Produced by Stephen Hutcheson, Marcia Brooks and the Online Distributed Proofreading Canada Team at http://www.pgdpcanada.net (This file was produced from images generously made available by The Internet Archive/American Libraries.) [Illustration: HEX CURASSOW FEEDING YOUNG BIRD, WITH PLUMAGE OF THE GLOBOSE CURASSOW] THE MAKING OF SPECIES BY DOUGLAS DEWAR, B.A. (Cantab), I.C.S., F.Z.S. AND FRANK FINN, B.A. (Oxon), F.Z.S., M.B.O.U. WITH FIFTEEN ILLUSTRATIONS LONDON: JOHN LANE THE BODLEY HEAD NEW YORK: JOHN LANE COMPANY MCMIX _Turnbull & Spears, Printers, Edinburgh_ PREFACE Post-Darwinian books on evolution fall naturally into four classes. I. Those which preach Wallaceism, as, for example, Wallaceâs _Darwinism_, Poultonâs _Essays on Evolution_, and the voluminous works of Weismann. II. Those advocating Lamarckism. Copeâs _Factors of Evolution_ and the writings of Haeckel belong to this class. III. The writings of De Vries, forming a group by themselves. They advocate the theory that species spring suddenly into being; that new species arise by mutations from pre-existing species. IV. The large number of books of a more judicial nature, books written by men who decline to subscribe to any of the above three creeds. Excellent examples of such works are Kellogâs _Darwinism To-Day_, Lockâs _Recent Progress in the Study of Variation, Heredity, and Evolution_, and T. H. Morganâs _Evolution and Adaptation_. All four classes are characterised by defects. Books of the two first classes exhibit the faults of ardent partisanship. They formulate creeds, and, as Huxley truly remarked, âScience commits suicide when it adopts a creed.â The books which come under the third category have the defects of extreme youth. De Vries has discovered a new principle, and it is but natural that he should exaggerate its importance, and see in it more than it contains. But, as time wears on, these faults will disappear, and the theory of mutations will assume its true form and fall into its proper place, which is somewhere between the dustbin, to which Wallaceians would relegate it, and the exalted pinnacle on to which De Vries would elevate it. In the present state of our knowledge, books of Class IV. are the most useful to the student, since they are unbiassed, and contain a judicial summing-up of the evidence for and against the various evolutionary theories which now occupy the field. Their chief defect is that they are almost entirely destructive. They shatter the faith of the reader, but offer nothing in place of that which they have destroyed. T. H. Morganâs _Evolution and Adaptation_, however, contains much constructive matter, and so is the most valuable work of this class in existence. Zoological science stands in urgent need of constructive books on evolutionâbooks with leanings towards neither Wallaceism, nor Lamarckism, nor De Vriesism; books which shall set forth facts of all kinds, concealing none, not even those which do not admit of explanation in the present state of our knowledge.âIt has been our aim to produce a book of this description. We have endeavoured to demonstrate that neither pure Lamarckism nor pure Wallaceism affords a satisfactory explanation of the various phenomena of the organic world. We have further, while recognising the very great value of the work of De Vries, tried to show that that eminent botanist has allowed his enthusiasm to carry him a little too far into the realm of speculation. We have followed up the exposure of the weak points of the theories, which at present occupy the field, with certain suggestions, which, we believe, throw new light on many biological problems. Our aim in writing this book has been twofold. In the first place we have attempted to place before the general public in simple language a true statement of the present position of biological science. In the second place, we have endeavoured to furnish the scientific men of the day with food for reflection. Even as the British nation seems to be slowly but surely losing, through its conservatism, the commercial supremacy it had the good fortune to gain last century, so is it losing, through the unwillingness of many of our scientific men to keep abreast of the times, that scientific supremacy which we gained in the middle of last century by the labours of Charles Darwin and Alfred Russell Wallace. To-day it is not among Englishmen, but among Americans and Continentals, that we have to look for advanced scientific ideas. Even as the Ultra-Cobdenites believe that Free Trade is a panacea for all economic ills, so do most English men of science believe that natural selection offers the key to every zoological problem. Both are living in a foolâs paradise. Another reason why Great Britain is losing her scientific supremacy is that too little attention is paid to bionomics, or the study of live animals. Morphology, or the science of dead organisms, receives more than its due share of attention. It is in the open, not in the museum or the dissecting-room, that nature can best be studied. Far be it from us to deprecate the study of morphology. We wish merely to insist upon the fact, that the leaders of biological science must of necessity be those naturalists who go to the tropics and other parts of the earth where nature can be studied under the most favourable conditions, and those who conduct scientific breeding experiments. Natural selectionâthe idea which has revolutionised modern biological scienceâcame, not to professors, but to a couple of field-naturalists who were pursuing their researches in tropical countries. It is absurd to expect those who stay at home and gain most of their knowledge second-hand to be the pioneers of biological science. We fear that this book will come as a rude shock to many scientific men. By way of consolation we may remind such that they will find themselves in much the same position as that occupied by theologians immediately after the appearance of the _Origin of Species_. At that time theological thought was cramped by dogma. But the clergy have since reconsidered their position, they have modified their views, and thus kept abreast of the times. Meanwhile scientific men have lagged behind. The blight of dogma has seized hold of them. They have adopted a creed to which all must subscribe or be condemned as heretics. Huxley said that the adoption of a creed was tantamount to suicide. We are endeavouring to save biology in England from committing suicide, to save it from the hands of those into which it has fallen. We would emphasise that it is not Darwinism we are attacking, but that which is erroneously called Neo-Darwinism. Neo-Darwinism is a pathological growth on Darwinism, which, we fear, can be removed only by a surgical operation. Darwin, himself, protested in vain against the length to which some of his followers were pushing his theory. On p. 657 of the new edition of the _Origin of Species_ he wrote: âAs my conclusions have lately been much misrepresented, and as it has been stated that I attribute the modification of species exclusively to natural selection, I may be permitted to remark that in the first edition of this work, and subsequently, I placed in a most conspicuous positionânamely, at the close of the Introductionâthe following words: âI am convinced that natural selection has been the main but not the exclusive means of modification.