BIOLOGY BY EDMUND BEECHER WILSONPROFESSOR OF ZOOLOGYCOLUMBIA UNIVERSITY New YorkTHE COLUMBIA UNIVERSITY PRESS1908 BIOLOGY A LECTURE DELIVERED AT COLUMBIA UNIVERSITY IN THE SERIES ON SCIENCE, PHILOSOPHY AND ART NOVEMBER 20, 1907 BIOLOGY BY EDMUND BEECHER WILSONPROFESSOR OF ZOOLOGYCOLUMBIA UNIVERSITY New YorkTHE COLUMBIA UNIVERSITY PRESS1908 COPYRIGHT, 1908, by THE COLUMBIA UNIVERSITY PRESS. Set up, and published March, 1908. BIOLOGY I must at the outset remark that among the many sciences that areoccupied with the study of the living world there is no one that mayproperly lay exclusive claim to the name of Biology. The word doesnot, in fact, denote any particular science but is a generic termapplied to a large group of biological sciences all of which alike areconcerned with the phenomena of life. To present in a single address, even in rudimentary outline, the specific results of these sciences isobviously an impossible task, and one that I have no intention ofattempting. I shall offer no more than a kind of preface orintroduction to those who will speak after me on the biologicalsciences of physiology, botany and zoology; and I shall confine it towhat seem to me the most essential and characteristic of the generalproblems towards which all lines of biological inquiry must sooner orlater converge. It is the general aim of the biological sciences to learn something ofthe order of nature in the living world. Perhaps it is not amiss toremark that the biologist may not hope to solve the ultimate problemsof life any more than the chemist and physicist may hope to penetratethe final mysteries of existence in the non-living world. What he cando is to observe, compare and experiment with phenomena, to resolvemore complex phenomena into simpler components, and to this extent, ashe says, to "explain" them; but he knows in advance that hisexplanations will never be in the full sense of the word final orcomplete. Investigation can do no more than push forward the limits ofknowledge. The task of the biologist is a double one. His more immediate effort isto inquire into the nature of the existing organism, to ascertain inwhat measure the complex phenomena of life as they now appear arecapable of resolution into simpler factors or components, and todetermine as far as he can what is the relation of these factors toother natural phenomena. It is often practically convenient to considerthe organism as presenting two different aspects--a structural ormorphological one, and a functional or physiological--and biologistsoften call themselves accordingly morphologists or physiologists. Morphological investigation has in the past largely followed the methodof observation and comparison, physiological investigation that ofexperiment; but it is one of the best signs of progress that in recentyears the fact has come clearly into view that morphology andphysiology are really inseparable, and in consequence the distinctionsbetween them, in respect both to subject matter and to method, havelargely disappeared in a greater community of aim. Morphology andphysiology alike were profoundly transformed by the introduction intobiological studies of the genetic or historical point of view byDarwin, who did more than any other to establish the fact, suspected bymany earlier naturalists, that existing vital phenomena are the outcomeof a definite process of evolution; and it was he who first fullybrought home to us how defective and one-sided is our view of theorganism so long as we do not consider it as a product of the past. Itis the second and perhaps greater task of the biologist to study theorganism from the historical point of view, considering it as theproduct of a continuous process of evolution that has been in operationsince life began. In its widest scope this genetic inquiry involvesnot only the evolution of higher forms from lower ones, but also thestill larger question of the primordial relation of living things tothe non-living world. Here is involved the possibility so strikinglyexpressed many years ago by Tyndall in that eloquent passage in theBelfast address, where he declared himself driven by an intellectualnecessity to cross the boundary line of the experimental evidence andto discern in non-living matter, as he said, the promise and potency ofevery form and quality of terrestrial life. This intellectual necessitywas created by a conviction of the continuity and consistency ofnatural phenomena, which is almost inseparable from the scientificattitude towards nature. But Tyndall's words stood after all for aconfession of faith, not for a statement of fact; and they soared farabove the _terra firma_ of the actual evidence. At the present day wetoo may find ourselves logically driven to the view that living thingsfirst arose as a product of non-living matter. We must fully recognizethe extraordinary progress that has been made by the chemist in theartificial synthesis of compounds