate comparative anatomy, thedistinguishing characteristics of the primates seem to be trivial innature. It is surprising to find how insignificant are the details towhich appeal must be made in order to draw a line between our own divisionof mammalia and the others. It is well to review them as they are given inthe standard text-books of comparative anatomy. Primates are eutheria, ortrue mammalia possessing a placental attachment of the young within theparent. The first digits, namely, the "great toe" and the "thumb, " arefreely movable and opposable to the others, so that the limbs areprehensile and clasping structures; usually but not always the animals ofthis order are tree-dwellers in correlation with the grasping powers ofthe feet and hands. The permanent teeth succeed a shorter series ofso-called "milk teeth, " and they are diverse in structure, being incisors, canines, or "eye teeth, " premolars, and molars; the particular numbers ofeach kind are almost invariable throughout the order and markedlydifferent from those of other orders. The number of digits is always five, and with few exceptions they bear nails instead of claws. The clavicles, or "collar bones, " are well developed in correlation with the prehensilenature of the fore limbs; a bony ring surrounds the orbit or eye socket. Finally there are two mammary glands by which the young are suckled. It isbecause any other details of difference between man and other forms arefar less marked than the agreements in these respects, that the humanspecies must be regarded as a primate mammalian vertebrate. 

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The comparative study of the human organism as a structural type has nowbeen narrowed down to a review of the various members of the order ofprimates. It is the duty of science to arrange these organisms accordingto the minor differences beneath the agreements in major qualities, and toshow how they are related in an order of evolution. It will appear, whenthis is done, that the supreme place is given to the human species onaccount of four and only four characteristics; these are (1) an entirelyerect posture, (2) greater brain development, (3) the power of articulatespeech, and (4) the power of reason. As we are treating the human body asa subject for comparative structural study, the third and fourthcharacters do not concern us here; but it is well to point out that theydepend entirely upon the second, and that they are the functionalconcomitants of the improved type of brain belonging to the highest type. Two characters remain, and in both cases it is significant thatdifferences in degree only are to be found by even the closest analysis. The human brain is the same kind of brain that lower primates possess; itsstructure is unique in no general respect. And as regards thefirst-mentioned character, comparative anatomy shows, in the first place, that this also is something differing only in degree, and in the secondplace, that it is due directly to the development of the brain. For thesereasons a survey of the various members of the order of primates must deallargely with the progressive elaboration of the brain and the entailedeffects of this enlargement. 

The order of primates is subdivided as follows :--

Sub-order 1. _PROSIMII_. Lemurs. Sub-order 2. _ANTHROPOIDEA_. Family 1. _Hapalidæ_. The marmosets. Family 2. _Cebidæ_. The American or tailed monkeys. Family 3. _Cercopithecidæ_. The baboons. Family 4. _Simiidæ_. The true apes. Family 5. _Hominidæ_. The human species. Primates

Each one of these subdivisions is interesting in its own way, eitherbecause its members depart from the typical condition of the whole orderin some respects, or because of some character that foreshadows and leadsto a more developed element of the animals placed in the higher sections. 

The lemurs are small animals very much like squirrels in their generalform and in their tree-climbing habits. They live now almost exclusivelyon the island of Madagascar, but palæontology shows that they were morewidely spread at an earlier time. Their teeth are exactly like our own, except that there is one more premolar on each side of each jaw. The"fingers" and "toes" bear nails like ours, again with an exception in thecase of the second digits of the hind limbs, which bear claws. The detailsof structure that set these animals apart from all the rest of theprimates are too small to deserve comment in the present connection. 

Passing to the true anthropoids, or man-like primates and man himself, thefirst forms encountered are the little marmosets, which are like thelemurs in some ways, but in other respects they resemble the familiartailed monkeys. They are peculiar in having three premolars and two molarson either side of both upper and lower jaws, and also in the fact that the"thumb" is not opposable to the other fingers, while all the digits exceptthe "great toes" bear claws instead of manlike nails. The proportion ofbrain-case and face does not differ much from that in the lemurs and evenlower forms like cats, for the brain has not increased greatly in totalmass, though the cerebrum is more convoluted than in the lower forms. 

The true monkeys, or Cebidæ, are more interesting, and at the same timethey are much more familiar to every one, as they are the commonestanthropoids of the menagerie and circus. Their wonderful agility andsureness in climbing about is partly due to the perfect grasping power ofthe lower limb. To all intents and purposes the foot is a hand; the firsttoe is shorter than the others, and its free motion is unrestricted as inthe thumb of the hand. These animals usually possess a long tail whichthey can use as a prehensile organ, curling it about the branch of a treewith hand-like ease and grasp. When they run on all fours, they plant thepalms and soles flat upon the ground. The feature of primary importance ina comparative sense is the advanced structure of the skull. Theseanthropoids are much more intelligent than the lower forms, which is acorrelate of their larger and more convoluted brains. The increase in thetotal bulk of the brain has wrought considerable change, not only in thehead, but also in the relation of head to the trunk. The cranium, orbrain-case of bone, is relatively larger than the "face, " and it bulgesupward so as to lie no longer behind the latter as it does in the lowermammalia. In consequence of this cranial enlargement, the face and eyesare swung downward, as it were, so that the line of vision is not straightahead, but depressed below the horizontal. In order to look to the frontand to the immediate foreground to which it is progressing or to where itsfood or enemies may be, the monkey must bend back its head; if it isstill, it finds greater ease in the upright sitting posture which itassumes readily and naturally. 

The next division, called the Cercopithecidæ, includes the baboons of theOld World. These animals also run upon all fours, and their feet arehandlike as before, but the tail is much reduced. The general appearanceof the head is doglike, and the brain-case arches little more than it doesin the monkeys, but the face projects forward as a long muzzle, withterminal nostrils close together. In some respects the baboons standsomewhat away from the line leading from the lower to higher anthropoids;in other characters they approach the latter, for in the teeth especiallythey are identical with the apes and with the human species. 

The Simiidæ, or true apes, possess an overwhelming importance, far beyondthat of the baboons and monkeys. There are only four principal kinds nowexisting, namely, the gibbon, orang-outang, chimpanzee, and the gorilla, of which the first is much less familiar than the others. The knownspecies of gibbons occur in Indo-China and the Malay Peninsula. Thetypical animal stands about three feet high; its overarching braincase, enlarged in conformity with the much greater brain development, has pushedthe eyes and face still further around underneath, so that if the animalwalks upon all fours the eyes look almost straight into the ground. Therefore it must bend back its head at an extremely uncomfortable angleif it is to remain upon all four feet, but it prefers to raise itself upinto the human sitting posture, or, when it walks, it stands erect uponits hind limbs. Hence we who are accustomed to think of ourselves as theonly erect animals must revise our opinion, for we find in the gibbon anorganism that is nearly, if not quite, as advanced in this respect as weare. One peculiar difference may be pointed out, --the walking gibbonstretches out its great long arms to the sides in order to preserve itsbalance. The animal seems awkward to us, perhaps, but it is possible thatthe human method of balancing the body by vigorously swinging the armsmight seem quite as awkward to a gibbon as its grotesque posture does tous. 

The orang-outang comes next in this series. It inhabits the islands ofBorneo and Sumatra, where we find two distinct species. It is a reddishcolored animal standing about four feet four inches high, with rather longhair. It is bulky, slow and deliberate in action, and when it walks in asemi-erect position it rests its knuckles upon the ground, swinging itslong arms as crutch-like supports. Like the gibbon, it does not walk uponall four feet in the way that the monkeys and baboons do, and we find inthe still further development of the brain and the higher arch of thecranium the reasons for its semi-erectness. It cannot remain with itshands and feet upon the ground and bend back its head so as to direct itsvision forward. 

The chimpanzee of intertropical Africa brings us to a still lessmonkey-like and more manlike stage. This creature attains the height offive feet, which is more than that of some of the lower races of man. Itpossesses large ears and heavy overarching brows; its thumb and great toeare more like those of man, though its foot is still practically a hand. Its lower limb curves like those of the other apes, and its soles areturned toward one another; in brief, it is naturally bow-legged, acharacter that adapts it for a tree-climbing life. This animal also isnearly, though not quite, erect. It shows a most marked advance in thematter of the brain, for the cerebrum is richly folded or convoluted, andwith this higher degree of physical complexity is correlated its superiorintelligence; it is well known that chimpanzees can be taught to wearclothing and to use a cup and spoon and bowl like a human child. Indeed, in mental respects, the chimpanzee surpasses all of the other mammalia, with the sole exception of man. An eminent psychologist has stated that itis about the equal, in mental ability, of a nine months' old human infant. 

The last form among the apes, the gorilla, is one that brings us to arealization of our own human physical degeneracy. The animal lives in WestEquatorial Africa, and it is a veritable giant in bulk, though its heightmay not exceed five feet six inches. The heavy ridges over the eyes, theupturned nostrils and triangular nose, place it near to the orang-outang, but it is superior to that form in its relatively greater brain-box, andin the fact that its heavy lower jaws do not protrude so greatly. It, too, is semi-erect, so that the line of the vertebral axis makes an angle withthe plane of the ground of about seventy degrees. Its anterior limbs, orarms, are again very long and bulky; and like the chimpanzee, it rests itsknuckles upon the ground in walking. 

It is a short step further to the human organism, whose brain has becomelarger and more complex, with a corresponding advance in the functionalpowers of reason and the like that owe their existence to the improvedstructural basis. After what has been said earlier regarding the relationbetween the erect attitude in walking and the increased size of thecranial part of the skull as compared with the face, it will not bedifficult to see how inevitably the former is the result of the latter. Should we get upon the ground upon our hands and knees in the position ofa tailed monkey, the eyes look straight into the ground, for the bulgingcranium has pushed out over the jaws and face so that they lie _under_ thebrain-case instead of in front. A person in this position can bend backthe head so as to look ahead, but the strain is too great for comfort. Rising to the knees, and lifting the hands from the ground, a feeling ofease at once succeeds that of tension. In the course of evolutionaccomplished primarily by the increase of the higher portions of thebrain, the erect position has been assumed gradually and naturally, and tomaintain it has necessitated many other changes in skeleton and muscles;for example, the pelvis has broadened to support the intestines, whichbear downwards instead of upon the abdominal walls; a double curve hasarisen in the axis of the vertebral column, giving an easier balance tothe upper part of the body and the head. Countless structures of the humanframe testify to an originally four-footed position and to a rotation ofthe longer axis through an angle of ninety degrees, as evolution hasproduced the human type. 

The conclusion that the human brain has made mankind is thus establishedas one of fundamental importance. Proceeding further, we learn that thisorgan proves to be essentially the same as the brain of lower primates; itdoes not gain its greater size and efficiency by the origination of whollynew and unique parts, but solely by the further elaboration of the onespresent in lower forms. In a word, it is only a difference in _degree_ andnot in essential _kind_ that separates man from the apes and otherprimates. Human nature is animal nature, and human structure is animalstructure, for nowhere can final and absolute differences be found. Thisdoes not mean that no differences appear, for it would be absurd tocontend that man and the apes are identical in every respect; but it doesmean that the resemblances are fundamental and comprehensive, and anydetails of dissimilarity are in the degree of complexity only. The supremeplace in nature attained by man is therefore due to progressive evolutionin the nervous system. The other systems have degenerated to a greater orless degree, but such regressive changes are more than compensated for bythe superior control exerted by the improved brain. In purely physical andmechanical respects, the human body is a degenerate as compared with agorilla; the arm of the latter is more powerful than the lower limb of theformer, while the gorilla's chest is more than twice as broad as thehuman, and more than four times as capacious. It is not through superiorphysique, but by superior ability to direct the activities of his body, that man excels in the struggle for existence with the lower animals. 

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Moreover, the human body is a veritable museum of rare and interestingrelics of antiquity. This characterization is justified by those vestigialand rudimentary structures that represent organs of value to humanrelatives among the lower animals, though they play a less active part atthe present time in human economy. There is scarcely a single system thatdoes not exhibit many or fewer of these rudimentary structures, but only afew need be specified. As compared with those of the apes, the humanwisdom teeth are degenerate; in the gorilla they are cut at the same timeas the other molars; and in the lower human races they come through thegums in early youth, while in the more advanced Caucasic races they arecut only in later life or not at all. The reduced vermiform appendix ofman, a source of much ill health, is another structure that is acounterpart of a relatively larger and useful part of the digestive tractin the lower primates and other animals. Furthermore, the human tail is areality, not a fiction. Now and then an individual is born with a tailthat may reach a length in later life of eight or ten inches; suchstructures are, of course, abnormal. But in every normal human being thereis a series of little bones at the lower end of the vertebral column, constituting the coccyx, and this is just where the abbreviated tail ofthe ape and the still longer prehensile tail of the monkey arises from thebody. Unless the coccyx is a tail, what can it be? And if it does notrepresent a reduced counterpart of the tails of other mammals, what doesit represent?

Many of the vestigial structures of man appear more clearly in infancy andin embryonic development. The human embryo possesses a complete coat ofhair, called the lanugo, which usually disappears before birth. This haircannot be regarded as any less significant than the coat of hair which theinfant whale possesses; it means a completely haired ancestor. Theelements of this coat are arranged precisely as they are in the apes; uponthe arm, for example, they point from shoulder to elbow and from wrist toelbow. Unless the anterior limb of the hairy human ancestor was held inthe position of the climbing ape's, this arrangement would bedisadvantageous, for the hair as a rain-shedding thatch would be effectiveonly upon the upper arm, while the hairs upon the forearm would catch therain. In a word, this vestigial coat indicates in the clearest possiblemanner that the ancestor of the human species was not only hairy, but alsoarboreal in its mode of life. 

Every human infant is bow-legged at birth, and the natural position of itscurved limbs is like that of the gorilla's, for the soles of the feet areturned toward one another. Again, the so-called great toe is at firstshorter than the others, and for a time it retains the power of freemovement that indicates a handlike character of the lower limb in theancestor. Many savage human races, however, whose feet remain unshod, makeuse of the primitive grasping power of the foot which the higher raceslose completely. An Australian and Polynesian can pick up small objectswith the foot very much as we may with the hand. 

Among the wonderful reminiscent characters displayed by the human infantis the firm clasping power of the hand, which it possesses for a timeafter birth and which enables it to hang suspended for several minutesfrom a stick placed in its grasp. The muscles which enable the infant todo this gradually dwindle, so that the two-year-old child can hangsuspended for only a few seconds. This grasping muscle is a heritage fromthe ape, where there is an obvious necessity for the newborn individual tohave a firm hold upon the hairy coat of its tree-climbing mother. When thenewborn child hangs in this way, it bends its curved lower limbs so thatthe soles of the feet are turned toward one another, thus increasing itsresemblance to the ape. 

Let us realize that these curious relics found in so many places in theframework of man are not unique, and that they are reduced counterparts oflarger and more valuable structures in the ape. Unless evolution is true, they have absolutely no sensible reasons for existence. Science prefersthe evolutionary explanation of their occurrence because this explanationis more in harmony with the facts known about other organisms, and it ismore reasonable than any other. 

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When we dealt with the general doctrine of natural transformation, itappeared that the evidence of embryology was in many respects more cogentand conclusive than that derived from the comparative study of animalstructures. In the case of man, as before, no one could demand any sureror more convincing proof that an organic mechanism with one structure canchange into an organic mechanism with a different structure, than theobvious facts of development. The embryo, which is not an infant or anadult, becomes an infant which must work its way onward by the gradualaccumulation of slight changes here and there and everywhere in itsanatomy, until it becomes mature. Each and every one of us has actuallyundergone the process of organic change in becoming what we are, and wecannot deny the reality of such a process without challenging the evidenceof our senses. 

When the full import of this history is realized, and when we look furtherinto the nature of these preliminary conditions through which the humanorganism passes in development, we are forcibly impressed by other factsthan the one to which I have directed your attention, for not only do wefind natural transformation, as in the other mammals, but the embryonicstages are marvelously similar to the earlier conditions in other mammals. Not very long before birth the human embryo is strikingly similar to theembryo of the ape; still earlier, it presents an appearance very like thatof the embryos of other mammals lower in the scale, like the cat and therabbit, --forms which comparative anatomy independently holds to be moreremote relatives of the human species. Indeed, as we trace back the stillearlier history, more and more characters are found which are the commonproperties of wider and wider arrays of organisms, for at one time theembryo exhibits gill-slits in the sides of its throat which in allessential respects are just like those of the embryos of birds andreptiles and amphibia, as well as of other embryo mammals and thesegill-slits are furthermore like those of the fishes which use themthroughout life. All the other organic systems exhibit everywhere thecommon characteristics in which the embryos of the so-called higher animalsagree with one another and with the adult forms among lower creatures; thehuman embryo possesses a fishlike heart and brain and primitive backbone, fishlike muscles and alimentary tract. Can we reasonably regard theseresemblances as indications of anything else but a community of ancestryof the forms that exhibit them?

Yet a still more wonderful fact is revealed by the study of the veryearliest stages of individual development. The human embryo begins itsvery existence as a single cell, --nothing more and nothing less; ingeneral structure the human egg, like the eggs of all other many-celledorganisms, is just one of the unitary building blocks of the entireorganic world. And yet the egg may ultimately become the adult man. Doesthis mean that man and all the other higher forms have evolved fromprotozoa in the course of long ages? Science asks if it can mean anythingelse. When the comparative anatomist bids us look upon the wide and variedseries of adult animals lower than man as his relatives, because theydisplay similar structural plans beneath their minor differences, it maybe difficult at first to obey him. But in the brief time necessary for thehuman egg to develop into an adult, the entire range is compassed from thesingle cell to the highest adult we know. There are no breaks in theseries of embryonic stages like those between the diverse adult animals ofthe comparative array. I do not think we could ask nature for morecomplete proof that human beings have evolved from one-cell ancestors assimple as modern protozoa beyond the obvious facts of human transformationduring development. They at least are real and not the logical deductionsof reason; yet their very reality and familiarity render us blind to thedeeper meaning revealed to us only when science places the facts inintelligible order. 

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And now, in the third place, we may look to nature for fossil evidenceregarding the ancestry of our species. Much is known about the remains ofmany kinds of men who lived in prehistoric times, but we need considerhere only one form which lived long before the glacial period in theso-called Tertiary times. In 1894 a scientist named Dubois discovered inJava some of the remains of an animal which was partly ape and partly man. So well did these remains exhibit the characters of Haeckel's hypotheticalape-man, _Pithecanthropus_, that the name fitted the creature like aglove. Specifically, the cranium presents an arch which is intermediatebetween that of the average ape and of the lowest human beings. Itpossessed protruding brows like those of the gorilla. The estimated braincapacity was about one thousand cubic centimeters, four hundred more thanthat of any known ape, and much less than the average of the lower humanraces. Even without other characters, these would indicate that the animalwas actually a "missing link" in the scientific sense, --that is, a formwhich is near the common progenitors of the modern species of apes and ofman. We would not expect to find a missing link that was actuallyintermediate in all respects between modern apes and modern men, any morethan we should look for actual connecting bands of tissue between any twoleaves upon a tree. A missing link, in the true sense, is like a bud ofearlier years which stood near the point from which two twigs of thepresent day now diverge. So _Pithecanthropus_ is a part of the chainleading to man, not far from the place where the human line sprang from alower primate ancestor. 

Of the fossil remains of true prehistoric men, little need be said. Wecannot know whether the races now living in the regions where theseremains are found are really the descendants of the older types, and so adirect comparison cannot be made. It is true that the brain capacities ofthe man of Spy, of the Neanderthal, and of the English caverns are lowerthan those of modern civilized races, but the differences are not sostriking and not so clearly indicative of the apelike ancestor of man asin the case of the previous comparison of _Pithecanthropus_ with apes andmen. 

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The foregoing facts illustrate the conclusive evidence brought forward byscience that human evolution in physical respects is true. Even if wewished to do so, we cannot do away with the facts of structure anddevelopment and fossil history, nor is there any other explanation morereasonable than evolution for these facts. If now we should inquire intothe causes of this process, we would find again that the present study ofman and men reveals their subjection to the laws of nature whichaccomplish evolution elsewhere in the organic world. 

The fact of human variation requires no elucidation; it is as real for menas for insects and trees. Indeed, some of the most significant facts ofvariation have been first made out in the case of the human species. Thestruggle for existence can be seen in everyday life. We cannot doubt itsreality when scores perish annually because of their failure to withstandthe extreme degrees of temperature during midwinter and midsummer; whenstarvation causes so many deaths, and when the incessant combat withbacterial enemies alone brings the list of casualties on the human side inour own country to more than two hundred and fifty thousand a year. As innature at large, the more unfit are eliminated as a result of thisstruggle, while the more adapted succeed. In the long run, that particularapplicant for a clerkship or any other work who may be the more fitted isthe one who gets it. While the severity of competition may be somewhatmitigated as the result of social organization, and while our altruisticcharitable institutions enable many to prolong a more or less efficientexistence, the struggle for existence cannot be entirely done away with. Heredity also is a real human process, and it follows the same course asin animals at large; as in the case of variation, some of the fundamentallaws of its operation have been first worked out in the case of humanphenomena, and have been found subsequently to be of general application. 

Reverting to the specific question as to the earliest divergence of manfrom the apes, we can readily see how the superior development of theape-man's brain gave him a great advantage over his nearest competitors, and how truly human ingenuity enabled the earliest men to employ weaponsand crude instruments instead of brute force. Thus the gap between men andapes widened more and more, as reasoning power increased throughsuccessive generations. This is another aspect of the statement that thesupreme position of man has been gained, not by superior organization inphysical respects outside of the nervous system, but by the superiorcontrol of human organization by the higher organs of this system. 

The unity of nature and of its processes is established more and moresurely as the naturalist classifies the facts of structure, development, fossil history, and evolutionary method. Our own species is not unique; ittakes its high place among other organic forms whose lives are controlledin every way by the uniform consistent laws of the world. 

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The physical evolution of human races is the next major division of thelarge subject before us. Heretofore the obvious differences displayed byvarious races have been disregarded and the species has been treated as aunit, in order that its evolution from pre-human ancestors might be madeclear. Knowing now how the facts of structure show that the supremeposition of our kind has been attained mainly as the result of theprogressive elaboration of the higher portions of the brain, and notbecause new and unique structures have been developed, we are prepared toturn our attention to the diverse characteristics of human races; andduring this inquiry anatomical matters will still be the only ones to bereviewed. The intellectual and social characters of numerous races belongto the category of physiological or functional phenomena, which are toreceive due consideration at a later time. It is the meaning of the factsof racial diversity for which we are now to look. 

For many reasons this subject is more difficult to describe in a conciseoutline than those taken up before. It is true that every one is familiarwith different types of human beings, such as the Negro and Japanese andChinese, while furthermore the obvious differences between such races asthe Norwegian and Italian are sufficiently marked to strike the attentionof any one who looks about at his fellow-passengers in a crowded streetcar. But few indeed have a comprehensive knowledge of the wider range ofracial variation in which these familiar examples find their place. Anthropology, or the science of mankind, is a large and well-organizeddepartment of knowledge, dealing with the entire array of structural andphysiological characters of all men. One of its subdivisions, anthropometry, is almost an independent discipline with methods of itsown; it describes the characteristics of human races as these aredetermined by statistical methods of a somewhat technical nature. There isstill another science, ethnology, which deals more particularly withinstitutions, customs, beliefs, and languages rather than with physicalmatters, although it is clear that ethnology and anthropology cannot besharply separated, and that each must employ the results of the other forits own particular purposes. 

Because men have always been interested in the study of themselves, thesubject of racial evolution is literally enormous, and the attempt to giveanything like a complete description of what is known would obviously befutile. But it is possible to obtain a clear conception of certain of thefundamental principles that fall into line with the other parts of thedoctrine of organic evolution with which we have now become acquainted. The main questions, therefore, may be stated in simple terms. The firstdeals with the evidences as to the reality of evolution during thehistorical and prehistoric development of the various types of man fromearlier common ancestors; the second asks whether the lines of racialevolution are further continuations of the line leading from ape-likeancestors to the human species as a type. In order to give the properperspective, it will be well to state at the present juncture, first, thatthe various kinds of men do not vary from each other in a chance manner soas to show all possible types and varieties, but that they fall intonatural groups or families distinguished by certain commoncharacteristics, just as do all other kinds of species of animals; in thesecond place, it appears that some of the differences between the racesdenoted higher on structural accounts and the lowest forms of man are ofthe same nature as those observed in the review of the various species ofprimates from the lemurs to man. 

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It is best to look at the whole question in a very simple and common-senseway before undertaking an extended examination of the details of humandiversity. The most casual survey of the peoples that we know best becauseof our own individual nearness to them enables us to realize that theraces now upon the earth have not existed forever and ever, or even forthe age of 6000 years as contended by Archbishop Ussher. They have allcome into existence as such, and they differ from their known antecedents;so that at the very outset common-sense leads us to accept evolution astrue, if we admit that human races have changed during the course ofrecent centuries. We know, for example, that the so-called Mexicans ofto-day are a people produced by a fusion of Spanish conquerors and Indianaborigines the Mexican is neither Spaniard nor Indian, though he mayresemble both in certain respects; he is a product of natural evolution, accomplished in this case by an amalgamation of two contrasted types. Whenwe speak of the American people, we must realize that it too has come intoexistence as such, and even, indeed, that it is in the actual process ofevolution at the present time. The various foreign elements that have beenadded during the last few decades by the hundreds of thousands arebecoming merged with the people who preceded them, just as the Dutch andthe French and the English coalesced during the days of early settlementto form the young American nation. Perhaps most of us call ourselvesAnglo-Saxon, but we are in reality somewhat different even in physicalrespects from the Englishmen of Queen Elizabeth's time, who alone deservedthe name Anglo-Saxon. This very term indicates an evolution of a type thatdiffers from both the Angles and the early Saxons of King Alfred's age. These are simple examples which illustrate many features of the universalhistory of human races wherever they are to be found. Even in thecomparatively peaceful times of our modern era the history of any race isa veritable turmoil of constant changes; conquerors impress theircharacters upon the vanquished, while the victors often adopt some of thefeatures of the conquered. Colonies split off from the mother nation tofollow out their destinies under other conditions. Nowhere does thenaturalist find evidence of long-established permanence, or an unentwinedcourse of an uninterrupted and unmodified line of racial descent. 