â This has been of no avail. Great is the power of steady misrepresentation; but the history of science shows that this power does not long endure.â Notwithstanding this protest the Wallaceians continue on their course, and give to the world a spurious Darwinism. It is our belief that were Darwin alive to-day his sympathies would be with us, and not with those who call themselves his followers. It was one of Darwinâs strong points that he never avoided facts. If new facts came to light which were incompatible with a theory of his, he promptly modified his theory. Since his death a number of new facts have come to light which, in our opinion, plainly indicate that the theory of natural selection as enunciated by Darwin needs considerable modification. We have in this book set forth certain of these facts and indicated the directions in which the Darwinian theory seems to require modification. This volume originated as the result of several conversations we, the joint authors, had last summer. We discovered that we had a great many ideas in common on the subject of evolution. This seemed strange, seeing that our education had not been on the same lines. One of us took a degree in natural science at Cambridge, and subsequently entered His Majestyâs Indian Civil Service, but continued his zoological studies in India as a hobby. The other, a naturalist from childhood, nevertheless took a classical degree at Oxford, then received a technical zoological training, adopted zoology as a profession, and held for some years a position in the Natural History Museum at Calcutta. Our conversations revealed that we were both of opinion that biology is in an unhealthy condition, especially in England, and that the science sorely needs some fresh impetus. Neither of us had the time to attempt, single-handed, to give the required impetus, but as one of us happened to be home on eighteen monthsâ leave, we thought we might undertake the task in collaboration. We felt that we might collaborate the more successfully because the large number of facts collected by the one of us form the necessary complement to the philosophical studies of the other. We have endeavoured, so far as possible, to avoid technical terms, and have made a special point of quoting, wherever practicable, familiar animals as examples, in order that the work may make its appeal not only to the zoologist but to the general reader. It may, perhaps, be urged against us that we have quoted too freely from popular writings, including those of which we are the authors. Our reply to this is that the study of bionomics, the science of living animals, occupies so small a place in English scientific literature that we have been compelled to have recourse to popular works for many of our facts; and we would, moreover, point out that a popular work is not necessarily inaccurate in its information. In conclusion, we would warn the reader against the danger of confounding Inference with Fact. The failure to distinguish between the two has vitiated much of the work of the Wallaceian school of biologists. Facts are always to be accepted. Inferences should be scrutinised with the utmost care. In making our deductions, we have endeavoured to act without bias. We shall, therefore, welcome any new facts, be they consistent with, or opposed to, our inferences. D. D. F. F. CONTENTS PAGE CHAPTER I 1 Rise of the Theory of Natural Selection and its Subsequent Development Pre-Darwinian EvolutionistsâCauses which led to the speedy triumph of the theory of Natural SelectionâNature of the opposition which Darwin had to overcomeâPost-Darwinian biologyâUsually accepted classification of present-day biologists as Neo-Lamarckians and Neo-Darwinians is faultyâBiologists fall into three classes rather than twoâNeo-Lamarckism: its defectsâWallaceism: its defectsâNeo-Darwinism distinguished from Neo-Lamarckism and WallaceismâNeo-Darwinism realises the strength and weakness of the theory of Natural Selection, recognises the complexity of the problems which biologists are endeavouring to solve. CHAPTER II 30 Some of the more Important Objections to the Theory of Natural Selection Brief statement of TheoryâObjections to the Theory fall into two classesâThose which strike at the root of the TheoryâThose which deny the all-sufficiency of Natural SelectionâObjections which strike at root of Theory are based on misconceptionâObjections to WallaceismâThe Theory fails to explain the origin of VariationsâNatural Selection called on to explain too muchâUnable to explain beginnings of new organsâThe Theory of change of functionâThe co-ordination of variationsâThe fertility of races of domesticated animalsâMissing linksâSwamping effects of intercrossingâSmall variations cannot have a survival valueâRaces inhabiting same areaâExcessive specialisationâChance and Natural SelectionâStruggle for existence most severe among young animalsâNatural Selection fails to explain mimicry and other phenomena of colourâConclusion, that scarcely an organism exists which does not possess some feature inexplicable on the theory of Natural Selection as held by Wallace and his followers. CHAPTER III 52 Variation The assumption of Darwin and Wallace that variations are haphazard in origin and indefinite in directionâIf these assumptions be not correct Natural Selection ceases to be the fundamental factor in evolutionâDarwinâs views regarding variation underwent modificationâHe eventually recognised the distinction between definite