formerly known only as the directproducts of living protoplasm. But it must also be admitted that we arestill wholly without evidence of the origin of any living thing, at anyperiod of the earth's history, save from some other living thing; andafter more than two centuries Redi's aphorism _omne vivum e vivo_retains to-day its full force. It is my impression therefore that thetime has not yet come when hypotheses regarding a different origin oflife can be considered as practically useful. If I have the temerity to ask your attention to the fundamentalproblem towards which all lines of biological inquiry sooner or laterlead us it is not with the delusion that I can contribute anything newto the prolonged discussions and controversies to which it has givenrise. I desire only to indicate in what way it affects the practicalefforts of biologists to gain a better understanding of the livingorganism, whether regarded as a group of existing phenomena or as aproduct of the evolutionary process; and I shall speak of it, not inany abstract or speculative way, but from the standpoint of theworking naturalist. The problem of which I speak is that of organicmechanism and its relation to that of organic adaptation. How ingeneral are the phenomena of life related to those of the non-livingworld? How far can we profitably employ the hypothesis that the livingbody is essentially an automaton or machine, a configuration ofmaterial particles, which, like an engine or a piece of clockwork, owes its mode of operation to its physical and chemical construction?It is not open to doubt that the living body _is_ a machine. It is acomplex chemical engine that applies the energy of the food-stuffs tothe performance of the work of life. But is it something more than amachine? If we may imagine the physico-chemical analysis of the bodyto be carried through to the very end, may we expect to find at lastan unknown something that transcends such analysis and is neither aform of physical energy nor anything given in the physical or chemicalconfiguration of the body? Shall we find anything corresponding to theusual popular conception--which was also along the view ofphysiologists--that the body is "animated" by a specific "vitalprinciple, " or "vital force, " a dominating "archæus" that exists onlyin the realm of organic nature? If such a principle exists, then themechanistic hypothesis fails and the fundamental problem of biologybecomes a problem _sui generis_. In its bearing on man's place in nature this question is one of themost momentous with which natural science has to deal, and it hasoccupied the attention of thinking men in every age. I cannot traceits history, but it will be worth our while to place side by side thewords of three of the great leaders of modern scientific andphilosophic thought. The saying has been attributed to Descartes, "Give me matter and I will construct the world"--meaning by this theliving world as well as the non-living; but Descartes specificallyexcepted the human mind. I do not know whether the great Frenchphilosopher actually used these particular words, but they express theessence of the mechanistic hypothesis that he adopted. Kant utterlyrepudiated such a conception in the following well known passage: "Itis quite certain that we cannot become adequately acquainted withorganized creatures and their hidden potentialities by means of themerely mechanical principles of nature, much less can we explain them;and this is so certain that we may boldly assert that it is absurd forman even to make such an attempt or to hope that a Newton may one dayarise who will make the production of a blade of grass comprehensibleto us according to natural laws that have not been ordered by design. Such an insight we must absolutely deny to man. " Still, in anotherplace Kant admitted that the facts of comparative anatomy give us "aray of hope, however faint, that something may be accomplished by theaid of the principle of the mechanism of nature, without which therecan be no science in general. " It is interesting to turn from this tothe bold and aggressive assertion of Huxley: "Living matter differsfrom other matter in degree and not in kind, the microcosm repeats themacrocosm; and one chain of causation connects the nebulous origin ofsuns and planetary systems with the protoplasmic foundations of lifeand organization. " Do not expect me to decide where such learned doctors disagree; but Iwill at this point venture on one comment which may sound the key-noteof this address. Perhaps we shall find that in the long run and in thelarge sense Kant was right; but it is certain that to-day we knowvery much more about the formation of the living body, whether a bladeof grass or a man, than did the naturalists of Kant's time; and forbetter or for worse the human mind seems to be so constituted that itwill continue its efforts to explain such matters, however difficultthey may seem to