_NATURE SERIES. _

 THE SCIENTIFIC EVIDENCES

 OF

 ORGANIC EVOLUTION. 

 BY GEORGE J. ROMANES, M. A. , LL. D. , F. R. S. , ZOOLOGICAL SECRETARY OF THE LINNEAN SOCIETY. 

 London: MACMILLAN AND CO. 1882. 

_The Right of Translation and Reproduction is Reserved. _

 LONDON: R. CLAY, SONS, AND TAYLOR, PRINTERS, BREAD STREET HILL. 

PREFACE. 

Several months ago I published in the _Fortnightly Review_ a lecture, which I had previously delivered at the Philosophical Institutions ofEdinburgh and Birmingham, and which bore the above title. The late Mr. Darwin thought well of the epitome of his doctrine which the lecturepresented, and urged me so strongly to republish it in a form whichmight admit of its being "spread broadcast over the land, " that Ipromised him to do so. In fulfilment of this promise, therefore--which Inow regard as more binding than ever--I reproduce the essay in the"Nature Series" with such additions and alterations as appear to me, onsecond thoughts, to be desirable. The only object of the essay is thatwhich is expressed in the opening paragraph. 

 LONDON, _June 1, 1882. _

Since this little Essay was published, it has been suggested to me that, in its mode of presenting the arguments in favour of Evolution, there isa similarity to that which has been adopted by Mr. Herbert Spencer inthe third part of his _Principles of Biology_. I should therefore liketo state, that while such similarity is no doubt in part due to thesimilarity of subject-matter, I think, upon reading again, after aninterval of ten years, his admirable presentation of the evidence it mayalso in part be due to unconscious memory. This applies particularly tothe headings of the chapters, which I find to be almost identical withthose previously used by Mr. Spencer. 

 G. J. R. 

CONTENTS. 

 PAGE

INTRODUCTION 1

I. THE ARGUMENT FROM CLASSIFICATION 17

II. THE ARGUMENT FROM MORPHOLOGY OR STRUCTURE 26

III. THE ARGUMENT FROM GEOLOGY 46

IV. THE ARGUMENT FROM GEOGRAPHICAL DISTRIBUTION 48

V. THE ARGUMENT FROM EMBRYOLOGY 63

VI. ARGUMENTS DRAWN FROM CERTAIN GENERAL CONSIDERATIONS 70

THE SCIENTIFIC EVIDENCES

OF

ORGANIC EVOLUTION. 

Although it is generally recognised that the _Origin of Species_ hasproduced an effect both on the science and the philosophy of our agewhich is without a parallel in the history of thought, admirers of Mr. Darwin's genius are frequently surprised at the ignorance of his workwhich is displayed by many persons who can scarcely be said to belong tothe uncultured classes. The reason of this ignorance is no doubt partlydue to the busy life which many of our bread-winners are constrained tolive; but it is also, I think, partly due to mere indolence. There arethousands of educated persons who, on coming home from their daily work, prefer reading literature of a less scientific character than that whichis supplied by Mr. Darwin's works; and therefore it is that such personsfeel these works to belong to a category of books which is to them avery large one--the books, namely, which never are, but always to be, read. Under these circumstances I have thought it desirable to supply ashort digest of the _Origin of Species_, which any man, of however busya life, or of however indolent a disposition, may find both time andenergy to follow. 

With the general aim of the present abstract being thus understood, Ishall start at the beginning of my subject by very briefly describingthe theory of natural selection. It is a matter of observable fact thatall plants and animals are perpetually engaged in what Mr. Darwin callsa "struggle for existence. " That is to say, in every generation of everyspecies a great many more individuals are born than can possiblysurvive; so that there is in consequence a perpetual battle for lifegoing on among all the constituent individuals of any given generation. Now, in this struggle for existence, which individuals will bevictorious and live? Assuredly those which are best fitted to live: theweakest and the least fitted to live will succumb and die, while thestrongest and the best fitted to live will be triumphant and survive. Now it is this "survival of the fittest" that Mr. Darwin calls "naturalselection. " Nature, so to speak, _selects_ the best individuals out ofeach generation to live. And not only so, but as these favouredindividuals transmit their favourable qualities to their offspring, according to the fixed laws of heredity, it follows that theindividuals composing each successive generation have a general tendencyto be better suited to their surroundings than were their forefathers. And this follows, not merely because in every generation it is only theflower of the race that is allowed to breed, but also because if in anygeneration some new and beneficial qualities happen to appear as slightvariations from the ancestral type, these will be seized upon by naturalselection and added, by transmission in subsequent generations, to thepreviously existing type. Thus the best idea of the whole process willbe gained by comparing it with the closely analogous process wherebygardeners and cattlebreeders create their wonderful productions; forjust as these men, by always selecting their best individuals to breedfrom, slowly but continuously improve their stock, so Nature, by asimilar process of selection, slowly but continuously makes the variousspecies of plants and animals better and better suited to the externalconditions of their life. 

Now, if this process of continuously adapting organisms to theirenvironment takes place in nature at all, there is no reason why weshould set any limits on the extent to which it is able to go up to thepoint at which a complete and perfect adaptation is achieved. Thereforewe might suppose that all species would attain to this condition ofperfect adjustment to their environment, and there remain fixed. And soundoubtedly they would, if the environment were itself unchanging. Butforasmuch as the environment--or the sum total of the externalconditions of life--of almost every organic type alters more or lessfrom century to century (whether from astronomical, geological, andgeographical changes, or from the immigrations and emigrations of otherspecies living on contiguous geographical areas), it follows that theprocess of natural selection need never reach a terminal phase. Andforasmuch as natural selection may thus continue, _ad infinitum_, slowlyto alter a specific type in adaptation to a gradually changingenvironment, if in any case the alteration thus effected is sufficientin amount to lead naturalists to denote the specific type by somedifferent name, it follows that natural selection has transmuted onespecific type into another. And so the process is supposed to go on overall the countless species of plants and animals simultaneously--theworld of organic types being thus regarded as in a state of perpetual, though gradual, flux. 

Such, then, is the theory of natural selection, or survival of thefittest; and the first thing we have to notice with regard to it is, that it offers to our acceptance a scientific explanation of thenumberless cases of apparent design which we everywhere meet with inorganic nature. For all such cases of apparent design consist only inthe _adaptation_ which is shown by organisms to their environment, andit is obvious that the facts are covered by the theory of naturalselection no less completely than they are covered by the theory ofintelligent design. Perhaps it may be answered, --"The fact that theseinnumerable cases of adaptation may be accounted for by naturalselection is no proof that they are not really due to intelligentdesign. " And, in truth, this is an objection which is often urged byminds--even highly cultured minds--which have not been accustomed toscientific modes of thought. I have heard an eminent professor tell hisclass that the many instances of adaptation which Mr. Darwin discoveredand described as occurring in orchids, seemed to him to tell more infavour of contrivance than in favour of natural causes; and anothereminent professor once wrote to me that although he had read the_Origin of Species_ with care, he could see in it no evidence of naturalselection which might not equally well be adduced in favour ofintelligent design. But here we meet with a radical misconception of thewhole logical attitude of science. For, be it observed, the exception_in limine_ to the evidence which we are about to consider, does notquestion that natural selection _may_ not be able to do all that Mr. Darwin ascribes to it: it merely objects to his interpretation of thefacts, because it maintains that these facts might _equally well_ beascribed to intelligent design. And so undoubtedly they might, if wewere all childish enough to rush into a supernatural explanationwhenever a natural explanation is found sufficient to account for thefacts. Once admit the glaringly illogical principle that we may assumethe operation of higher causes where the operation of lower ones issufficient to explain the observed phenomena, and all our science andall our philosophy are scattered to the winds. For the law of logicwhich Sir William Hamilton called the law of parsimony--or the law whichforbids us to assume the operation of higher causes when lower ones arefound sufficient to explain the observed effects--this law constitutesthe only logical barrier between science and superstition. For it ismanifest that it is always possible to give a hypothetical explanationof any phenomenon whatever, by referring it immediately to theintelligence of some supernatural agent; so that the only differencebetween the logic of science and the logic of superstition consists inscience recognising a validity in the law of parsimony whichsuperstition disregards. Therefore I have no hesitation in saying thatthis way of looking at the evidence in favour of natural selection isnot a scientific or a reasonable way of looking at it, but a purelysuperstitious way. Let us take, for instance, as an illustration, aperfectly parallel case. When Kepler was unable to explain by any knowncauses the paths described by the planets, he resorted to a supernaturalexplanation, and supposed that every planet was guided in its movementsby some presiding angel. But when Newton supplied a beautifully simplephysical explanation, all persons with a scientific habit of mind atonce abandoned the metaphysical explanation. Now, to be consistent, theabove-mentioned professors, and all who think with them, ought still toadhere to Kepler's hypothesis in preference to Newton's explanation;for, excepting the law of parsimony, there is certainly no other logicalobjection to the statement that the movements of the planets afford asgood evidence of the influence of guiding angels as they do of theinfluence of gravitation. 