and indefinite variations, and between continuous and discontinuous variationsâDarwin attached but little importance to either definite or discontinuous variationsâDarwinâs views on the causes of variationsâCriticism of Darwinâs viewsâVariations appear to occur along certain definite linesâThere seems to be a limit to the extent to which fluctuating variations can be accumulatedâDe Vriesâ experimentsâBateson on âdiscontinuous variationââViews held by De VriesâDistinction between continuous and discontinuous variationsâThe work of De VriesâAdvantages enjoyed by the botanist in experimenting on the making of speciesâDifficulties encountered by the animal breederâMutations among animalsâThe distinction between germinal and somatic variationsâThe latter, though not transmitted to offspring, are often of considerable value to their possessor in the struggle for existence. CHAPTER IV 111 Hybridism The alleged sterility of hybrids a stumbling-block to evolutionistsâHuxleyâs viewsâWallace on the sterility of hybridsâDarwin on the sameâWallaceâs theory that the infertility of hybrids has been caused by Natural Selection so as to prevent the evils of intercrossingâCrosses between distinct species not necessarily infertileâFertile crosses between species of plantsâSterile plant hybridsâFertile mammalian hybridsâFertile bird hybridsâFertile hybrids among amphibiaâLimits of hybridisationâMultiple hybridsâCharacters of hybridsâHybridism does not appear to have exercised much effect on the origin of new species. CHAPTER V 133 Inheritance Phenomena which a complete theory of inheritance must explainâIn the present state of our knowledge it is not possible to formulate a complete theory of inheritanceâDifferent kinds of inheritanceâMendelâs experiments and theoryâThe value and importance of Mendelism has been exaggeratedâDominance sometimes imperfectâBehaviour of the nucleus of the sexual cellâChromosomesâExperiments of Delage and LoebâThose of CuÃ©not on mice and Castle on guinea pigsâSuggested modification of the generally-accepted Mendelian formulÃ¦âUnit charactersâBiological isomerismâBiological moleculesâInterpretation of the phenomena of variation and heredity on the conception of biological moleculesâCorrelationâSummary of the conception of biological molecules. CHAPTER VI 170 The Colouration of Organisms The theory of protective colouration has been carried to absurd lengthsâIt will not bear close scrutinyâCryptic colouringâSematic coloursâPseudo-sematic coloursâBatesian and MÃ¼llerian mimicryâConditions necessary for mimicryâExamplesâRecognition markingsâThe theory of obliterative colourationâCriticism of the theoryâObjections to the theory of cryptic colouringâWhiteness of the Arctic fauna is exaggeratedâIllustrative tablesâPelagic organismsâObjectors to the Neo-Darwinian theories of colouration are to be found among field naturalistsâG. A. B. Dewar, Gadow, Robinson, F. C. Selous quotedâColours of birdsâ eggsâWarning colourationâObjections to the theoryâEisigâs theoryâSo-called intimidating attitudes of animalsâMimicryâThe case for the theoryâThe case against the theoryââFalse mimicryââTheory of recognition coloursâThe theory refutedâColours of flowers and fruitsâNeo-Darwinian explanationsâObjectionsâKay Robinsonâs theoryâConclusion that Neo-Darwinian theories are untenableâSome suggestions regarding the colouration of animalsâThrough the diversity of colouring of organisms something like order runsâThe connection between biological molecules and colourâTylor on colour patterns in animalsâBonhoteâs theory of pÅcilomeresâSummary of conclusions arrived at. CHAPTER VII 297 Sexual Dimorphism Meaning of the termâFatal to WallaceismâSexual SelectionâThe law of battleâFemale preferenceâMutual SelectionâFinnâs experimentsâObjections to the theory of Sexual SelectionâWallaceâs explanation of sexual dimorphism stated and shown to be unsatisfactoryâThe explanation of Thomson and Geddes shown to be inadequateâStolzmannâs theory stated and criticisedâNeo-Lamarckian explanation of sexual dimorphism stated and criticisedâSome features of sexual dimorphismâDissimilarity of the sexes probably arises as a sudden mutationâThe four kinds of mutationsâSexual dimorphism having shown itself, Natural Selection determines whether or not the organisms which display it shall survive. CHAPTER VIII 345 The Factors of Evolution Variation along definite lines and Natural Selection are undoubtedly important factors of evolutionâWhether or not sexual selection is a factor we are not yet in a position to decideâ_Modus operandi_ of Natural SelectionâCorrelation an important factorâExamples of correlationâCorrelation is a subject that requires close studyâIsolation a factor in evolutionâDiscriminate isolationâIndiscriminate isolationâIs the latter a factor?âRomanesâ viewsâCriticism of theseâIndiscriminate isolation shown to be a factorâSummary of the methods in which new species ariseâNatural Selection does not make speciesâIt merely decides which of certain ready-made forms shall surviveâNatural Selection compared to a competitive examination and to a medical boardâWe are yet in darkness as to the fundamental causes of the Origin of SpeciesâIn experiment and observation rather than speculation lies the hope of discovering the nature of these causes. Footnotes 389 Index 389 LIST OF ILLUSTRATIONS FACING PAGE Heckâs Curassow feeding Young Bird, which has the Plumage of the Hens of the Globose Curassow, its Fatherâs Species _Frontispiece_ _By permission of the Avicultural Society._ A Turbit belonging to Mr H. P. Scatliff 92 _From âThe Modern Turbit,â published by âThe Feathered World,â London._ Yellow-Rumped and Chestnut-Breasted Finches, with Specimens in Transitional State 98 On the left, the yellow-rumped finch; on the right, the chestnut-breasted; birds in state of change in the middle. _By permission of the Avicultural Society._ Male Amherst Pheasant 122 The chief colours of this species (_Chrysolophus amherstiÃ¦_) are white and metallic green, so that it is very different in appearance from its near ally the gold pheasant. Harlequin Quail (_Coturnix delegorguei_) 124 _By permission of the Avicultural Society._ Rain Quail (_Coturnix coromandelica_) 124 The markings on the throats of these quails are of the type usually put down as ârecognition marks,â but as the Harlequin Quail is African and the Rain Quail Indian, the two species cannot possibly interbreed. The pattern, then, can