be. But I return to our more specific inquiry withthe remark that the history of physiology in the past two hundredyears has been the history of a progressive restriction of the notionof a "vital force" or "vital principle" within narrower and narrowerlimits, until at present it may seem to many physiologists that noroom for it remains within the limits of our biological philosophy. One after another the vital activities have been shown to be ingreater or less degree explicable or comprehensible considered asphysico-chemical operations of various degrees of complexity. Everyphysiologist will maintain that we cannot name one of theseactivities, not even thought, that is not carried on by a physicalmechanism. He will maintain further that in most cases the vitalactions are not merely accompanied by physico-chemical operations butactually consist of them; and he may go so far as definitely tomaintain that we have no evidence that life itself can be regarded asanything more than their sum total. He is able to bring forward cogentevidence that all modes of vital activity are carried on by means ofenergy that is set free in protoplasm or its products by means ofdefinite chemical processes collectively known as metabolism. When thematter is reduced to its lowest terms, life, as thus viewed, seems tohave its root in chemical change; and we can understand how an eminentGerman physiologist offers us a definition or characterization of lifethat runs: "The life-process consists in the metabolism of proteids. "I ask your particular attention to this definition since I now wish tocontrast with it another and very different one. I shall introduce it to your attention by asking a very simplequestion. We may admit that digestion, for example, is a purelychemical operation, and one that may be exactly imitated outside theliving body in a glass flask. My question is, how does it come to passthat an animal has a stomach?--and, pursuing the inquiry, how does ithappen that the human stomach is practically incapable of digestingcellulose, while the stomachs of some lower animals, such as the goat, readily digest this substance? The earlier naturalists, such asLinnaeus, Cuvier or Agassiz, were ready with a reply which seemed sosimple, adequate and final that the plodding modern naturalist cannotrepress a feeling of envy. In their view plants and animals are madeas they were originally created, each according to its kind. Thebiologist of to-day views the matter differently; and I shall give hisanswer in the form in which I now and then make it to a student whomay chance to ask why an insect has six legs and a spider eight, orwhy a yellowbird is yellow and a bluebird blue. The answer is: "Forthe same reason that the elephant has a trunk. " I trust that a certainrugged pedagogical virtue in this reply may atone for its lack ofelegance. The elephant has a trunk, as the insect has six legs, forthe reason that such is the specific nature of the animal; and we mayassert with a degree of probability that amounts to practicalcertainty that this specific nature is the outcome of a definiteevolutionary process, the nature and causes of which it is ourtremendous task to determine to such extent as we may be able. Butthis does not yet touch the most essential side of the problem. Whatis most significant is that the clumsy, short-necked elephant has beenendowed--"by nature, " as we say--with precisely such an organ, thetrunk, as he needs to compensate for his lack of flexibility andagility in other respects. If we are asked _why_ the elephant has atrunk, we must answer because the animal needs it. But does such areply in itself explain the fact? Evidently not. The question whichscience must seek to answer, is _how_ came the elephant to have atrunk; and we do not properly answer it by saying that it hasdeveloped in the course of evolution. It has been well said that eventhe most complete knowledge of the genealogy of plants and animalswould give us no more than an ancestral portrait-gallery. We mustdetermine the causes and conditions that have cooperated to producethis particular result if our answer is to constitute a truescientific explanation. And evidently he who adopts the machine-theoryas a general interpretation of vital phenomena must make clear to ushow the machine was built before we can admit the validity of histheory, even in a single case. Our apparently simple question as towhy the animal has a stomach has thus revealed to us the fullmagnitude of the task with which the mechanist is confronted; and ithas brought us to that part of our problem that is concerned with thenature and origin of organic adaptations. Without tarrying to attempta definition of adaptation I will only emphasize the fact that many ofthe great naturalists, from Aristotle onward, have recognized thepurposeful or design-like quality of vital phenomena as their mostessential and fundamental characteristic. Herbert Spencer