It is the task of the student of human evolution to unravel the tangledthreads of human histories. The task is relatively simple when it isconcerned with recent times where the aid of written history may besummoned but when the events of remote and prehistoric ages are to beplaced in order, the difficulties seem well-nigh insuperable. All is notknown, nor can it ever be known; but wherever facts can be established, science can deal with them. By a study of the present races of mankind, much of their earlier history can be worked out, for their geneticrelations may be determined by employing the principle that likeness meansconsanguinity. Let us suppose an alien visitor to reach our planet fromsomewhere else; if he were endowed with only ordinary human common-sense, he would very soon ascertain the common origin of the English-speakingpeople in Canada, the United States, Australia and New Zealand, SouthAfrica, and many other places. Even if he could not understand a word ofthe English language, he would be justified in regarding them all as thedescendants of common ancestors because they agree in so many physicalqualities. The anthropologist works according to the same common-senseprinciple, obtaining results that find no explanation other than evolutionwhen the varying characters that are used to determine social relationshipare properly classified and related. It is to these characters that wemust now give some attention. 

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The average stature of adults varies in different races from four feet oneinch in certain blacks to nearly six feet and seven inches, as among thePatagonians. These are the extreme values for normal averages, althoughdwarfs only fifteen inches high have been known, while "giants" sometimesoccur with a height of nine feet and five inches. Such individuals are ofcourse rare and abnormal, and are not to be taken into account inestablishing the average stature of a race for use in comparison with thatof another group. 

The color of the skin is another criterion of racial relationship, thoughit is more variable in races of common descent than we are wont to assume. We are familiar with the fair and florid skin of the northern European, the fair and pale skin in middle and southern Europe, the coppery red ofthe American Indian, the brown of the Malay, of the Polynesian and of theMoor, the yellowish cast of the Chinese and Japanese, and the deepervelvety black of the Zulu; but it has been found that many of the closerelatives of the black are lighter in skin color than some of ourCaucasian relatives, so that this character cannot be taken by itself as asingle criterion of racial affinity. 

Perhaps the most conservative and most reliable character that serves forthe broad classification of the human races is the shape of the individualhairs of the head. We are familiar with the straight lank hair of theMongolian peoples and of the various tribes of American Indians, in whomthe hair possesses these peculiarities because each element grows as anearly perfect cylinder from the cells of the skin at the bottom of a tinypit or hair-follicle. The familiar wavy hair of white men owes itscharacter to the fact that the individual elements are formed by the skin, not as pencil-like rods, but as flattened cylinders. They are oval orelliptical in cross-section, and when they emerge from the skin they growinto a long spiral. If, now, the hair is formed as a very much flattenedrod about one-half as wide in one diameter as in the other, it curls intoa very tight close spiral and gives the frizzly or woolly head-covering ofthe Papuan and of the Negro. 

In the next place, the shape of the cranium is a character of much value. This is determined as the proportion between the transverse diameter ofthe skull above the ears to the long diameter, namely, the line that runsfrom the middle of the brow to the most posterior point of the skull. Inthe so-called "long-headed" or dolichocephalic races, the proportion isseventy-five to one hundred, while in those forms that have more roundedor brachycephalic heads, like the Polynesian and the black pygmy, therelation is eighty-three to one hundred. The cranial capacity again variesconsiderably, from nine hundred cubic centimeters to twenty-two hundredcubic centimeters. Many striking variations are also found in theprojection of the jaws. A line drawn from the lower end of the nose to thechin makes a certain angle with the line drawn from the chin to theposterior end of the lower jaw; if the jaw projects very greatly, thisangle will be much less than when they do not. In most of the Caucasianpeoples, the lines meet at an angle of eighty-nine degrees, or very nearlya right angle, but in some of the lower races the figure may be onlyfifty-one degrees. Additional characters of the teeth and of the palateare also taken into account, and have proved their utility. Finally, thenose exhibits a wide range of variation from the small delicate feature ofthe Chinaman to the large, well-arched nose of the Indian. It may behollowed out at the bridge instead of arched; again, it may be nearly anequilateral triangle in outline, as in the Veddahs, and the nostrils mayopen somewhat forward instead of downward. As many as fifteen distinctvarieties of the human nose have been catalogued by Bertillon. 

These are the principal bodily characters which the anthropologist uses todistinguish races and by their means to determine the more immediate orremote community of origin of comparable types. Many of thesecharacteristics, as indeed we may already see, are decidedly important inconnection with the second problem specified above, for in the case of theflat triangular nose and projecting jaws of a low negroid we may discernclear resemblances to certain features of the apes. 

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Long before the doctrine of evolution was understood and adopted, studentsof the human races had been deeply impressed by their naturalresemblances. As early as 1672 Bernier divided human beings according tocertain of these fundamental similarities into four groups; namely, thewhite European, the black African, the yellow Asiatic, and the Laplander. Linnæus, in the eighteenth century, included _Homo sapiens_ in his list ofspecies, recognizing four subspecies in the European, Asiatic, African, and Indian of America. Blumenbach in 1775 added the Malay, thus giving thefive types that most of us learned in our school days. But the differentvarieties of men recognized by these observers were believed to be createdin their modern forms and with their present-day characteristics; thecommon character of skin color exhibited by any group of peoples of asingle continent was to them only a convenient label for purposes ofdescription and classification. It was not until years later thatfundamental resemblances were recognized as indicating an actual bloodrelationship of the races displaying them, and therefore of evolution. Since the doctrine of human descent and of the divergence of human racesin later evolution has been accepted, those who have attempted to work outfully the complete ancestry of different peoples have found that no singlecharacter can be taken by itself, while the various criteria themselvesdiffer in reliability; the color of the skin is not so sure a guide as thecharacter of the hair and skull, wherefore the classifications of recenttimes, notably those of Huxley and Haeckel, have been based largely uponthe latter. The latest systems have been more rigidly scientific and morein accord with the most modern conceptions of organic relationships ingeneral, as evidenced by the thoroughgoing methods of Duckworth in hisrecent treatise on human classification. 

It now remains to present the salient facts regarding the geneticrelationships of typical human races, although it is obviously impossibleto go into all of the details of the subject. But these are not essentialfor the main purpose, which is to show that the evolutionary explanationis the only one that is reasonable and self-consistent. Opinions aresometimes widely at variance regarding countless minor points, but noanthropologist of to-day can be anything but an evolutionist, because themain principles upon which the specialists agree fall directly into linewith those established elsewhere in zoölogy. It seems best to state theseprinciples without reverting to controversial matters which find theirplace in the monographs of the experts. Any comprehensive account such asthat of Keane, even if it may not give the final word, will be entirelysufficient to demonstrate how fruitful are the methods of evolution whenthey are employed for the study of human races, and indeed how impossibleit is to discuss human histories without finding conclusive evidences oftheir evolutionary nature. 

The facts that are available indicate that the first members of ourspecies evolved in an equatorial continent which is now submerged, andwhich occupied a position between the present continents of Asia andAfrica. From this center hordes of primitive men migrated to distantcenters where they differentiated into three primary and distinct groups. The first of these was gradually resolved into the darker-skinned peoplesmost of whom now live in the continent of Africa, although many dwell alsoin the islands of the western Pacific Ocean. The second branch dividedalmost immediately to produce, on the one hand, the Indians of the newworld and, on the other, the yellow-skinned inhabitants of Asia and otherplaces. The third branch developed as such in the neighborhood of theMediterranean Sea, and produced the series of so-called Caucasian peoples, which are by far the most familiar to us and to which most of us belong. But so early did the second branch divide that there are virtually fourmain divisions of the human species that are to be examined in serialorder. 

It is best to begin with our own division, because its greater familiaritymakes it easier to become acquainted with the methods and results ofanthropology, on the basis of facts that we already know. Threesubordinate types exist, located primarily in northern, central, andsouthern Europe respectively, but many other races dwell elsewhere thatare assignable to one or another of these subdivisions. In northeasternEurope we find people such as the Norwegians, Swedes, Danes, and northGermans, that average five feet eight inches in height. They have thelong, wavy, and soft hair which is a general characteristic of the wholeCaucasian group, although its light flaxen color is distinctive. The blueeye and florid complexion accompany the light color of the hair. The skullis of the longer type, the jaws and forehead are straight and square, thenose is large and long without a distinct arch, and the teeth arerelatively small. It is not so well known that the Scandinavian type is soclosely copied by many people of Asia, such as the western Persians, Afghans, and certain of the Hindus, living in a continent that we areinclined to assign to the Mongol only. In the possession of thesecharacters the Northern Europeans and other races specified displayevidences of their common ancestry and evolution quite as conclusively asin the case of the cats discussed in an earlier chapter where the meaningof essential likeness was first demonstrated. 

A broad zone may be drawn from Wales, across Europe and Asia, and even tothe eastern islands of the South Seas, in which we find peoples that areobviously of Caucasian descent, but they differ from the members of thefirst group in some details of structure. On the average they are aboutfive feet five or six inches in height, the hair is dark and wavy, but itis not the pencil-like structure of the Mongol. The complexion is pale, the skull is rounder, and the eyes are usually brown in color. Thesepeoples agree also in their volatile temperament and vivacious manner andare thus markedly different from the more stolid northerners. To thisminor branch of the Caucasian stock belong the Welsh, most of the French, South Germans and Swiss, Russians and Poles, Armenians, eastern Persians, and finally some of the inhabitants of Polynesia. The last, it is true, form a well-marked group of darker-skinned and taller races, but in spiteof the admixture of these and other unusual features, we can still discernthe bodily characters that supplement their traditions, telling of anAsian origin, in demonstrating their common ancestry with round-headedPersians and middle Europeans. Below the zone of middle Europe and Asia isanother broad region inhabited by the "Mediterranean" type of Caucasian. The Spaniard, Italian, Greek, and Arab are sufficiently familiar toillustrate the distinctive qualities of this subdivision. These peoplehave the smaller stature, dark hair, dark eyes, and paler skin of themiddle Europeans, but the skull is of the long instead of the roundedtype. A well-marked subordinate group is formed by the so-called Semiticpeoples, such as the Arabs and their Hebrew relatives. The Berbers andother North African races possess a darker skin probably because of theadmixture of Ethiopian stock, and they, too, are so well characterizedthat they form a clearly marked outlying group as the so-called Hamites. Passing over into Asia we find relatives of the Mediterranean man in theDravidas and Todas of India, possibly in the degenerate Veddahs of Ceylon, and finally in the Ainus or "hairy men" of some of the Japanese islands. The last-named people certainly possess some Mongolian features, but theseseem to have been added to a more fundamental form of body that isdistinctly Caucasian. 

All of the races we have mentioned, together with their relatives, may becompared to the leaves borne upon three branches that take their originfrom a single limb of the widespread human part of the tree. They cannotbe classified in any mode on the basis of their primary and secondaryresemblances without employing the treelike plan of arrangement, which tothe man of science is a sure indication of their evolutionaryrelationships. 

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The people of the second or Mongolian group agree in certain well-markedcharacteristics in such a way as to be well separated from the otherdivisions of mankind; these characteristics we may speak of asconstituting a second "theme, " of which the various peoples of the groupare so many variations. To visualize them we need only to recall theappearance of the Chinaman, perhaps the most familiar example of theentire series. Here the hair is coarse and black, and straight because ofits round transverse section; the mustache and beard of the Caucasians areseldom found except in later life; the skin is a fleshy yellow in color;the skull is round, indeed, it is one of the roundest that we know; thejaws are not so straight as in the Caucasian, for the angle at the pointof the chin is about sixty-eight degrees. The cheek bones projectlaterally, with greater or less prominence; the nose is very small, tiltedup slightly at the end, and is usually hollowed instead of arched. Theeyes are small and black in color, set somewhat obliquely, and the upperlid is drawn down over the eye at its inner corner so as to make theobliquity still more marked. The teeth are larger than those of theCaucasian. Finally, the Mongol is below the average of all men as regardsheight, being usually about five feet four inches tall. 

The original Mongolians probably developed the characteristic features wehave just noted in a Central Asiatic region, and then almost immediatelythey divided into two great groups. Each of these evolved along certainlines of its own, one sweeping northward to develop into what are nowcalled the Northern Mongols, the other working its way eastward andsouthward to produce the peoples of China proper, Indo-China, and manyparts of Malaysia. Considering first the peoples of the Northern Mongoliandivision, we find in the typical Manchurian what is perhaps the nearestamong modern people to the original race. Spreading northward and westwardfrom the middle Asiatic plains, this great wave has produced the nomadictribes of Siberia, like the Chukchi, the Buryats, and the Yukaghir. Thepresent inhabitants of Turkestan connect those forms which have remainednear the original home with the races of Mongolian origin that livefarther to the westward, like the Turks of Asia. But the Mongolian tideoriginally swept much farther to the west, although it was driven backlater by conquering Caucasian peoples; and it has left behind suchremnants as the Finlander and the Laplander, the Bulgar, and the Magyar. It is evident that these western branches of the Mongol stock are not atall pure in their racial characteristics, for they clearly show theeffects of a mixture with alien European peoples. To assign them to theNorthern Mongol division means only that their dominant characteristicsare mainly those of Mongolian nature. We have referred the Russians to themiddle Caucasian division even though the Slav or Tartar infusion is verygreat, but it does not dominate over the Caucasian peculiarities as itdoes in the case of the peoples we have mentioned. As regards theremaining types we must add to this brief list the Koreans and theJapanese, the former being far purer in Mongolian nature than the latterpeople, which has apparently been affected by a Malay influence from thesouth. 

Turning now to the southern Mongol, we find that from their cradle in theTibetan plateau they too have spread widely, and their descendants havealso come to differ in certain respects as they have establishedthemselves in other lands. Most of the present people of Tibet belong tothis section; the Gurkhas of Hindustan, the people of Burma proper, ofAnnam, and Cochin China are close relatives of one another and of the morecharacteristic Mongolians of China proper who make up the vast bulk of thepopulation. From this stock we may also derive the Malays of Sumatra andJava, of Borneo and Celebes, and the Tagals and Bisayans of the PhilippineIslands. Even the Hovars and other tribes of Madagascar may be referred tothis division, for although in them the skin has become somewhat darker, we may still discern the characteristics which indicate their commonancestry with the Oceanic Mongols. 

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The American Indians taken collectively constitute a group that is wellset off from the rest of mankind by such characters as taller stature, small, straight, and black eyes, a large nose that is usually bridged oraquiline, a skull of medium roundness, and the yellow copper color of theskin. The common origin with the Mongols is demonstrated by the straightand long, coarse, black hair and by the absence of a beard; the mustachealso is almost always absent. 

All of us have seen Indians belonging to the tribes of the plains, whichserve as excellent examples of this grand division. Many have also visitedthe homes of the Pueblo Indians, and have learned how uniform is thephysical appearance of the tribes living in various parts of the UnitedStates. Indeed throughout all of North America the basic characteristicsof Indians prove to be strikingly conservative, although in the Eskimothere are some departures which seem to indicate a closer connection ofthese peoples with the Mongols, probably as the result of some more recentinflux from the neighboring and not very distant region of northeasternSiberia. Extending our survey southward through Central America, theAztecs and Mayas are found to possess many of the same characters, thoughin some respects they are transitional to the Caribs of the northern edgeof South America and to the Indians of South America. Traveling stillfarther southward, we meet the very tall Patagonian, still an Indian inessential respects, and finally, the Yahgan and Alacaluf of the Fuegianregion, the most degenerate members of the race. The last-mentioned peopleare dull and brutish and most degraded in all respects, and stand at thelowest end of the red Indian series as regards intellectual ability andcultural attainment. 

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We now come to the last of the four great divisions of the human specieswhich includes the races usually spoken of as Africans or Ethiopians. Butthese races are by no means restricted to the continent of Africa, forquite as typical black types are found in far-distant lands such asAustralia and many islands of the Pacific Ocean. The races assigned tothis division group themselves about two subordinate types, --the tallnegro proper and the shorter or dwarf negrito, --and each of these hasrepresentatives both in Africa and in the oceanic territory. 

The black slaves of America were all descended from typical negros broughtfrom the western part of Africa, and they provide us with adequateillustrations of Ethiopians as a group. In them the stature is above theaverage of men in general, specifically about five feet ten inches. Theshort jet-black hair is strikingly different from the head covering of theother great groups of human races; each individual hair is so flat incross-section that it curls into a very tight close spiral, and thisbrings about a frizzly appearance of the whole head covering. There islittle or no beard, the skin is soft and velvety and of various shadesapproaching black in color. The skull is long, the cheek bones are small, but the most distinctive characteristics of the head are found in theapelike ridges over the eyes and in the very broad flat nose whichprojects only slightly and turns up so that the nostrils open forward to amarked degree, while in the jaws there is an astonishing divergence fromthe Caucasian condition in the great protrusion which causes the angle atthe chin to be about sixty degrees. 

The warlike Zulus and other peoples of Southern and Central Africa areperhaps the most characteristic races in this division. Their relativesare found to the northward as far as the Sahara desert, along the southernborders of which they have spread out to the eastward and westward. Fusionwith other races has taken place along this border so that many of thesenorthern tribes are much lighter than the Zulus in the color of the skin. But many relatives of the taller African negro are found in other parts ofthe world, namely in Australia, and in New Hebrides and NewCaledonia--islands to the north and east of this continent. The Papuan ofNew Guinea is a typical negro in all true respects, with strongly markedEthiopian characteristics, though there are some differences which aretransitional to the more aberrant natives of Melanesia, which includesmany archipelagos like the Fiji, Bismarck, Marshall, and Solomon islands. Undoubtedly the most degenerate member of the tall negro division is theAustralian native, the so-called "blackfellow. " The bulbous nose and thewell-grown beard mark him off from the typical stock, but his obviousrelationship to this is indicated by the low brain capacity, the prominentridges over the eyes, and the heavy projecting jaws. 

Taking up the other division of the so-called Ethiopian race, constitutingthe Negrito section, we may begin with its Oceanic members. The natives ofthe Andaman Islands, the Kalangs and the Sakais of Java and neighboringregions, and the Aetas of the Philippine Islands agree in a dwarfedstature of four feet or a little over, in their yellowish brown skincolor, a round head, and woolly reddish-brown hair. They, too, possesslarge ridges over the eyes and extremely prominent jaws, and in theselatter characteristics particularly we see evidences of their relationshipto the negro. But perhaps the most characteristic pygmies are found inAfrica. The little Bushmen and Hottentots are low types of the Negritostock, and they lead us to the lowest men of all, the Akkas of the WestCongo region. It is difficult for us to realize how utterly degenerate andapelike these pygmies are. The jaws are disproportionately large ascompared with the cranium or brain-case, and project to a degree whichbrings the skull very close to that of the higher apes; while in mentalrespects, in the absence of dwellings, and in many other ways they proveto be the lowest of all mankind, --veritable brutes in form and mode oflife. 

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Without a full series of photographs before us the foregoing sketch of thevarious races of men cannot make us fully acquainted with all the strangevarieties of the human body, but it will suffice to establish twofundamental results. While all men agree in the possession of certainfeatures which set them apart from other members of the primate order, they differ among themselves in such a way as to fall into fourwell-marked subdivisions branching out from a common starting-point. Furthermore, in each of these primary groups the subordinate types arrangethemselves also in the manner of branches arising from a common limb. Thisis the relation that we have earlier found to be a universal onethroughout the animal kingdom, and science believes that it indicateseverywhere an evolutionary history--an actual development along differentlines of descent of forms which have a common starting-point and ancestry. 

The second principle is perhaps even more significant: when we review themany races from the Caucasian to the dwarf Negrito, we traverse a downwardpath which will bring us inevitably to the higher apes. In our survey ofhuman races, we have passed from the Caucasian, with the largest brain andcranium and with straight jaws well underneath the brain-case, to thepygmy with a relatively small brain, with huge projecting jaws and withprominent ridges over the eyes; one step more along that path would bringus to the gorilla or the chimpanzee. The array of lower primates, from thelemur to the gorilla, gives a series of forms exhibiting a progressiveadvance in respect to the size of the brain and cranium, and a gradualretreat of the jaws to a position underneath the cranium; and one stepfurther brings us to man. In a word, these two lines join--in fact, theyare directly continuous. There is a far smaller difference between thelowest man and the highest ape than we have been accustomed to suppose. 

Thus in general terms, it can justly be said that process of evolutionwhich developed the first man from its ape-man progenitor seems to havecontinued during subsequent ages. Spreading out in diverging lines ofevolutionary descent no less clearly than they have in geographicalrespects, certain races have far surpassed their fellows of a lower order, which, like the brute pygmy, remain nearer the common structural form fromwhich all men have sprung. 

VI

THE MENTAL EVOLUTION OF MAN

The problems dealing with the make-up of the human mind and with theevidences of mental evolution bring the student to matters of more vividhuman interest. Mental phenomena are so complex and intricate that it iswell-nigh impossible to analyze their history without a knowledge of theprinciples derived from the broad study of evolution as a generaldoctrine, where human prejudice is not so large a factor and where hisperspective is less affected by the proximity of the observer to hisfacts. For these and other reasons the foregoing treatment of humanevolution has been confined to the purely structural characteristics ofman as a species and of human races as so many varieties of this type. When the broad comparative methods of biological science are employed forthe elucidation of human anatomical facts, the result in this specialcase, like that established through the study of the characteristics ofliving things in general, is the proof that evolution gives the mostrational and natural explanation of the observed data. This being true, the naturalist who turns from purely structural matters to human intellectand its history, finds well-tried methods of inquiry already available, and he approaches his further studies with a conviction that evolution, having proved to be universal so far, in all probability will be foundequally true in the case of psychological phenomena. This expectation isindeed realized, and the scope of the doctrine is extended over a newfield, when the facts of human psychology are treated as materials forimpersonal comparative study; and this result is not only useful andvaluable in and by itself, but it also provides in the principles ofmental evolution the transition to the field of social relations andethical ideas and ideals which are apparently the unique possessions ofmen as individuals and as associated groups. 

The field of comparative psychology might seem at first sight to be aforeign territory to the average well-informed layman in science, but thecontrary is really the case. Every one has thought at one time or anotherabout his own mental make-up, and about the minds of others. No one canwatch a child at play with his toys or at work with his schoolbookswithout being struck by many evidences of marked differences between theimmature and the experienced types of mind. Every one knows also that themental "scheme of things" is by no means the same for all nations or racesof mankind existing to-day, while furthermore the fact is entirelyfamiliar that the intellectual heritage of a present race has changed inthe course of previous ages. Therefore in this field as before we needonly to amplify our knowledge of such representative psychological factsas these by drawing upon the full stores of the special investigator, inorder to learn that human thought, like the human frame, has undergone anatural history of transformation to become what it is and what it wasnot. 

Many who would be ready to accept the evolution of physicalcharacteristics find it impossible to treat the history of human mentalityas a subject for dispassionate consideration, because above all else theintellectual powers of mankind seem to be truly distinctive. It is onlyafter constant use of the methods of science that we can bring ourselvesto see how closely we resemble lower forms in physical make-up; stillgreater reluctance must be overcome before we can view our mentalprocesses as counterparts of those of inferior animals, so essential toour very humanity do they seem. But our duty to undertake the task isplain, and its discharge will be greatly facilitated by a clearrealization that mental evolution is but a part of human transformation intimes past, as the latter is only a small fraction of the universalprocess of organic evolution in general. While our own nature andinquisitiveness give us so intense an interest in the teachings of sciencethat relate to the constitution and history of human faculty, whereforethese matters gain an undue prominence in perspective, it must never beforgotten that these teachings do not stand by themselves, for they arebuilt upon the sure foundations already laid in physical evolution; andthese foundations cannot be disturbed by our failure to use them as abasis when we construct our own conceptions of human intellect and itshistory. 

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Before passing to the systematic review of the facts and principles ofcomparative psychology which demonstrate evolution, there are certaingeneral aspects of the subject to be considered so as to clear the ground, as it were, for further progress. When the several organic systems of thehuman body were compared with those of the apes and of lower animals, their evolution was proved as far as the purely physical and materialcharacteristics were concerned. But we know that there is no part of anyone of these systems which has not its own particular function, eventhough this may be a relatively passive one; while furthermore, sciencedoes not know of any physiological activity without some organ or tissueor cell as its material basis. Therefore the evolution of an organicsystem in material respects involves its functional or dynamic evolutionas an inseparable correlate; the two proceed in unity, and they cannot beregarded as entirely distinct without violating common-sense. 

The fin of a fish is used as an organ of locomotion in water; from somesuch organ have evolved the walking limbs of amphibia and reptiles, constructed for progression upon land. Among the mammalia the fore limbshave become structurally adapted so as to be such diverse organs oflocomotion as the stilt-like leg of a horse, the flipper of a seal, thewhale's paddle, and the bat's wing, while among the birds the wing maychange into a flipper like that of the penguin, or become reduced to avestige as in _Apteryx_. We may focus our attention upon the materiallikenesses and differences in such a series of locomotory organs, but aninevitable accompaniment of their physical changes in the transformationof species has been an evolution in the functional matter of locomotion. The most complex and differentiated tracts of even the highest animalshave evolved from a simple sac like that of a polyp or jellyfish, as weknow from the independent testimony of comparative anatomy and embryology;in this case also the evolution of alimentary functions is no lessinseparable from the transformations in structural respects. And again, wecannot understand the historical development of vision without taking intoaccount the eyes of various types belonging to lower and higher animals. 

So it is with the nervous systems of man and other animals, and with theirfunctions. The nervous system of the human organism comprises identicalorgans with the same arrangements that are found in other primates and inlower vertebrates as well; the differences in structure are differences inthe degree of the complexity of certain parts, notably of the cerebrum. Therefore the evolution of human mentality, which depends upon a humantype of brain as a physical basis, is already demonstrated with the proofthat the human brain and nervous system have evolved. It is true that aninvariable and necessary connection between mind and matter is implied inthe foregoing statement, and this is something which demands furtherconsideration at a later point. But just _how_ the human mind is producedby or depends upon the brain, is of far less importance for us at thistime than the obvious fact that mental performance requires active nervoustissues. So far investigation has been unable to discover a valid reasonfor a belief in the existence of mental phenomena, as such, apart fromsome kind of material basis. And while we may prefer to restrict the useof the word _mind_ to the series of nervous processes going on in thehuman organ of thought, in so far as these processes are carried on by thepeculiar tissues of the nervous system they cannot be finallydistinguished from the functional products or accompaniments of the samekind of active tissues and organs in lower creatures. Thus the subject ofmental evolution becomes much clarified at the outset by understandingthat nervous processes and nervous systems evolve together. 