have no ârecognitionâ significance. _By permission of the Avicultural Society._ Bouru Friar-Bird 222 Like most of the group to which it belongs, this honey-eater (_Tropidorhynchus bouruensis_) is a soberly coloured bird, but is noisy, active, and aggressive. _By permission of Messrs Hutchinson & Co._ Bouru Oriole 222 This âmimickingâ oriole (_Oriolus bouruensis_) is of the same tone of colour as its supposed model the Friar-bird of the same island. _By permission of Messrs Hutchinson & Co._ King-Crow or Drongo 232 This very conspicuous black bird (_Dicrurus ater_), ranging from Africa to China, is a striking feature of the landscape wherever it occurs. _By permission of Messrs Hutchinson & Co._ Drongo-Cuckoo 232 The fork of the tail in this bird is unique among cuckoos, but is nevertheless much less developed than in the supposed model, and may be an adaptation for evolutions in flight, as such tails usually appear to be. _By permission of Messrs Hutchinson & Co._ Shikra Hawk 236 The upper surface of the tail, not shown in this drawing, exactly corresponds with that of the cuckoo âmimic.â _By permission of Messrs Hutchinson & Co._ Hawk-Cuckoo 236 This species (_Hierococcyx varius_) is commonly known in India as the âBrain-fever bird.â _By permission of Messrs Hutchinson & Co._ Brazilian Troupial 284 This species (_Icterus vulgaris_) is that most frequently seen in captivity; the pattern of colour is found in several other allied forms. _By permission of Messrs Hutchinson & Co._ Indian Black-Headed Oriole 284 Several other orioles besides this (_O. melanocephalus_) have the black head. _By permission of Messrs Hutchinson & Co._ Queen Whydah 298 This species (_Tetraenura regia_) is a typical example of seasonal sexual dimorphism, the male being long-tailed and conspicuously coloured only during the breeding season, and at other times resembling the sparrow-like female. _By permission of the Foreign Bird Club._ Courtship of Skylark 314 Illustrating display by a species with no decorative colouring or sex difference. THE MAKING OF SPECIES CHAPTER I RISE OF THE THEORY OF NATURAL SELECTION AND ITS SUBSEQUENT DEVELOPMENT Pre-Darwinian EvolutionistsâCauses which led to the speedy triumph of the theory of Natural SelectionâNature of the opposition which Darwin had to overcomeâPost-Darwinian biologyâUsually accepted classification of present-day biologists as Neo-Lamarckians and Neo-Darwinians is faultyâBiologists fall into three classes rather than twoâNeo-Lamarckism: its defectsâWallaceism: its defectsâNeo-Darwinism distinguished from Neo-Lamarckism and WallaceismâNeo-Darwinism realises the strength and weakness of the theory of Natural Selection, recognises the complexity of the problems which biologists are endeavouring to solve. Darwinism and evolution are not interchangeable terms. On this fact it is impossible to lay too much emphasis. Charles Darwin was not the originator of the theory of evolution, nor even the first to advocate it in modern times. The idea that all existing things have been produced by natural causes from some primordial material is as old as Aristotle. It was lost sight of in the mental stagnation of the Middle Ages. In that dark period zoological science was completely submerged. It was not until men shook off the mental lethargy that had held them for many generations that serious attention was paid to biology. From the moment when men began to apply scientific methods to that branch of knowledge the idea of evolution found supporters. Buffon suggested that species are not fixed, but may be gradually changed by natural causes into different species. Goethe was a thorough-going evolutionist; he asserted that all animals were probably descended from a common original type. Lamarck was the first evolutionist who sought to show the means whereby evolution has been effected. He tried to prove that the efforts of animals are the causes of variation; that these efforts originate changes in form during the life of the individual which are transmitted to its offspring. St Hilaire was another evolutionist who endeavoured to explain how evolution had occurred. He believed that the transformations of animals are effected by changes in their environment. These hypotheses were considered, and rightly considered, insufficient to explain anything like general evolution, so that the idea failed for a time to make headway. Strength of Darwinâs Position As knowledge grew, as facts accumulated, the belief in evolution became more widespread. Hutton, Lyell, Spencer, and Huxley were all convinced that evolution had occurred, but they could not explain how it had occurred. Thus, by the middle of last century, all that was needed to make evolution an article of scientific belief was the discovery of a method whereby it could be effected. This Darwin and Wallace were able to furnish in the shape of the theory of natural selection. The discovery was made independently, but Darwin being the older man, the more influential, and the one who had gone the more deeply and carefully into the matter, gained the lionâs share of the credit of the discovery. The theory of natural selection is universally known as the Darwinian theory, notwithstanding the fact that Darwin, unlike Wallace, always recognised that natural selection is not the sole determining factor in organic evolution. From the moment of the enunciation of his great hypothesis, Darwinâs position was an exceedingly strong one. Everything was in his favour. As we have seen, the theory was enunciated at the psychological moment, at the time when zoological science was ripe for it. Most of the leading zoologists were evolutionists at heart, and were only too ready to accept any theory which afforded a plausible explanation of what they believed to have occurred. Hence the rapturous welcome accorded to the theory of natural selection by the more progressive biologists. Another point in Darwinâs favour was the delightful simplicity of his hypothesis. Nothing could be more enticingly probable. It is based on the unassailable facts of variation, heredity, and the tendency of animals to multiply in numbers. Everybody knows that the breeder can fix varieties by careful breeding. Darwin had simply to show that there is in nature something to take the part played among domesticated animals by the human breeder. This he was able to do. As the numbers of species remain stationary, it is evident that