defined lifeas the continuous _adjustment_ of internal relations to externalrelations. It is one of the best that has been given, though I am notsure that Professor Brooks has not improved upon it when he says thatlife is "response to the order of nature. " This seems a long way fromthe definition of Verworn, heretofore cited, as the "metabolism ofproteids. " To this Brooks opposes the telling epigram: "The essence oflife is not protoplasm but purpose. " Without attempting adequately to illustrate the nature of organicadaptations, I will direct your attention to what seems to me one oftheir most striking features regarded from the mechanistic position. This is the fact that adaptations so often run counter to direct orobvious mechanical conditions. Nature is crammed with devices toprotect and maintain the organism against the stress of theenvironment. Some of these are given in the obvious structure of theorganism, such as the tendrils by means of which the climbing plantsustains itself against the action of gravity or the winds, theprotective shell of the snail, the protective colors and shapes ofanimals, and the like. Any structural feature that is useful becauseof its construction is a structural adaptation; and when suchadaptations are given the mechanist has for the most part a relativelyeasy task in his interpretation. He has a far more difficult knot todisentangle in the case of the so-called functional adaptations, wherethe organism modifies its activities (and often also its structure) inresponse to changed conditions. The nature of these phenomena may beillustrated by a few examples so chosen as to form a progressiveseries. If a spot on the skin be rubbed for some time the first resultis a direct and obviously mechanical one; the skin is worn away. Butif the rubbing be continued long enough, and is not too severe, anindirect effect is produced that is precisely the opposite of theinitial direct one; the skin is replaced, becomes thicker than before, and a callus is produced that protects the spot from further injury. The healing of a wound involves a similar action. Again, remove onekidney or one lung and the remaining one will in time enlarge toassume, as far as it is able, the functions of both. If the leg of asalamander or a lobster be amputated, the wound not only heals but anew leg is regenerated in place of that which has been lost. If aflatworm be cut in two, the front piece grows out a new tail, the hindpiece a new head, and two perfect worms result. Finally, it has beenfound in certain cases, including animals as highly organized assalamanders, that if the egg be separated into two parts at an earlyperiod of development each part develops into a perfect embryo animalof half the usual size, and a pair of twins results. In each of thesecases the astonishing fact is that a mechanical injury sets up in theorganism a complicated adaptive response in the form of operationswhich in the end counteract the initial mechanical effect. It is nodoubt true that somewhat similar self-adjustments or responses may besaid to take place in certain non-living mechanical systems, such asthe spinning top or the gyroscope; but those that occur in the livingbody are of such general occurrence, of such complexity and variety, and of so design-like a quality, that they may fairly be regarded asamong the most characteristic of the vital activities. It is preciselythis characteristic of many vital phenomena that renders theiraccurate analysis so difficult and complex a task; and it is largelyfor this reason that the biological sciences, as a whole, still standfar behind the physical sciences, both in precision and incompleteness of analysis. What is the actual working attitude of naturalists towards the generalproblem that I have endeavored to outline? It would be a piece ofpresumption for me to speak for the body of working biologists, and Iwill therefore speak for only one of them. It is my own convictionthat whatever be the difficulties that the mechanistic hypothesis hasto face, it has established itself as the most useful workinghypothesis that we can at present employ. I do not mean to assert thatit is adequate, or even true. I believe only that we should make useof it as a working program, because the history of biological researchproves it to have been a more effective and fruitful means ofadvancing knowledge than the vitalistic hypothesis. We shouldtherefore continue to employ it for this purpose until it is clearlyshown to be untenable. Whether we must in the end adopt it willdepend on whether it proves the simplest hypothesis in the largesense, the one most in harmony with our knowledge of nature ingeneral. If such is the outcome, we shall be bound by a deeply lyinginstinct that is almost a law of our intellectual being to accept it, as we have accepted the Copernican system rather than the Ptolemaic. Ibelieve I am right in saying that the attitude I have