In the direct treatment of the facts and principles of mental evolution wecan use exactly the same classification and subdivisions of the materialsof study as heretofore, because psychological data are the correlates ofmaterial organic systems, and also because the former, being naturalphenomena, are subject to the methods of analysis which can be employedfor any series of objects that have undergone evolution. Separating thematter of fact from the question as to the method, and recalling the mainbodies of evidence as to the reality of evolution, we may establish foursections of the subject before us: these are (1) the anatomy, (2) theembryology, and (3) "palæontology" of mind, and (4) an inquiry into theway nature deals with the psychical characteristics of organisms inaccomplishing their evolution. To specify more particularly, it ispossible in the first place to compare the activities belonging to thecategory of mental and nervous operations, displayed by man and otherorganisms, and the results form the subject of comparative descriptivepsychology; the second division, namely, developmental or geneticpsychology, deals with the sequence of events in the life of a singleindividual by which the infantile and adolescent types of mind becomeadult intellectuality; in the third place, in speaking of the palæontologyof mind, the phrase is used to refer to the varied and changing mentalabilities of human races in historic and prehistoric times as they may bedemonstrated and determined by the evidences of the culture of suchearlier epochs. In considering the matter of method, the questions arewhether variation, inheritance, and selection are as real in the world ofmental phenomena as they are in the material world, and whether the lawsare the same or similar in the two cases. We shall learn how the resultsof such studies prove with convincing clearness, first, that the contentsof the individual mind and of the minds of various human races are trulythe products of natural evolution, and second, that the human mind differsonly in degree from that of lower organisms, and not in kind orfundamental nature. 

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When the operations of human mental life are examined, they include whatare called processes of _reason_ as apparently distinctive elements. Thelower mammalia exhibit a simpler order of "mentality" denoted_intelligence_, while the nervous processes of still simpler forms arecalled _instinctive_ and _reflex_ activities. These are the terms of thecomparative array of psychology which are to be separately examined andclassified, and to be brought into an evolutionary sequence ifcommon-sense directs us to do so. 

Let us begin our comparative study with an example of the simplest animalsthat consist of only a single cell, such as the little protozoon_Amoeba_. We have become familiar with this organism as one that carrieson all of the vital functions within the limits of a single structuralunit; it is a mass of protoplasm enclosing a nucleus, and as a biologicalindividual it must perform all of the eight tasks that are essential forlife. It does not possess a digestive tract, but it does digest; it doesnot have breathing organs, but it does respire; and it is particularlynoteworthy that it must coordinate the different activities of its parts, and maintain definite relations with the environment, even though itscoordination and sensation are not accomplished by any special parts thatwould deserve the name of elementary nervous organs. Its many activitiesare simple responses to stimuli that reach it from without, and itsreactions to such stimuli are called reflex processes. Should the lightbecome too strong, it will slowly crawl to a shady place; should the waterin which it lives become warmer, it responds by displaying greateractivity. It exhibits, in a word, the property of _irritability_--that is, simply the power of receiving and reacting to stimuli; and being only asingle cell this property is held in common by all of its parts. 

We come next to a simple many-celled animal like the polyp _Hydra_, or ajellyfish. In such an animal the body is composed of numerous cells whichare not all alike either in their make-up or in their functions. Some ofthem are concerned primarily with digestion, others with protection, whilestill others are exempt from these tasks and as sense-cells they devoteall their energies to the reception of stimuli from without, or, beneaththe outer sheet of cells of the two-layered body, they conduct impulsesfrom one part of the animal to another, and thus serve as coordinatingmembers of the community. For the first time, then, a nervous system assuch is set apart and specialized to devote itself to the two tasks ofsensation and coordination that are performed by nervous systemsthroughout the entire range of organisms higher in the scale. But theactivities of _Hydra_, like those of _Amoeba_, are reflex andmechanical, --that is to say, _given similar stimuli and similarphysiological states of the animal, the reactions will be the same_. Alittle water-crustacean like _Daphnia_ may swim against the tentacles of_Hydra_; it is stung to death by the minute cell-batteries which theanimal possesses, and then in a mechanical way the tentacles transport thefood to the mouth, through which it is passed inward to the digestivecavity. There is nothing that can be called "mentality" throughout theseprocesses, but the series of activities is much more complex than in_Amoeba_ because the whole organism is constructed more elaborately, andbecause the special and peculiar mechanism directing the activities hasadvanced to a far higher condition. 

Passing to the jointed animals like worms and insects, we find nervousmechanisms that are still more intricate, and with their advance instructural respects there is a corresponding and correlated progress intheir functions. Because the whole organism has developed more highlydifferentiated groups of organs to perform the several biological tasks, such as eating and respiring and moving, it is necessary for the nervousstructures concerned with the direction of these actions to become moreefficient. An earthworm avoids the light of day and digs its burrow andseeks its food by wonderfully coördinated activities of its muscles andother parts, which are controlled by a double chain of ganglia along itsventral side, connected with a similar pair of grouped nerve-cells abovethe anterior part of the digestive tract. The ganglia of each segmentexercise immediate supervision over the structures of their respectiveterritory, while they pass on impulses to other ganglia so that movementsinvolving many segments can be properly adjusted. Everything an earthwormdoes is controlled by the cells grouped in these ganglia, or scatteredalong the intervening connecting cords. We speak of its acts asinstinctive, employing a term which seems to indicate a different kind ofoperation carried on by the nervous system, but a moment's thought willshow that an instinctive act is simply a complex group of reflex acts. Thephysical basis and ultimate unit is a cell, and the functional unit islikewise a cell act; therefore the seeming difference proves to be onemerely of degree and not of kind. The greater complexity of the worm'snervous system as compared with that of _Hydra_ gives to the wholemechanism a plasticity that diverts the attention from the mechanicalnature of the entire instinctive act and of its basic cell elements. 

The instinct, like the elementary reflex, is determined by heredity. Because a certain configuration of the cells and fibers making up anervous system is inherited as well as the characters of the constituentelements themselves, a worm or an insect is enabled to act as it does. Abutterfly does not have to learn how to fly, for it flies instinctively. When it emerges from its chrysalis with its complete adult series of wingsand muscles, it has also the nervous mechanism by which these parts aremechanically controlled. A ground-wasp deposits its eggs in a small burrowin which it places also a caterpillar or a grasshopper paralyzed bystinging, so that when the larva is hatched from an egg it finds an amplesupply of fresh food provided by a complex series of its mother's actsthat seem to be directed by conscious maternal solicitude. When the larvapasses through the later stages of development and makes its way to theopen air as a fully formed adult, it in its turn may go through the samecourse of action as its parent, but it is clear that it cannot have anyremembrance of its mother's work or any personal knowledge of the value ofburying its own eggs in a chamber with a living prisoner to serve as food. It was an egg when its parent did these things; as a parent itself it doesnot remain on watch to see how beneficial or fruitless its acts may be. Amechanism produced by nature's methods, the ground-wasp behaves as it iscapable of working with its inherited structure and its inheritedinstinctive powers of coördination and sensation. 

The complex lives of communal insects like ants and bees bring us to thelevel of mentality where an understanding of causes and effects seems tobe the guide for conduct. Nevertheless the facts do not warrant theassumption that reason and intelligence play any part in the mental lifeof these creatures, as they do in the lives of man and the apes. Becausewe ourselves can see the utility of the definite and peculiar behavior ofthe queen and the worker, there is no logical necessity for assuming anidentical form of knowledge as a possession of these insects. Manyinvestigators have dealt with these fascinating subjects, and they arealmost unanimous in the conclusion that the instinct of an insect is amechanical and hereditary synthesis of combined reflex acts. 

The lower orders of psychological processes play a far larger part in thelives of the higher animals than we are wont to believe. A pointer andsheep dog possess different qualifications in the way of instincts thatmake them useful to man in different ways. A bulldog or a game-cock doesnot reason out its course of action during a contest, but like a mechanismwhen the spring is released, it acts promptly and with effect. A ballflashing past the human eye causes the lids to close unconsciously, and itis not always possible to inhibit this instinctive mechanical act by theexercise of the will. An examination of the workings of the human bodyreveals manifold activities of an even lower or reflex nature, like themovements of the viscera and the adjustments in respect to the amount ofsupplies of blood sent to different parts of the body as local needsarise. Directed always by specific portions of the nervous system, suchreflex actions play their part in human life without any effort on thepart of reason and so-called will, and without coming into consciousnessexcept indirectly and subsequently. 

Passing by many interesting members of the psychological series ofintergrading forms, we reach the familiar animals like the cat and dog andhorse which display what is called intelligence. This is the power tolearn by experience, and to improve the quality and promptitude ofreactions to stimuli. In certain respects intelligence seems to differfrom instinct, inasmuch as it involves a response to stimuli that may bealtered and quickened by repeated experience, but in ultimate analysis thetwo forms of psychological processes are fundamentally alike. A singleexample chosen from Thorndike's extensive investigation will serve tobring out the primary characteristics of intelligence. A cat was placed ina latticed cage provided with a door that could be opened from within whena catch was pressed down, and meat was put in a dish outside the doorwhere the cat could see it. At first, the animal escaped from the cage byfreeing the door during its aimless scrambling about the catch, but astrial after trial was made, the time necessary for the cat to make its wayout was shortened, until after seventy-five or one hundred trials, theanimal immediately opened the door and seized the food. In mechanicalterms, the connection between "scrambling about the door" and "freedom toget the meat" became established by numerous repetitions until theoriginally disconnected elements were physiologically associated and madeinseparable. When animals like horses and seals and dogs are trained forthe circus, it is by exactly the same method, for training consists merelyin the establishment of a psychological sequence so that the performanceof one series of acts leads mechanically to others. Thus we learn that thepsychological property called intelligence is the ability to establishwide relations between numerous activities which are themselves of a moreor less complex nature; and we find also that because these elements areultimately nerve-cell and sense-cell reflexes, an intelligent response isquite as machine-like as any and all of its elements. A difference indegree of complexity and extent is the only thing that places intelligenceapart from instinct and reflex action, for the units are the same in allcases, --so far as science knows. 

The apes are of the greatest value in providing the transition from thegrade of intelligence to the human level where reason is found. Whether ornot a chimpanzee can reason at all is less important than the fact thatits total "mental" powers are lower than those of man, and higher thanthose of inferior mammalia. Apes are far more susceptible to training thancats and dogs, because their improved nervous mechanism enables them toestablish a psychological sequence with greater facility. If we are tojudge by the facts at hand, these creatures possess a low order ofmentality, like, but by no means equivalent to, that of man. 

At the end of the comparative scale, we reach the human mind which ischaracterized by its ability to perceive and recognize far wider relationsthan those which are involved in intelligence. Human consciousness is thestream of thoughts and feelings which constitute the immediate contents ofmind. In our own case, we know both the activities we perform and some ofthe internal phenomena with which such activities are connected. Then weare impelled to compare the objective phenomena of action with thebehavior of other men and of lower organisms, and if their behavior doesnot coincide with our own we are justified in believing that its directionlacks some of the elements we know about in our own case. This is themethod of comparative psychology, which establishes the conclusion thatreason is the more complex term of a series to which reflex action, instinct, and intelligence directly lead. 

Were we to study in detail the psychology of adult human beings, we wouldfind only more truly that instinct and intelligence play a large part inour everyday mental life, and more certainly that even the highestreasoning powers we possess are only more complex in nature than thenervous processes of lower mammals and invertebrates. Just as the nervoussystems advance in physical or structural respects, so must theiractivities become more and more complex until the result is human faculty. 

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We must now briefly consider what may be called the "comparativeanthropology" of mind which deals with the various degrees of mentalability displayed by different human races; this subject followsinevitably upon the comparison of the human mind viewed as a single typewith the psychological processes of lower animals. When we reviewed thediverse characteristics of human races--the protrusion of the jaws, greater or lesser stature, and the like--it appeared that so-called"lower" races could be distinguished which differed from the "higher"races in the direction of the apes; the question immediately ariseswhether similar distinctions and relations are discoverable on the basisof mental traits. But in the present case there are not so manywell-substantiated differentia at the disposal of the student, and it doesnot appear so clearly that the "higher" races are furthest from the lowerprimates and lower mammalia as regards their mental processes. What factsthere are, however, prove to be highly significant, and they materiallyamplify our conception of human faculty as a product of evolution. Theessential point is that the intellectual attainments of various races areby no means the same. The calculus is a mental product of the white raceonly; gunpowder and printing from movable type were independently inventedby the Caucasian and Mongolian races; but the American Indian and theNegro never originated them. Human faculty, to employ the most generalterm for all that distinguishes man from the brutes, proves to be a veryvaried thing when we draw comparisons between and among races withindependent lines of ancestry and heredity occupying widely separatedareas. Should we analyze it, we find it to be composed of threeconstituents; namely, the physical elements of the brain, the degree towhich the observational or perceptual and higher elements cooperate inbuilding up the conceptions peculiar to the type, and the materials withwhich the physical mechanism deals, in the way of environmental, educational, and social "grist for the mental mill. " Many anthropologistsaccord too great an importance to the third constituent of human faculty, I believe, and they are therefore led to deny that races differ in mentalrespects to so large a degree as the thoroughgoing evolutionist wouldcontend. They hold that differences in such things as powers ofobservation are due to training: that, for example, an American Indian ora South Sea Islander sees certain things in his environment more quicklythan a white man only because these are the things which the experiencesof his earlier life have accustomed him to look for and to find. This maybe granted, and it may also be admitted that children of so-called "lower"races can be educated side by side with the youth of white races withoutnoticeably falling behind, up to a certain point when, at the age ofadolescence, in the classic case of the Australian natives, other factorsprove to be obstacles to further progress. We must also recognize that thecharacter of the environment of a race determines to a large extent themode of life of the people; a forest-dwelling Indian of the interior is ahunter as well as a warrior, while a South Sea Islander is a navigator anda fisherman. 

But the fact remains that the inhabitants of similar countries havereached markedly different grades of intellectual and cultural life. Anglo-Saxon dominance must be referred ultimately to Anglo-Saxon heredityand not to the peculiarities of the land. Although adaptation is no lessnecessary for men as individuals and as social groups than it is for allother living things, I believe that it is to diversity in constitutionalendowments, however these may have arisen, that we must attribute thesuperiority of some races over others. The question is not whether asavage race can or cannot adopt the higher conceptions of a civilizedpeople; the fact is that they have not actually become civilized bythemselves. Thus, while evolution in mental respects has not resulted inthe loss of plasticity in the case of the brain and the nervous system asa whole, wherefore the activities of these organs still remain capable ofindividual and racial modifications that are impossible in the case of theskeleton and in the color and shape of the eye, it remains true that racesdo differ intellectually, and that their differences are marks of a mentalevolution quite as definite as their physical natural histories of change. 

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In my own view the strongest and most impressive evidence bearing upon thegreat problem before us is provided by the series of transformations bywhich the human intellect develops during an individual life. Mind has anembryology no less significant than that of the skull or of any otherelement of the body; and its investigation leads to the evolutionaryinterpretation quite as surely as the study of the various grades of adultpsychology constituting the anatomical sequence, which we have reviewedpreviously. When in the earlier part of the book we dealt with embryologyin general, we learned how the changes which take place when an organismdevelops from an egg demonstrate the actuality of true organictransformation without the necessity of concluding or inferring that thisprocess might occur. It is not superfluous to insist again that theessential fact in evolution is the alteration of one organiccharacteristic into another type; must we not recognize at the very outsetthat mental transformation is as real as physical development?

In the first instance we might concern ourselves with the physical basisof mind and its history. In the earliest stages of human embryology nonervous system whatsoever is present, and it is unreasonable to supposethat there is anything going on which corresponds to human thought. Alittle later a cellular tube is established as a primitive nerve axis, which at first is nearly uniform throughout its entire length and displaysno differentiation into brain and spinal cord. Before long an enlargementof the anterior end expands and develops into a primitive three-partedbrain. It is not yet a real brain, however, and it is entirely incapableof functioning in such a way as to justify the use of the word _mental_for the results of its operations. We know that it is only in the cerebralhemisphere of the adult brain that the processes of true humanconsciousness go on. But it is not until long after the three-parted stagethat the cerebral hemispheres make their appearance therefore we cannotspeak of mind as present when the cell and tissue basis of mind is notpresent. When, now, the cerebral hemispheres do appear, they are smallbean-shaped structures no larger relatively than those of a fish. Laterthey enlarge so as to attain the relative size of the cerebral hemispheresof an amphibian, and still later they are like those of a reptilian brain. Continuing to enlarge, they begin to fold so that the total surface isincreased without very much addition to their bulk. At this time thecerebral hemispheres of the brain of the human embryo are like those of anadult cat or dog. The process of general enlargement and of progressiveconvolution are continued, and stages are reached and passed whichcorrespond with the monkey and ape conditions. 

Nothing in human development is more impressive than the origin of thecerebrum and its development by passing through successive stages whichare counterparts in the main of the adult brains of other and loweranimals. The alteration of a tissue-mechanism constructed in one way intoa tissue-mechanism of a more complex nature, provides the most conclusiveevidence of the reality of brain evolution, because the process oftransformation actually takes place. 

But in the present connection we are more interested in the dynamic orfunctional aspects of mental evolution, which it must be remembered areinseparably bound up with the physical structures and their modifications. After a human infant is born its activities are reflex and mechanical likethose of the adult members of lower groups. As it grows it performsinstinctive acts because its inherited nervous system operates in thepurely mechanical manner of a lower mammal's nervous system. For thesereasons an eminent psychologist has said that the mental ability of aninfant six months old is about that of a well-bred fox terrier. The sameinfant at nine months displays an intelligence of a higher order equal tothat of a well-trained chimpanzee; it has become what it was not, and inso far it has truly evolved in mental respects. At two years of age thechild is incapable of solving problems of the calculus, for its reasoningpowers are elementary and restricted, but these same powers change andintensify so as to render the older mind quite capable of grasping thehighest of human conceptions and ideas. In my judgment the unbrokentransformation of a child's mind that exhibits only instinct andintelligence into an adult's mind with its power of reasoning, is far moreconclusive as proof of mental evolution than the inference drawn from thecomparisons we have made above of the adult psychological phenomena ofman, ape, cat, and fish. It is surely natural for such mentaltransformations to take place, for they do take place in the vast majorityof human beings; when they do not, in cases where the brain fails tomature, we speak of unnatural or diseased minds. 

The third division of our evidence relating to mental evolutionconstitutes what we have called the palæontology of mind. By this term wemean the study of human minds of the past as we may know them through themany varied relics and documents which indicate their characters. It isonly too obvious to every one that human knowledge has advanced in thecourse of time and that every department of human thought and mentalactivity has participated in this progress. No one would have the temerityto assert that we know nothing more than our ancestors of 5000 or even1000 years ago. Our common-sense teaches us even before the man of scienceproduces the full body of evidence at his disposal that human facultieshave evolved. With regard to reasoning powers, which form one of the fourdistinguishing characteristics of the human species as contrasted withother animals, the case has already been reviewed, and we now turn tospeech and language and other departments of human mentality. When wecompare the attainments of present day men with the abilities and ideas oftheir ancestors we will do for mental phenomena precisely what was donewhen we compared the skeletons of modern animals with those of creaturesbelonging to bygone geological ages; in this reason is found thejustification for the phrase employed in the present connection. 

Written history furnishes a wealth of material for interpreting the mentalconditions of ancient peoples, but beside documentary evidence theanthropologist learns to use inscriptions of prehistoric times, theprimitive graphic representations on tombs and monuments, and even thecharacteristics of crude implements like axes and arrow-heads. The laymanfinds it difficult at first to regard such relics as indications of themental stature of the people who made and possessed them; but a littlethought will show that a man who used a rough stone ax in the time of theancient Celts could not possibly have had a mind which included theconception of a finished iron tool or modern mechanism. So in alldepartments of human culture, the evolution of material objects may bejustly employed in interpreting and estimating the mental abilities ofancient peoples. 

Language is undoubtedly the most important single intellectual possessionof mankind, for it constitutes, as it were, the very framework of socialorganization. Without a ready means of communication the myriad humanunits who perform the varied tasks necessary for the economic well-beingof a body-politic would be unable to coordinate their manifold activitieswith success, and the structure of civilized societies at least wouldcollapse. It needs no legend of a Tower of Babel to make this plain. Sofundamental is this truth that although we may not have recognized itexplicitly, we unconsciously form the belief that speech and language areexclusive properties of the human species, and even more characteristic ofman alone than the power of reason itself. While organized language isclearly something that as such we do not share with the lower animals, nevertheless we cannot regard the communication of ideas or states offeeling by sound as an exclusive property of mankind. All are familiarwith the difference between the whine and the bark of a dog and with thewidely different feelings that are expressed by these contrasted sounds. And we know too that dogs can understand what many of their master's wordssignify, as when a shepherd gives directions to his collie. We could evengo further down in the scale and find in the shrill chirping of thekatydid at the mating season a still more elementary combination ofsignificant instinctive sound elements. To the comparative student thespeech of man differs from these lower modes of communication only in itsgreater complexity, and in its employment of more numerous and variedsounds, --in a word, only in the higher degree of its evolution. And it iseven more evident that the diverse forms of speech employed by variousraces have gradually grown to be what they now are. 

At the outset it is well to distinguish between writing, as theconventional mode of symbolizing words, and spoken language itself; thetwo have been more independent in their evolution than we may be wont tobelieve. Speech came first in historical development, just as a child nowlearns to talk before it can understand and use printed or writtenletters. Furthermore, many races still exist who have a well-developedform of language without any concrete way of recording it. It is true, ofcourse, that back of the conventions of speech and writing are the ideasthemselves that find expression in the one way or the other, or even bythe still more primitive use of signs and gestures. But it is not withthese ultimate elements of thought that we are now concerned; our task isto learn, first, what evidences are discoverable which show that theproperty of human language in general has originated by evolution, andthen, in the second place, to perceive how this development proves anevolution of one group of ultimate ideas, namely, human concepts of themodal value of words and symbols as expressions of ideas themselves. 

A simple common-sense treatment of obvious facts will greatly facilitateour progress. We know very well that the English we speak to-day differsin many ways from the language of Elizabethan times, and that the formeris a direct descendant of the other. The latter, in turn, was a product ofNorman French and Anglo-Saxon, --a combination of certain elements of both, but identical with neither of its immediate parents. The Saxon tongueitself has a history that leads back to King Alfred's time and earlier. Thus we are already aware of the fact that our speech has truly evolved, like the physical structure of the men who employ it; and we know, too, how readily new words are adopted into current English, like _tabu_ fromPolynesia, or _garage_ from the French, showing that language is even nowin process of evolution. 

The sounds that make up spoken words can be resolved into a single elementwith its modifications; this basic element is the brute-like call or shoutmade with the mouth and throat opened wide--a sound we may have hearduttered by men under the stress of pain or terror. All of the variousvowels are simply modifications of this element by altering the shape ofthe mouth cavity and orifice, while the consonants are produced byinterrupting the sound-waves with the palate or lips or tongue. Like thecell as a unit of structure throughout the organic world, this elementalutterance proves to be the basic unit of all human languages, which varyso widely among races of to-day no less than they have in the history ofany single people. 

One of the first steps in the making of spoken words was taken by humanbeings when they imitated the calls or other sounds produced by livingthings, and tacitly agreed to recognize the imitation as a symbol of thecreature making it. Thus the names for the cuckoo and the crow in manylanguages besides our own are simply copies of the calls uttered by thesebirds; a Tahitian calls a cat _mimi_; the name for a snake almostinvariably includes the hissing attributed to that creature. After a timewords which were at first simply imitations and which referred only to thethings that made these sounds came to refer to certain qualities of thethings imitated, so that the naming of other than natural objects, such asqualities, began, leading ultimately to the use of words for qualitiesbelonging to many and different objects in the way of abstractions. 

Much light upon the evolution of language is obtained when we treat thespeech of various races as we did the skeletal structures of cats andseals and whales. When we compare the Italian, Spanish, Portuguese, andFrench languages, they reveal the same general structure in thousands oftheir words, --a common basis which in these cases is due to theirderivation from the same ancestor, the Latin tongue. The Latin word forstar is _stella_, and the Italian word of to-day is an identical andunchanged descendant, like a persistent type of shark which lives now inpractically the same form as did its ancestor in the coal ages. TheSpanish word is _estrella_, a modified derivative, but still one thatbears in its structure the marks of its Latin origin; the French word_étoile_ is a still more altered product of word evolution. Even in theGerman _stern_, Norse _stjern_, Danish _starn_, and English _star_ we mayrecognize mutual affinities and common ancestral structure. Choosingillustrations from a different group, the Hebrew salutation "Peace be withyou, " _Shalom lachem_, proves to be a blood cousin of the Arabic _Salaamalaikum_, indicating the common ancestry of these diverse languages. AmongPolynesian peoples the Tahitian calls a house a _fare_, the Maori of NewZealand uses _whare_, while the Hawaiian employs the word _hale_, and theSamoan, _fale_. Whenever we classify and compare human languages, we findsimilar consistent anatomical evidences of their relationships andevolution. We can even discern counterparts of the vestigial structureslike the rudimentary limbs of whales. In the English word _night_ certainletters do not function vocally, though in the German counterpart _Nacht_their correspondents still play a part. In the word _dough_ as correctlypronounced the final letters are similarly vestigial, although in thephonetic relative _tough_ they are still sounded. 

The evolution of the art of writing appears with equal clearness when wecompare the texts of modern peoples with inscriptions found on ancienttemples and monuments and tablets. Even races of the present day employmethods of communicating ideas by writing symbols that are counterparts ofthe earliest stages in the historic development of writing. An Eskimodescribes the events of a journey by a series of little picturesrepresenting himself in the act of doing various things. A simple outlineof a man with one arm pointing to the body and the other pointing awayindicates "I go. " A circle denotes the island to which he goes. He sleepsthere one night, and he tells this by drawing a figure with one hand overthe eyes, indicating sleep, while the other hand has one finger upraisedto specify a single night. The next day he goes further and he employs thefirst figure again. A second island is indicated, in this case with a dotin the center of the circle to show a house in which he sleeps two nights, as his figure with closed eyes and two fingers uplifted shows. He huntsthe walrus, an outline of which is given alongside of his figure waving aspear in one hand; likewise he hunts with a bow and arrow, which isdemonstrated by the same method. A rude drawing representing a boat withtwo upright lines for himself and another man with paddles in their handsgives a further account of his journey, and the final figure is the circledenoting the original island to which he returns. 