only a small portion of the animals that are born can reach maturity. A child can see that the individuals most likely to survive are those best adapted to the circumstances of their life. Even as the breeder weeds out of his stock the creatures not suited to his purpose, so in nature do the unfit perish in the everlasting struggle for existence. In nature there is a selection corresponding to that of the breeder. It is useless to deny the existence of this selection in nature, this natural selection. The only disputable point is whether such selection can do all that Darwin demanded of it. The man in the street, then, was able to comprehend the theory of natural selection. This was greatly in its favour. Men are usually well disposed towards doctrines which they can readily understand. The nineteenth century was a superficial age. It liked simplicity in all things. If Darwin could show that natural selection was capable of producing one species, men were not only ready but eager to believe that it could explain the whole of organic evolution. The simplicity of the Darwinian theory has its evil side. It has undoubtedly tended to make modern biologists superficial in their methods. It has, indeed, stimulated the imagination of men of science; but the stimulation has not in all cases been a healthy one. So far from adhering to the sound rule laid down by Pasteur, ânever advance anything that cannot be proved in a simple and decisive manner,â many modern naturalists allow their imagination to run riot, and so formulate ill-considered theories, and build up hypotheses on the most insecure foundations. âA tiny islet of truth,â writes Archdale Reid, âis discovered, on which are built tremendous and totally illegitimate hypotheses.â Another source of Darwinâs strength was the vast store of knowledge he had accumulated. For twenty years he had been steadily amassing facts in support of his hypothesis. He enunciated no crude theory, he indulged in no wild speculations. He was content to marshal a great array of facts, and to draw logical conclusions therefrom. He was as cautious in his deductions as he was careful of his facts. He thus stood head and shoulders above the biologists of his day. He was a giant among pigmies. So well equipped was he that those who attempted to oppose him found themselves in the position of men, armed with bows and arrows, who seek to storm a fortress defended by maxim guns. Nor was this all. The majority of the best biologists of his time did not attempt to oppose him. They were, as we have seen, ready to receive with open arms any hypothesis which seemed to explain how evolution had occurred. Some of them perceived that there were weak points in the Darwinian theory, but they preferred not to expose these; they were rather disposed to make the best of the hypothesis. It had so many merits that it seemed to them but reasonable to suppose that subsequent investigation would prove that the defects were apparent rather than real. Opponents of Darwin We hear much of the âmagnitude of the prejudicesâ which Darwin had to overcome, and of the mighty battle which Darwin and his lieutenant Huxley had to fight before the theory of the origin of species by natural selection obtained acceptance. We venture to say that statements such as these are misleading. We think we may safely assert that scarcely ever has a theory which fundamentally changed the prevailing scientific beliefs met with less opposition. It would have been a good thing for zoology had Darwin not obtained so easy a victory. Sir Richard Owen, a distinguished anatomist, certainly attacked the doctrine in no unmeasured terms, but his attack was anonymous and so cannot be considered very formidable. Far more important was the opposition of Dr St George Mivart, whose worth as a biologist has never been properly appreciated. His most important work, entitled the _Genesis of Species_, might be read with profit even now by many of our modern Darwinians. For some time after the publication of the _Origin of Species_ Mivart appears to be almost the only man of science fully alive to the weak points of the Darwinian theory. The great majority seem to have been dazzled by its brilliancy. The main attack on Darwinism was conducted by the theologians and their allies, who considered it to be subversive of the Mosaic account of the Creation. Now, when one whose scientific knowledge is, to say the best of it, not extensive, attacks a man who has studied his subject dispassionately for years, and invariably expresses himself with extreme caution, the onslaught can have but one resultâthe attacker will be repulsed with heavy loss, and the onlookers will have a higher opinion of his valour than of his common sense. The theologians were in the unfortunate position of warriors who do not know what it is against which they are fighting; they confounded natural selection with evolution, and directed the main force of their attack against the latter, under the impression that they were fighting the Darwinian theory. It was the misfortune of those theologians that it is possible to prove that evolution, or, at any rate, some evolution has occurred; they thus kicked against the pricks with disastrous results to themselves. When this attack had been repulsed men believed that the theory of natural selection had been demonstrated, that it was as much a law of nature as that of gravitation. What had really happened was that the fact of evolution had been proved, and the theory of natural selection obtained the credit. Men thought that Darwinism was evolution. Had the theologians admitted evolution but denied the ability of natural selection to explain it, the Darwinian theory, in all probability, would not have gained the ascendency which it now enjoys. Evolution and Natural Selection To us who are able to look back dispassionately upon the biological warfare of the last century, Darwinâs opponentsâor the majority of themâappear very foolish. We must, however, bear in mind that at the time of the publication of the _Origin of Species_ both natural selection and evolution were comparatively unknown ideas. Darwin had to fight for both. He had to prove evolution as well as natural selection. Many of the facts adduced by him supported both. It is, therefore, not altogether surprising that many of his opponents failed to distinguish between them. A glance at the _Origin of Species_ will suffice