So much, then, for the absurdly illogical position that, granting theevidence in favour of natural selection and supernatural design to beequal and parallel, we should hesitate for one moment in our choice. But, of course, if the evidence is supposed _not_ to be equal andparallel--_i. E. _, if it is supposed that the theory of natural relationis not so competent a theory to explain the facts of adaptation as isthat of intelligent design--then the objection is no longer the one thatwe are considering. It is quite another objection, and one which is not_primâ facie_ absurd; it requires to be met by examining how far thetheory of natural selection _is_ able to explain the facts. Let us statethe problem clearly. 

Innumerable cases of adaptation of organisms to their environment arethe observed facts for which an explanation is required. To supply thisexplanation two, and only two, hypotheses are in the field. Of thesetwo hypotheses one is, intelligent design manifested in creation; andthe other is, natural selection manifested during the countless ages ofthe past. Now it would be proof positive of intelligent design if itcould be shown that all species of plants and animals were_created_--that is _suddenly_ introduced into the complex conditions oftheir life; for it is quite inconceivable that any cause other thanintelligence could be competent to adapt an organism to its environment_suddenly_. On the other hand, it would be proof presumptive of naturalselection if it could be shown that one species becomes slowlytransmuted into another--_i. E. _, that one set of adaptations may begradually transformed into another set of adaptations according aschanging circumstances require. This would be proof presumptive ofnatural selection, because it would then become amply probable thatnatural selection might have brought about many, or most, of the casesof adaptations which we see; and if so, the law of parsimony excludesthe rival hypothesis of intelligent design. Thus the whole question asbetween natural selection and supernatural design resolves itself intothis--Were all the species of plants and animals separately created, orwere they slowly evolved? For if they were specially created, theevidence of supernatural design remains unrefuted and irrefutable;whereas if they were slowly evolved, that evidence has been utterly andfor ever destroyed. The doctrine of natural selection therefore dependsfor its validity on the doctrine of organic evolution; for if once thefact of organic evolution were established, no one would dispute thatmuch of the adaptation was probably effected by natural selection. _How_much we cannot say--probably never shall be able to say; for even Mr. Darwin himself does not doubt that other causes besides that of naturalselection have assisted in the modifying of specific types. For thesake of simplicity, however, I shall not go into this subject; but shallalways speak of natural selection as the only cause of organicevolution. Let us, then, weigh the evidence in favour of organicevolution. If we find it wanting, we need have no complaints to make ofnatural theologians of to-day; but if we find it to be full measure, shaken together and running over, we ought to maintain that naturaltheologians can no longer adhere to the arguments of such writers asPaley, Bell, and Chalmers, without deliberately violating the onlylogical principle which separates science from fetishism. 

To avoid misapprehension, however, I may here add that while Mr. Darwin's theory is thus in plain and direct contradiction to the theoryof design, or system of teleology, as presented by the school of writerswhich I have named, I hold that Mr. Darwin's theory has no point oflogical contact with the theory of design in the larger sense, thatbehind all secondary causes of a physical kind, there is a primary causeof a mental kind. Therefore throughout this essay I refer to design inthe sense understood by the narrower forms of teleology, or as an_immediate_ cause of the observed phenomena. Whether or not there is an_ultimate_ cause of a psychical kind pervading all nature, a _causacausarum_ which is the final _raison d'être_ of the cosmos, this isanother question which, as I have said, I take to present no point oflogical contact with Mr. Darwin's theory, or, I may add, with any of themethods and results of natural science. The only position, therefore, which I here desire to render plain is that, if the doctrine ofevolution is seen to be established by sufficient evidence, andtherefore the causes which it sets forth are recognised as adequate tofurnish a scientific explanation of the results observed, then thefacts of organic nature necessarily fall into the same logical category, with reference to any question of design, as that of all or any otherseries of facts in the physical universe. 

This being understood, I shall now proceed to render an epitome of theevidence in favour of organic evolution, and I shall do so byclassifying the arguments in a way tending to show their distinct orindependent character, and therefore calculated to display theadditional force which they acquire from their cumulative nature. 

I. 

THE ARGUMENT FROM CLASSIFICATION. 

I shall first take the argument from classification. Naturalists findthat all species of plants and animals present among themselvesstructural affinities. According as these structural affinities are moreor less pronounced, the various species are classified under genera, orders, families, classes, sub-kingdoms, and kingdoms. Now in such aclassification it is found impossible to place all the species in alinear series, according to the grade of their organization. Forinstance, we cannot say that a wolf is more highly organized than a foxor a jackal; we can only say that the specific points wherein itdiffers from these animals are without significance as proving the onetype to be more highly organized than the others. But of course in manycases, and especially in the cases of the larger divisions, it is oftenpossible to say--The members in this division are more highly organizedthan are the members in that division. Our system of classificationtherefore may be likened to a tree, in which a short trunk may be takento represent the lowest organisms which cannot properly be termed eitherplants or animals. This short trunk soon separates into two largetrunks, one of which represents the vegetable and the other the animalkingdom. Each of these trunks then gives off large branches signifyingclasses, and these give off smaller, but more numerous branches, signifying families, which ramify again into orders, genera, and finallyinto the leaves, which may be taken to represent species. Now, in sucha representative tree of life, the height of any branch from the groundmay be taken to indicate the grade of organization which the leaves, orspecies, present; so that, if we picture to ourselves such a tree, wewill understand that while there is a general advance of organizationfrom below upwards, there are numberless slight variations in thisrespect between leaves growing even on the same branch; but in a stillgreater number of cases, leaves growing on the same branch are growingon the same level--that is, although they represent different species, it cannot be said that one is more highly organized than the other. Now, this tree-like arrangement of specific organisms in nature is anarrangement for which Mr. Darwin is not responsible. I mean that theframing of this natural classification has been the work of naturalistsfor centuries past; and although they did not know what they were doing, it is now evident to evolutionists that they were tracing the lines ofgenetic relationship. For, be it observed, a scientific or naturalclassification differs very much from a popular or hap-hazardclassification, and the difference consists in this, that while apopular classification is framed with exclusive reference to theexternal appearance of organisms, a scientific classification is madewith reference to the whole structure. A whale, for instance, is oftenthought to be a fish, because it resembles a fish in form and habits;whereas dissection shows that it is beyond all comparison more unlike afish than it is like a horse or a man. This is, of course, an extremecase; but it was cases such as this that first led naturalists to seethat there are resemblances between organisms much more deep andimportant than appear upon the surface; and consequently, that if anatural classification was possible at all, it must be made withreference to these deeper resemblances. Of course, it took time toperceive this distinction between fundamental and superficialresemblances. I remember once reading a very comical disquisition in oneof Buffon's works on the question as to whether or not a crocodile wasto be classified as an insect; and the instructive feature in thedisquisition was this, that although a crocodile differs from an insectas regards every conceivable particular of its internal anatomy, noallusion at all is made to this fact, while the whole discussion is madeto turn on the hardness of the external casing of a crocodile resemblingthe hardness of the external casing of a beetle; and when at last Buffondecides that, on the whole, a crocodile had better not be classified asan insect, the only reason given is, that as a crocodile is so verylarge an animal, it would make "altogether too terrible an insect. "