Pictography, as this method of communicating ideas is called, is oftenhighly developed among the American Indians. For example, a petition froma tribe of Chippewa Indians to the President of the United States askingfor the possession of certain lakes near their reservation is a series ofpictures of the sacred animals or "totems" which represent the severalsubtribes. Lines run from the hearts of the totem animals to the heart ofthe chief totem, while similar lines run from the eyes of the subsidiarytotems to the eyes of the chief, and these indicate that all of thesubtribes feel the same way about the matter and view it alike, --thesentiment is unanimous. From the chief totem run out two lines, one goingto the picture of the desired object, while the other goes to thePresident, conveying the petition. Thus pictography, a method of writingthat belongs to the childhood of races, may be made to communicate ideasof a strikingly complex nature. 

The ancient and modern inscriptions of Asia, from the Red Sea to China, present many significant stages in the development of picture-writing. Inearliest ages the men of Asia made actual drawings of particular objects, such as the sun, trees, and human figures; subsequently these becameconventionalized to a certain degree, but even as late as 3000 B. C. TheAkkadian script was still largely pictographic. From it originated theknife-point writing of Babylonian and Chaldean clay tablets, while amongthe peoples of Eastern Asia, who continued to draw their symbols, thetransition to conventionalized pictures such as those made by the Chinamanwas slower and less drastic. 

In another line of evolution, the hieroglyphics of Egyptian tombs andmonuments illustrate a most interesting intermediate condition ofdevelopment. These inscriptions have been deciphered only since thediscovery of the famous Rosetta stone-fragment, which bears portions ofthree identical texts written in hieroglyphics, in Greek, and in anotherseries of symbols. The Egyptian used more or less formalized characters torepresent certain sounds, while in addition to the group of suchcharacters combined to make a word, the scribe drew a supplementarypicture of the thing or act signified. For instance, _xeftu_ meansenemies, but the Egyptian graver added a picture of a kneeling bowman toavoid any possible misapprehension as to his meaning. The symbols denoting"to walk" are followed by a pair of legs; the setting sun is described notonly by a word but also by its outline as it lies on the horizon. Hereagain one is struck by the similarity between a stage in the historicdevelopment of racial characteristics and a method employed at the presenttime to teach the immature minds of children that certain lettersrepresent a particular object; in a kindergarten primer the sentence "seethe rat and the cat" is accompanied by pictures of the animals specified, in true hieroglyphic simplicity. 

Just as the child's mind develops so that the aid of the picture can bedispensed with, and the symbolic characters can be used in increasinglycomplex ways, in like manner the minds of men living in successivecenturies have evolved. While an evolution of human conceptual processesin general is not necessarily implied by the evolution of the forms ofwritten language, the former process is in part demonstrated by the latterin so far as the change from the writing of pictures to the use ofconventional symbols involves an advance in human ideas of theinterpretation and value of the symbols in question. A man of ancienttimes drew a tree to represent his conception of this object; in thewriting of English we now use four letters to stand for the same object, and none of these symbols is in any way a replica of the tree. It iscertainly obvious that some change in the mental association of symbol andobject has been brought about, and to this extent there has been mentalevolution. 

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Passing now to other departments of human culture, we must deal in thenext place with the basic "arts of life"; that is, the modes of conductingthe necessary activities of every day. All men of all times, be theycivilized or savage, are impelled like the brutes by their biologicalnature to seek food and to repel their foes. The rough stone club and axwere fashioned by the first savage men, when diminishing physical prowessplaced them at a disadvantage in the competition with stronger animals. Smoother and more efficient weapons were made by the hordes of their moreadvanced descendants, some of whom remained in the mental and culturalcondition of the stone age like the Fuegian, until the white travelers ofrecent centuries brought them newer ideas and implements. In Europe andelsewhere the period of stone gave place to the bronze and iron ages, andthroughout the changing years human inventiveness improved the missile andweapon to become the bow and arrow of medieval civilization and recentAfrican savagery. The artillery and shells of modern warfare are theirstill more highly evolved descendants. 

So it is with the dwellings of men, and the significance of the changesdisplayed by such things. The cave was a natural shelter for primitive manas well as for the wolf, and it is still used by men to-day. Where it didnot exist, a leafy screen of branches served in its stead; even now thereare human beings, like the African pygmy and the Indian of Brazil, who arelittle beyond the orang-outang as regards the character of the shelterthey construct out of vegetation. From such crude beginnings, on a parwith the lairs and nests of lower animals, have evolved the grass huts ofthe Zulu, the bamboo dwelling of the Malay, the igloo of the Arctictribes, and the mud house of the desert Indians. The modern palace andapartment are merely more complex and more elaborate in material andarchitectural plan, when compared with their primitive antecedents. 

Baskets, clay vessels, and other household articles testify in the sameway to an evolution of the mental views of the people making them. Themeans of transportation are even more demonstrative. The wagon of theearly Briton was like a rough ox-cart of the present day, evolved from thesimple sledge as a beginning. In its turn it has served as a prototype forall the conveyances on wheels such as the stage-coach and the modernPullman. The history of locomotives, employed in the first chapter todevelop a clear conception of what evolution means, takes its place hereas a demonstration of the way human ideas about traction have themselvesevolved so as to render the construction of such mechanisms possible. 

The primitive savage swimming in the sea found that a floating logsupported his weight as he rested from his efforts. By the strokes of hisarms or of a club in his hand, he could propel this log in a desireddirection; thus the dugout canoe arose, to be steadied by the outrigger asthe savage enlarged his experience. A cloth held aloft aided his progressdown or across the wind, and it became an integral element of the sailingcraft, which evolved through the stages of the galley and caravel to theschooner and frigate of modern times. When the steam-engine was inventedand incorporated in the boat, a new line of evolution was initiated, leading from the "Clermont" to the "Lusitania" and the battleship. 

The history of clothing begins with the employment of an animal's hide ora branch of leaves to protect the body from the sun's heat or the coldwinds. Other early beginnings of the more elaborate decorative clothingare discerned by anthropologists in the scars made upon the arms andbreast as in the case of the Australian black man, and in the figuredpatterns of tattooing, so remarkably developed by the natives in theislands of the South Pacific Ocean. A visit to a gallery of ancient andmedieval paintings clearly shows that the conventional modes of clothingthe human body have changed from century to century, while it is equallyplain that they alter even from year to year of the present time, according to the vagaries of fashion. 

A brief review of the "arts of pleasure, " including music and sculptureand painting, demonstrates their evolution also. The earliest cavemen ofEurope left crude drawings of reindeer and bears and wild oxen scratchedupon bits of ivory or upon the stone walls of their shelters; the paintingand sculpture of early historic Europe were more advanced, but they werefar from being what Greece and Rome produced in later centuries. Indeed, the evolution of Greek sculpture carried this higher art to a point thatis generally conceded to be far beyond that attained by even our modernsculptors, just as flying reptiles of the Chalk Age developed wings andlearned to fly long before birds and bats came into existence. 

In the field of music, the earliest stages can be surmised only by a studyof the actual songs and instruments of primitive peoples now living inwild places. No doubt the song began as a recitation by a savage of theevents of a battle or a journey in which he had participated. In givingsuch a description he lives his battles again, and his simulated moods andpassions alter his voice so that the spoken history becomes a chant. Fromthis to the choral and oratorio is not very far. 

Musical instruments seem to have had a multiple origin. The ram's horn ofthe early Briton and the perforated conch-shell of the South Sea Islanderare natural trumpets; when they were copied in brass and other metals theyevolved rapidly to become the varied wind instruments typified to-day bythe cornet and the tuba. In the same way the reed of the Greek shepherd isthe ancestor of the flute and clarionet. Stringed instruments like theguitar, zither, and violin form another class which begins with the bowand its twanging string. The power of the note was intensified by holdinga gourd against the bow to serve as a resonance-chamber. When the musicianof early times enlarged this chamber, moved it to the end of the bow, andmultiplied the strings, he constructed the cithara of antiquity, --theancestor of a host of modern types, from the harp to the bass-viol andmandolin. 

The dance and the drama find their beginnings in the simple reënactment ofan actual series of events. Among Polynesians of to-day the dances stillretain the rhythmic beat of the war-tread measure, and many of the motionsof the arms are more or less conventionalized imitations of the act ofstriking with a club, or hurling a spear, and other acts. To such elementsmany other things have been added, but the fact remains that our ownformal dances, as well as the sun-dance of the Indian and the mad whirl ofthe Dervish, are modern products which have truly evolved. 

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When we turn to science and philosophy and other intellectual attainmentsof modern civilized peoples, it is easier to see how evolution has beenaccomplished, because we possess a wealth of written literature whichexplains the way that human ideas have changed from century to century. Inthese cases there can be no question that such evidences provide accurateinstruments for estimating the mental abilities of the writers whoproduced them. We shall take up the higher conceptions of mankind at alater juncture, so at this point we need only to note that even thesemental possessions, like household culture and even the physicalstructures of a human body, have changed and differentiated to become thewidely different interpretations of the world and supernature that areheld by the civilized, barbarous, and savage races of to-day. 

As we look back over the facts that have been cited, and as we contemplatethe large departments of knowledge about human psychology, mentaldevelopment, and racial culture which these few details illustrate, wecome to realize how securely founded is the doctrine that even the humanmind with all its varied powers has grown to be what it is. Indeed, it issolely due to his mental prowess that man has attained a position abovethat of any lower animal. And yet every human organ and its function canbe traced to something in the lower world; it is a difference only indegree and not in category that science discovers. The line connectingcivilized man with the savage leads inevitably through the ape to thelower mammalia possessing intelligence, and on down to the reflex organicmechanisms which end with the _Amoeba_. It is a long distance from themechanical activities of the protozoön to the processes of human thought;yet the physical basis of the latter is a cellular mechanism and nothingmore, developed during a single human life in company with all otherorgans from a one-celled starting-point--the human egg. 

 * * * * *

The method by which mental evolution has been accomplished is likewisedemonstrable, because the factors are identical with those which bringabout specific transformation in physical respects. This is to beexpected, for the contention that the structures and the functions of theseveral organs constituting any system are inseparable has never beengainsaid. 

Mental variation is real. It needs no scientist to tell us that humanbeings differ in intellectual qualifications and attainments, and that notwo people are exactly similar even though they may be brothers orsisters. The struggle for existence or competition on the basis of mentalability is equally real, and every day we see the prize awarded to themore fit, while those who lose are crowded ever closer to the wall. As inall other fields of endeavor, the goal of success can be attained only byadaptation, which involves an adjustment to all of the conditions ofexistence--to social and ethical as well as to the more expressly materialbiological circumstances. 

Heredity of mental qualities has also been demonstrated notably by Galton, Pearson, Woods, and Thorndike, who have also shown that the strength ofinheritance in the case of mental traits is approximately the same as forphysical characteristics like stature and eye-color. Just as a worker-beeinherits a specific form of nervous system which coöperates with the otherequally determined organic systems, wherefore the animal is forced toperform "instinctively" its peculiar specialized tasks, so the mentalcapacity of a human being is largely determined by congenital factors. Upon these primarily depends his success or failure. It is quite true thatenvironment has a high degree of influence, so great indeed that somespeak of a "social heredity"; they mean by this phrase that the mentalequipment of an individual is determined by the things he finds about him, or learns from others without having to invent or originate them himself. Thus a Zulu boy acquires the habits of a warrior and a huntsman when hegrows up in his native village, although he would undoubtedly developquite different aptitudes if he should be taken as an infant to a city ofwhite men. Nevertheless his mental machinery itself would be no lesssurely determined by heredity, even though the things with which it dealtwould be provided by an alien environment. 

Our present knowledge of the nature and history of human mentality enablesus to learn many lessons that have a direct practical value, although itis impossible under the present limitations to give them the fulldiscussion they deserve. Starting from the dictum that physicalinheritance provides the mechanism of intellect, education and training ofany kind prove to be effective as agents for developing hereditaryqualities or for suppressing undesirable tendencies. Just as wind-strewngrains of wheat may fall upon rock and stony soil and loam, to grow wellor poorly or not at all according to their environmental situations, sochildren with similar intellectual possibilities would have their growthfostered or hampered or prevented by the educational systems to which theywere subjected. But the common-sense of science demonstrates that themental qualities themselves could not be altered _in nature_ by thecircumstances controlling their development any more than the hereditarycapability of the wheat grains to produce wheat would be altered by thecharacter of the ground upon which they fell. Education and training thusfind their sphere of usefulness is developing what it is worth while tobring out, and inhibiting the growth of what is harmful. That heredity inmental as well as in physical aspects provides the varying materials withwhich education must deal is a fundamental biological fact which is toooften disregarded. It would be as futile for an instructor to attempt thetask of forcing the children in a single schoolroom into the same mentalmold, as it would be for a gymnasium master to expect that by a similarcourse of exercise he could make all of his students conform to the sameidentical stature, the same shape of the skull, or the same color of theeye and hair. 

 * * * * *

Before leaving the subject of mental evolution we must return to theconception of inseparable mind and matter with which the presentdiscussion began. The whole problem of human mental evolution is solvedwhen we accept the conclusion that the nervous mechanism and the totalseries of its functional operations have evolved together in theproduction of the human brain and human faculty. The case regarding thephysical organs rests solidly on the basis of the evidences outlined in aprevious chapter; the special examination of purely mental phenomena haslikewise been made in the foregoing sections. Just here we must pause togive further attention to the invariable relation between the human mindand the human brain. 

The personality of human consciousness consists of the current of thoughtsand feelings flowing continuously as one of them rises for a time todominance only to fade when it leads to and is replaced by anotherdominant element of thought. This current is affected by the messagesbrought to the brain by nerves from the outer parts of the body where liethe eye and ear and other sense-organs. In like manner the variousnon-nervous parts of the body exert their influences upon consciousness, but the affective processes, as they are called, are not as well understoodas the impressions passed inwards by the sense-organs along their nervousroadways to the central organ, the brain. But the brain is the place wherethe thinking individual resides; and this is one of the most importantteachings of psychology, for not only does it help us to understand theevidence that human faculty has evolved, but it also inevitably brings usto consider certain vital questions of metaphysics, such as theimmortality of the thinking individual after the material person with itsbrain ceases to exist. However, the latter question is something whichdoes not concern us here; now it is most important to realize howcompletely mind is connected with the brain. 

Many of the facts demonstrating this connection are matters of commonknowledge. In deep and dreamless sleep the essential tissues of the brainare inactive, and in correspondence with the cessation of material eventsthe thinking individual actually ceases to exist for a time. Any one whohas ever fainted is subsequently aware of the break in the current ofhuman consciousness when the blood does not fully supply the brain andthis organ ceases to function properly; a severe blow upon the headlikewise interrupts the normal physical processes, and at the same timethe mind is correspondingly affected. Again, a progressive alteration ofthe brain as the result of diseased growth causes the mind to grow dim andincapable. Sometimes infants are born which are so deficient mentally asto be idiots, and an examination of the brain in such a case revealscertain correlated defects in physical organization. These and similarfacts form the basis for the dictum that the development and evolution ofthe brain mean the growth and evolution of human intellect. 

The further question as to the nature of the connection is interesting, but it relates to matters of far less consequence to the naturalist thanthe central fact of the invariable relation which does exist. Throughoutthe centuries many philosophers and naturalists of numerous peoples haveendeavored to explain the connection in question in ways that have beenlargely determined by the changing states of knowledge of various periods, as well as by differences in individual temperament. Three generalconceptions have been developed: first, that the material and mentalphenomena _interact_; second, that they are _parallel_; and third, thatthey are _one_. 

According to the first view, the individual thoughts and feelings formingelements in the chain of consecutive consciousness are affected by theevents in the material physiology of the brain as a physical structure;the latter in turn react upon the psychical or mental elements. Thus therewould be two complete series of phenomena, which are interdependent andinteracting at all times, although each would be in itself a completechain of elements. 

The second interpretation is that the two series of events--namely, thephysical processes of the brain and the elements of consciousness--arecompletely _independent_ but entirely parallel. As one writer has put thecase, it is as though we had two clocks whose machinery worked at the samerate and whose relationships were such that "one clock would give theproper number of strokes when the hands of the other pointed to the hour. "But in my opinion this attempted explanation of the relation of mind tomatter evades the whole question, as it does not account for thedependence of the former upon the latter, but merely assumes the existenceof a more ultimate and unknown group of causes for a parallelism in therates of operation of two series of things regarded as disconnected. 

The third conception recommends itself to many on account of its greatersimplicity. Formulated as the doctrine of monism, it states that the mindand its material basis are merely different _aspects_ of one and the samething, and that there is only one series of connected elements which areknown to us directly as the current of our thoughts and indirectly as thephysiological processes going on mainly in the cerebrum. Thus mind ispurely subjective, the brain is only mediately objective. It is becausethe mental and the material are so intimately related that the monistbelieves them to be connected as are the lungs and respiration, the handand grasping, or the eye and the reception of visual impressions fromwithout. 

But whichever one of these explanations we choose to adopt as our own, thebasic fact of primary importance is that there is an invariable dependenceof human thought upon a brain comprising a highly developed cerebrum, whatever may be the ultimate nature of the way mental processes aredetermined by physical processes, or _vice versa_. This fact standsunquestioned and unassailable; human faculty and the brain cannot beconsidered apart, even if they may not actually be different aspects ofthe same basic "mind-stuff, " as Clifford calls the ultimate dual thing. 

Like all of the other organs of lesser importance belonging to the nervoussystem, the brain is a complex of tissues which in the last analysis aregroups of cell-bodies with their fibrous prolongations. When thesecellular elements are in operation, mental processes go on; the unit ofthe mental process therefore is the functioning of a brain-cell. But weknow that the substance of a brain-cell is the wonderful physical basis oflife called protoplasm, that demanded our attention at the outset. Thechemicals that go to make up protoplasm are everywhere carbon, hydrogen, oxygen, and other substances that are exactly the same outside the body asinside. It is the combination of these substances in a peculiar way whichmakes protoplasm, and it is the combination of their individual propertieswhich in a real even though unknown manner gives the powers to protoplasm, even to that of a living brain-cell. Does science teach us, then, that theultimate elements of human faculty are carbon-_ness_ and hydrogen-_ness_, and oxygen-_ness_, which in themselves are not mind, but which when theyare combined, and when such chemical atoms exist in protoplasm, constitutemental powers? Plain common-sense answers in the affirmative. We need not, indeed, we must not, attribute mind as such to rock salt or to the waterof a stream, but we do know that salts and water and other dead substancesmay enter into the composition of the material brain which is the physicalbasis of mind. 

In my opinion the individual argument renders the monistic conception ofmind and matter unassailable. The food that we may eat and the water wemay drink are dead, and as such they display absolutely no evidence ofnervous or mental processes. When they enter our bodies, they with otherfoods replenish the various tissues, and among these the parts of thebrain. In a material sense they become actual living protoplasm, replacingthe worn-out substances destroyed during our previous thinking; and theirproperties are combined to make brain and thought, to play for a timetheir part in life, and to pass back into the world of dead, unthinkingthings. Every one of us knows that hunger reduces our ability to thinkclearly and fully, and every one knows also that mental vigor is renewedwhen fresh supplies of nourishment reach the brain. What can be the sourceof mentality, if it is not something brought in from the outer world alongwith the chemical substances which taken singly are devoid of mind?Scientific monism frankly replies that it is unable to find anotherorigin. 

We are thus brought to recognize, not only the continuity taught byorganic evolution, but also the uniformity of the materials constitutingthe entire sensible world, inasmuch as the ultimate unit of all nervousphenomena is the reflex act of a protoplasmic mass, which itself is asynthesis of properties inhering in the chemical elements making up livingmatter. Among inorganic things the mind-stuff units are combined inrelatively simple ways, and the "stuff" does not give any outwardevidences of "mind" as such. Living things are almost infinitely complexas regards their chemical organization, and even in the very lowest ofthem we can discern a cell-reflex element which, combined with others likeit, forms the unit of the compounds we call instinct, intelligence, andreason. Hence through an analysis of mental evolution we are enabled toform the larger conception of a continuous universe whose ultimateelements are the same everywhere. 

VII

SOCIAL EVOLUTION AS A BIOLOGICAL PROCESS

We now reach a critical juncture in our study of the foundations ofevolutionary doctrine, for we must pass at this point to an inquiry intothe nature and origin of human social relations. In undertaking this taskwe may seem to leave the field which is properly that of organicevolution, and many perhaps will be unwilling to view such aspects ofhuman life as materials for purely biological analysis, arrangement, andexplanation. But even before the reasons for doing so may be madeapparent, every one must admit that the subject of mental evolution, whichcomprises so large a bulk of details expressly social in their characterand value, virtually compels us to scrutinize the history of the economicand other interrelationships maintained by the human constituents ofcivilized, barbarous, and savage communities. Language has been treated asan individual mental product, and so have the arts of life and ofpleasure; but all of these things find their greatest utility in theirsocial usage, --in their value as bonds which hold together the few or manyhuman beings composing groups of lower or higher grade. Withoutdiscovering any other reasons we would be impelled to take up socialevolution, for this process is inextricably bound up with the origin anddevelopment of all departments of human thought and action. 

If now this new field is actually to be included within the scope of thelaws controlling the rest of nature's evolution, two general conclusionsmust be established. Although no formal order need be followed, it must atsome time be shown that human social relations are biological relations, to be best explained only through their comparison with the far simplermodes of association found by the biologist among lower orders of beings;and in the second place it must be demonstrated that identical biologicallaws, uniform in their operation everywhere in the organic world, havecontrolled the origin and establishment of even the most complex societiesof men. So far no reason has been discovered by science for believing thatevolution has been discontinuous, holding true only for the merelyphysical characteristics of humanity as a whole; and furthermore, theimpersonal student of nature finds ample positive evidences showing thatthe basic laws of associations of whatever grade are exactly the same. Forthese laws we are to seek. 

Heretofore the doctrine of organic evolution has been discussed withreference to the single individual organism viewed as a natural objectwhose history and vital relations require elucidation. Both in the generalarguments of the first few chapters and in the fifth and sixth chaptersdealing with the single case of the human species, the proof has beengiven that all of the structural and physiological characters of any andevery organic type fall within the scope of the principles of evolution, by which alone they can be reasonably interpreted. It has been unjust in asense to ignore completely the importance of the organic relations of asocial nature to which we are now to turn, because no individual can existwithout having its life directly influenced, not only by other kinds oforganisms, but even more intimately by other members of its own species. In a single day's activity we who are citizens of a great metropolis areforced into contact with almost countless other lives, glancing off fromone and another after influencing them to some degree, and gainingourselves some impetus and stimulus from our longer or shorter intercoursewith each of them. Our varied social relations are so many and obviousthat it is quite superfluous to specify them as essential things in humanlife. For the very reason that they are so obvious and constitute so largea part of our daily life, we are in danger of conceiving them to beexclusively human; we unconsciously regard them as different from anythingto be found elsewhere and quite independent of the biological lawscontrolling the human unit. 

On the contrary, as we trace the development of social organization fromits earliest rudiments it becomes ever clearer that evolution has beencontinuous, and that during later ages there has been no suspension of thenatural laws which earlier produced the human type of organism. Thelessons we have learned are by no means to be ignored from this pointforward; all of our conceptions of human biological history must be keptin mind, for anything new that we may learn is superadded to the rest, --itcannot disturb or alter the foundations already laid. It is even moreimportant to realize that the same scientific method is to be employedwhich has been so fruitful heretofore. It has given us interesting facts;it has indicated the most profitable lines of attack upon one and anotherscientific problem; and it has demonstrated the practical value ofaccurate knowledge, even of information about the evolutionary process. Asfamiliarity with the laws of human physiology enables one to lead a morehygienic and efficient life, and as the results of analyzing the evolutionof mentality make it possible to advance intellectually with greatersureness, conserving our mental energies for effort along linesestablished by hereditary endowment, so now we are justified in expectingthat a clear insight into the origin of our social situation and socialobligations will have a higher usefulness beyond the value of the mereinterest inhering in our new knowledge. Every one is necessarily concernedwith social questions; never before has there been so much world-widediscussion of topics in this field. And while it is true that much goodmay be accomplished in utter ignorance of the past history of humaninstitutions and of the underlying principles which control the variedtypes of organic associations, surely enlightened efforts will be moreeffective for good. Therefore every member of a community who is capableof thinking straight rests under an obligation imposed by nature to learnhow he is related to his fellow-men; he must act in concert with them orelse he forfeits his rights as a social unit. And it is his clear duty tosearch among the results of science for aid in ascertaining what he oughtto do, and what reasons are given by evolution for the nature of his vitalduties. 

Despite the growing appreciation of the fundamental relation betweenbiology and sociology, it is still far from universal. That the latterscience is in a sense a division of the former is more often recognized bythe biologist than by the average well-informed student of human socialphenomena. The layman in sociology too often concerns himself solely withthe complexities of the human problems, and he remains unaware of themanifold products in the way of communal organisms far lower in the scaleof life firmly established as primitive biological associations agesbefore the first human beings so advanced in mental stature that tribalunions were found good. Among insects especially the biologist finds manytypes of organized living things, ranging widely from the solitaryindividual--a counterpart of something even more primitive than the mostunsocial savage now existing--up to communities that rival humancivilization, as regards the concerted effect of the diversified lives ofthe component units. The student of the whole of living nature is favoredstill more in that he learns how the make-up of such a simple organism asa jellyfish displays principles underlying the structure of the whole andthe interplay of the parts that are identical with principles oforganization everywhere else. And all of these things can be dealt with ina purely impersonal way which is impossible when attention is restrictedto the human case alone. Thus it becomes the biologist's privilege and hisduty as well to place his findings before those who wish to understand theconstitution of human society in order that evils may be lessened andbenefits may be extended. He does this so far as he may be able in fullconfidence that the elements and basic principles are discoverable inlower nature, just as they are in the case of the material make-up andmental constitution of the single human individual. 

A more explicit preliminary statement must now be given of the grounds forthe belief that social evolution is but a part of organic evolution ingeneral. Some of these reasons are not far to seek, but their cogency canscarcely be appreciated until we have examined the concrete facts of thewhole biological series. Any human society selected for examination--be ita tribe, a village community, or a nation--is in last analysis anaggregate of human units and nothing besides. Its life consists of thecombined activities of such components--and nothing else. Could wesubtract the members one by one, there would be no intangible residuumafter all the people and their lives had been taken away. When thesesimple facts are recognized, it is clear at once that the concertedactivities performed by biological units cannot be anything but organic intheir ultimate basis and nature; the evolution of such activities thustakes its place as a part of organic evolution. 