to show how considerable is the portion of the book that deals with the evidence in favour of evolution rather than of natural selection. Of the fourteen chapters which make up the book no fewer than nine are devoted to proving that evolution has occurred. It has been truly said, that for every one fact biologists have found in support of the special theory of natural selection they have found ten facts supporting the doctrine of evolution. Darwin, then, was in the position of a skilled barrister who has a plausible case and who knows the ins and outs of his brief, while his opponents stood in the shoes of inexperienced counsel who had but recently received their brief, and who had not had the time to master the details thereof. In such circumstances it is not difficult to predict which way the verdict of the jury will go. Darwin, moreover, had a charming personality. Never was a man with a theory less dogmatic. Never was the holder of a theory more careful of the expressions he used. Never was a scientific man more ready to give ear to his opponents, to meet them half way, and, where necessary, to compromise. Darwin was not afraid of facts, and was always ready to alter his views when they appeared to be opposed to facts. The average scientific man of to-day makes facts fit his theory; if they refuse to fit it he ignores or denies them. Darwin continually modified his views; when he found himself in a tight place he did not hesitate to resort to Lamarckian factors, such as the inheritance of the effects of use and disuse and of the effects of environment. He conceded that natural selection was insufficient to account for all the phenomena of organic evolution, and advanced the theory of sexual selection in order to account for facts which the major hypothesis seemed to him incapable of explaining. Darwin, moreover, having ample private means, was not obliged to work for a living, and was therefore able to devote the whole of his time to research. The advantages of such a position cannot be over-estimated, and, perhaps, have not been sufficiently taken into account in apportioning the praise between Darwin and Wallace for their great discovery. Huxley To all these factors in Darwinâs favour we must add his good fortune in possessing so able a lieutenant as Huxley. Huxley was an ardent evolutionist, an able writer, and a brilliant debater. A man of his mental calibre was able, like a clever barrister, to make out a plausible case for any theory which he chose to take up. While nominally a strong supporter of the Darwinian theory, he was in reality fighting for the doctrine of descent. Had _any_ plausible theory of evolution been enunciated, Huxley would undoubtedly have fought for it equally earnestly. A firm believer in evolution, Huxley was, as Professor Poulton says, confronted by two difficulties,âfirst, the insufficiency of the evidence of evolution, and, secondly, the absence of any explanation of how the phenomenon had occurred. The _Origin of Species_ solved both these difficulties. It adduced much weighty evidence in favour of evolution, and suggested a _modus operandi_. Small wonder, then, that Huxley became a champion of Darwinism. But, as Poulton writes, on page 202 of _Essays on Evolution_, âwhile natural selection thus enabled Huxley freely to accept evolution, he was by no means fully satisfied with it.â âHe never committed himself to a full belief in natural selection, and even contemplated the possibility of its ultimate disappearance.â To use Huxleyâs own words: âWhether the particular shape which the doctrine of evolution, as applied to the organic world, took in Darwinâs hands, would prove to be final or not, was, to me, a matter of indifference.â The result of the fortuitous combination of the circumstances which we have set forth was that in a surprisingly short time the theory of natural selection came to be regarded as a law of nature on a par with the laws of gravitation. Thus, paradoxical though it seems, practical certainty was given to a hitherto uncertain doctrine by the addition of a still more uncertain theory. âAt once,â writes Waggett, âthe theory of development leapt from the position of an obscure guess to that of a fully-equipped theory and almost a certainty.â Darwin thus became a dictator whose authority none durst question. A crowd of slavish adherents gathered round him, a herd of men to whom he seemed an absolutely unquestionable authority. Darwinism became a creed to which all must subscribe. It still retains this position in the popular mind. Growing Opposition to Darwinism The ease with which the theory of natural selection gained supremacy was, as we have already said, a misfortune to biological science. It produced for a time a considerable mental stagnation among zoologists. Since Darwinâs day the science has not made the progress that might reasonably have been expected, because the theory has so captivated the minds of the majority of biologists that they see everything through Darwinian spectacles. The wish has been in many cases the father to the observation. Zoologists are ever on the lookout for the action of natural selection, and in consequence frequently imagine they see it where it does not exist. Many naturalists, consciously or unconsciously, stretch facts to make them fit the Darwinian theory. Those facts which refuse to be so distorted are, if not actively ignored or suppressed, overlooked as throwing no light upon the doctrine. This is no exaggeration. A perusal of almost any popular book dealing with zoological theory leaves the impression that there is nothing left to be explained in the living world, that there is no door leading to the secret chambers of nature to which natural selection is not an âopen sesame.â But the triumph of natural selection has not been so complete as its more enthusiastic supporters would have us believe. Some there are who have never admitted the all-sufficiency of natural selection. In the British Isles these have never been numerous. In the United States of America and on the Continent they are more abundant. The tendency seems to be for them to increase in numbers. Hence the recent lamentations of Dr Wallace and Sir E. Ray Lankester. Modern biologists are commonly supposed to fall into two schools of thoughtâthe Neo-Darwinian and the Neo-Lamarckian. The former are the larger body, and pin their faith absolutely to natural selection. They deny the inheritance of acquired characters, and preach the all-sufficiency of natural selection to explain the varied phenomena of nature. The Neo-Lamarckians do not admit the omnipotency of natural selection. Some of them allow it no virtue. Others regard it as a force which keeps variation within fixed limits, which says to each organism, âthus far shalt thou vary and no farther.