indicated as amore or less personal one is also that of the body of workingbiologists, though there are some conspicuous exceptions. In endeavoring to illustrate how this question actually affectsresearch I will offer two illustrative cases, one of which mayindicate the fruitfulness of the mechanistic conception in theanalysis of complex and apparently mysterious phenomena, the other thenature of the difficulties that have in recent years led to attemptsto re-establish the vitalistic view. The first example is given by theso-called law or principle of Mendel in heredity. The principlerevealed by Mendel's wonderful discovery is not shown in all thephenomena of heredity and is probably of more or less limitedapplication. It possesses however a profound significance because itgives almost a demonstration that a definite, and perhaps a relativelysimple, mechanism must lie behind the phenomena of heredity ingeneral. Hereditary characters that conform to this law undergocombinations, disassociations and recombinations which in certain waysuggest those that take place in chemical reactions; and like thelatter they conform to definite quantitative rules that are capable ofarithmetical formulation. This analogy must not be pressed too far;for chemical reactions are individually definite and fixed, whilethose of the hereditary characters involve a fortuitous element ofsuch a nature that the numerical result is not fixed or constant inthe individual case but follows the law of probability in theaggregate of individuals. Nevertheless, it is possible, and hasalready become the custom, to designate the hereditary organization bysymbols or formulas that resemble those of the chemist in that theyimply the _quantitative_ results of heredity that follow the union ofcompounds of known composition. Quantitative prediction--not preciselyaccurate, but in accordance with the law of probability--has thusbecome possible to the biological experimenter on heredity. I willgive one example of such a prediction made by Professor Cuénot inexperimenting on the heredity of color in mice (see the followingtable). The experiment extended through three generations. Of the fourgrandparents three were pure white albinos, identical in outwardappearance, but of different hereditary capacity, while the fourth wasa pure black mouse. The first pair of grandparents consisted of analbino of gray ancestry, AG, and one of black ancestry, AB. The secondpair consisted of an albino of yellow ancestry, AY, and a black mouse, CB. The result of the first union, AG x AB is to produce again purewhite mice of the composition AGAB. The second union, AY x CB is toproduce mice that appear pure _yellow_, and have the formula AYCB. What, now, will be the result of uniting the two forms thusproduced--_i. E. _ AGAB × AYCB? Cuénot's prediction was that they shouldyield eight different kinds of mice, of which four should be white, two yellow, one black and one gray. The actual aggregate result ofsuch unions, repeatedly performed, compared with the theoreticexpectation, is shown in the foregoing table. As will be seen, thecorrespondence, though close, is not absolutely exact, yet is nearenough to prove the validity of the principle on which the predictionwas based, and we may be certain that had a much larger number ofthese mice been reared the correspondence would have been stillcloser. I have purposely selected a somewhat complicated example, andtime will not admit of a full explanation of the manner in which thisparticular result was reached. I will however attempt to give anindication of the general Mendelian principle by means of whichpredictions of this kind are made. This principle appears in itssimplest form in the behavior of two contrasting characters of thesame general type--for instance two colors, such as gray and white inmice. If two animals, which show respectively two such characters arebred together, only one of the characters (known as the "dominant")appears in the offspring, while the other (known as the "recessive")disappears from view. In the next generation, obtained by breedingthese hybrids together, both characters appear separately and in adefinite ratio, there being in the long run three individuals thatshow the dominant character to one that shows the recessive. Thus, inthe case of gray and white mice, the first cross is always gray, whilethe next generation includes three grays to one white. This is thefundamental Mendelian ratio for a single pair of characters; and fromit may readily be deduced the more complicated combinations thatappear when two or more pairs of characters are considered together. Such combinations appear in definite series, the nature of which maybe worked out by a simple method of binomial expansion. By the use ofthis principle astonishingly accurate numerical predictions may bemade, even of rather complex combinations; and furthermore, newcombinations may be, and have