The task of tracing out the history of social organizations of whatevergrade can now be defined in precise terms: in simple words, it is to learnhow the activities of the component biological units making up anyassociation really differ from the vital performances of biological unitsexisting by themselves. What is it that distinguishes a savage ofantiquity from an American of to-day? The modern example is just as muchan animal as the earlier type, and his physiology is essentially the same. It is something added to the common biological qualities of all men, somerelation which does not appear as such in the life of rude tribes, thatmakes the distinction. And it is just this superadded relation thatrequires explanation, as regards its exact biological value and itshistoric development as well. 

In undertaking this difficult task, it seems best to begin with the verysimplest organisms that biology knows, working upwards through the scaleto man. By this course the most basic elements of organization can bediscovered without having to look for them among the intricate details ofour own vital situation, where secondary and adventitious elements standout in undue prominence, and where the impersonal view is well-nighimpossible. Step by step we will then work up the scale of socialmorphology, approaching in the natural evolutionary order that part of thesubject which interests us most deeply. 

Just as the construction of an edifice must begin with the fashioning ofthe individual brick and bolt and girder, so the evolution of a biologicalassociation begins with the unitary organisms consisting of single cells, like _Amoeba_. We have had occasion to discuss this animal many timesin our previous studies of one or another aspect of evolution, and onceagain we must return to it in order to reëstablish certain points that areof fundamental importance for our present purposes. Within the limits ofits simple body, _Amoeba_ performs the several tasks which naturedemands a living thing shall do; it feeds and respires and moves, continually utilizing matter and energy obtained from the environment forthe reconstruction of its substance and replenishment of its vital powers;it coördinates the activities of its simple body, and by its reflexresponses to environmental influences it maintains its adjustment to theexternal conditions of life. The animal does all of these things with apurely individual benefit, namely, the prolongation of its own life. Whileit is performing these individual tasks, it does not concern itself withanything else but its own welfare; the interests of other living thingsare not involved in any way, excepting in the case of other organisms thatmay serve the animal as food. _Amoeba_, like every other living thing, if it is to exist, must unconsciously obey the first great commandment ofnature, --"_Preserve thyself_. "

But its life is incomplete if it stops with the furtherance of aims thatwe may call purely selfish. Nature also demands that an _Amoeba_, againlike every other living thing, shall perpetuate its kind. The mode bywhich it reproduces is ordinarily quite simple; the animal grows to acertain bulk and then it divides into two masses of protoplasm, each ofwhich receives a portion of the mother nucleus. Sometimes by a peculiarprocess it breaks up into numerous small fragments called spores, whichalso receive portions of the parent nucleus. The most striking feature inboth kinds of reproduction in _Amoeba_ is the complete destruction ofthe individual parent that exists before the act and does not afterwards. It is quite true that every part of the mother animal passes over into oneor another of its products, but it is equally true that no one of theseproducts is by itself the original individual. So even the simplest animalwe know performs a task that is not only useless to itself, but iscompletely destructive of itself, for nature's greater purpose ofpreserving the race. We can readily see why this must be so; there is noplace in the world for a species whose members put individual well-beingabove the welfare of the race, for which the production of new generationsis essential, even though the satisfaction of this demand shouldnecessitate the sacrifice of the parent organism. We might hesitate to usethe word "altruistic" in describing the self-destructive reproductive actof an _Amoeba_, because this word connotes some degree of consciousnessof the existence of other than personal interests, and of the welfare ofdifferent individuals. There is no reason to believe that such consciousrecognition of any natural duties is possible in the case of so low anorganism. But the fact remains that the result worked out by nature is thesame as though there were a definite understanding of real duties. Eventhis unitary organism, then, acts mechanically so as to fulfil two primalobligations, first _to itself_, through activities with individual benefitas the result, and _to the race_ by the act of reproduction which closesits individual existence and inaugurates a new generation. 

The life of this example, representing the whole series of one-celledorganisms, is almost infinitely simpler than that of a member of a humancommunity, yet it reveals the beginnings of certain characteristics of thelatter. Here, it is true, the natural obligations in question are not likethose which are ordinarily denoted social, but it is equally true thateven in this most elementary instance a living thing does not live untoitself alone. It is easy to see the value to the species as a whole ofobedience to the second great law--"_Preserve thy kind_. " But a littlefurther thought makes it plain that even the performance of acts incompliance with the first mandate--"_preserve thyself_"--are not purelyselfish, although their immediate value is realized as individual benefit. Surely an organism that failed to live an efficient individual life wouldbe ineffective in reproduction, so that from one point of view everythingan animal does is tributary to the culminating act performed for thelarger good of the life of the whole species. It is a nice balance thatnature has worked out in _Amoeba_, as well as in all other cases, between the personal life of the individual, complete only when the finalprocess of multiplication supervenes, and this process itself, whichdemands an efficient performance, even though this is destructive of theperformer. 

Before passing to the next members of the series, which reveal additionalprinciples more truly social in the human sense, let us pause to note thatalready we have found certain natural criteria that belong in thedepartment of ethics. Even in the case of the biological unit like_Amoeba_, which is entirely solitary and unrelated to other individualsof its kind excepting in so far as it is a link in the chain of successivegenerations, any vital activity can be called good or bad, right or wrong. Nature judges an act good and right if it tends to preserve the animal andthe species; an act is wrong and evil if it is biologically destructive ofthe animal or if it interferes with the perpetuation of its kind. Again itmust be pointed out that these terms are human words, employed for thecomplex conceptions that belong alone to retrospective and contemplativehuman consciousness to most of us they seem to imply the existence of someabsolute standard or ideal by which a given act may be tested to see if itis right or the opposite. 

If human ethics is truly unrelated to beginnings found in lower nature, something that has arisen by itself from supernature, then we must not usethe terms in question except by way of analogy. If, however, nature hasbeen continuous in the working out of every department of human life andhuman thought through evolution, then the criteria of the righteousness ofthe acts performed even by an _Amoeba_ may be found to be basic andfundamental for ethical systems of whatever human race or time. Thissubject remains to be discussed in the final chapter, but it must be clearthat we cannot survey the evolutionary process by which social systemshave come into being without dealing at the same time with the origin andgrowth of ethical conduct as such. 

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Without leaving the group of one-celled animals typified by _Amoeba_, wefind colonies of the most elementary biological nature, where othernatural obligations are added to the two of greatest importance. Somespecies of the bell-animalcule, _Vorticella_, provide characteristicexamples of these primitive compound protozoa. Here the assemblage is madeup of one-celled individuals essentially similar to one another instructure and in physiological activities; in the latter respect each oneof them is like _Amoeba_ as well. They may remain together for a longeror shorter period, or during their whole existence until the time ofreproduction. Like the solitary protozoön, each member leads a completelife in and by itself, equivalent to that of every biological unit. Itobeys the two great laws already laid down, but in addition it seems to berequired to remain with the others for some mutual good. The biologicalvalue of the association which imposes this additional obligation may befound perhaps in the fact that a large group is not so readily eaten by anenemy as an individual cell; but it is clearer that the process ofreproduction, which consists of the fusion of small "gametes, " ornucleated fragments produced by diverse or similar parents, must begreatly facilitated by the occurrence of gamete-forming individuals in oneand the same colony. "_To remain together_" is the new duty imposed bynature for the good of all and for the welfare of each member of thegroup. Some biological advantage accrues to the several components, justas the banding of wolves enables the pack to accomplish something whichthe single wolf is unable to do, although in the latter case it is not somuch a reproductive alliance that is formed as an offensive and defensiveunion. 

One step higher in the scale stands the plant-form called _Volvox_, nearthe border-line between the one-celled and the many-celled organisms. Thisaquatic type, about the size of the head of an ordinary pin, is a hollowspherical colony, with a wall composed of closely set cellular components. These elements are not all alike, as in the case of colonial protozoa like_Vorticella_, for they fall into two classes which are distinguished bycertain structural and functional characteristics. Most of them are simplefeeding individuals which absorb nourishment for themselves primarily, butthey pass on their surplus supplies to less favored neighbors if occasiondemands. The other members begin life like the first-named, but later theybecome specialized to serve as reproductive individuals solely. Everymember of the colony must obey the first precept of nature, otherwise itwould be unable to play its part in the life of the whole community. Butthe discharge of the second natural obligation, namely to preserve therace, is here assigned to some, and to some only, of the whole group ofcell individuals. It follows therefore that the division of the tasksnecessary for the maintenance of a complete biological individual, and thedifferentiation of the members of the group into two kinds, leads to theestablishment of an individuality of a higher order than the cell. Neitherthe purely nutritive nor the reproducing member is complete in itself; thetwo kinds must be combined to make a perfect organism. The life of anymember can be selfish no longer, for if it is to exist itself, it musthelp others for the mutual advantage of all. A clear social relation isthus established; and the reflex conduct of the units of a _Volvox_ colonycan be justly denoted altruistic, even though in this case, as before, there can be no conscious recognition of the reasons why mutual interestsare best served by what is actually done. 

One of the most interesting and significant aspects of the life-history of_Volvox_ is the appearance for the first time of biological death. Moreelementary organisms are immortal potentially even if not actually, forevery portion of the body is capable of passing over into an animal of asucceeding generation. But in _Volvox_ a division of labor has beeneffected of such a nature that most of the components discharge the tasksof individual value, and with the performance of these they die. Only thereproductive members are immortal in the sense that _Amoeba_ is, forthey only have a place in the chain of consecutive generations of _Volvox_colonies. From the standpoint of the nutritive individual it is better tobe relieved of the reproductive task in order that there may be nointerruption of its specialized activities for the good of all, but theentailed mortality is certainly disadvantageous to it. It is the higherinterest of the colony as a whole that supersedes the welfare of the partstaken singly, and this larger welfare is safeguarded by a differentiationworked out by natural evolution which results in the assignment ofpersonal and racial duties to different individuals, at the costultimately of the lives of the former. 

We now reach the realm of the true many-celled animals, or Metazoa, wherethe biological units are combined to form an organic associationdisplaying many more resemblances to a human society. The freshwater polyp_Hydra_, like the foregoing illustrations, is one whose structure hasalready been discussed in the earlier chapters, but now we may use it foran analysis of another series of biological phenomena. Its sac-like bodyconsists of two cell-layers; the outer one is concerned primarily withoffense and defense, while the inner layer is made up of digesting ornutritive elements. The essential cells concerned solely with reproductionlie below the outer sheet. Comparing this animal with an association like_Volvox_, we discover the same differentiation into immortal germ-elementsand mortal cells, concerned respectively with the _Hydra's_ racialexistence and with its individual life; but far-reaching changes have comeabout in the biological relationships of the second class of cells. Indescribing the new phenomena it is absolutely necessary to employ theterms of human social organization, because the _Hydra's_ body is a truecolony of diverse cells in exactly the same sense that a nation is a bodyof human beings with more or less dissimilar social functions. 

To begin with the differentiation into ectoderm and endoderm, the organismis comparable to a human community made up of military and agriculturalclasses. The cells of the former group protect themselves and the feedingelements also, while the units of the second defenseless type devotethemselves to the task of provisioning the whole community, givingsupplies of food to the defenders in exchange for the protection theyafford; each kind needs the other, and each performs some distinctive taskfor the other as well as for itself. But the parallel thus drawn need notstop here. In the case of the outer layer, the cells are mostly flatcovering elements that are the first to be torn off and injured when theanimal is attacked. Scattered about among them are sense-cells standinglike sentinels with delicate upright processes which receive stimuli fromwithout the sense-cells transmit impulses to the network of nerve-cellsbelow, which is a counterpart of the signal corps of an army, keeping allparts of the whole organization in communication with one another. Mostwonderful of all are the stinging-cells of the outer layer; these producea flask-shaped, poisoned bomb which is discharged by the convulsivecontraction of the cell itself so as to stun and injure the enemy or prey. The bomb-throwing cells die immediately after they have ejected theirmissiles; like soldiers participating in a forlorn hope, they sacrificetheir lives in one supreme effort of service to the cell-community ofwhich they are members. 

These and similar facts prove conclusively that _Hydra_ is a truecommunity even in the human sense, and that the laws of biologicalassociation are established at a point far below the level of the insects. The individuality of the unit is still maintained, and each cell mustguard its own interests to a certain degree, but the original independenceof the unit has become so altered by differentiation and division of laborthat a close interdependent relation has come about. The completeindividual is now the _whole_ aggregate; it is the entire _Hydra_ itselfwhich must obey the primary commands of nature to live efficiently and toperpetuate its kind. True it is that the life of the higher individual isthe sum total of the activities performed by its constituent cells, but noone of the varied specialized elements is biologically perfect by itselfor equivalent to the whole. And, as we have seen, the welfare of thecomplete animal takes precedence over that of any one of its parts, justas the existence of a nation may be preserved only by the death ofsoldiers warring for its honor and life. 

If, now, we should pass on to the more complex organisms like worms andinsects and vertebrates, and should disregard the communal relations ofsome of these animals, each individual proves to be like _Hydra_ asregards the principles underlying its make-up and workings. A single bee, like a man, is a definitely constituted aggregate of cells, differing as awhole from _Hydra_ only in the _degree of differentiation_ exhibited byits constituent elements. Instead of a loose network of nerve-cells thereis the far more complex nervous system whose evolution has been outlinedin the sixth chapter. The blood-vascular and respiratory and excretorysystems have become well organized, in response, so to speak, to thedemands on the part of the nervous and alimentary organs that they may berelieved of the tasks of circulation and respiration and the discharge ofash-wastes. Therefore the cells which make up an insect and a man are morediverse, they have more varied interrelationships, and they are far moreinterdependent then in the case of the components of _Hydra_. Yet all themany-celled organisms that we are so accustomed to regard as individualsare really communities, demonstrating the existence and partial antithesisof the great laws of egoism and altruism, which are traceable even down to_Amoeba_ and its like. 

So much has been made of the lower kinds of cell-associations because themind of the layman is unconsciously imbued with the idea that humansociety is a new thing, --an idea which we now see it is necessary todiscard at the outset. Indeed, the cell-association of the _Hydra_ andinsect type is a more compact and a more stable kind of community than anygroup of human individuals worked out by nature toward the present end ofthe whole scheme of evolution. That is to say, the subordination ofcell-interest to cell-group welfare, while it must not go so far as torender the unit incapable of doing its work, is sufficiently advanced tomake uncontrolled individualism impossible. Let any class of _Hydra's_cells, such as the nerve or muscle network, assume to exercise a selfishpreeminence or to conduct a "strike, " the other classes, like the feedingcells, would not be properly served and they would be unable inconsequence to work efficiently for the strikers. The immediate resultwould be suicidal, for the selfish nerve-class would inevitably sufferthrough the downfall of the whole social fabric. It is a nicely adjustedequilibrium that is established, where the "equal rights" of all thediverse cells consist in freedom to play a special part in the life of thegroup, serving other individuals in return for their service. The GoldenRule is a natural law as old as nature; for even in _Hydra's_ life, unconscious discharge of duties to the race, and hence to others, isobligatory. And all these low types of organic associations evolved agesbefore the rules of human social order were vaguely recognized by thereflective self-consciousness of man, to be formulated as the science ofethics. 

The evolution of the wonderfully varied societies found among insectsbegins with the solitary insect itself, just as this, viewed as acell-community, originates from one-celled beginnings like _Amoeba_through progressive evolution in time. The similarity between socialinsects and human associations is clearer than in the case of a comparisonbetween an example from either group and a cell-community, because thehigher forms lack the organic contact of the components which is soprominent a feature in the lower instance. The social bonds are looser andthey allow a freer play of the constituents; but nevertheless the same lawsthat control the activities of the cells making up what we now take as theindividual element, command obedience on the part of the interrelatedmembers of an insect community with equal strictness. 

A butterfly or a moth is primarily egoistic and unsocial in the ordinarysense during its entire life-history, until the final reproductive actwhich has a value to the species. The caterpillar larva devotes all of itsenergies to feeding and growing, unconcerned with the final duties of themoth with which it is connected just as the indifferent unit of a young_Volvox_ colony is related to a reproducing member of the full-grownorganism. Now and then, it is true, species like the so-called tentcaterpillar are met with where numerous larvæ spin silken communal neststo which they retire at night and in which they remain to molt. The pupa, like the larva, is individualistic and employs its time in producing thefinal adult form. The mature individual, however, is constructed almostsolely for the greater purpose of perpetuating the species. Indeed thelarger silkworm moths do not and cannot feed, and their value is only thatof a device for keeping the race established. Adult may-flies live only afew minutes, just long enough to provide for the fertilization anddeposition of the eggs, although to prepare for these acts the youngindividuals must have toiled for months; the preparatory time may amountto many years in such a case as the seventeen-year locust. But nature issatisfied, as long as the organic mechanisms obey her double commandment, "Live and grow so as to multiply. " Like an _Amoeba_, the solitary insectmust be egoistic at first, in order to be altruistic in a racial sense inits last days. 

Wasps, bees, and ants provide many familiar examples of colonialorganizations that become all the more marvelous on closer acquaintance, on account of their resemblances to human associations on the one hand, and to cell-associations on the other. Their illustrative beauty isenhanced by their wide variety, for they grade from counterparts of highlycivilized men down to a savage among insects, such as the strictlysolitary digger-wasp, whose instincts served to exemplify the insect typeof "mentality" in the discussions of the preceding chapter. 

The true communities founded by wasps and hornets must be assigned to alow grade in the scale because they originate during a single season andbreak up at its end; for this very reason the wasp community is intenselyinteresting to the student of comparative social evolution. In the springa solitary female emerges from the crevice where she has hibernated andresumes active life; she feeds for a time to renew her strength and thenshe constructs a simple nest of mud or masticated wood-pulp. In the firstfew cells of this nest she deposits her eggs, and when they hatch sheherself provides the larvæ with food, but still continues to enlarge thehouse and to produce more eggs. Thus during the first few weeks of thecolony's existence this single individual performs a variety of tasks ofracial as well as of purely egoistic value; but as time goes on, aprofound change comes about in her activities and in the life of the wholecommunity. The members of the first brood do not grow into counterparts oftheir mother; they are all sexless "workers" who progressively relievetheir parent of the tasks of nest-building and foraging and nursing, sothat their mother becomes a "queen" who devotes her entire time to thespecial reproductive task which she only can perform. We may justlycompare the queen to the reproductive organ of _Hydra_, for the values tothe life of the species are identical in the two cases, while the variousclasses of workers are counterparts of such units as the muscle and nerveand nutritive components of the _Hydra_ or any other cell-communityindividual. Another resemblance between the two is found in the death ofall the sexless individuals at the end of the season, when reproducingmales and females are finally formed, of whom the fertile queens onlysurvive in their winter hiding places; and again we can discover the causefor biological death in that division of labor which calls upon certainmembers of the whole community to perform tasks that have no value whenonce provision has been made for perpetuating the species. Finally themode by which the colony grows and amplifies is in all respects like theembryonic development of an egg into a _Hydra_, so that we may add thephrase "social embryology" to our vocabulary. The original female is anundifferentiated master of all trades; the small tribe she firstestablishes is little better off than a horde of savages; but during itsseasonal existence the community increases in numbers and complexity untilit advances well toward the civilized condition, when each class performsits special task for the good of all. 

The bees take us higher in the scale, although many solitary speciesoccur, as well as social forms like the bumblebees where colonies areformed in a single season only to break up with the advent of coldweather. The honeybees, however, establish permanent communities fromwhich swarms may set out during the warm months to become new colonieselsewhere. Many hundreds of bees make up a hive, and they belong to threeclasses or castes, which differ in structure and social function. Thequeen is a fertile female, the drones are males, and the workers arestunted and infertile females which take no part in reproduction. In thiscase the queen never discharges any menial duties, for these are attendedto by the workers; she devotes her entire time to laying eggs, which arecared for by her subjects, who act as nurses and guards for the monarch aswell. The young workers serve at first as doorkeepers, and only later dothey take the field in the search for nectar and pollen, and work ashouse-builders. Each individual performs its special task for its ownbenefit and for the weal of all; each possesses an equal right to share inthe prosperity of the whole community so long as it acts altruistically aswell as egoistically. And just as the welfare of _Hydra_ is superior tothat of any one of its constituent cells, so the well-being of a hive ofbees may be safeguarded only by the actual sacrifice of some of itsmembers. Should food supplies be inadequate, the superfluous drones arestung to death, --the victims of legalized murder. But more marvelous stillis the provision that is said to be made by certain individuals for theirown destruction should this become desirable. As every one knows, areigning queen may leave the hive with many of her subjects and "swarm" ina new locality. When she does this, during the warm months, the workers ofthe original hive feed some of the female larvæ with richer food, andplace these potential queens or princesses in special roomy cells apartfrom the ordinary brood chambers; one of them soon emerges to become a newsovereign. Let us note in passing how similar this is to the production ofnew egg-cells in a _Hydra_, when the mature germs of an earlier generationare prepared and discharged. When, now, the colder weather sets in, andthe possibility of subsequent swarming is set aside, the reigning queen isallowed by her attendant guards to visit the royal cells, whose occupantsshe stings to death, thus destroying any possible claimant to her place. And when the royal princess constructs her part of the pupal case, sheleaves an aperture so that if and when it should become necessary for thequeen to kill her, the sovereign would not injure her sting and be unableto kill the other individuals who might become aspirants for the throneand so precipitate a civil war! As in the case of the self-destructive acton the part of a stinging cell in _Hydra_, altruistic subservience to theinterests of the colony can go no farther. 

The ants form stable colonies of still higher grades, where the workersare not all alike in general structure, but become more rigidlyspecialized for the performance of restricted tasks. As before, there isthe fundamental differentiation into the sexual "queens" and males, andthe sterile workers concerned with the immediate material life of thecommunity. In some species the workers serve as herdsmen, caring for theant-cattle or aphids, from which they receive minute drops of a sweetjuice for food. The aphids are tended on the leaves of various plantsduring the summer, and are carefully reared and stabled and fed belowground during the winter months. In other species seeds are procured andstored in underground granaries. The leaf-cutters are forms which growfood supplies of fungi in subterranean mushroom gardens; the compostconsists of cuttings brought from the leaves of bushes by myriads ofworkers, whose processions are guarded by larger-headed soldiers ofseveral ranks. In the honey-ants of Colorado and tropical America certainindividuals pass their time suspended from the roof of a largenest-chamber, where they receive the sweet juice brought in by the workers. They serve as animated preserve jars, distended sometimes to the size of agrape with the communal stores of food, which they return to the workerswhen external sources of food may fail. Finally there are the slaveholdingspecies which conduct forays upon the nests of other forms, to procure theyoung of the latter, which grow up in their captors' nests and serve themas nurses and masons and foragers. So long has this custom beenestablished that some slaveholders are entirely unable to feed themselves, and would die out if their slaves failed to support them. 

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Let us pause at this point to summarize the results of the foregoinganalysis, in order that we may approach the biological study of humanassociations with definite and clear conceptions of the fundamental lawscontrolling living communities of all grades. 

We have dealt mainly with _Amoeba_, _Hydra_, and the ant-communitywhich exemplify three somewhat distinct types of organic individuality. Some of the transitional forms have been specified to show how the secondkind originates from the first, and how in its turn this grows in timeinto the third and most complex association; thus _Vorticella_ and_Volvox_ connect _Amoeba_ with the cell-community individual like_Hydra_ and a solitary wasp, while the annually established colonies ofsocial wasps and of bumblebees lead to the permanent colony-individual. Restricting attention to the three primary examples, and remembering thatthe criterion of completeness is the ability to discharge satisfactorilyall of the eight biological tasks, it is clear that the entire _Hydra_ andthe whole ant-community correspond _physiologically_ with _Amoeba_, although the first-named is _structurally_ a cell-community equivalent tomany protozoa, and the insect colony is composed of many suchcell-communities as elements. In the third type, neither a single queennor a single worker is able to carry on all of the biological tasks anymore than a muscle-cell or an unformed egg of _Hydra_ can maintain itselfcapably in isolation. Therefore the ant-society as a whole and the _Hydra_in its entirety are organic individuals on the same physiological planewith _Amoeba_, and they are equally subject to the same great laws ofnature demanding selfish maintenance and racial perpetuation. 

But we must not lose sight of the fundamental value of the unit during theevolution of a higher from a lower type. The tissue-cell of _Hydra_ muststill obey the mandate to live an efficient personal life, because this isnecessary for the welfare of other cells and of the whole complex. Theoriginal egoistic tasks are not abolished, but new duties are added tothem in ways we have learned to distinguish. In _Vorticella_ the productsof fission do not separate, and certain advantages accrue from the organiccontinuity thus maintained. The success of _Hydra_ in its ceaselessstruggle to live depends wholly upon the cooperation of its differentiatedcell-units, now no longer equivalent in function to the all-powerful_Amoeba_, although each one must be kept alive until its task is done, or the whole association would have no place in nature. Similarly in thehigher insect community, the superadded duties to fellow-components areeven clearer, for in the competition of colony with colony, involvingterrific battles whose casualties may be numbered by thousands, thestronger wins; and strength depends upon the concerted efforts of all themembers of the kingdom, that only collectively constitute a completebiological whole. Mere self-protection demands altruistic conduct: if theworker ceased to bring in food when its own hunger was satisfied, therewould be no tribal stores for the stay-at-home queens and nurses; and ifthe soldier fled from the field of battle to save its own life, its actwould be suicidal ultimately, for to the degree of one unit the defense ofits non-military supporters would be weakened and they would be so muchthe less unprotected during their service for the soldiers and all others. Furthermore, we must admit the reality of natural criteria of ethicalvalues, established far below mankind in the scale of life. In anant-republic, laws are instinctively obeyed quite as implicitly as thoughthey were intelligibly proclaimed to all of the emmet citizens. Right ismight when community battles with community, for right is that which isbiologically favorable. And what may be correct conduct on the part of themembers of one species may be naturally wrong and evil in another case. Tokill the princesses in order to obviate the possibility of civil war seemsadvantageous and therefore right when the queen remains in the persistentcolony of honeybees, ready to do her part the following spring; but itmight result in disaster and evil in the case of the social wasps, wherethe community dies as such in the fall, and the continuity of the speciesfrom one year to another requires the production of many queens lest thesevere conditions of the winter's hibernation should kill all fertilefemales if only one or two were available. The standards of conduct aresimple indeed; and whether or not it may seem best to separate theprocesses of social and ethical evolution culminating in human phenomena, the fact remains that these processes begin with elements discovered bythe biologist among organisms of the lower levels in the scale. 