â This school lays great stress on the inheritance of acquired characters, especially on the inheritance of the effects of use and disuse. The above statement of the recent developments of Darwinism is incomplete, for it fails to include those who occupy a middle position. If it be possible to classify a large number of men of which scarcely any two hold identical views, it is into three, rather than two, classes that they must be divided. Speaking broadly, evolutionists of to-day may be said to represent three distinct lines of thought. For the sake of classification we may speak of them as falling into three schools, which we may term the Neo-Lamarckian, the Wallaceian, and the Neo-Darwinian, according as their views incline towards those held by Lamarck, Wallace, or Darwin. The Neo-Lamarckian School As adherents of the Neo-Lamarckian school, we cite Cope, Spencer, Orr, Eimer, Naegeli, Henslow, Cunningham, Haeckel, Korchinsky, and a number of others. It may almost be said of these Neo-Lamarckians that each holds a totally distinct theory of evolution. So heterogeneous are their views that it is difficult to find a single article common to the evolutionary belief of all. It is commonly asserted that all Neo-Lamarckians are agreed, firstly, that acquired characters are transmissible; and, secondly, that such transmission is an important factor in the production of new species. This assertion is certainly true of the great bulk of Neo-Lamarckians, but it does not appear to hold in the case of those who believe that evolution is the result of some unknown inner force. So far as we can see, a belief in the inheritance of acquired characters is not necessary to the theories of orthogenesis held by Naegeli and Korchinsky. For that reason it would possibly be more correct to place those who hold such views in a fourth school. Since, however, a number of undoubted Neo-Lamarckians, as, for example, Cope, believe in an inner growth-force, it is convenient to regard Naegeli as a Neo-Lamarckian. His views need not detain us long. Those who wish to study them in detail will find them in his _Mechanisch-physiologische Theorie der Abstammungslehre_. Naegeli believes that there is inherent in protoplasm a growth-force, which makes each organism in itself a force making towards progressive evolution. He holds that animals and plants would have become much as they are now even if no struggle for existence had taken place. âTo the believers in this kind of . . . orthogenesis,â writes Kellog (_Darwinism To-day_, p. 278), âorganic evolution has been, and is now, ruled by unknown inner forces inherent in organisms, and has been independent of the influence of the outer world. The lines of evolution are immanent, unchangeable, and ever slowly stretch toward some ideal goal.â It is easy to enunciate such a theory, impossible to prove it, and difficult to disprove it. It seems to us that the fact that, so soon as organisms are removed from the struggle for existence, they tend to degenerate, is a sufficient reason for refusing to accept theories of the description put forth by Naegeli. More truly Lamarckian is Eimerâs theory of orthogenesis, according to which it is the environment which determines the direction which variation takes; and the variations which are induced by the environment are transmitted to the offspring. Orrâs Views Spencer and Orr preach nearly pure Lamarckism. The former, while fully recognising the importance of natural selection, considered that sufficient weight has not been given to the effects of use and disuse, or to the direct action of the environment in determining or modifying organisms. The similarity of the views of Orr and Lamarck is best seen by comparing their respective explanations of the long neck of the giraffe. Lamarck thought that this was the direct result of continual stretching. The animal continually strains its neck in the search for food, hence it grows longer as the individual grows older, and this elongated neck has been transmitted to the offspring. Orr writes, on page 164 of his _Development and Heredity_: âThe giraffe seems to present the most remarkable illustration of the lengthening of the bones as the result of the frequent repetition of such shocks. As is well known, this animal feeds on the foliage of trees. From the earliest youth of the species, and the earliest youth of each individual, it must have been stretching upwards for food, and, as is the custom of such quadrupeds, it must have constantly raised itself off its forefeet, and, as it dropped, must have received a shock that made itself felt from the hoofs through the legs and vertical neck to the head. In the hind legs the shock would not be felt. It is impossible to imagine that an animal which, during the greater part of every day of its life (both its individual and racial life), performed motions so uniform and constant, would not be peculiarly specialised as a result. The forces acting upon such an animal are widely different from the forces acting upon an animal which eats the grass at its feet like an ox, or one which must run and climb like a goat or a deer, and the resultant modifications of growth in the several cases must also be different. The principle of increased growth in the direction of the shock, resulting from superabundant repair of the momentary compression, explains how the giraffe acquired the phenomenal length of the bones of its forelegs and neck; and the absence of the shock in the hind-quarters shows why they remained undeveloped and absurdly disproportionate to the rest of the body.