been, artificially produced, the number, character and hereditary capacity of which are known in advance. Thefundamental ratio for a single pair of characters is explained by avery simple assumption. When a dominant and a recessive character areassociated in a hybrid, the two must undergo in some sense adisjunction or separation in the formation of the germ-cells of thehybrid. This takes place in a quite definite way, exactly half thegerm-cells in each sex receiving the potentiality of the dominantcharacter, the other half the potentiality of the recessive. This isroughly expressed by saying that the germ-cells are no longer hybrid, like the body in which they arise, but bear one character or theother; and although in a technical sense this is probably notprecisely accurate, it will sufficiently answer our purpose. If, now, it be assumed that fertilization takes place fortuitously--that isthat union is equally probable between germ-cells bearing the samecharacter and those bearing opposite characters, --the observednumerical ratio in the following generation follows according to thelaw of probability. Thus is explained both the fortuitous element thatdifferentiates these cases from exact chemical combinations, and thedefinite numerical relations that appear in the aggregate ofindividuals. Grandparents AG (white) AB (white) AY (white) CB (black) | | | | +---------+ +-----------+ | | Parents AGAB (white) AYCB (yellow) | | +----------------------+ | Observed Calculated {AGAY} {ABAY} (White) 81 76 {AGAB} Offspring ---------------{ABAB} { {AGCY} (Yellow) 34 38 {ABCY} { {ABCB (Black) 20 19 {AGCB (Gray) 16 19 ---- ---- 151 152 Now, the point that I desire to emphasize is that one or two verysimple mechanistic assumptions give a luminously clear explanation ofthe behavior of the hereditary characters according to Mendel's law, and at one stroke bring order out of the chaos in which facts of thiskind at first sight seem to be. Not less significant is the fact thatdirect microscopical investigation is actually revealing in thegerm-cells a physical mechanism that seems adequate to explain thedisjunction of characters on which Mendel's law depends; and thismechanism probably gives us also at least a key to the long standingriddle of the determination and heredity of sex. These phenomena aretherefore becoming intelligible from the mechanistic point of view. From any other they appear as an insoluble enigma. When such progressas this is being made, have we not a right to believe that we areemploying a useful working hypothesis? But let us now turn to a second example that will illustrate a classof phenomena which have thus far almost wholly eluded all attempts toexplain them. The one that I select is at present one of the mostenigmatical cases known, namely, the regeneration of the lens of theeye in the tadpoles of salamanders. If the lens be removed from theeye of a young tadpole, the animal proceeds to manufacture a new oneto take its place, and the eye becomes as perfect as before. That sucha process should take place at all is remarkable enough; but from atechnical point of view this is not the extraordinary feature of thecase. What fills the embryologist with astonishment is the fact thatthe new lens is not formed in the same way or from the same materialas the old one. In the normal development of the tadpole from the egg, as in all other vertebrate animals, the lens is formed from the outerskin or ectoderm of the head. In the replacement of the lens afterremoval it arises from the cells of the iris, which form the edge ofthe optic cup, and this originates in the embryo not from the outerskin but as an outgrowth from the brain. As far as we can see, neitherthe animal itself nor any of its ancestors can have had experience ofsuch a process. How, then, can such a power have been acquired, andhow does it inhere in the structure of the organism? If the process ofrepair be due to some kind of intelligent action, as some naturalistshave supposed, why should not the higher animals and man possess asimilar useful capacity? To these questions biology can at presentgive no reply. In the face of such a case the mechanist must simplyconfess himself for the time being brought to a standstill; and thereare some able naturalists who have in recent years argued that by thevery nature of the case such phenomena are incapable of a rationalexplanation along the lines of a physico-chemical or mechanisticanalysis. These writers have urged, accordingly, that we mustpostulate in the living organism some form of controlling orregulating agency which does not lie in its physico-chemicalconfiguration and is not a form of physical energy--something that maybe akin to a form of intelligence (conscious or unconscious), and towhich the physical energies are in some fashion subject. To thissupposed factor in the vital processes have been applied such terms asthe "entelechy" (from Aristotle), or the "psychoid"; and some writershave even employed the word "soul" in this sense--though thistechnical and limited use of the word should not be confounded withthe more usual and general one with which we are familiar. Views ofthis kind represent a return, in some measure, to earlier vitalisticconceptions, but differ from the latter in that they are an outcome ofdefinite and exact experimental work. They are therefore often spokenof collectively as "neo-vitalism. " It is not my purpose to enter upon a detailed critique of thisdoctrine. To me it seems not to be science, but either a kind ofmetaphysics or an act of faith. I must own to complete inability tosee how our scientific understanding of the matter is in any wayadvanced by applying such names as "entelechy" or "psychoid" to theunknown factors of the vital activities. They are words that have beenwritten into certain spaces that are otherwise blank in our record ofknowledge, and as far as I can see no more than this. It is myimpression that we shall do better as investigators of naturalphenomena frankly to admit that they stand for matters that we do notyet understand, and continue our efforts to make them known. And havewe any other way of doing this than by observation, experiment, comparison and the resolution of more complex phenomena into simplercomponents? I say again, with all possible emphasis, that themechanistic hypothesis or machine-theory of living beings is not fullyestablished, that it _may_ not be adequate or even true; yet I canonly believe that until every other possibility has realty beenexhausted scientific biologists should hold fast to the workingprogram that has created the sciences of biology. The vitalistichypothesis may be held, and is held, as a matter of faith; but wecannot call it science without misuse of the word. When we turn, finally, to the genetic or historical part of our task, we find ourselves confronted with precisely the same general problemas in case of the existing organism. Biological investigators havelong since ceased to regard the fact of organic evolution as open toserious discussion. The transmutation of species is not an hypothesisor assumption, it is a fact accurately observed in our laboratories;and the theory of evolution is only questioned in the same verygeneral way in which all the great generalizations of science are heldopen to modification as knowledge advances. But it is a very largequestion what has caused and determined evolution. Here, too, thefundamental problem is, how far the process may be mechanicallyexplicable or comprehensible, how far it is susceptible of formulationin physico-chemical or mechanistic terms. The most essential part ofthis problem relates to the origin of organic adaptations, theproduction of the fit. With Kant, Cuvier and Linnaeus believed thisproblem scientifically insoluble. Lamarck attempted to find a solutionin his theory of the inheritance of the effects of use, disuse andother "acquired characters"; but his theory was insecurely based andalso begged the question, since the power of adaptation through whichuse, disuse and the like produce their effects is precisely that whichmust be explained. Darwin believed he had found a partial solution inhis theory of natural selection, and he was hailed by Haeckel as thebiological Newton who had set at naught the _obiter dictum_ of Kant. But Darwin himself did not consider natural selection as an adequateexplanation, since he called to its aid the subsidiary hypotheses ofsexual selection and the inheritance of acquired characters. If Icorrectly judge, the first of these hypotheses must be considered asof limited application if it is not seriously discredited, while thesecond can at best receive the Scotch verdict, not proven. In anycase, natural selection must fight its own battles. Latter day biologists have come to see clearly that the inadequacy ofnatural selection lies in its failure to explain the origin of thefit; and Darwin himself recognized clearly enough that it is not anoriginative or creative principle. It is only a condition of survival, and hence a condition of progress. But whether we conceive with Darwinthat selection has acted mainly upon slight individual variations, orwith DeVries that it has operated with larger and more stablemutations, any adequate general theory of evolution must explain theorigin of the fit. Now, under the theory of natural selection, pureand simple, adaptation or fitness has a merely casual or accidentalcharacter. In itself the fit has no more significance than the unfit. It is only one out of many possibilities of change, and evolution bynatural selection resolves itself into a series of lucky accidents. For Agassiz or Cuvier the fit is that which was designed to fit. Fornatural selection, pure and simple, the fit is that which happens tofit. I, for one, am unable to find a logical flaw in this conceptionof the fit; and perhaps we may be