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We come at length to the biological interpretation of human socialevolution, in so far as this may be expounded in a simple and conciseform. The comparative method must be employed in order to discover thefundamental attributes of savage, barbarous, and civilized communitieswhich seem to differ so considerably in their complexity of socialstructure, and in order also to show that such basic elements are likethose of communities formed by lower animals, and are equally the productsof natural evolution. This whole subject seems to be exceedingly complex, because in our daily contact with others of our kind and in our occasionalviews of foreign races like our own, the smaller details occupy ourattention, diverting it from the great basic principles according to whichevery society is organized and operates. But when once the major elementshave been discovered in civilized and more primitive nations, thesecondary and less essential phenomena fall into their proper relations, and a statement of the whole process of development becomes relativelysimple. So much space has been devoted to lower types of communalorganisms in order to learn what the fundamentals are, and not merely toprovide analogies that may be useful hereafter. It now remains to arrangethe evidences of social progress during the history of mankind itself, andto bring such human facts into relation with what has been discovered inlower nature. It is helpful to begin this part of the subject by askingourselves what is already part of common knowledge about human history. Dowe know of any civilized nation that is absolutely stable and unvarying insocial structure, or one that has remained unchanged throughout historictime? The answer must be negative, for in no case does the past disclosean example of permanence in social or in any other respect; monarchies andrepublics are plastic like the human frame itself. The AmericanCommonwealth is a relatively young social organism, and it is an easy taskto trace its growth from beginnings in the diffuse and uncorrelatedcolonies of pre-Revolutionary years. Those colonies that were formed byEnglish settlers were transplanted outgrowths from a civilized socialparent which in its turn had clearly evolved from the state of King John'stime and the still cruder form it had under King Alfred. 

Should we follow back the recorded history of any people now civilized, wewould always find evidence of ceaseless change; and the writings ofancient historians like Herodotus and Cæsar and Tacitus give a great dealof information about the barbarous conditions from which civilizationevolved. 

But much more is known that materially amplifies the account of humanprogress based upon documents alone. The student of existing human racesearly learns that social structure is a very varied thing. The natives ofnorthern Africa now live in a semi-civilized state which is very like thatof medieval England. In Siberia and the American Southwest are tribes thatcorrespond socially with the barbarians of Europe described by Greek andRoman writers. The American Indians discovered by the earliest colonists, the Polynesians of a century ago, and the Fuegians of recent decadesprovide counterparts of the ancient stone-wielding people who were thesavage ancestors of European barbarians. Hence the comparative study andclassification of modern races establishes a scale of social grades whichcorresponds with the order of their historic succession, just as in alarger way the complete series of comparative anatomy from _Amoeba_ toman displays the order of evolution from unicellular beginnings to thepresent culminating types. Savagery, barbarism, and civilization are thethree major terms of this social scale, but by no means are theydiscontinuous, for many intermediate forms of organization occur which aretransitional from one major type to a higher one. 

In human social evolution the starting point is not so simple as thesolitary unit from which insect societies evolved, --that is, an organismwhich lives alone and is associated with another of its species only atthe time of mating. The lowest human beings now existing have some form offamily organization, traceable to the more or less continuous unionsformed among certain of the apes and even among many lower animals, andnot a characteristic that belongs to mankind alone. The savage and hismate constitute the social unit out of which all else is built up; the manand the woman must perform all of the vital tasks demanded by nature. Fruits and vegetables must be secured from the wild forest or bycultivation; the flesh of game animals or of a human victim is no lessessential for food. The savage is his own weapon maker and warrior; hehimself builds the rude shelter for his family and fashions the canoe ifsuch is required. He is also his own judge, recognizing no control savethe dictates of his wishes and needs, for he does not consciously realizethat he must obey the primal commands of nature to preserve himself andhis family so that the species shall persist. In brief, the elementaryfamily unit carries on all of the individual biological tasks of foraging, righting, home-building, and the like, and it also discharges the racialtask of multiplying, quite as instinctively as it provides for its ownmaintenance. 

By the union of several families, a primitive association arises, likethat of the Veddahs in Ceylon. The primal duties of each family areunchanged, and their biological activities are identical, as in theprotozoön colony of _Vorticella_ or in a pack of wolves; but certain newrelations are established. A member of such an inchoate tribe must nottreat his confrères as he might a man of another group; robbery and murderwithin the limits of the small association are detrimental to communalinterests, though they may remain unchecked if the victims are strangers. Coöperation for mutual offense and defense makes the group stronger thanits constituent family units taken singly, and every man of such a tribegains something by looking out for others as well as for himself. Bynatural selection alone the bonds of union would be strengthened in directproportion to the subordination of individual interest to group welfare, and to the amount of altruistic action that in a true sense grows out ofpurely selfish conduct. 

But when such a primitive biological association forms and grows, anopportunity arises for increasing the effectiveness of the whole group bydifferentiation. Some of the men are stronger in battle and they soonbecome the chief warriors; others prove to be more skilful in the hunt orin the construction of canoes and weapons. Just as among the insects, thehunter seeks food not only for himself but for the warriors, who in theirturn defend themselves, but do not cease fighting when they have disposedof their own enemies if foes of their comrades still survive. Thebarbarous state of society thus arises, and the division of labor broughtabout during its origin makes it possible and indeed essential for manyfamily units to remain together for mutual good. The union is stable andefficient, however, only if the individual suppresses his own selfishinclinations, suspending private quarrels when public wars are toward, andacting at all times in concert with his fellows. Self-control increasesnecessarily, and lines of conduct deemed right by a solitary savage unitcome more and more under the sway of social inhibition, for although theprimitive savages must inhibit individualistic action to some degree, thebarbarian must suppress much more of his purely personal wishes for thepurpose of social solidarity. Thus it comes about that a barbarouscommunity can number thousands, while a tribe of savages with a higherdegree of individualism and less altruism cannot cohere if it comprisesmore than hundreds or scores. 

Civilization is a product of evolution by precisely the same natural modeof development, that is, through further subordination of individual tocommunal interests and through progressive dividing up of the tasksnecessary for the life of the group. The final result is so obvious andfamiliar that we take it for granted, accepting it as self-sufficientwithout realizing how it has come about and how modern is the presentstate of affairs. Let us compare the life of an Indian savage living onManhattan Island four centuries ago with that of a New Yorker to-day, asregards so simple a matter as the procuring of fish food. The Indianemerged from his tepee, built by himself, and walking to the shore, stepped into a canoe which also he had made with his own hands. Paddlingto the fishing ground, he patiently cast his line until the desired fishwere caught. Does any one of us do all of these things for himself? Welive in houses constructed for us by others who devote their lives tobuilding; we are very apt to go about the city in conveyances that demandspecial and peculiar skill for their invention, manufacture, andoperation. Arriving at a market-place, we obtain such an article of foodas a fish without having to go out upon the water ourselves, for manyother workers have built vessels that we do not know how to make and maynot know how to handle, and hundreds of fishermen devote their lives totheir special task, not for themselves, but for us and all others, such asthe builder, the subway operator, the boat maker, and the manufacturerswho supply their clothing and apparatus. 

What has come about then is a higher degree of specialization in theperformance of the fundamental biological tasks, resulting in theformation of coherent and efficient groups comprising millions as comparedwith the thousands of barbarism and the hundreds of savagery. Just so thecommunities of insects with the greatest degree of altruism and divisionof labor far exceed in numbers the small colonies of the social wasps withlower social differentiation. 

But the great biological functions of an entire complex civilized societyremain the same as those of a primitive savage family unit, of an insectcommunity, of _Hydra_, and of _Amoeba_. Let any nation fail to maintainitself in material individual respects, it must inevitably die out; in theislands of the South Seas many a tragic death-struggle of a people can bewitnessed. If in the second place a nation should concern itself toogreatly with the material benefits of human life without obeying thenatural mandate to propagate itself, its place in the scheme of thingsbecomes insecure, as in the case of the French Republic. Natural sociallaws that go back to _Amoeba_ must be observed, consciously orunconsciously, or else even the civilized community must fall, like scoresand hundreds of others that lie along the road of historic progress--aroad strewn with the remains of the unfit thrown out by natural selection. 

What now are the lessons of social evolution and what guidance doesscience give for human endeavor? Although it may seem that the biologistleaves his field when he considers these questions, his duty would beunfulfilled if he neglected an opportunity to give his results theirhighest utility through their use for the betterment of human life. 

The first lesson is that the history of human social organization is farfrom unique, and that it is identical with the process by which insectcommunities and cell-aggregates have evolved; in a word, the laws ofbiological association are uniform throughout the entire organic scale. Insome respects evolution in mankind has yet to equal the heights attainedby some insects, inasmuch as no human society has accomplished so rigid aspecialization of its members that a given individual is foreordained byits inherited structure to be a particular kind of worker and nothingelse. Furthermore, evolution in human society is still far short of astate where some and some only are reproductive members of the group whilethe others are necessarily sterile; social insects with stable coloniesare so organized that the queens and drones are solely reproductive whilethe workers are destined to care for the material wants of the colony. Itis true that the birth-rate is by no means the same in all classes ofsociety, but the social and other adventitious restrictions that bringthis about are not on the same plane with the hereditary determiningfactors which operate among insects. Therefore the scale of humancommunities proves to be only a part of the wider range of organicassociations in general--a part which can be definitely placed in such awider scheme and so become more intelligible in itself. 

In all departments of social evolution, progress is made by the twofoldprocess of combination and differentiation. We have dealt with detailedinstances, and now it is profitable to treat the process in a larger way, with a view toward the possibilities of the future. The Thirteen Colonies, somewhat similar in their earlier economic activities, united for mutualsupport much as wolves combine to form a pack. Later, as circumstancesdirected, they differentiated into farming or manufacturing or commercialorgans of the body politic, each to some degree freeing itself of thefunctions undertaken by others, and becoming thereby more dependent thanbefore upon those that specialized in different ways. As in the history ofthe insects in a growing wasp community and of savages evolving intobarbarians, the original condition of relative independence passed into astate of interdependence and cooperation. In like manner, if natureremains the same, as there is every reason to believe it will, nations nowseparate will unite to make more complex combinations that will beveritable empires of world-wide scope. Countries on opposite sides of anocean are now more closely connected by lines of communication and meansof travel than were the Carolinas and New England a century ago. Diplomatic activities give many signs of a growing appreciation of thevalue of reciprocal agreements for mutual advantage, and the HagueConference is a concrete manifestation of a continuing process of socialevolution that finds its beginnings and its interpretation far below humanhistory in lower organic nature. 

But perhaps the most important result of this whole discussion is thelesson of social service that it teaches. We are members of a vastcommunity whose complex total life seems far removed from anything goingon in an ant-colony, and our daily tasks vary greatly in specificcharacter and degree when compared with those of lower communal organisms. It seems scarcely credible that any principles of social relationship, however general, can hold true for us and for them. But when therock-bottom foundations are reached, they are simple and instructiveindeed. Being here, we cannot escape our personal obligations as livingthings or our equally clear duties as members of our community. Thesefacts being as they are, what must we do? Self-interest is rightly to beserved, otherwise we would be incapable of discharging our secondarytasks, namely, those of service to others in ways that are determined byhereditary endowment and conditional circumstances. The difficulty is tofind the right compromise between the two sets of obligations; but theright balance must be found, or else the health of the community isimpaired. Should any class demand more than its just dues, others mustsuffer through the diversion of what they require, and the well-being ofthe selfish class is jeopardized to some degree, so closely interwoven arethe interests of all. Freedom of opportunity within the limits of abilityand efficiency is the right of every one, but freedom of conduct mustnever result in trespass upon the equal rights of others to make the mostof their abilities and opportunities. 

To summarize, then, social evolution is a continuous process accomplishedthrough differentiation and division of labor among the components ofbiological associations. Although the total form remains the sameeverywhere, progress has been made in content through the furthersubordination of selfish to altruistic conduct; only by this means does anindividual gain liberty to pursue the social task for which he is bestfitted by nature. 

VIII

EVOLUTION AND THE HIGHER HUMAN LIFE

We have now reached the last division of the large subject that hasoccupied our thoughts for so long. The present title has been chosenbecause the questions now before us relate to the highest human ideasbelonging to the departments of ethics, religion, theology, science, andphilosophy. These matters may seem at first sight to be far removed fromthe territory of the naturalist as such, and quite exempt from the controlof laws which determine the nature and history of the human individual inphysical, mental, and social respects. Yet one reason alone would impel usonward: we cannot close the present examination into the basic facts ofevolution and into the scope of the doctrine without asking to what extenta belief in its truth may affect our earlier formed conceptions of natureand supernature. Heretofore these possible effects upon what may be dearlycherished intellectual possessions have received no attention, so that wemight learn how evolution works in the lower fields of organic life ingeneral and human life in particular without being disturbed by them. Nodoubt, however, the conviction has grown with each step in our progressthat the principles we have learned must cause us to readjust our views ofthe highest elements in human thought to a degree that must be inverselyproportional to our previous acquaintance with the laws and processes ofnature. But the seeker after truth is fearless of consequences. He knowsthat truth cannot contradict itself; and if those to whom he looks forauthority give him conflicting accounts of nature's history, he knows thatone of these must be less surely grounded than the other. The investigatorsoon learns to withhold final judgment, realizing that the primaryconditions for intellectual development are the plasticity and openness ofmind that dogmatism and finality destroy. He knows that while hisresearches may be, and indeed must be, iconoclastic, they provide him withbetter icons in place of the old. 

Let us recall the steps in our progress through one and another field ofknowledge, from which representative facts have been chosen forclassification and summary. We began with the basic principles of organicstructure and workings, and then we examined serially the largercategories of the evidences relating to evolution as a fact, and to themode of its accomplishment by natural factors. Proceeding to the specialcase of our own species, we learned that human beings are inevitably apart of nature and not outside it; in structure, development, andpalæontological history, mankind is subject to the control of the uniformlaws which operate throughout the entire range of living things. Finally, the mental characters and the social relations of human organisms werederived from beginnings lower down in the scale, and were proved to be nomore exceptional than the physical constitution of a single human being. 

Are we to forget all of these things when we try to put in order our ideasbelonging to the categories of higher thought? Can we hope to find thetruth if we fail to employ the methods of scientific common-sense whichonly yield sure results? It is no more justifiable to discard ourhard-earned knowledge than it would be for an advocate to undertake theconduct of a case in deliberate disregard of what he had learned of thelaw, or for a surgeon to leave his knowledge at the door when he enteredthe operating room. Too often we are bidden to view the larger conceptionsof nature and supernature as something outside the realm of orderedknowledge too frequently we are given statements upon authority that takesno account of reason, and we are asked to accept these views whether or notthey accord with the demonstrated facts of common-sense. But those whohave followed the present description of evolution can readily recognizetheir obligation to use for the further analysis of higher human life themeans which have given in that doctrine the most reasonable explanation ofthe natural phenomena already investigated. 

I need hardly say that we now enter upon the most difficult stage of ourprogress. The regions we have traversed were more readily explored becausethey were remote from the matters now before us; even in the case of man'smental and social evolution it was possible to take a partially impersonalview of certain of the essential elements in human life, which we cannotdo now. For ethics and religion and philosophy are groups of ideas thatare familiar to us as the property of mankind alone. Countless obstaclesare in the way. Much mental inertia must be overcome, for it is far easierto accept the average and traditional judgments of other men--to let wellenough alone--than it is to win our own way to the heights from which wemay survey knowledge more fully. Human prejudices confront us as averitable jungle, hemming us in and obstructing our vision on all sides;and perhaps much underbrush must be cut away if we are to see widely andwisely. Nevertheless, to those imbued with a desire to learn truth, anything and everything gained must surely repay a thousand times allefforts to obtain clearness of vision and breadth of view. With ourperspective thus rectified by our backward glance, we turn to the threedivisions of human thought now to be examined. The conceptions of ethicscome first for reasons that must be apparent from the classification ofthe facts of social evolution; just as mental attributes and communalorganization are inseparable, so rules of conduct arise _pari passu_ withthe origin of a biological association. Religion and theology form thesecond division, which takes its origin in part from the first, for thesetwo groups of ideas are largely concerned with the authority for rightconduct and with human responsibility for taking the right attitude towardthe entire visible and unseen universe. Finally, science and philosophyare briefly treated as evolved products which include within their scopeall that there is in human knowledge; for this reason they take thehighest place, instead of the position below religion usually assigned tothem. At the last, having reached our final standing ground, we must lookback in order that we may clearly define the lessons and ultimate valuesof the whole doctrine of evolution. 

 * * * * *

Ethics is the science of duty. It is usually restricted to an examinationof purely human obligations, and to a search for the reasons why menshould do certain things and refrain from committing other acts. Likepsychology and sociology, ethics began as a strictly formal and _a priori_system of dogmas which related to the life of cultured human beings alone. Again, like the sciences specified, it gradually broadened its scope so asto include the conventions of races lower in the scale than the civilizedpeoples who only were sufficiently advanced intellectually to conceive it. Thus the comparative method came to be employed, and in direct proportionto its use, more liberal views have developed regarding the diversemethods of thought and standards of social life and of conduct amongdifferently conditioned peoples. Still more important is the demonstrationthat human ethics as a whole, like human faculty and civilization, takesits place at the end of a scale whose beginnings can be found in lowerorganic nature. 

Those who have followed the account of social evolution given in thepreceding chapter must realize that the basic general principles ofnatural ethics, as contrasted with "formal" ethics, have already beendiscovered and formulated. A biological association of whatever grade anddegree of complexity is impossible unless biological duties aredischarged. Human ethical conduct differs from insect and protozoönethical conduct only in the element of a participation in the process bythe explicit consciousness of man that he has definite obligations toothers; and this distinguishing characteristic is the direct outcome of anevolution which adds reflection and conceptual thought to a mentalframework derived from prehuman ancestors. The insect hurries about in itsdaily life as an animated machine, whose activities are defined byheredity; its special mode of conduct is just what nature has produced byselection from among countless other forms of living which have not hadthe same degree of biological utility. But man alone recognizes vaguely orclearly the "why and wherefore" of his acts that are far more instinctivethan he supposes; he only is consciously aware of the bonds of kinship andeconomic interdependence. He looks about for the authority which imposeshis duties and fashions his bonds, and conceives this authority assomething superhuman, until the comparative studies of evolutionaryphenomena reveal the true causes in uniform nature itself. 

According to biological ethics, the fundamental obligations of all livingthings are the same, even though the modes of discharging them may bevarious. Every individual must lead an efficient personal life byprocuring food, but animals differ very much in their alimentaryapparatus; among other things they must respire, but some are so simplyorganized that they do not need elaborate organs like the tufted gills ofa crustacean or the lungs of higher vertebrates. Every individual ofwhatever grade must also provide in some way for the maintenance of thespecies, but some, like a conger eel, produce enormous numbers of eggswhich are left uncared for, while others, like birds, bring forth only afew young, which receive constant attention and protection until they areable to shift for themselves. Nature has no place for even a humancommunity unless individual and racial interests are conserved, so thatthe greatest duties are definitely formulated--all else is secondary andless essential. Selfish action on the part of every unit is obligatory, but it must always be antecedent to endeavor in the wider interests of therace if the unit is a solitary individual; if it is a member of anassociation of any grade, then it must serve its fellows in some way. Egoism and altruism are natural essential guides to conduct; neither cansafely exclude the other, and their antithesis sets a problem for everyorganism, which is to work out the proper compromise that will be mostsatisfactory to nature. The Golden Rule is taught by biology because it isdemonstrated empirically, and not because it has any _a priori_ value asan ideal ethical principle. 

But utilitarian or natural ethics need not stop with the statement ofvague generalities like the foregoing. In human society, as in the life oflow animals, the worth and value of any form of conduct and of everysingle act can be estimated by definite biological criteria. Theinstitution of marriage and the conventions of common morality have theirbiological value in their provision for the care of children; thesafeguards of property rights enable the industrious--the biologicallyefficient--to keep the fruits of their labors; the establishment of formalcivil and criminal laws is biologically valuable in a social way, in sofar as such laws diminish the unsettling effects of personal animosity andthe desire to wreak personal vengeance; the establishment anddifferentiation of legislative, executive, and judicial organs ofgovernment lead to greater social solidarity and higher biologicalefficiency. Thus unchecked individualism is just as wrong ethically andbiologically among men as it would be in the case of insect communities, as pointed out in the preceding chapter; no one has a right to expectservice or deference to personal interest from others if he fails to workfor them and for the good of all. It is true that the social structurewill stand a great amount of tension, but if this becomes too great, either a readjustment is effected, as when King John was forced by thebarons to concede their rights, or else the whole nation suffers, owing tothe selfishness of a few. In the war between Russia and Japan, the latterwon because the individual soldier merged his individuality in the largermechanism of the regiment and brigade and army corps, gladly sacrificinghis life for the nation represented by the person of its Emperor. Thesingle Russian soldier may have been far superior to a Japanese inmuscular strength, and perhaps in arms also, but selfishness and greed onthe part of many who were responsible for the organization and equipmentof the Russian armies rendered the whole fighting machine less coherentand therefore less efficient than that of the Japanese. 

In the evolution of ethics the recognition of ideals of conduct hasfollowed long after the institution of a particular precept by nature, which is obeyed instinctively and mechanically by force of inheritance. Inthe case of the communities of insects, the results are the same as thoughthe individual animal fully recognized the value of concerted endeavor. Soamong primitive savages of to-day there is only a vague conception ofabstract duty as such, or it may be practically lacking, as in the case ofthe Fuegians. So also a growing child is substantially egoistic, and itmust be taught by precept and example that the rights of others can besafeguarded only by the altruistic correction of personal action, longbefore the child can grasp the higher conceptions of ethics. If a humanbeing never learns to do so, and becomes a criminal through force ofheredity or circumstances, the machinery of the law automatically comesinto operation to conserve the welfare of the community. Such a criminalmay be unable to control his destiny, and may not be responsible for beingwhat he is, but nevertheless he must pay the penalty for his unsocialheritage by suffering elimination. 

Ethical systems are built around man's vague recognition of certainnatural obligations, and they have thus become more or less complex, andmore or less varied as worked out by different peoples. They mustnecessarily be much concerned with social questions, with morals in theusual sense and the more rigid principles enacted into the spoken andprinted law, but they have also become closely connected with religion andtheological elements. Especially is this true in the ethics of barbarousand savage peoples, who accredit the "categorical imperative" to somesupernatural power, as we are to see in a later section. The one pointthat comes out clearly is that the systems of conduct and duties haveevolved so as to be very different among various races, and that in thehistory of any one people, ethics has passed through many variedconditions. What may be deemed right at one period becomes wrong atanother when conditions may be changed; in medieval England the penalty ofdeath was prescribed for one who killed a king's deer, as well as for ahighway murderer. The Fijian of a quarter century ago killed his parentswhen they became too old to be effective members of their tribe. And sodeeply ingrained was this principle of duty that elderly people wouldvoluntarily go to a living grave surrounded by their friends; while inother authentic cases, parents have first killed their sons who failed toobey the tribal law, and have then committed suicide. We can see hownature and necessity would institute a law requiring such conduct where atribe must carry on almost incessant warfare and where the available foodsupplies would be enough for only the most efficient individuals. Infanticide also has been practised for reasons of biological utility, asamong the Romans, who at first maintained their racial vigor bydeliberately ordering the death of weak babes. But times have changed, andethics has become very different with passing decades. Our civilizationhas resulted in a development of human sympathy as an emotional outgrowthof necessary altruism; this motive directs us through charitableinstitutions and hospitals to prolong countless lives which are more orless inefficient, but which do not render the whole body politicincompetent in its struggle for existence. 

Nature then has itself attended to the development and institution ofethics. As we look back over the long series of stages leading to our ownsystem of conduct the most striking feature of the history is theincreasing power of self-control or inhibition. As a natural instinct thistends to prevent the committing of acts which for one reason or anotherare naturally harmful to society as a whole. What we call conscience is aninstinct implanted by purely natural factors, and it unconsciously turnsthe course of human action in the directions of selfish and altruisticinterests. Conscience, then, without ceasing to have validity andefficiency, appears on the same plane with all of the other products ofevolution which owe their existence to individual or social utility. 

Theology and religion involve intimately related conceptions of the world, its make-up, and its causes. Strictly speaking, religion is a system ofpiety and worship, while theology deals more particularly with theultimate and supernatural powers conceived in one way or another as theGod and the gods who have constructed the universe and have subsequentlyordered its happenings. A religion is a group of ideas having the effectof motives; it is dynamic and directs human conduct. Theology, on theother hand, is more theoretical and descriptive, and its conceptions, together with those of other departments of human thought, give thematerials for the formulation of the religious beliefs which determine theattitudes of men toward all of the great universe in which they play theirpart and whose mysteries they attempt to solve. 

Defined and distinguished in these ways, these two departments of higherhuman life present themselves for comparative study and historicexplanation. They differ much among the varied races of mankind, so much, indeed, that an investigator who approaches their study with a knowledgeonly of Christian religion and theology finds it difficult at first torecognize that the same fundamental ideas, although of far cruder nature, enter into the conceptions of an idol-worshiping fanatic living in theheart of Africa. But, nevertheless, beliefs that fall within the scope ofthe definitions adopted above are to be found among all men, and they mustbe examined so that their agreements and differences may be demonstrated, and their common elements may be explained as the natural products of aprocess of evolution. 

Such a broad comparative study, like that of physical, mental, and socialphenomena discussed heretofore, must be conducted objectively; that is, each and every particular belief of a religious or theological naturewhich can be discovered in any race is entitled to a place in the array ofmaterials which demand scientific treatment. They must be verified, classified, and summarized, in order that their total meaning and valuecan be discovered. It must be strongly emphasized that for such purposesthe inherent validity and truth or falsity of diverse religions are notcalled into question when they are so considered as objects of study; manystill entertain the view that the mere task of conducting an analysis of agroup of religious beliefs of whatever nature must tend to destroy oralter that system of religion in some way and degree. But whatever thecomparative student may himself believe, the conception of Jehovah in theHebrew religion is quite as legitimate an object of study as theBuddhistic concept of Brahma as the Ultimate Being, or the Polynesian ideaof Tangaroa as the god of the waves. We would naturally be inclined toexclude the last from our own personal system of piety and worship as thechildish concept of an imaginative, adolescent race; but whatever thetruth may be, the fact of a belief in Tangaroa is as real as the fact ofChristian belief in God. We can no more destroy any one of these ideas byinvestigating its nature and origin than we destroy the efficacy of thehuman arm when we study its muscles and bones and sinews. The former, likethe latter, take their places among natural phenomena whose history mustbe inquired into if there are any reasons for supposing that they fallwithin the scope of evolution. I would be the last to lead or to take partin an attack upon any system of religion, but as a student who isinterested in the universality of organic evolution, I am forced toscrutinize each and every authentic account of a religion to see if suchsystems present objective evidence of the fact of their evolution throughthe operation of purely natural causes. 