â Inheritance of Acquired Characters It seems to us that a fatal objection to all these Neo-Lamarckian theories of evolution is that they are based on the assumption that acquired characters are inherited, whereas all the evidence goes to show that such characters are not inherited. In these days, when scientific knowledge is so widely diffused, it is scarcely necessary to say that all the characteristics which an organism displays are either congenital or inborn, or acquired by the organism during its lifetime. Thus a man may have naturally a large biceps muscle, and this is a congenital character; or he may by constant exercise develop or greatly increase the size of the biceps. The large biceps, in so far as it has been increased by exercise, is said to be an acquired character, for it was not inherited by its possessor, but acquired by him in his lifetime. We must bear in mind that the period in the life history of an organism at which a character appears, is not necessarily a test as to whether it is congenital or acquired, for a great many congenital characters, such as a manâs beard, do not appear until some years after birth. As we have seen, the Neo-Lamarckians believe that it is possible for an organism to transmit to its offspring characters which it has acquired during the course of its existence. But, as we have already said, the evidence goes to show that such characters are not inherited. For example, the tail of the young fox-terrier is not shorter than that of other breeds of dogs, notwithstanding the fact that its ancestors have for generations had the greater portion of their caudal appendage removed shortly after birth. We do not propose to discuss at any great length the vexed question of the inheritance of acquired characters, for the simple reason that the Neo-Lamarckians have not brought forward a single instance which indubitably proves that such characters are inherited. Mr J. T. Cunningham, in a paper of great value and interest, entitled âThe Heredity of Secondary Sexual Characters in relation to Hormones: a Theory of the Heredity of Somatogenic Characters,â which appeared in vol. xxvi., No. 3, of the _Archiv fÃ¼r Entwicklungsmechanik des Organismen_, states: âThe dogma that acquired characters cannot be inherited . . . is founded not so much on evidence, or the absence of evidence, as on _a priori_ reasoning, on the supposed difficulty or impossibility of conceiving a means by which such inheritance could be effected.â Such appears certainly to be true of some zoologists, but we trust that Mr Cunningham will do us the justice to believe that our opinion that the inheritance of acquired characters does not play an important part in the evolution of, at any rate, the higher animals, is based, not on the ground of _a priori_ reasoning, but on facts. All the evidence seems to show that such characteristics are not inherited. If, as Mr Cunningham thinks, all secondary sexual characters are due to the inheritance of the effects of use, etc., how is it that no Neo-Lamarckian is able to bring forward a clear case of the inheritance of a well-defined acquired character? If such characteristics are habitually inherited, countless examples should be forthcoming. Fanciers in their endeavours are constantly âdoctoringâ the animals they keep for show purposes; and it seems to us certain that if acquired characters are inherited, breeders would long ago have discovered this and acted upon the discovery. If Neo-Darwinians are charged with refusing to believe that acquired characters are inherited because they âcannot conceive the means by which it could be effected,â may it not be said with equal justice that many Neo-Lamarckians believe that acquired characters are inherited, not on evidence thereof, but because if such characters are not inherited it is very difficult to account for many of the phenomena presented by the organic world? In many of the lower animals, as, for example, the hydra, the germinal material is diffused through the organism, so that a complete individual can be developed from a small portion of the creature. In such circumstances it seems not improbable that the external environment may act directly on the germinal substance, and induce changes in it which may perhaps be transmitted to the offspring. If this be so, it would seem that some acquired characters may be inherited in such organisms. Very many plants can be propagated from cuttings, buds, etc., so that we might reasonably expect some acquired characters to be hereditary in them. The majority of botanists appear to hold Lamarckian views; but on the evidence at present available, it is doubtful whether such views are the correct ones. Plants are so plastic, so protean, so sensitive to their environment that their external structure appears to be determined by the external conditions in which they find themselves quite as much as by their inherited tendencies. In this respect they differ very considerably from the higher animals. The peacock, for example, presents the same outward appearance[1] whether bred and reared in Asia or Europe, in a hot or cold, a damp or a dry climate. The same plant, on the other hand, differs greatly in outward appearance according as it is grown in a dry or a damp soil, a hot or a cold country. In his recent book _The Heredity of Acquired Characters in Plants_, the Rev. G. Henslow cites several examples of the celerity with which plants react to their environment. On page 32 he writes: âThe following is an experiment I made with the common rest-harrow (_Ononis spinosa, L._) growing wild in a very dry situation by a roadside. I collected some seeds, and also took cuttings. These I planted in a garden border, keeping this well moist with a hand-light over it, and a saucer of water, so that the air should be thoroughly moist as well. Its natural conditions were thus completely reversed. They all grew vigorously. The new branches of the first yearâs growth bore spines, proving their hereditary character, but instead of their being long and stout, they were not an inch long, and like needles. This proved the spines to be a hereditary feature. In the second year there were none at all; moreover, the plants blossomed, and, taken altogether, there was no appreciable difference from _O. repens, L._â From this experiment Professor Henslow draws the inference that acquired characters tend to be inherited in plants. In our opinion the experiment affords strong evidence against the Lamarckian doctrine. Here we have a plant which has, perhaps, for thousands of generations developed spines owing to its dry environment. If acquired characters are inherited we should have expected this spiny character to have become fixed and persisted under changed conditions, for some generations
{'title': 'The Making of Species by Douglas Dewar and Frank Finn', 'source': 'Project Gutenberg', 'lang': 'en'}