But now, when at last it came to be recognised that internal anatomyrather than external appearance was to be taken as a guide toclassification, the question was, What features in the internal anatomyare to take precedence over the other features? And this question it wasnot hard to answer. A porpoise, for instance, has a large number ofteeth, and in this feature resembles most fish, while it differs fromall mammals. But it also gives suck to its young, and in this feature itdiffers from all fish, while it resembles all mammals. Now, looking atthose two features alone, should we say that a porpoise ought to beclassed as a fish or as a mammal? Assuredly as a mammal, and for thisreason: The number of teeth is a very variable feature both in fish andin mammals, whereas the giving of suck is an invariable feature amongmammals, and occurs nowhere else in the animal kingdom. This, of course, is purposely chosen as a very simple illustration; but it exemplifiesthe general fact that the guiding principle of scientificclassification is the comparing of organism with organism, with the viewof seeing which of the constituent organs are of the most invariableoccurrence, and therefore of the most typical signification. 

Now, since the days of Linnæus this principle has been carefullyfollowed, and it is by its aid that the tree-like system ofclassification has been established. No one, even long before Darwin'sdays, ever dreamed of doubting that this system is in reality, what italways has been in name, a _natural_ system. What, then, is theinference we are to draw from it? An evolutionist answers, that it isjust such a system as his theory of descent would lead him to expect asa natural system. For this tree-like system is as clear an expression asanything could be of the fact that all species are bound together by theties of genetic relationship. If all species were separately created, itis almost incredible that we should everywhere observe this progressiveshading off of characters common to larger groups, into more and morespecialized characters distinctive only of smaller and smaller groups. At any rate, to say the least, the law of parsimony forbids us toascribe such effects to a supernatural cause, acting in so whimsical amanner, when the effects are precisely what we should expect to followfrom the action of a highly probable natural cause. The classificationof animal forms, indeed, as Darwin, Lyell, and Hæckel have pointed out, strongly resembles the classification of languages. In the case oflanguages, as in the case of species, we have genetic affinitiesstrongly marked; so that it is possible to some extent to construct alanguage-tree, the branches of which shall indicate, in a diagrammaticform, the progressive divergence of a large group of languages from acommon stock. For instance, Latin may be regarded as a fossil language, which has given rise, by way of genetic descent, to a group of livinglanguages--Italian, Spanish, French, and, to a large extent, English. Now what should we think of a philologist who should maintain thatEnglish, French, Spanish, and Italian were all specially createdlanguages--or languages separately constructed by the Deity, and by asmany separate acts of inspiration communicated to these severalnations--and that their resemblance to the fossil form, Latin, is to beattributed to special design? Yet the evidence of the naturaltransmutation of species, is, in one respect, much stronger than that ofthe natural transmutation of languages--in respect, namely, of therebeing a vastly greater number of cases all bearing testimony to the factof genetic relationship. 

II. 

THE ARGUMENT FROM MORPHOLOGY OR STRUCTURE. 

I now pass to another line of argument. The theory of evolution bynatural selection supposes that hereditary characters admit of beingslowly modified wherever their modification will render an organismbetter suited to a change in its conditions of life. Let us, then, observe the evidence we have of such adaptive modifications ofstructure, in cases where the need of such modification is apparent. Forthe sake of clearness, I shall begin by again taking the case of thewhales and porpoises. The theory of evolution infers, from the wholestructure of these animals, that their progenitors must have beenterrestrial quadrupeds of some kind, which became aquatic in theirhabits. Now the change in the conditions of their life thus broughtabout would render desirable great modifications of structure. Thesechanges would, in the first instance, begin to affect the leasttypical--that is, the least strongly inherited structures--such as theskin, claws, and teeth, &c. But as time went on, the adaptation wouldbegin to extend to the more typical structures, until the shape of thebody began to be affected by the bones and muscles required forterrestrial locomotion becoming better adapted for aquatic locomotion, and the whole outline of the animal more fish-like in shape. This is thestage which we actually observe in the seals, where the hind legs, although retaining all their typical bones, have become shortened upalmost to rudiments, and directed backwards, so as to be of no use forwalking, but serving to complete the fish-like taper of the body. But inthe whales the modification has gone even further than this, so that thehind legs have ceased to be apparent externally, and are onlyrepresented internally by remnants so rudimentary that it is impossibleto make out with certainty the homologies of the bones; moreover, thehead and the whole body have become completely fish-like in shape. Butprofound as these changes are, they only affect those parts of theorganism which it was for the benefit of the organism to have altered, so that it might be adapted to an aquatic mode of existence. Thus thearm, which is used as a fin, still retains the bones of the shoulder, fore-arm, wrist, and fingers, although they are all inclosed in afin-shaped sack, so as to render them quite useless for any otherpurpose than swimming. Similarly, the head, although it so closelyresembles the head of a fish in shape, still retains the bones of themammalian skull in their proper anatomical relation to one another, butmodified in form so as to offer the least possible amount of resistanceto the water. In short it may be said that all the modifications havebeen effected with the least possible divergence from the typicalmammalian type, which is compatible with securing so perfect anadaptation to a purely aquatic mode of life. 

Now I have chosen the case of the whale and porpoise group because theyoffer so extreme an example of profound modification of structure inadaptation to changed conditions of life. But the same thing may be seenin hundreds and hundreds of other cases. For instance, to confine ourattention to the arm, not only is the limb modified in the whale forswimming, but in another mammal--the bat--it is modified for flying, byhaving the fingers enormously elongated and overspread with a membranousweb. In birds, again, the arm is modified for flight in a whollydifferent way--the fingers here being very short and all run together, and the chief expanse of the wing being composed of the shoulder andfore-arm. In frogs and lizards, again, we find hands more like our own;but in an extinct species of flying reptile the modification wasextreme, the wing having been formed by a prodigious elongation of thefifth finger, and a membrane spread over it and the rest of the hand. Lastly, in serpents the hand and arm have disappeared altogether. 

Thus, even if we confine our attention to a single structure, howwonderful are the modifications which it is seen to undergo, althoughnever losing its typical character! How are we to explain this? Bydesign manifested in special creation, or by descent with adaptivemodification? If it is said by design manifested in special creation, wemust suppose that the Deity formed an archetypal plan of certainstructures, and that He determined to adhere to this plan through allthe modifications which those structures exhibit. Now the difficultiesin the way of this supposition are prodigious, if not quiteinsurmountable. In the first place, why is it that some structures areselected as typical and not others? Why should the vertebral skeleton, for instance, be tortured into every conceivable variety of modificationin order to make it serviceable for as great a variety of functions;while another structure, such as the eye, is made in differentsub-kingdoms on fundamentally different plans, notwithstanding that ithas throughout to perform the same function? Will any one have thehardihood to assert that in the case of the skeleton the Deity hasendeavoured to show His _ingenuity_ by the manifold functions to whichHe has made the same structure subservient; while in the case of theeye He has endeavoured to show his _resources_ by the manifoldstructures which He has to subserve the same function? If so, it appearsto me a most unfortunate circumstance, that throughout both thevegetable and animal kingdoms, all cases which can be pointed to asshowing ingenious adaptation of the same typical structure to theperformance of widely different functions, are cases which come withinthe limits of the same natural group of plants and animals, andtherefore admit of being equally well explained by descent from a commonancestry; while all cases of widely different structures performing thesame function are to be found in different groups of plants or animals, and are therefore suggestive of independent variations arising in thedifferent lines of hereditary descent. 