But before passing to a detailed treatment of the analysis, synthesis, andgenesis of religious systems, let us employ our common-sense for a briefbackward glance over the known history of familiar facts. Every one isaware that the Christian religions of our time and community have notexisted forever; this, indeed, is indicated by the way the passing yearsare denominated. We call the present year 1907 Anno Domini, and this wholeexpression explicitly refers to the fact that less than two thousand yearsago the Christian systems of piety and worship collectively took theirorigin from their Hebrew ancestor. The same parent has produced therelatively unchanged Judaism of the present day. Judaism itself evolvedunder the influence of the Prophets, of Moses, and of Abraham. Turning toAsia, we learn how Buddhism evolved from Brahmanism. The teachings ofMohammed at a later time developed into the formulated precepts of theKoran. Would any one venture to assert that all or any of these systems ofthought have stood firm and immutable from the finite or infinitebeginnings of time? Would any one contend that the creeds of Protestantismhave remained unchanged even during the past twenty years? Like alldepartments of human belief and knowledge, religious concepts haveobviously altered in natural adjustment to changing times and to advancingconditions of human intellect; and the question turns to the mode by whichthey have been modified, to see whether natural causes of evolution havechanged them, and have originated their earliest beginnings at the veryoutset of human history. It has been stated above that every race ofmankind, however primitive or advanced it may be, holds some form ofreligious belief based upon some conception of the supernatural powersback of the world; and what the universe is conceived to be must largelydetermine the particular characteristics of a theology, and through thisthe special form of its attendant religion. We have before us a wide arrayof types to study and to compare, which vary so greatly, partly for thereason specified, that an inclusive definition of religion must be couchedin very general terms. If we define it as the attitude and reaction of ahuman being conditioned by his knowledge of the immediate materials andhis conception of the ultimate powers of the universe, its scope is soextended as to include the ideas of the atheists and agnostics as well asthe crude conceptions of lower races and those systems of piety andworship conventionally regarded as religions by civilized peoples. Morethan this: we cannot regard the total reaction of a thinking being asessentially different in ultimate value from the attitudes toward theirworlds of animals lower than man. The situation of a well-trained sheepdog is one of pastures and fences and gates, of rain and sunshine, ofsheep, and of a master whose voice is to be obeyed. What the dog may do ispartly determined by what it finds in its world of animate and inanimatethings. Although the animal's "conception" of such things must be farsimpler than a human being's, nevertheless its life is lived in reactionto all of its surroundings as they are presented to its cerebral apparatusby the proper organs. So in the human case, conduct is directly affectedby the living and lifeless objects of a total human situation, the onlydifference being that reflective consciousness and reasoned interpretationhave their share in determining the assumed attitude in ways that seem tohave no counterparts as such in the mental lives of lower animals. Butwhether or not the similarity between human religion and lower organicreaction be admitted, --and the admission is one that greatly facilitatesan understanding of evolution in this field, --the general resemblance ofall religions in fundamental character at least must be accepted. 

Another general feature of religious systems is their complexity. Theessential elements of all of them are few indeed, as we shall see at alater point; they are beliefs regarding ultimate powers, humanresponsibility to such powers, and future existence. These have taken onespecific form or another in various lines of racial evolution, but asidefrom their own changes they have gathered about them many other articlesof creed relating to other departments of thought and life. Ethical rulesof conduct are so added, as in the Hebrew religion where the idea ofJehovah involves God the Ruler and Judge who imposes and administers thelaws of right living. Social customs are almost invariably intertwinedwith religious views, among savages as well as among the more advancedMohammedans whose rules relating to family organization form an integralpart of the whole cult. The emotional elements play a large part in somecases, in the fanatical creeds of the Dervish and Mahdist and in the"revivals" under nearer observation. In Greek cosmology and worship, aesthetics figured to a large degree. Temperamental and otherpsychological characteristics have profound effects upon religions, whichwe may illustrate by such extreme examples as the austerities of NewEngland and Scotch Presbyterianism and the contrasted liberties of thenatural religions of tropical races. But all of these accessory elementsbelong to other well-defined departments, some of which have already beenconsidered, and among the materials of their proper divisions they findtheir interpretation and historical explanation in evolution. It is withthe basic elements themselves that we are now concerned. 

Only within recent years have systematic attempts been made to classifyreligions on the basis of impersonal objective study. Throughout all timesmen have instinctively set up their own religion as the only true one, besides which all others are designated simply as false--a very naturaldistinction, but one which is too naïve for science, as well as one thattakes into account subjective or personal values which are not to beconsidered in an objective comparison and analysis. The linguistic basiswas first employed by Müller, with the result that religions were placedin the category of evolutionary accompaniments of the other mentalpossessions and of the physical qualities of genetically connectedpeoples. Thus the nations of Europe that branched out in all directionsfrom very nearly the same sources possessed common linguistic charactersand somewhat similar creeds. The Sanskrit-speaking races were the originalBrahmins and Buddhists. Ancestor worship is an accompaniment of thepeculiar languages spoken by eastern Mongolian peoples. And although thecorrelation specified is by no means invariable, because a race of onestock can readily accept the religion of a neighbor or of a conqueror, yetmuch is gained through the introduction of the idea of evolutionaryrelationships. 

A more logical classification frankly adopts the genetic method andclearly recognizes the direct effects of cultural and intellectualattainments upon the way a religious system becomes formulated. In such anarrangement, similar to that of Jastrow, religions can be classed as thoseof savagery, of barbarism, of advanced culture, and of civilization. Amongthe first named, notably those of Polynesian and African tribes, beliefsin diversified ghosts and spirits bulk largely, and every moving thing, beit a river or a cloud or a tree or animal, is held to be animated by aninvisible conscious genius; the spirits reside in everything, as well asin the great unknown beyond. Above these in the scale are the religions ofso-called primitive cults, more elaborate and formalized in the ancientbeliefs of Egypt and Assyria, but still below those of advanced culture, which make up a third group. The fourth class includes the religions whichtend to be coextensive with life, and which enjoin the higher harmony ofpractical and theoretical conceptions. Taking Christianity as an example, the contrast with the beliefs of savagery brings out clearly the nature ofprogressive development. Here religious thought is no longer esoteric, confined to a chosen sect like the Levites among the Hebrews or the shamanand medicine-man among the American Indians; nor is religious observancerestricted to the innermost shrine of the tabernacle or sacred dwelling, accessible to few or only one. It comes to be regarded as something inwhich each and every individual can participate, and a personal possessionthat has a direct part in determining all forms of human life and action. This is another way of saying that the more highly evolved religions owetheir character to the greatly varied and abundant intellectual elementswhich are built into them. And this is why religion in the highest form, more clearly than in the lowest forms, is to be spoken of as an outlookupon the world which is determined by the total intellectual equipment ofthe individual man who thinks about the universe and directs his course ofaction by what he finds. 

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We come now to a closer concrete study of the basic elements of religion;that is, of those beliefs that are invariably present, in one form oranother, in every system of piety and worship, and that constitute theinnermost framework beneath the secondary creeds added to them. FollowingMallock and others, we may distinguish three such elemental conceptions. These are, first, the belief in the existence of a supernatural being orbeings, endowed with intelligence like, but superior to, our own; second, the idea of human responsibility to this or these powers; and, third, thebelief in immortality as an attribute of the supreme powers and of humanindividuals also. Let us see how these beliefs appear in characteristicsystems of religion. 

In all forms of Christianity the central idea is the conception of atriple unity personified as God. He is regarded as the Creator who hasmade all things and who demands reverence from his subjects. He is theAuthor and Finisher of the faith as well as the sole Cause of the universeitself. Much of this element is directly derived from Judaism, theprogenitor of Christianity; but a difference consists in the triple natureof the supreme being according to the newer creed. As the original andsupreme being, God is not only the Creator, but the watchful Judge aswell, demanding reverent obedience to the laws of the world in which hehas placed man, and imposing sacrifices and penitential observances whenhis mandates have been disobeyed. As the God of Mercy he is incarnated inthe person of Jesus of Nazareth, and offered as a vicarious sacrifice forsinners who are thus enabled to escape the penalties they would otherwisehave suffered. As the Holy Ghost, God is the vaguely personified ultimatesource of the higher and nobler elements of human thought, aspiration, andlife in general. The second basic tenet of Christianity is that of humanresponsibility to God, to whom man is related as the created to a creator, as a subject to a ruler, and as one saved to his redeemer. Theinstitutions of sacrifice and ritual are outward signs of human subjectionto God himself and to his laws, according to which the universe isconceived to operate. Finally, Christianity teaches that just as God inhis single and triune form is eternal, so the soul of man is immortal, with or without its earthly temple of flesh and blood. The essentialthinking individual is believed to pass to heaven, where rewards for rightliving are bestowed, or to hell, in order to suffer punishment for sinduring all eternity, or some part of it, according to different viewsregarding the efficacy of Christ's vicarious atonement. 

It is true that the manifold sects of Christianity differ somewhat in thedetailed forms of these three essential beliefs, but not to the samedegree as in the case of the secondary additions. God's laws, Christ'steachings, and the inspiration of the Holy Ghost are the recognized guidesto conduct; but human frailty has been such that the history of Europepresents a panorama of warring sects in almost unceasing strife aboutdetails of ritual and interpretation, while the great fundamental truthshave been too frequently ignored. The conflicts of Catholics andProtestants, Puritan and Cavalier, and Northern and SouthernPresbyterianism, have not been waged on account of basic beliefs like thethree outlined above, or about the Golden Rule, but on account ofcomparatively trivial details which to the impersonal student havescarcely more than the value of individual preference. 

Judaism, the next great religion, has already been mentioned as the parentof Christianity, to which it gave the concept of a Supreme Being, as wellas that of a Messiah. It is a purer monotheism than its outgrowth, whosetrinity is more like certain elements of Greek theology. Jehovah is theone supernatural power, the creator and lawgiver and immediate cause ofall the workings of nature. It is he who shapes the world out ofnothingness and who separates the waters from the dry land; he parts thewaters of the Red Sea to save the Israelites, and brings them togetheragain to overwhelm the pursuing hosts of Pharaoh. It is his voice thatthunders from Mt. Sinai, and his finger that traces the commandments torule the lives of his chosen people upon the tablets of stone intrusted toMoses the Seer. At the behest of Joshua he holds the sun and the moon intheir courses above the vale of Ajalon so that there will be more time forthe destruction of the Philistines. In brief, Jehovah is the eternal godof law and power, demanding sacrifice and priestly atonement, andpromising happiness eternal upon the bosom of Abraham to those whorecognize their responsibility to him and obey his precepts. Again, thereare three fundamental beliefs, that differ from those of Christianity asthe Talmud diverges from the New Testament scriptures. 

Mohammedanism is another outgrowth from this group of religions. Theteachings of the Koran give the institutional and ritual forms to the samethree elements distinguished above. God is the identical single God; andMohammed is His Prophet, as Jesus is the New Prophet of Christendom. Thetrue believer's responsibility entails active warfare upon the heretics, that is, those who do not accept the Koran. The immortal state ofMohammedanism is a very different thing from the heavenly bliss ofChristianity, for the promised rewards are such as would appeal to thewarm-blooded Southern temperament. 

Turning now to Asia, we find in Brahmanism and Buddhism two systems ofreligion that are related to one another exactly as are Judaism andChristianity. The analogue of the Old Testament is a group of priestlyhymnal writings known as the Vedas, which date back to about thefourteenth century before Christ lived. Their objects of worship at firstare numerous invisible beings that actuate the things of the world, as inGreek theology, but later one of them assumes preëminence as theall-pervading essence of things, --Brahma. The precepts of Brahmanismenjoined adoration of the unseen powers and of their works, as well aspractical rules of human conduct, such as those which divided a man's lifeinto the four periods when he should be successively a student, the headof a family, a counselor, and a religious mendicant who should renouncethe world of social activities and human desires. In earlier writings, theimmortal state is a kind of heaven, but later it meant simply anabsorption into Brahma, the eternal impersonal being. 

Buddha was an orthodox Brahman reformer of the sixth century before ourpresent era, just as Jesus was an orthodox Hebrew reformer. The essentialcreed of Buddha made his religion far more ethical than earlier forms, andplaced it on a plane even above Christianity of later centuries. Thiscreed relates to the element of human responsibility particularly, theother two remaining much as they were found by Buddha. According to histeachings, a man rested under an obligation to live nobly in the truestsense, and he acquired merit--_karma_--or lost it, in proportion to hisdeserts. At death a human soul is reincarnated, in a lower form of animalor even in a being residing in one of a series of unseen hells, ifpunishment is due; if a higher state is merited, progress is made throughthousands of existences until perfection is rewarded by an eternal fusionwith the essence of Brahma. It is because there is no escape from justpunishment that Buddhism in its original form is properly denoted moreethical than a religion which teaches that sacrifice of any kind willexempt the sinner from deserved penalties and bring about the bestowal ofunearned rewards. 

Polytheism is the name given to a religion such as that of the Greeks orRomans, who believed in many gods and spirits of greater and lesser power. These supernatural beings, each in its own sphere, immediately directedthe processes of nature and controlled the lives of men. One of them, Zeus, was regarded as the supreme "father of gods and men, " who delegatedspecific duties to others; Ares was the god of battles, Hermes was themessenger, Athena implanted wisdom in the minds of men, and Poseidon ruledthe sea. The gods were very human to the Greek mind, living in Olympus asmen do upon earth, and even visiting the mortals. Their worship involvedpropitiatory sacrifices and rites as well as thanksgiving offerings whenfavors were bestowed. But although they were immortal, they did not allowthe immortal souls of human beings to join them in their elysium, butcompelled the disembodied shades to wander unhappily among the tombs andabout their earthly abodes. 

Roman theology and religion comprise almost identical forms of the threefundamental elements. The names are changed, and Zeus becomes Jove, hiswife Hera is Juno, Ares is Mars, and Hermes is called Mercury. In allother respects, however, the two systems are as much alike as the Greekand Roman languages and Greek and Roman physique. 

The religions of savagery are far less analytical, and much more naïve intheir reference of natural happenings to the direct interposition ofmalevolent and benevolent spirits. Their gods are numerous as in Greekreligion, and likewise one of them is usually set up as the superiordeity, to be the Tirawa of the Indian, the greater Atua of Polynesia, andthe Mumbo Jumbo of a West African negro. There is no centralization of thesupernatural powers, as in the Jehovah of Judaism and the still subtlerBrahma of the Asian. Then, too, the gods must be concretely materializedfor purposes of worship and sacrifice; consequently idols are made, to beregarded as the actual spirits themselves permanently or for the timebeing, and not viewed as representations of an ideal, like the statues ofmore advanced peoples. The immortal state is described in low religions invarious ways that seem to be determined by what the believer himself mostdesires. The spirit of an American Indian goes to the happyhunting-grounds, where it mounts a spirit pony and forever pursues theghosts of bison which it kills with spirit bow and arrows; to provide thesenecessaries his earthly possessions are laid beside his dead body. TheNorseman was conducted to Valhalla and, attended by the Valkyrie ashandmaidens, he eternally drank mead from the skull of an enemy andgloried over his mundane prowess in battle. It is unnecessary to expandthe foregoing list, because the examples sufficiently represent thevarious grades of human religions. Regarding them as typical, we can seehow universal are the three fundamental ideas with which we are concerned. Every race has its own conception of future bliss, as well as itsconception of responsibility to the immortal and supernatural powers ofthe universe. Whatever may be the actual reality, and however closely theconceptions of one or another religion may approximate to the truth, suchreality and approximation are not the subjects of the present discussion. Nor is it our purpose to bring out more explicitly the geneticrelationship of one religion to another; the evolution of Buddhism fromBrahmanism, the origin of Christianity from Judaism, and the divergentdevelopment of the several creeds of Christendom amply illustrate thenature of religious history. It is evolution here as elsewhere andeverywhere. 

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Having distinguished the three general elements of all religions, beyondwhich everything else is of minor importance, we now turn to the questionas to the _natural_ origin of these elements. Clearly they cannot ariseindependently, for the belief in supernatural and eternal spirits isclosely connected with the conception of an immortal soul. 

The first is the conception of infinite personalities that later becomemore or less merged into one supreme being. This begins with the idea ofthe soul as the human ego, conventionally regarded as somethingindependent of the material body during life and immortal after death. Thesavage goes to sleep, and in his dreams he goes upon journeys and battlesstrenuously with other men and with beasts, only to find when he awakesthat his body is not fatigued, and that it has not really taken part inthe activities of his dream life. His companions about the fire also tellhim that this is so, while he is equally sure that his essential self hasbeen doing many things during the interval of sleep. In his dream life hefinds himself joined by others whom he knows are dead. He sees again eventhose whose bodies he may have assisted in eating. His total world verysoon comes to have an unseen region which is the abode of ordinarilyinvisible beings having the forms of men, with whom his own dream personcan associate; this unseen sphere is furnished also with ghostlycounterparts of the trees and rocks and waters with which he is familiarwhen he is awake. Before long his soul or ghost or spirit is conceived assomething which possesses two qualities: it can be disassociated from hisbody and enter the spirit-world where it seems to defy all the laws ofwaking life, for with the quickness of thought it visits neighboringislands as readily as it passes to the next hut; and it possessesimmortality, for it is exactly like the persistent spirit-individualitiesof those who have died before him. The other cause for the development ofthe conception of gods and God in the mind of the savage is the fact thatthings have been made which neither he nor any other man can make. He candig a ditch, and make a house, and fashion a canoe, and build ramparts ofearth; but human power has obviously been insufficient to construct riversand mountains and forests and their denizens. Mankind itself has certainlybeen made in some way, for it exists. Because the savage cannot conceiveof things being made excepting as they are made by the human hand, andbecause so much confronts him that is beyond the power of humanconstruction, he comes to postulate the existence of man-like, but greaterthan human, personalities, and as he cannot see them in the light of day, they belong to the spirit-world to which souls go. Imagination sometimesgives human outlines to shadows among the moon-lit trees, so that elvesand pixies, nymphs and fairies, become established in the world as theprimitive man conceives it. Larger tasks are discharged by more importantspirits, and everything natural thus becomes animated by supernaturalbeings. Thor was the god of thunder; Freia the goddess of spring andvernal awakening; Athena inspired the minds of men. Venus and Aphroditeplayed their special parts, also. But such powers as these, established bythe untutored mind, needed to be accounted for, and so in the moreadvanced religions Jove and Jupiter were created as the more ultimatecauses, in response to intellectual demands. By combining all powers intoone, God and Brahma are the results. 

Thus in merest outline the conception of the infinite personality worksout its evolution. At all times, among primitive and higher religions, thepowers are clothed with human forms, and gods are pictured as men endowedwith intellects and passions, and motives of vengeance and benignity. Mancannot shape his postulated deities save in such forms, with the possibleexception of the most philosophical concept of all, Brahma. 

The second fundamental belief, namely, in immortality, owes its origin ingreatest measure to the psychological processes described above. Anotherpotent factor, however, has been the natural desire to continue existencehereafter, usually in order to reap rewards not bestowed here. This desireis implanted by nature through the operation of purely biological factors, and it has the value of an organic instinct. To specify more particularly, nature has placed every organic individual under the necessity of doingits utmost to prolong its own life in the interests of itself, of othersof its tribe, and of its species. Extinction is not faced willingly by ahuman being endowed with full consciousness any more than it is passivelytolerated by a lower animal which instinctively struggles with its foesuntil death. So the desire to continue alive--the "will to live"--is anatural instinct, which combines with the belief in persistent disembodiedspirits and, no doubt, with many other elements, to develop the basicconception of some kind of an immortal existence. 

The third element, human responsibility to the infinite personality, isvariously recorded in lower and higher religions. Its conception growspartly out of the feelings of awe and terror inspired by great works ofnature such as the thunder-storm, the cyclone, and the volcano, while theorderly and regular workings of even everyday nature seem to demonstratethe direct control of the powers who rule man as well. The savage sees hiscrops destroyed by a tempest or drought; he attributes the disaster to theparticular powers concerned with such things whom he must have angeredunwittingly, and whom he must propitiate by sacrifice or penitence. Hisindividual and tribal acts do not always accomplish the desired ends, andagain the laws of infinite and ultimate powers must have been contravened, as he interprets the situation. Therefore his whole religiousconsciousness was exerted in the direction of finding out what was theultimate constitution of nature, with which human activities mustharmonize if they are to be successful. Bound by custom and convention andbiological law, he looks about wonderingly to find the external authorityfor his bonds. To his mind this authority must be the host of spirits andgods who had made him and the things of his world. It is in this way thatso many ethical elements have found places in religious doctrines, to beviewed as absolute rules of conduct coming from outside of nature, and notfrom nature itself, in the way the earlier sections of this chapter haveshown. 

Let us now summarize the results of the foregoing brief survey, conductedby the identical methods employed for the analysis of other bodies offact. We have sought for those characteristics which are common to allreligions of whatever time and place and race. Combined with manysecondary and adventitious elements of other fields of thought and action, such as social, political, ethical, and psychological factors, they haveproved to be the three essential beliefs in God or gods, humanresponsibility, and immortality. As a veritable backbone, they underlieand support the whole body of religious doctrine and organs of thoughtformed about them. We have seen, furthermore, that a natural explanationof the way these elements have originated can be discovered by thecomparative student of religion, who describes also how they havevariously evolved among different peoples. In all of this we have notquestioned at any time the validity or reality of any one of theseconcepts; to ask whether or not they correspond actually to the truth isbeyond our purpose, which is simply and solely to inquire whether eventhese mental conceptions furnish evidence of their evolution in the courseof time. I believe that such evidence is found, and I believe also thatthis discovery must be of the greatest importance to everyone informulating a system of religious belief, but the construction of this isnot the task of science as such. Every individual must work out his ownrelation to the world on the basis of knowledge as complete as he can makeit, but every individual must accomplish this end for himself. Because notwo men can be exactly alike in temperament, intellect, and socialsituation, it is impossible for entire agreement in religious faith toexist. One's outlook upon the whole universe is and must be an individualmatter; science and evolution are of overwhelming value, not by directingthe mind to adopt this or that attitude toward the unseen, but byproviding the seeker after the truth with definite knowledge about thethings of the world, so that his position may be taken on the sound basisof reasonable and common-sensible principles. 

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When we take up science and philosophy, or knowledge as a whole, afterreligion, it may seem that we have reversed the proper sequence. There aremany reasons for following this course, inasmuch as "knowledge" is theall-inclusive category of thought; our world is after all a world ofindividual consciousness and ideas. In dealing with religion, ethics, social organization, and human culture, we have been concerned with theevolution of so many departments of thought and action; and now we are todevelop a final conception of evolution as a universal process in theprogress of all knowledge. 

Let us look back over the history of mathematics. The primitive humanindividual did not need to count. He dealt with things as he met them, andhe disposed of them singly and individually. A squirrel does not count thenuts it gathers; it simply accumulates a store, and it perishes orsurvives according to its instinctive ability to do this. Just so wasprimitive man. The savage, when he organized the first formed tribes, learned to count the days of a journey and the numbers engaged on oppositesides in battle. He employed the "score" of his fingers and toes, and ouruse of this very word is a survival of such a primitive method ofcounting. The abacus of the Roman and Chinese extended the scope of simplemathematical operations as it employed more symbolic elements. With thedevelopment of Arabic notation capable of indefinite expansion, thescience progressed rapidly, and in the course of long time it has becomethe higher calculus of to-day. The conceptions of geometry have likewiseevolved until to-day mathematicians speak of configurated bodies in fourthand higher dimensions of space, which are beyond the powers of perception, even though in a sense they exist conceptually. The behavior ofgeometrical examples in one dimension leads to the characteristics ofbodies in two dimensions. Upon these facts are constructed the laws ofthree-dimensional space which serve to carry mathematical thought to theremoter conceptual spaces of which we have spoken. It may seem that we arerecording only one phase of mental evolution, but in fact we are dealingwith a larger matter, namely, with the progressive evolution of knowledgein the Kantian category of number. 

Natural science began with the savage's rough classification of the thingswith which he dealt in everyday life. As facts accumulated, lifelessobjects were grouped apart from living organisms, and in time two greatdivisions of natural science took form. Physics, chemistry, astronomy, geology, and the like describe the concrete world of matter and energy, while the biological sciences deal with the structure, development, interrelationships, and vital activities of animals and plants. Surelyknowledge has evolved with the advance in all of these subjects fromdecade to decade and from year to year. And just as surely must evolutioncontinue, for the world has not stopped developing, and therefore thegreat principles of science must undergo further changes, even though theyare the best summaries that can be formulated at the present time. 

Philosophy deals with general conceptions of the universe. When we lookback through the ages we find men picturing the world as an aggregate ofdiverse and uncorrelated elements--earth, air, fire, and water. Thesynthesis of facts and the construction of general principles down throughBacon, Newton, and Schopenhauer to modern world conceptions results in theunification of all--"the choir of heaven and furniture of earth. " Thelineal descendant of the long line of ancestral philosophies is the monismwhich sees no difference between the living and lifeless worlds save thatof varying combinations of ultimate elements which are conceived asuniform "mind-stuff" everywhere. Whether or not this universal conceptionof totality is true, remains for the future to show. For us the importanttruth is that here, as in all other departments of knowledge, evolutionproves to be real. 

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In closing the present description of the basis, nature, and scope of thedoctrine of evolution, I find great difficulty in choosing the right wordsfor a concise statement of the larger values and results of thisdepartment of science. So much might be said, and yet it is not fittingfor the investigator to preach unduly. The lessons of the doctrine must bebrought home to each individual through personal conviction. But because Ifirmly believe in the truth of the statement made in the opening pages, namely, that science and its results are of practical human value, it isin a sense my duty as an advocate of evolution to make this plain. 