forced to accept it as sufficient. But I believe that naturalists do not yet rest content with it. Darwinhimself was repeatedly brought to a standstill, not merely by specificdifficulties in the application of his theory, but also by a certaininstinctive or temperamental dissatisfaction with such a generalconclusion as the one I have indicated; and many able naturalists feelthe same difficulty to-day. Whether this be justified or not, it isundoubtedly the fact that few working naturalists feel convinced thatthe problem of organic evolution has been fully solved. One of thequestions with which research is seriously engaged is whethervariations or mutations are indeterminate, as Darwin on the wholebelieved, or whether they may be in greater or less degreedeterminate, proceeding along definite lines as if impelled by a _visa tergo_. The theory of "orthogenesis, " proposed by Naegeli and Eimer, makes the latter assumption; and it has found a considerable number ofadherents among recent biological investigators, including some of ourown colleagues, who have made important contributions to theinvestigation of this fundamental question. It is too soon to venturea prediction as to the ultimate result. That evolution has beenorthogenetic in the case of certain groups, seems to be wellestablished, but many difficulties stand in the way of its acceptanceas a general principle of explanation. The uncertainty that stillhangs over this question and that of the heredity of acquiredcharacters bears witness to the unsettled state of opinion regardingthe whole problem, and to the inadequacy of the attempts thus far madeto find its consistent and adequate solution. Here, too, accordingly, we find ourselves confronted with wide gaps inour knowledge which open the way to vitalistic or transcendentaltheories of development. I think we should resist the temptation toseek such refuge. It is more than probable that there are factors ofevolution still unknown. We can but seek for them. Nothing is morecertain than that life and the evolution of life are naturalphenomena. We must approach them, and as far as I can see must attemptto analyze them, by the same methods that are employed in the study ofother natural phenomena. The student of nature can do no more thanstrive towards the truth. When he does not find the whole truth thereis but one gospel for his salvation--still to strive towards thetruth. He knows that each forward step on the highway of discoverywill bring to view a new horizon of regions still unknown. It will bean ill day for science when it can find no more fields to conquer. Andso, if you ask whether I look to a day when we shall know the wholetruth in regard to organic mechanism and organic evolution, I answer:No! But let us go forward. COLUMBIA UNIVERSITY PRESS A Series of twenty-two lectures descriptive in untechnical language of the achievements in Science, Philosophy and Art, and indicating the present status of these subjects as concepts of human knowledge, are being delivered at Columbia University, during the academic year 1907-1908, by various professors chosen to represent the several departments of instruction. MATHEMATICS, by Cassius Jackson Keyser, _Adrain Professor of Mathematics_. PHYSICS, by Ernest Fox Nichols, _Professor of Experimental Physics_. CHEMISTRY, by Charles F. Chandler, _Professor of Chemistry_. ASTRONOMY, by Harold Jacoby, _Rutherfurd Professor of Astronomy_. GEOLOGY, by James Furman Kemp. _Professor of Geology_. BIOLOGY, by Edmund B. Wilson, _Professor of Zoology_. PHYSIOLOGY, by Frederic S. Lee, _Professor of Physiology_. BOTANY, by Herbert Maule Richards, _Professor of Botany_. ZOOLOGY, by Henry E. Crampton, _Professor of Zoology_. ANTHROPOLOGY, by Franz Boas. _Professor of Anthropology_. ARCHAEOLOGY, by James Rignall Wheeler, _Professor of Greek Archaeology and Art_. HISTORY, by James Harvey Robinson, _Professor of History_. ECONOMICS, by Henry Rogers Seager, _Professor of Political Economy_. POLITICS, by Charles A. Beard, _Adjunct Professor of Politics_. JURISPRUDENCE, by Munroe Smith, _Professor of Roman Law and Comparative Jurisprudence_. SOCIOLOGY, by Franklin Henry Giddings, _Professor of Sociology_. PHILOSOPHY, by Nicholas Murray Butler. _President of the University_. PSYCHOLOGY, by Robert S. Woodworth, _Adjunct Professor of Psychology_. METAPHYSICS, by Frederick J. E. Woodbridge, _Johnsonian Professor of Philosophy_. ETHICS, by John Dewey, _Professor of Philosophy_. PHILOLOGY, by A. V. W. Jackson, _Professor of Indo-Iranian Languages_. LITERATURE, by Harry Thurston Peck, _Anthon Professor of the Latin Language and Literature_. These lectures are published by the Columbia University Press separately in pamphlet form, at the uniform price of twenty-five cents, by mail twenty-eight cents. Orders will be taken for the separate pamphlets, or for the whole series. Address THE COLUMBIA UNIVERSITY PRESS Columbia University, New York * * * * *