To take a specific illustration. The octopus or devil-fish belongs to awidely different class of animals from a true fish, and yet its eye, ingeneral appearance, looks wonderfully like the eye of a true fish. Now, Mr. Mivart pointed to this fact as a great difficulty in the way of thetheory of evolution by natural selection, because it must clearly be amost improbable thing that so complicated a structure as the eye of afish should happen to be arrived at through each of two totallydifferent lines of descent. And this difficulty would, indeed, be almostfatal to the theory of evolution by natural selection, if the apparentsimilarity were a real one. Unfortunately for the objection, however, Mr. Darwin clearly showed, in his reply, that in no one anatomicalfeature of typical importance do the two structures resemble oneanother; so that in point of fact the two organs do not resemble oneanother in any particular further than it is necessary that they should, if both are to serve as organs of sight. But now, suppose that this hadnot been the case, and that the two structures, besides presenting thenecessary superficial resemblance, had also presented an anatomicalresemblance; with what tremendous force might it have then beenurged, --"Your hypothesis of hereditary descent with progressivemodification being here excluded, by the fact that the animals comparedbelong to two widely different branches of the tree of life, how are weto explain the identity of type manifested by these two complicatedorgans of vision? The only hypothesis open to us is intelligentadherence to an ideal type. " But as this cannot now be urged in any onecase throughout the whole organic world, we may, on the other hand, present it as a most significant fact, that, while within the limits ofthe same large branch of the tree of life we constantly find the sametypical structures modified so as to perform very different functions, we never find any vestige of these particular types of structure inother large divisions of that tree. In other words, we never findtypical structures appearing except in cases where their presence may beexplained by the hypothesis of hereditary descent; while in thousands ofsuch cases we find these structures undergoing every conceivable varietyof adaptive modification. 

Consequently, special creationists must fall back upon another positionand say, --"Well, but it may have pleased the Deity to form a certainnumber of ideal types, and never to allow the structures occurring in theone type to appear in any of the others. " I answer, undoubtedly it mayhave done so; but if it did, it is a most unfortunate thing for yourtheory; for the fact implies that the Deity has planned His types insuch a way as to suggest the counter-theory of descent. For instance, itwould seem to me a most capricious thing in the Deity to make the eyesof an innumerable number of fish on exactly the same ideal type, andthen to make the eye of the octopus so exactly like these other eyes insuperficial appearance as to deceive so accomplished a naturalist as Mr. Mivart, and yet to take scrupulous care that in no one ideal particularshould this solitary eye resemble all the host of other eyes. However, adopting for the sake of argument this gigantic assumption, let ussuppose that God laid down these arbitrary rules for His own guidance increation, and let us see to what it leads. If, as is assumed, the Deityformed a certain number of ideal types, and determined that on noaccount should He allow any part of one type to appear in any part ofanother, surely we should expect that within the limits of the same typethe same typical structures should always be present. Thus, rememberwhat desperate efforts, so to speak, there have been made to maintainthe uniformity of type in the case of the arm, and should we not expectthat in other and similar cases similar efforts should be made? Yet werepeatedly find that this is not the case. Even in the whale, as we haveseen, the hind-limbs are not apparent; and it is impossible to see inwhat respect the hind-limbs are of any less ideal value than thefore-limbs, which, as we have also seen, are so carefully preserved innearly all vertebrated animals except the snakes, where again we meet inthis particular with a sudden and sublime indifference to themaintenance of a typical structure. Now I say that if the theory ofideal types is true, we have in these facts evidence of the mostunreasonable inconsistency; for no explanation can be assigned why somuch care should have been taken to maintain the type in some cases, while such reckless indifference should have been displayed towardsmaintaining it in others. But the theory of descent with continuedadaptive modification fully explains all the known cases; for in everycase the degree of divergence from the typical structure which anorganism presents corresponds with the length of time during which thedivergence has been going on. Thus we scarcely ever meet with any greatdeparture from the typical form--such as the absence of limbs--withoutsome of the other organs in the body being so far modified as ofthemselves to indicate, on the supposition of descent with modification, that the animal or plant must have been subject to the modifyinginfluences for a long series of generations. And this combined testimonyof a number of organs in the same organism is what the theory of descentwould lead us to expect, while the rival theory of design can offer noexplanation of the fact, that when one organ shows a conspicuousdeparture from the supposed ideal type, some of the other organs in thesame organism should tend to keep it company by doing likewise. [1]

[1] This consideration is, I believe, original. Several exceptions toits validity might be adduced, but as a general principle it certainlyholds good. 

I will now briefly touch on another branch of the argument frommorphology--the argument, namely, from rudimentary structures. 

Throughout the animal and vegetable kingdoms we constantly meet withorgans which are the dwarfed and useless representatives of organswhich, in other and allied kinds of animals and plants, are of largesize and functional utility. Thus, for instance, the unborn whale hasrudimentary teeth, which are never destined to cut the gums; and we allknow that our own rudimentary tail is of no practical service. Now, rudimentary organs of this kind are of such common occurrence, thatalmost every species presents one or more of them. The question, therefore, is--How are they to be accounted for? Of course the theory ofdescent with adaptive modification has a delightfully simple answer tosupply, viz. , that when, from changed conditions of life, an organ whichwas previously useful becomes useless, natural selection, combined withdisuse and so-called economy of growth, will cause it to dwindle till itbecomes a rudiment. On the other hand, the theory of special creationcan only maintain that these rudiments are formed for the sake ofadhering to an ideal type. Now, here again the former theory istriumphant over the latter; for, without waiting to dispute the wisdomof making dwarfed and useless structures merely for the whimsical motiveassigned, surely if so extraordinary a method is adopted in so manycases, we should expect that in consistency it would be adopted in allcases. This reasonable expectation, however, is far from beingrealised. In numberless cases, such as that of the fore-limbs ofserpents, no vestige of a rudiment is present. But the vacillatingpolicy in the matter of rudiments does not end here; for it is shown, ifpossible, in a more aggravated form where, within the limits of the samenatural group of organisms, a rudiment is sometimes present andsometimes absent. For instance, to take again the case of limbs, innearly all the numerous species of snakes there are no vestiges of limbsat all; but in the python we find beneath the skin very tiny rudimentsof the hind limbs. Now, is it a worthy conception of Deity that, whileneglecting to maintain His unity of ideal in the case of nearly all thenumerous species of snakes, He should have added a tiny rudiment in thecase of the python, and even in that case should have maintained Hisideal type very inefficiently, inasmuch as only two limbs instead offour are represented? Or, again, take the case of the limb in otheranimals. Five toes seem to constitute the ideal type, notwithstandingthat in numberless cases this ideal fails in its structural expression. Now, in the case of the horse, one toe appears to have become developedat the expense of the others; for the so-called knee of the horse isreally the wrist or ankle, and the so-called shank the middle toe orfinger very much enlarged. But on each side of this enlarged toe thereare, beneath the skin, rudimentary bones of two other toes--theso-called splint-bones. So far good, but three toes are not five; sospecial creationists must suppose that while in this case the Deity has, so to speak, struggled to maintain the uniformity of His ideal, Hisefforts have nevertheless conspicuously failed. How much less strainedis the scientific interpretation; for I may mention that in thisparticular case, besides the general inference that rudiments point usto a remote ancestry, we have direct palæontological evidence that therehave been a whole series of extinct horse-like animals, that began lowdown in the geological strata with five toes (on the fore-feet, onebeing rudimentary), which afterwards became reduced to four and then tothree; after which the two lateral toes began to become rudimentary, aswe now see them in oxen, and later on still more so. Lastly, as we comenearer to recent times, we find fossils of the existing horse, with thelateral toes shortened up to the condition of splint-bones. Thus we havesome half-dozen different genera of horse, all standing in a linearseries in time as in structure, between the earliest representative withthe typical number of five toes, and the existing very aberrant formwith only one toe. 