The method of science is justified of its fruits. At the very beginning welearned how, and how only, sure knowledge can be obtained and how itdiffers from a belief which may or may not correspond with the truth. Based upon facts of smaller or larger groups, scientific laws are so manysummaries of past experience, and they describe in concise conceptualshorthand the manifold happenings of nature. Their difference from beliefinheres in their ability to serve as guides for everyday and futureexperience. This entire volume is a plea for the employment ofcommon-sense as we look upon and interpret the world in which we have ourplaces and in which we must play our rôles. Our search for truth will berewarded in so far as we organize our common-sense observations into clearconceptions of the laws of nature's order. 

The doctrine of evolution enjoins us to learn the rules of the great gameof life which we must play, as science reveals them to us. It is well toremember that a little knowledge is a dangerous thing, but becauseevolution is true always and everywhere, an understanding of its workingsin any department of thought and life clears the vision of other realms ofknowledge and action. Perhaps the greatest lesson is at the same time themost practical one. It is that, however much we may concern ourselves withultimate matters, our immediate duties are here and now, and we cannotescape them without giving up our right to a place in nature. We aretaught by science that we live under the control of certain fundamentalbiological, social, and ethical laws; we might well wish that they wereotherwise, but having recognized them we have no recourse save to obeythem. Evolution as a complete doctrine commands every one to live a lifeof service as full as hereditary endowments and surrounding circumstanceswill permit. Thus we are taught that the immediate problems of life oughtto concern us more than questions as to the ultimate nature of theuniverse and of existence. 

Every one can find something worth while in the lessons of evolution, summarized in the foregoing statements. The atheist, who declines topersonify the ultimate powers of the universe, may, nevertheless, finddirection for his life in the principles brought to light by science. Theagnostic, who doubts the validity of many conventional dicta that may notseem well grounded, can also find something to believe and to obey. Finally, the orthodox theist of whatever creed may discover cogent reasonsfor many of his beliefs like the Golden Rule previously accepted throughconvention; and he must surely welcome the fuller knowledge of their soundbasis in the materials and results of comparative analytical study. Toevery one, then, science and evolution offer valuable principles of life, but great as their service has been, their tasks are not yet completed, and cannot be completed until the end of all knowledge and of time. 

INDEX

Achatinellidæ, 103, 104. 

Activities, instinctive and reflex, 203, 205, 208; of familiar animals, 208, 209; differ from instinct, 209, 210. 

Adaptation, universal relation to environment, 15; principle of, 17; degenerate forms enlarge our conception of, 50; results of larval short cuts in development, 71; 109, 213. 

Africa, fauna of, 103, 164, 165. 

Agassiz, a believer in special creation, 98. 

Ages, Palæozoic, 92; Mesozoic or Secondary, 93, 94; Cenozoic or Tertiary, 93; Coal or Carboniferous, 94. 

Albumen, of egg, 60. 

Alligators, a diverging branch of lizard, 45. 

Amoeba, 21, 51, 69; comparative study of, 203, 205, 231, 247, 251, 254, 257, 258, 259, 265, 266. 

Amphibia, frogs, salamanders, a lower class, 45, 62; order of evolution of, 63; evolved from fishes, 64; most primitive backboned animals, 92; 94, 157; embryos of, 171; 200. 

Anatomy, of mind, 202. 

Ant-bears, 42. 

Anthropoidea, 160. 

Anthropology, 177; methods and results of, 186; types of, 186, 187; comparative, of mind, 211. 

Anthropometry, 177. 

Ants, communities of, 125; mental life of, 207, 208; organizations of, 260, 263, 264. 

Apes, 158; susceptible to training, 210; line from Amoeba, 231. 

Appendix, vermiform, 168. 

Apteryx, wingless bird of New Zealand, 44, 200. 

Arachnida, 49. 

Archæopteryx, a famous "link, " 99. 

Ares, 300. 

Armadillo, 42. 

"Arts of life, " 226-230; dwellings of men, utensils, 227; history of clothing, 228; arts of pleasure, 228-230. 

Atom, carbon, 22; nitrogen, 23; hydrogen, oxygen, 24; chemical, 25. 

Atua, 301. 

Azores, animals of, 103. 

Bacteria, amazing production of, 123; relation of, 127. 

Baldwin, 148. 

Bandicoot, 42. 

Barnacles, really crustacea, 50. 

Bats, 41, 94. 

"Beagle, " 102, 117, 136. 

Bear, 38, 39. 

Bees, mental life of, 207, 208; nervous system of, 232, 256, 257; organizations of, 260, 261, 262; queen, workers, 262, 263. 

Beetles, 67. 

Bernier, 183. 

Bertillon, 183. 

Birds, 44; have they descended from gill-breathing ancestors? 61; evolution of, 63; primitive, 99; embryos of, 171, 200. 

Blastula, 68. 

Blumenbach, 183. 

Bonnet, 70. 

Borneo, 164. 

Brachiopods, 95. 

Brahma, 299, 304. 

Brain, 215, 235-240. 

Brontosaurus, 94. 

Brown-Séquard, 148. 

Buddha, 299. 

Buffon, 114, 135. 

Butterflies, 67, 206, 207, 259. 

Carbohydrate, 23, 24. 

Carbon, atom, 22; 25, 27. 

Carnivora, 35, 37, 38, 39, 40; order of, 157. 

Caterpillar, larva of, 259. 

Cats, Manx, Angora, Persian, 37, 39; domesticated, 137; intelligence of, 208, 209. 

Cattle, products of human selection, 137; resemblance, 157. 

Cebidæ, true monkeys, 160, 161, 162. 

Cells, 19, 20, 21; sex, 144; human, composition of, 156; of ectoderm and endoderm, 255, 256, 257, 258. 

Celts, 218. 

Cercopithecidæ, 160, 162. 

Cerebrum, 215. 

Cetacea, 40. 

Chemical transformation, 17. 

Chick, development of, 60, 61. 

Chimpanzee, 163, 164, 195. 

Chromatin, 143, 144. 

Civilization, a product of evolution, 272. 

Classes, 32. 

Classification, 32. 

Clifford, 238. 

Coccyx, 168. 

Communities, cell, 258; insect, 258, 260-264. 

Comparative anatomy, 35, 37, 39; any form will disclose development, 57; amphibia evolved from fishes, 64; Law of Recapitulation, 66; insects arisen from wormlike ancestors, 67; larvæ of insects, 67; higher animals evolved from two-layered saccular ancestors, 68; 70, 71; supplements comparative embryology, 72; appearance of great classes of vertebrates, 94; proves order of evolution, 163. 

Composition, chemical, 15. 

Compounds, organic, 29. 

Conger-eel, 123, 124, 127. 

Consanguinity, essential likeness, 54. 

Conscience, 287. 

Consciousness, human, 234, 235. 

Crabs, 48, 49, 66; hermit, 66. 

Crustacea, lobsters, crabs, 48, 49; barnacles, 49, 50; 82. 

Cuvier, 158, 78; a believer in special creation, 79. 

Curve of error, 120. 

Cyclones, 85. 

Cyclostomes, 156. 

Daphnia, 205. 

Darwin, Charles, 80, 100, 102, 115, 116, 117; Origin of Species, 116, 124, 130, 132, 135; Erasmus, 135, 136, 138, 142, 143. 

Deer, 42; fossil, of North America, 97, 98. 

Development, 54; a natural process, 56. 

De Vries, 145, 146; his mutation theory, 147, 148. 

Dinosaurs, 94. 

Distribution, geographical, 32. 

Dogs, 38, 39; embryo of, 66; varied forms of, 137; pointer, sheep-dog, instincts of, 208; intelligence of, 208, 209. 

Dubois, 173. 

Ducksbill, or Ornithorhynchus, bottom of mammalian scale, 43. 

Ducksworth, 184. 

Eagle, 44. 

Earthquake, 85. 

Echidna, bottom of mammalian scale, 43. 

Ectoderm, 255. 

Egg, of common fowl, 60; of frog, 68; nuclei contains factors of development, 71; 144, 145; human, 231. 

Eimer, 148. 

Elements, chemical, 15. 

Elephant, 41; place in zoölogical science, 95; 96, 97; age of, 124. 

Embryo, of frog, 58; of chick, 60-62, 63, 64, 65; embryos of carnivora, rodents, hoofed animals alike in earlierdevelopment, 65; of cat, dog, rat, sheep, rabbit, squirrel, cattle, pig, 65; of skate, shark, hammerhead, 66; the human, 168, 170, 171; of birds, reptiles, amphibia, 171; human hemispheres of brain like adult cat or dog, 215. 

Embryology, 32, 33, 34; of no form fully understood, 57; general principles of, 57-67; embryonic agreement, 65; of insects, 67; weight of facts of, 69; comparative, a distinct division of zoölogy, 70, 71; 76, 94, 100; evidence of, 170; of mind, 202, 214; in early stages of human, no nervous system present, 214; development of, 215. 

English sparrow, 123, 127. 

Environment, 111, 112; influences of, 126; determines mode of life of a race, 213. 

Epoch, Glacial, 86; Silurian and Devonian, rich array of types, 93; Cenozoic, 96. 

Erosion, 89. 

Eskimo, picture-writing, 223. 

Ethics, 281; biological, 283; natural, 284; evolution of, 285. 

Ethnology, 177. 

Evolution, the Doctrine of, 1; is it a science, 3; the conception of, 8; organic, 10-12; 31, 32; evidence of, 54, 95; of amphibia, 62; of birds, 63; of protozoa, 69; theory of, supported by palæontology, 76; cosmic, 84; biological evidence of, 91; three important elements of, 109; adaptation, variation and inheritance, 110; mechanical, 109; dynamics of, 109; second element of, 122; human, 150-196; 174; physical, of man, falls into two groups, 153; of human races, 176; racial, 177, 178; mental, 197-240; human faculty as a product of, 212; mental as real as physical, 214; of brain, 214-217; of art of writing, 223; method of mental, 231; social, 241; of societies of insects, 258; human, biological interpretation of, 267-274; of higher human life, 278-311; of ethics, 285; final conception of, 307-311. 

Factors, primary, secondary, 110; three kinds, 111; congenital, 113. 

Falls of St. Anthony, 86. 

Fishes, lowest among common vertebrates, 46; trunk-fish, cow-fish, puff-fish, mouse-fish, flounder, 46; most primitive backboned animals, 92; 94; 157; embryos of, 171. 

Fiske, 139. 

Flies, may, 259. 

Flounder, a variant of the fish theme, 66. 

Fossilization, conditions of, 77-78. 

Fossils, 73-105; remains of, 73; groups, 77; 78, 79; order of succession, 91; oldest rocks devoid of, 92; forms, 99. 

Fowl, game cock, 138; pigeons, 138. 

Frog, 45; eggs of, larva, development of, 58, 59, 60, 68. 

Galapagos Islands, 102, 103, 104. 

Galton, 142, 147; heredity of mental qualities, 232. 

Gametes, 252. 

Gastrula, 68. 

Gemmules, 143. 

Genera, 32. 

Generation, spontaneous, 78. 

Geographical distribution, 32. 

Geological agencies, rain, rivers, glaciers, 88; construction, volcanoes, 88. 

Geology, data of, 83, 84. 

Germ, Bonnet's idea of, 70; cells, 144, 146; plasm, 145, 146. 

Gibbon, 163. 

Gills, 58, 62. 

Gill-slits, bars, clefts, 61, 62, 64; in embryos of lizards, birds, mammals, 69; 171. 

Giraffe, 133. 

Glaciers, alterations made by, 87. 

Goats, 157. 

Gorilla, 163, 165, 195. 

Grand Cañon of the Colorado, 85, 90. 

Gravitation, 155. 

Guinea-pigs, Brown-Séquard's, 148. 

Gulick, 103. 

Haeckel, 63, 71, 184. 

Hæmoglobin, 22. 

Hapalidæ, 160. 

Harvey, 70. 

Hawaiian Islands, 103; snails of, 104. 

Heredity, 142; a real human process, 175; instinct determined by, 206; Anglo-Saxon, 213; of mental qualities, 232. 

Heron, 44. 

Hesperornis, 99. 

Hippopotamus, 42. 

Hominidæ, 160. 

Homo sapiens, 183. 

Hoofed animals, 95, 96, 97. 

Hornets, communities of, larvæ of, 260. 

Horse, 41, 42, 65; place of in zoölogical science, 95, 96; development of, 97; perfection of one type of, 136, 157; 167; intelligence of, 209. 

House-fly, eggs of, 67. 

Human faculty, 212; its three constituents, 212. 

Huxley, 6, 26, 30, 63, 184. 

Hydra, 50, 51, 52, 53, 68, 69; comparative study of, 204, 205, 206; 254; cells of, 255; 256, 257, 258, 261, 262, 263, 265, 266. 

Hydrogen, 25, 27. 

Hyracotherium, 96. 

Ichthyornis, 99. 

Ichthyosaurus, 94. 

Indians, American, pictography of, 223, 224; of Brazil, 227; life of, 272. 

Individual development, a résumé of history of species, 63. 

Inertia, 155. 

Infant, human, activities of, 216. 

Ingestive structures, 17. 

Inheritance, 110, 131; biological laws of, 142; paternal and maternal basis of, 144; 145; Mendelian phenomena of, 146; Galton's Law of, 147; laws of, in mental phenomena, 203; strength of, in mental traits, 232; physical, provides mechanism of intellect, 233. 

Insects, butterflies, beetles, bees, grasshoppers, spiders, scorpions, 49; 66; eggs of common house-fly, 67; 82; nervous mechanism of, 205; communities of, 207, 258-260, 267; nervous system of, 256, 257. 

Instinct, determined by heredity, 206; of higher animals, 208; differs from intelligence in degree, 210. 

Intelligence, 203; in mental life of communal insects, 207. 

Invertebrates, lower animals devoid of backbone, 47; structural plan, 48; branches of, 49; groups, two layer animals, 50; hydra, sea-anemones, soft-polyps, 50; more complicated, 68; palæontological materials, 82; evolution of lowest members, 92. 

Jaguar, 101. 

Jastrow, 294. 

Java, 173. 

Jellyfish, 81. 

Jordan, David Starr, 123. 

Kangaroo, 42. 

Keane, 185. 

Lamarck, 115, 133, 135. 

Lampreys, 156. 

Language, most important single possession of mankind, 218. 

Laplace, 29. 

Larvæ, of lobster, 66; of insects, 67; of ground wasp, 207; of caterpillar, 259; of wasps, 260. 

Lavoisier, 29. 

Law of Recapitulation, 66; stated by Von Baer and Haeckel, 71. 

Lemurs, 158, 160, 161, 195. 

Life, what is it? 27. 

Limestone, 89, 90. 

Links, 99. 

Linnæus, 79, 158, 183. 

Lions, 101; environment of, 112. 

Lizard, nearest form to remote ancestor, 45. 

Lobsters, 66; larvæ of, 66. 

Lyell, 80, 107, 135, 136. 

MacDougal, 148. 

Madagascar, 161. 

Mallock, 295. 

Malthus, 136. 

Mammalia, lower orders of, 42; their own mode of growing up, 64; embryos of, 64; 97; members of class differ, 157, 158; 200; order of mentality, 203. 

Mammals, 40, 43, 157; embryo of, 171. 

Mammoth, 97. 

Marmosets, 161. 

Marquesas, 103. 

Marsupials, 104. 

Mastodon, 97. 

Mechanism, organic, 14; living, 110. 

Melanesia, 103. 

Mendel, Gregor, 145; his law, 146; 147, 148. 

Mentality, human, 233. 

Metazoa, 254. 

Mice, 41, 134; field, 139. 

Miller, 293. 

Mind, anatomy of, 202; human, differs only in degree, 203; 210, 211; embryology of, 214; palæontology of, 217; and matter inseparable, 234-237. 

Missing links, 77. 

Moeritherium, a significant fossil, 97. 

Molecule, protein, 22, 23, 24. 

Mollusks, 81, 82; connecting widely separated ages, 95. 

Monkeys, 158. 

Morgan, Lloyd, 148. 

Morphology, 32. 

Moths, 67. 

Müller, 293. 

Mutation theory, 146. 

Naegeli, 143, 148. 

Natural Selection, doctrine of, 116, 117, 118; the struggle for existence, 124, 125; simply trial and error, 131; Darwin recognized it as incomplete, 142; germ-plasm theory supplements, 145. 

Nebula, gaseous, 84. 

Nervous systems, 201, 202, 205, 206, 211; of worker-bee, 232. 

Niagara, 85, 86, 89. 

Ontogeny, recapitulates phylogeny, 63. 

Orang-outang, 163, 164. 

Orders, 32. 

Organic, 15; systems, 17; transformation, analogies of, 43, a real and natural process, 55, 56, 76; mechanism, alteration of, 55. 

Organisms, living, 14; analysis of, 16; 17, 18, 19, 26, 28, 29, 31, 32; characteristic early stages, 55; are they adapted by circumstances? 109; environment, 111; physical heritage of, 113; variation of, 119; difference, 121; universal conflict of, 127; change, 130; human, 32, 156, 159, 165-171; nervous system of, 201; psychical characteristics of, 202; many-celled, 257. 

Organs, 16, 17, 28; of human body, 156. 

Origin of Species, 136, 149. 

Origination of new parts, 109. 

Osborn, 148. 

Ostrich, 44. 

Over production, 122-124, 129. 

Owls, horned, of Arizona, 45; 139. 

Palæontology, 32, 34, 73, 74, 76; evidence of, not complete, 80, 81; table of facts of, 91; 94; second division of evidence, 95; does it throw light on antiquity of man? 155; of mind, 202, 203, 217. 

Paludina, 95. 

Partulæ, 103. 

Pearson, Karl, 6, 7, 142, 147; heredity of mental qualities, 232. 

Penguin, a counterpart of the seal, 44. 

Peoples, fusion of, 178, 179; Mexicans, 178, 181; Anglo-Saxon, 179; American, 179; Indians, 181, 183, 185, 191, 192; Patagonian, 180, 192; Polynesian, 181, 182, 187; Moor, 181; Zulu, 181, 183; Malay, 181, 183, 190; Mongolian, 181, 186-190; Papuan, 182; Negro, African, Ethiopian, 182, 183, 192-195; Caucasian, 182, 185-189, 195; Veddahs, 182, 188; European, 183; Asiatic, 183; Laplander, 183, 190; Scandinavian types, Norwegians, Swedes, Danes, Germans--north and south--186, 187; types of, 186-196; Persians, 186, eastern, 187; Afghans, Hindus, 186; Welsh, French, Swiss, 187; Russians, 187-190; Poles, Armenians, 187; Mediterranean type, Spaniard, Italian, Greek, Arab, 187; subordinate group, Semitic, Arab, Hebrew, 187; North African, Berber, Hamites, 187; relatives of the Mediterranean, Dravidas, Todas, Veddahs, Ainus, 188; Manchurian, Chukchi, Buryats, Yukaghir, 189; Finlander, Bulgar, Magyar, Korean, Japanese, Gurkhas, Burmans, Annams, Cochin Chinese, Tagals, Bisayans, Hovars, 190; Pueblos, Eskimos, Aztecs, Mayas, Caribs, 191; Yahgan, Alacaluf, 191; Papuan, Australian, 193; Negrito section, Adamans, Kalangs, Sakais Ætas, Bushmen, Hottentots, Akkas, 194. 

Periods, Triassic, Jurassic, 94; Eocene, Miocene, 96. 

Phenacodus, 96. 

Phyla, 32. 

Phylogeny, 63. 

Pictography, 223-226; of Eskimos, of American Indians, 223, 224; of Asia, 224; of Egypt, 224, 225. 

Pig, 42, 157. 

Pithecanthropus, 174. 

Plesiosaurus, 94. 

Polynesia, 103, 104. 

Pouched animals, kangaroo, opossums, 42. 

Primates, name given by Linnæus, 158; eutheria, 158, 159; order of, 160; anthropoids, 161; arrangement of organs, 201. 

Processes, psychological, of higher animals, 208, 209. 

Prosimii, 160. 

Proteins, 22, 23, 24. 

Protoplasm, 22-30; the physical basis of life, 143; 144; human, 156; chemicals that make up, 156. 

Protozoa, 52, 53, 68, 70; relations of, 126. 

Protozoön, 251. 

Psychology, comparative, 198; principle of, 199; descriptive, genetic, 202; terms of, 203; human, 210, 211. 

Pseudopodia, 52. 

Puma, 101. 

Pupa, 259. 

Pygmy, 195, 196, 227. 

Rabbits, 41, 101; domesticated, 137; introduced into Australia, 140. 

Races, human, age of, 178; divisions of, 183-195; character of: status, variations of, 180, 181; color, a criterion of racial relationship, 181, 184; hair, character of, as means of classification, 181, 182; cranium, shape of, as means of identification, nose, jaws, 182. 

Racoon, 38. 

Rats, 41, 134. 

Reason, 203; in mental life of communal insects, 207. 

Religions, 288; Christian, Hebrew, Buddhistic, Tangaroan, 289, 290; Mohammedan, 290, 298; Dervish, Mahdist, 293; linguistic basis of, 293, 294; of savagery, 294, 300, 301; barbarism, civilization, 294; elements of, 295; forms of Christianity, 296; sects, Judaism, 297, 298; Brahmanism, Buddhism, 298, 299; Polytheism, Roman, 300. 

Reptiles, variations about a central theme, 45; lizard, typical, 46; 157; embryos of, 171; 200. 

Retention of better invention, 109. 

Rhinoceros, 41. 

Rivers, Mississippi, 86, 89; Hoang-ho, Ganges, Thames, 87; alterations made by, 87. 

Rocks, crystalline or plutonic: sedimentary, 85; eruptive, 88; new, 59; of Grand Cañon, 90; testimony of, establishes evolution, 100. 

Salamanders, 45, 46. 

Salts, of sodium, chlorine, magnesium, potassium, 24. 

Samoan Islands, 103. 

Sandstone, 90. 

Science, what is it? 5, 6; physiological, 14. 

Sea anemones, 68. 

Sea elephant, 38. 

Seals, 38, 39, 40, 209. 

Selection, natural, doctrine of, 116, 117, 118; struggle for existence, 124, 125; simply trial and error, 131, 136, artificial, 136, 137, 138; laws of, in mental phenomena, 203. 

Sequence, physiological, in training animals, 209; 210. 

Series, sedimentary, 84, 90, 92; crystalline or plutonic, 85; Azoic or Archæan, age of, 92. 

Shale, 89. 

Shark, common, most fundamental form, 46; embryo of, hammerhead; embryos of, 66. 

Sheep, 157. 

Simiidæ, 160, 163. 

Skate, embryos of, 66. 

Snails, 45; shells of, 95; land snails, 103; Hawaiian and Polynesian, 104. 

Society Islands, 103. 

Solar system, origin of, 84. 

Solomon Islands, 103. 

Species, origin of human, 153. 

Spencer, Herbert, 8. 

Squirrels, evolved from terrestrial rodents, 14; 41; flying, true rodents, 41. 

Starch, 24. 

Stephenson, 10. 

Strata, 88, 89; arranged according to ages, 89; 90; time of formation, 92. 

Struggle for existence, 124; intra-specific, 125; three divisions of, 126-129; 139, 174, 175. 

Substances, inorganic, 29. 

Sugar, 23, 24. 

Survival of the fittest, 129. 

Systems, respiratory, excretory, circulatory, 17; organic, reproductive, 18; nervous, 256, 257; blood-vascular, respiratory and excretory, 257; ethical, 286; religious, 288. 

Tadpole, 58, 59, 60; larvæ, 64. 

Tapeworm, a relative of simple worms, 50; 123. 

Tapir, 41; Moeritherium, 97. 

Thorndike, 209; heredity of mental qualities, 232. 

Tidal waves, 85. 

Tigers, 101. 

Tirawa, 301. 

Tissue-cells, 28. 

Torga, 183. 

Tortoise, soft shelled, of the Mississippi, 45. 

Tower, 148. 

Transformation, natural, 170. 

Tribes, 32. 

Tuberculosis, bacillus of, 127. 

Turtles, evolution of, 45. 

Ungulates, 65. 

Uniformitarianism, Lyell's doctrine, 80. 

Urea, 29. 

Ussher, Archbishop, 178. 

Variation, 110; causes of, 111; among individuals, 112, 113; fact of difference, phenomenon of, 114; 115, 118, 119, 121, 129; congenital, 138; human, 174; racial, 177; laws of, in mental phenomena, 203; 232. 

Vertebrata, 43. 

Vertebrates, backboned animals, fishes the lowest order of, 46; principles of relationship, families, tribes, 47; 53-59; great classes originate together, 64; more complicated, 68; skeleton remains of, succeed invertebrates, 92; testimony of the rocks, 93; largest, 94; appearance of great classes of, 94; 95; classes that make up, 156; lower, arrangement of organs, 201; nervous system of, 256, 257. 

Volcanoes, 88. 

Volvox, 252, 254, 259, 265. 

Von Baer, law of recapitulation, 71. 

Vorticella, 251, 252, 265. 

Wagner, 100. 

Wallace, Alfred Russel, 117, 100. 

Walruses, 38. 

Wasps, ground, 207; organizations, of digger, 260; 261. 

Weismann, 71, 72; proved nuclei of egg contains, essential factors, 71, 145, 148. 

Weisner, 143. 

Whales, 40. 

Wilson, 146. 

Woehler, 29. 

Wolf, Tasmanian, a true marsupial, 42. 

Wolff, 70. 

Wolves, 140. 

Wombat, 42. 

Wood-frog, 71. 

Woods, heredity of mental qualities, 232. 

Worms, blindworm of England, 45; 48, 50, 53, 81; nervous mechanism of, 205, 206; nervous system of, 256, 257. 

Zebras, 96, 97, 112. 

Zoölogy, 34, 75, 78; geographical distribution, 100. 

"Zoönomia, " 135. 

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ORATORY. By CHARLES FORSTER SMITH, Ph. D. , Professor of Greek and ClassicalPhilology, University of Wisconsin. 

PHILOSOPHY. By FREDERICK J. E. WOODBRIDGE, Ph. D. , Johnsonian Professor ofPhilosophy, Columbia University. 

HELLENISTIC LITERATURE. By HENRY W. PRESCOTT, Ph. D. , Professor ofClassical Philology, University of Chicago. 

GREEK INFLUENCE ON ROMAN LITERATURE. By GONZALEZ LODGE, Ph. D. , Professorof Latin and Greek, Columbia University. 

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