It is sometimes said that a striking corroboration of a scientifictheory is furnished when it enables us correctly to _predict_discoveries. Such a corroboration is afforded in this instance; forProfessor Huxley, speaking in 1870, said, "If the expectation raised bythe splints of the horses that, in some ancestor of the horses, thesesplints would be found to be complete digits, has been verified, we arefurnished with very strong reasons for looking for a no less completeverification that the three-toed _plagiolophus_-like 'avus' of the horsemust have had a five-toed 'atavus' at some earlier period. No suchfive-toed 'atavus, ' however, has yet made its appearance. " But sincethen the "atavus" has made its appearance, if not with five completetoes, at least with four complete and one rudimentary; and any day wemay hear that Professor Marsh has found in still earlier strata a moreprimitive form with all five toes complete. 

I have no space to go into the evidence of similar "missing links" whichhave been recently supplied by palæontological researches in the case ofseveral other groups of animals; but their consideration seems to mequite to justify a more recent utterance of Professor Huxley, who, in1878, wrote in the _Encyclopædia Britannica:_ "On the evidence ofpalæontology, the evolution of many existing forms of animal life fromtheir predecessors is no longer an hypothesis, but an historical fact;it is only the nature of the physiological factors to which thatevolution is due which is still open to discussion. "

III. 

THE ARGUMENT FROM GEOLOGY. 

But this allusion to fossils leads me to the next division of mysubject--the argument from geology. It is not, however, necessary to saymuch on this head, for the simple reason that the whole body ofgeological evidence is for the most part of one kind, which although ofa very massive, is of a very simple character. That is to say, apartfrom the increasingly numerous cases, such as the one just mentioned, which geology supplies of extinct "intermediate links" between_particular_ species now living, the great weight of the geologicalevidence consists in the _general_ fact, that of all the thousands ofspecific forms of life which palæontology reveals to us as having livedon this planet in times past, there is no instance of a highly organisedform occurring low down in the geological series. [1] On the contrary, there is the best evidence to show that since the first dawn of life inthe occurrence of the simplest organisms, until the meridian splendourof life as now we see it, gradual advance from the general to thespecial--from the low to the high, from the few and simple to the manyand complex--has been the law of organic nature. And of course it isneedless to say that this is precisely the law to which the process ofdescent with adaptive modification would of necessity give rise. 

[1] Some of the lower vertebrata (Elasmobranch and Ganoid fishes) occur, indeed, in early strata (upper Silurian); but still far from theearliest in which some of the invertebrata are found. The generalstatement in the text applies chiefly to the more highly organised formsof the vertebrate series. 

IV. 

THE ARGUMENT FROM GEOGRAPHICAL DISTRIBUTION. 

The argument from geology is the argument from the distribution ofspecies in time. I will, therefore, next take the argument from thedistribution of species in space--that is, the present geographicaldistribution of plants and animals. It is easy to see that this must bea most important argument, if we reflect that as the theory of descentwith adaptive modification implies slow and gradual change of onespecies into another, and a still more slow and gradual change of onegenus, family, or order into another genus, family, or order, we shouldexpect on this theory that the organic types living on any givengeographical area should be found to resemble or to differ from organictypes living elsewhere, according as the area is connected ordisconnected with other geographical areas. And this we find to be thecase, as abundant evidence proves. For, to quote from Mr. Darwin, "barriers of any kind, or obstacles to free migration, are related in aclose and important manner to the differences between the productions ofvarious regions. We see this in the great difference in nearly all theterrestrial productions of the New and Old Worlds, excepting in thenorthern parts, where the land almost joins.... We see the same fact inthe great difference between the inhabitants of Australia, Africa, andSouth America under the same latitude, for these countries are almost asmuch isolated from one another as possible. On each continent, also, wesee the same fact; for on the opposite sides of lofty and continuousmountain ranges, of great deserts, and even of large rivers, we finddifferent productions; though as mountain chains, deserts, &c. , are notso impassable, or likely to have endured so long as the ocean-separatedcontinents, the differences are very inferior in degree to thosecharacteristic of distinct continents. " That is to say, the differencesare usually confined to species and genera, whereas in the case ofcontinents the differences extend to orders. Similarly in marineproductions the same laws prevail--the species on the different sides ofthe American continent, for instance, being very distinct. Now, this lawcannot be explained by any reasonable argument from design. 

And still stronger does the present argument become when we look to thefossil species contained on different continents; for these fossilspecies invariably present the same characteristic stamp as the livingspecies now flourishing on the same continents. Thus, in America we findfossils all presenting the characteristically American types of animals, in Australia the characteristically Australian types, and so on. That isto say, on every continent the dead species resemble the living species, as we may expect that they should, if they are all bound together by theties of hereditary descent; while, if different continents are compared, the fossil species are as unlike as we have seen the living species tobe. 

Turning next to the case of oceanic islands, situated at some distancefrom a continent. In these cases the plants and animals found on theisland, though very often differing from all other plants and animals inthe world as regards their specific type, nevertheless in generic typeresemble the plants and animals of the neighbouring continent. Theinference clearly is, that the island has been stocked from thecontinent with these types--either by winds, currents, floating trees, or numerous other modes of transport--and that, after settling in theisland, some of these imported types have retained their specificcharacters, while others have varied so as to become specific typespeculiar to that island. The Galapagos Archipelago islands areparticularly instructive in this connection; for while the whole groupof islands lies at a distance of over five hundred miles from the shoresof South America, the constituent islands are separated from one anotherby straits varying from twenty to thirty miles. Now, to quote fromDarwin, "Each separate island of the Galapagos Archipelago is tenanted, and the fact is a marvellous one, by many distinct species; but thesespecies are related to each other in a very much closer manner than tothe inhabitants of the American continent. " That is to say, theAmerican continent being some fifteen times the distance from theseislands that they are from one another, emigration to them from thecontinent is of much more rare occurrence than emigration from oneisland to another; and therefore, as more time for variation is thusallowed, while the differences between the inhabitants of island andisland are only specific, the differences between the inhabitants of theislands as a group and the inhabitants of the American continent arevery often generic. I may mention, in passing, that it was upondiscovering these relations in the case of the Galapagos Archipelago, and pondering upon them as "marvellous facts, " that Mr. Darwin was firstled to entertain the idea that the doctrine of descent might be thegrand truth for which the science of the nineteenth century was waiting. 

The evidence from oceanic islands, however, is not yet exhausted; forin no part of the world is there an oceanic island more than a certaindistance from a mainland in which any species of the large class offrogs, toads, and newts is to be found. Why is this? Simply becausethese animals, and their spawn, are quickly killed by contact withsea-water; and therefore frogs, toads, and newts have never been able toreach oceanic islands in a living state. Similarly in all oceanicislands situated more than three hundred miles from land, no species ofthe whole class of mammals is to be found, excepting species of the onlyorder of mammals which can fly, viz. , bats. And, as if to make the casestill stronger, these forlornly created species of bats sometimes differfrom all other bats in the world. But can we, as reasonable men, supposethat the Deity has chosen, without any apparent reason, never to createany frog, toad, newt, or mammal on any oceanic island, save only suchspecies as are able to fly? Or, if we go so far as to say, --"There mayhave been some hidden reason why batrachians and quadrupeds should nothave been created on oceanic islands, " I will adduce another veryremarkable fact, viz. , that on some of these islands there occur speciesof plants, the seeds of which are provided with numerous hooks adaptedto catch the hair of moving quadrupeds, and so to become disseminated. But, as we have just seen, there are no quadrupeds in these islands tomeet this case of adaptation; so that special creationists must resortto the almost impious hypothesis, that in these cases the Deity onlycarried out half His plan, in that while He made an elaborate provisionfor plants which depended for its efficiency on the presence ofquadrupeds, He nevertheless, after all, neglected to place thequadrupeds in the same islands as the plants! Now, I submit that suchabortive attempts at adaptation bring the thesis of the specialcreationists to a _reductio ad absurdum_; so that the only possibleexplanation before us is, that while the seeds of these plants were ableto float to the islands, the quadrupeds were not able to swim. 

Perhaps in sheer desperation, however, the special creationists will tryto take refuge in the assumption that oceanic islands differ fromcontinents in not having been the scenes of creative power, and havetherefore depended on immigration for their inhabitants. But here againthere is no standing-room; for we have already seen that oceanic islandsare particularly rich in peculiar species which occur nowhere else inthe world; so that, as a matter of fact, if the special creation theoryis true, we must conclude that oceanic islands have been the theatres ofextraordinary creative activity; although an exception has always beencarefully made to the detriment of frogs, toads, newts, and mammals, save only such as are able to fly. 

If space permitted, I might adduce several other highly instructivefacts in this argument from geographical distribution; but I willcontent myself with mentioning only one other. When Mr. Wallace was atthe Malay Archipelago, he observed that the quadrupeds inhabiting thevarious islands belonged to the same or to closely allied species. Buthe also observed that all the quadrupeds inhabiting the islands lying onone side of an imaginary sinuous line, differed widely from thequadrupeds inhabiting the islands lying on the other side of that line. Now, soundings showed that in exact correspondence with this imaginarysinuous line the sea was much deeper than in any other part of theArchipelago. Consequently, how beautiful is the explanation. We haveonly to suppose that at some previous time the sea bottom was raisedsufficiently to unite all the islands on each side of the deep waterinto two great tracts of land, separated from one another by the deepstrait of water. Each of these great tracts of land would then have hadtheir own distinctive kinds of quadrupeds--just as the Americanquadrupeds are now distinct from the European; for the comparativelynarrow strait between the then Malay continents would have offered aseffectual a barrier to the migration of quadrupeds as does the AtlanticOcean at the present day. Hence, when all the land slowly subsided so asto leave only its mountain chains and table lands standing above thesurface in the form of islands, we now have the state of things whichMr. Wallace describes--viz. , two large groups of islands with thequadrupeds on the one group differing widely from the quadrupeds on theother, while within the limits of the same group the quadrupedsinhabiting different islands all belong to the same or to closelyallied species. On this highly interesting subject Darwin writes, "Ihave not as yet had time to follow up this subject in all quarters ofthe globe; but as far as I have gone the relation holds good. Forinstance, Britain is separated by a shallow channel from Europe, and themammals are the same on both sides, and so it is with all the islandsnear the shores of America. The West Indian islands, on the other hand, stand on a deeply submerged bank nearly 1, 000 fathoms in depth, and herewe find American forms, but the species, and even the genera, aredistinct. As the amount of modification which animals of all kindsundergo partly depends on lapse of time, and as the islands which areseparated from each other or from the mainland by shallow channels aremore likely to have been continuously united within a recent period thanthe islands separated by deeper channels, we can understand how it isthat a relation exists between the depth of the sea separating twomammalian faunas, and the degree of their affinity--a relation which isquite inexplicable on the theory of independent acts of creation. "

So much, then, for the argument from geographical distribution--the manyfacts of crucial importance which it affords almost resembling so manyexperiments devised by Nature to prove the falsity of the specialcreation hypothesis. For now, let it in conclusion be observed, thatthere is no _physiological_ reason why animals and plants of thedifferent characters observed should inhabit different continents, islands, seas, and so forth. As Darwin observes, "there is hardly aclimate or condition in the Old World which cannot be paralleled in theNew ... And yet how widely different are their living productions. " Andthat it is not the suitability of organisms to the areas which theyinhabit which has determined their creation upon those areas, isconclusively proved by the effects of the artificial transportation ofspecies by man. For in such cases it frequently happens that theimported species thrives quite as well in its new as in its old home, and indeed often supplants the native species. As the Maoris say, --"Asthe white man's rat has driven away the native rat, so the European flyhas driven away our fly, so the clover kills our fern, and so will theMaori himself disappear before the white man. "

Upon the whole then we are driven to the conclusion, that if the specialcreation theory is true, the various plants and animals have not beenplaced in the various habitats which they occupy with any reference tothe suitability of these habitats to the organisations of theseparticular plants and animals. So that, considering all the evidenceunder the head of geographical distribution, I think we are driven tothe yet further conclusion, that if the special creation theory is true, the only principle which appears to have been consistently followed inthe geographical deposition of species, is the principle of sodepositing them as in all cases to make it appear that the suppositionof their having been thus deposited is not merely a highly dubious one, but one which, on the face of it, is conspicuously absurd. 

V. 

THE ARGUMENT FROM EMBRYOLOGY. 

There is still another important line of evidence which we cannot affordto overlook; I mean the argument from embryology. To economise space, Ishall not explain the considerations which obviously lead to theanticipation that, if the theory of descent by inheritance is true, thelife history of the individual ought to constitute a sort of condensedepitome of the whole history of its descent. But taking thisanticipation for granted, as it is fully realised by the facts ofembryology, it follows that the science of embryology affords perhapsthe strongest of all the strong arguments in favour of evolution. Fromthe nature of the case, however, the evidence under this head requiresspecial training to appreciate; so I will merely observe, in generalterms, that the higher animals almost invariably pass through the sameembryological stages as the lower ones, up to the time when the higheranimal begins to assume its higher characters. Thus, for instance, totake the case of the highest animal, man, his development begins from aspeck of living matter similar to that from which the development of aplant begins. And, when his animality becomes established, he exhibitsthe fundamental anatomical qualities which characterise such lowlyanimals as the jelly-fish. Next he is marked off as a vertebrate, but itcannot be said whether he is to be a fish, a snake, a bird or a beast. Later on it is evident that he is to be a mammal; but not till stilllater can it be said to which order of mammals he belongs. 

Now this progressive inheritance by higher types of embryologicalcharacters common to lower types is a fact which tells greatly in favourof the theory of descent, whilst it seems almost fatal to the theory ofdesign. For instance, to take a specific case, Mr. Lewes remarks of aspecies of salamander--which differs from most salamanders in beingexclusively terrestrial--that although its young ones can never requiregills, yet on cutting open a pregnant female we find the young ones topossess gills like aquatic salamanders; and when placed in the water theyoung ones swim about like the tadpoles of the water newt. Now, tosuppose that these utterly useless gills were specially designed is tosuppose design without any assignable purpose; for even the far-fetchedassumption that a unity of ideal is the cause of organic affinities, becomes positively ridiculous when applied to the case of embryonicstructures, which are destined to disappear before the animal is born. Who, for instance, would have the courage to affirm that the Deity hadany such motive in providing, not only the unborn young of speciallycreated salamanders, but also the unborn young of specially created man, with the essential anatomical features of gills?

But this remark leads us to consider a little more attentively theanatomical features presented by the human embryo. The gill-slits justmentioned occur on each side of the neck, and to them the arteries runin branching arches, as in a fish. This, in fact, is the stage throughwhich the branchiæ of a fish are developed, and therefore in fish theslits remain open during life, while the so called "visceral arches"throw out filaments which receive the arterial branches coming from theaortic arches, and so become the organs of respiration, or branchiæ. But in all the other vertebrata (_i. E. _ except fish and amphibia) thegill-slits do not develop branchiæ, become closed (with the frequentexception of the first), and so never subserve the function ofrespiration. Or, as Mr. Darwin states it, "At this period the arteriesrun in arch-like branches, as if to carry the blood to branchiæ whichare not present in the higher vertebrata, though the slits on the sidesof the neck still remain, marking their former position. "

The heart is at first a simple pulsating vessel, like the heart of thelowest fishes, and the excreta are voided through a common cloacalpassage--an anatomical feature so characteristic of the lowervertebrata, that it occurs in no fully formed member of the mammaliangroup, with the exception of the bird-like order of monotremata, whichtakes its name from presenting so striking a peculiarity. 

At a later period the human embryo is provided with a very conspicuoustail, which is considerably longer than the rudimentary legs occurringat that period of development, and which Professor Turner has found tobe provided with muscles--the extensor, which is so largely developed inmany animals, being especially well marked. 

Again, as Mr. Darwin says, "In the embryos of all air-breathingvertebrates, certain glands, called the corpora Wolffiana, correspondwith and act like the kidneys of mature fishes;" and during the sixthmonth the whole body is covered very thickly with wool-like hair--eventhe forehead and ears being closely coated; but it is, as Mr. Darwinobserves, "a significant fact that the palms of the hands and the solesof the feet are quite naked, like the inferior surfaces of all fourextremities in most of the lower animals, " including monkeys. 

Lastly, Professor Wyman has found that in a human embryo about an inchin length, "the great toe was shorter than the others; and, instead ofbeing parallel to them, projected at an angle from the side of the foot, thus corresponding with the permanent condition of this part in thequadrumana. "[1]

Therefore, on the whole, we may conclude these brief remarks onembryology with the words of Professor Huxley:--"Without question, themode of origin, and the early stages of the development of man, areidentical with those of the animals immediately below him in the scale;without a doubt, in these respects he is far nearer to apes than theapes are to the dog. "[2]

[1] _Proc. Amer. Acad. Scs. _, vol. Iv. , 1860, p. 17. It should be added, however, that although the direction taken by the great toe of man atthis early age is doubtless, as Prof. Wyman states, more like that whichobtains in the quadrumana, there is a slight anatomical difference inthe mode of its articulation with the foot, which seems to assist insecuring the forward direction taken by it in later life. 

[2] _Man's Place in Nature_, p. 65. 

VI. 

ARGUMENTS DRAWN FROM CERTAIN GENERAL CONSIDERATIONS. 

There are two or three arguments of a somewhat weighty character, whichdo not fall under any of the previous headings, but which we must not onthis account neglect. 

1. It is justly deemed a substantiation of a scientific theory if it isfound to furnish an explanation of other classes of phenomena than thosefor the explanation of which it was first devised. And this is the casewith the theory of natural selection in the region of psychology. Thetheory was first devised to explain the facts of biology, and provingso successful in that region, Mr. Darwin proceeded to test it in theregion of psychology. The result has been to show that large classes ofphenomena in this region which were previously unaccountable becomefully intelligible. This is especially the case with the phenomena ofinstinct, and in a lesser degree with those of reason and conscience. For the theory shows that if structures admit of being moulded to theirspecial uses by natural selection, the same must be true of instincts;and it is found an easy matter to understand how, by seizing upon andfixing, through hereditary beneficial variations of habit (whetherinstinctive or intelligent), natural selection is as competent tofashion the mental structure of an animal as it is to shape its bodilystructure into agreement with the external conditions of life. Thus thewhole philosophy of animal intelligence is greatly elucidated, and thisfact may justly be regarded as lending much additional credence to thetheory. 

Again, by observing that sympathy and the social instincts generally aredeveloped to a large extent in many of the lower animals, andparticularly so in the quadrumana, the theory of natural selection isprovided with a reasonable basis for furnishing a scientific explanationof the moral sense in man; and by observing that many of the loweranimals are capable of drawing simple inferences, the theory is likewiseable to explain the development of reason. So that in the province ofhuman psychology no less than in that of animal, the theory of naturalselection, in showing itself competent to explain much which isotherwise inexplicable, is seen to derive a large additional measure ofargumentative support. 

2. Although the majority of structures and instincts met with in theanimal kingdom are in a marvellous degree suited to the performance oftheir functions and uses, it is nevertheless far from being aninvariable rule that the suitability is perfect. Thus, for instance, even in the case of the eye--which is perhaps the most wonderful andmost highly elaborated structure in organic nature--it is demonstrablethat the organ, considered as an optical instrument, is not ideallyperfect; so that, if it were an artificial production, opticians wouldknow how to improve it. And as for instinct, numberless cases might beadduced of imperfection, ranging in all degrees from a slight deficiencyto fatal blundering. 

Now if all organic structures are supposed to be mechanisms designed bythe Deity, and all instincts are supposed to be mental attributesimplanted by Him, it becomes unintelligible that in the result the humanmind should thus be able to perceive, either an ignorance of naturalprinciples in the Author of nature, or a singular absence of thought inapplying His knowledge. But, on the other hand, if all the structuresand instincts are supposed to be due to natural selection (whether aloneor in conjunction with other natural causes), we have no need to feelstaggered at flagrant cases of imperfection; we have only to wonder atthe number of cases in which perfection, more or less complete, has beenattained. 

3. Lastly, there is still another general consideration, and one whichappeals to my mind as of immense weight. The question, it will beremembered, lies between beneficent design and natural selection, and Ithink that the consideration about to be adduced is in itself alonesufficient to decide the question. 

This consideration is that amid all the millions of mechanisms andinstincts in the animal kingdom, there is no one instance of amechanism or instinct occurring in one species for the exclusive benefitof another species, although there are a few cases in which a mechanismor instinct that is of benefit to its possessor has come also to beutilised by other species. Now, on the beneficent design theory it isimpossible to explain why, when all the mechanisms in the same speciesare invariably correlated for the benefit of that species, there shouldnever be any such correlation between mechanisms in different species, or why the same remark should apply to instincts. For how magnificent adisplay of divine beneficence would organic nature have afforded, ifall, or even some, species had been so inter-related as to minister toeach other's necessities. Organic species might then have been likenedto a countless multitude of voices all singing in one harmonious psalmof praise. But, as it is, we see no vestige of such co-ordination;every species is for itself, and for itself alone--an outcome of thealways and everywhere fiercely raging struggle for life. 

Such, then, is a sketch of the evidence in favour of organic evolution. Of course in such a meagre outline it has not been possible to dojustice to that evidence, which should be studied in detail rather thanlooked at in such a bird's-eye view as I have presented. Nevertheless, enough, I hope, has been said to convince all reasonable persons, thatany longer to withhold assent from so vast a body of evidence is atoken, not of intellectual prudence, but of intellectual incapacity. With Professor Huxley, therefore, I exclaim, --"Choose your hypothesis; Ihave chosen mine, " and "I refuse to run the risk of insulting any saneman by supposing that he seriously holds such a notion" as that ofspecial creation. These words, I submit, are not in the least toostrong; for if any man can study the many and important lines ofevidence all converging on the central truth that evolution has been thelaw of organic nature, and still fail to perceive the certainty of thattruth, then I say that that man--either on account of his prejudices, orfrom his inability to estimate the value of evidence--must properly beregarded as a weak-minded man. Or, to state the case in another way, ifsuch a man were to say to me, --Notwithstanding all your lines ofevidence, I still believe in special design manifested in creation; Ishould reply, --And in this I fully agree with you; for if, notwithstanding these numerous and important lines of evidence, thetheory which they substantiate is false, then to my mind we have thebest conceivable evidence of very special design having been manifestedin creation--the special design, namely, to deceive mankind by anelaborate, detailed, and systematic fraud. For, if the theory ofspecial creation is true, I hold that as no one fact can be adduced inits favour, whilst so vast a body of facts can be adduced against it, the only possible explanation of so extraordinary a circumstance is thatof a mendacious intelligence of superhuman power carefully disposing allthe observable facts of his creation in such a way as to compel hisrational creatures, by the best and most impartial use of their rationalfaculties, to conclude that the theory of evolution is as certainly trueas the theory of special creation is conspicuously false. 

But having now concluded this brief review of the leading arguments infavour of organic evolution, and having expressed as forcibly as I amable my own opinion upon them, I do not wish it to be supposed, eitherthat I am intolerant of opinions which are held by others, or that Ihave been trying to, "make out a case" by suppressing adverse facts. Iam not intolerant, because I believe that dissent from the generaldoctrine of evolution can only arise either from ignorance of somespecial departments of science, or from a bias of feeling against thedoctrine--to both of which weaknesses evolutionists can afford to beindulgent. And in order to show that I have not been trying unfairly tomake out a case, I shall conclude by briefly reviewing the argumentswhich have been adduced against the doctrine in question. 

The only argument of this kind that I know from the side of reason (ifwe neglect those special objections which have been fully shown by Mr. Darwin himself to be based on inadequate information or erroneousconception, and therefore futile), is that which says:--Evolution, iftrue, can only be proved so by an actual observation of the process, andas no one pretends to have witnessed the transmutation of species, itfollows that evolution has not been proved. 

Now, it is perfectly right to draw a clear distinction between a theoryand a demonstration; but it is a great mistake to suppose that a theorymay then only be admitted by science when it has been demonstrated. Bishop Butler tells us that "Probability is the guide of life, " and notless true is it that probability is likewise the guide of science. Thebusiness of science, as of common life, is to estimate correctly therelative degrees of probability presented by this and that theory orhypothesis; when once a theory or hypothesis is demonstrated it ceasesto be a matter of scientific inquiry, and becomes a matter of scientificfact. Thus received, we have to consider the doctrine of evolution ascertainly standing in the first rank of scientific theories in respectof probability sustained by evidence, although no less certainly notdemonstrated as a matter of scientific fact. But when a theory has beenraised to such a level of probability as this, it is, for all practicalpurposes, as good as a demonstration. Thus, in the particular instancebefore us, even if the sceptical demand for evidence, which from thenature of the case is clearly impossible, were granted, and if we couldactually observe the transmutation of species, the fact would not exertany further influence on the progress of science than is now exerted bythe large and converging bodies of evidence which leave no otherrational theory open to us than that such transmutation has taken place. Therefore, it seems to me, the hypercritical objection which we areconsidering is really founded on a misconception of scientific method, and of what it is that justifies a scientific doctrine. Assuredly, inthe case of every theory, as distinguished from a demonstration, theremust always be a proportion between the evidence of and the warrant forthe proposition which the theory states; and if gauged by this simplerule the warrant for accepting the theory of evolution is now estimatedby the judgment of all scientifically trained minds as so high, that byno additional evidence could it be placed higher without becoming a fulldemonstration. Or, otherwise stated, as a theory the doctrine of descentis now in the topmost position of probability, so that by no amount ofadditional evidence could it be raised higher without ceasing to be aprobability and becoming a certainty. That is to say, we do not need anymore evidence in any of the lines of evidence to add to the strength ofour belief in, as distinguished from our knowledge of, the truth ofevolution. For the strength of our conviction could not be increased bythe discovery of any additional number of connecting links among fossilspecies, further facts relating to geographical distribution, tomorphology, classification, embryology, or any of the other lines ofevidence which have been mentioned; no further evidence the same in kindis now competent to raise in degree the probability which has alreadybeen raised, as far as from its very nature as a probability it can beraised. 

I have no doubt, however, that the principal obstacle which the doctrineof evolution encounters in the popular mind is not one of reason, but ofsentiment. It is thought that the conception of man being a linealdescendant of the monkey is a conception which is degrading to thedignity of the former animal. Now this obstacle being, as I have said, amatter of feeling or sentiment, as such I am not able to meet it. If youthink that man is shown to be any less human because his origin is nowshown to have been derivative, I cannot change that decision on yourpart; I can only express dissent from it on my own. But although Icannot affect your sentiments in this matter, I may be permitted topoint out that, as they are only sentiments, they are quite worthless asarguments or guides to truth. I have yet to learn that the "dignity ofman" is a matter of any concern to our Mother Nature, who in all herdealings appears, to say the least, to treat us in rather amatter-of-fact sort of way. Indeed, so far is she from respecting ourideas of "dignity, " that whenever these ideas have been applied to anyof her processes, the progress of science has been destined rudely todispel them. Thus, for instance, when the sun-spots were first observedthey were indignantly denied by the Aristotelians, on the ground of itsbeing "impossible that the eye of the universe could suffer fromophthalmia;" and when Kepler made his great discovery of the acceleratedand retarded motion of the planets in different parts of their orbits, many persons refused to entertain the conception, on the ground that itwas "undignified" for heavenly bodies to hurry and slacken their pace inaccordance with Kepler's law. This now seems most absurd to us; but toposterity it will not seem nearly so much so as that, notwithstandingsuch precedents, persons should still be found to object to Darwin'sdiscovery, not because they were anxious to maintain the dignity of theheavenly bodies, but because they were so ludicrously anxious tomaintain the dignity of their own! Good it is for man, puffed up withsuch silly pride, that Nature teaches him humility. 

But, before leaving this subject, I should like further to point outthat those who advance this preposterous objection from dignity appearto forget one all-important point, viz. , that whether or not the monkeyis the parent of the man, the man is certainly made in every way to_look like_ a child of the monkey. For it is a matter of anatomicaldemonstration, that in all the features of our bodily structure--even upto our brains--we more closely resemble the man-like apes than theman-like apes resemble the lower quadrumana. And I beg it to beremembered that the tremendous significance of this fact can only beduly appreciated by those who know the astounding complexity of ourbodily structure. Those who are ignorant of human anatomy cannot formany adequate--probably not even an approximate--conception of itsintricacy. Yet we find that this terrifically intricate organisation isrepeated down to all the minute bones and muscles, blood-vessels, nervesand viscera, in the bodies of the higher apes. Here, then, I say, wehave a fact--or rather let me say a hundred thousand facts--which cannotpossibly be attributed to chance. As reasonable beings we must concludethat there has been some definite cause for this extraordinary imitationby the most highly organised being in creation of the next most highlyorganised. And if we reject the natural explanation of hereditarydescent from a common ancestry, we can only suppose that the Deity, increating man, took the most scrupulous pains to make him in the image ofthe ape. This, I say, is a matter of undeniable fact--supposing thecreation theory true--and as a matter of fact, therefore, it calls forexplanation. Why should God have thus conditioned man as an elaboratecopy of the ape, when we know from the rest of creation how endless areHis resources in the invention of types?

I present the matter thus to show that even the weight of sentiment isnot all on the side of special creation. Look on this picture and onthis:--

The Creator has exhibited the extraordinary and unaccountable design ofcasting the complex structure of man in the same mould that He had justpreviously used to cast the complex structure of the ape. 

"When I view all beings, not as special creations, but as the linealdescendants of some few beings which lived long before the first bed ofthe Cambrian system was deposited, they seem to me to becomeennobled.... There is grandeur in this view of life, with its severalpowers, having been originally breathed by the Creator into a few formsor into one; and that, whilst this planet has gone cycling on accordingto the first law of gravity, from so simple a beginning endless formsmost beautiful and most wonderful have been and are being evolved. "

THE END. 

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