WAR & OUGLAS DE rp) LABORATORY OF ORNITHOLOGY LIBRARY Ee “ZY DY f | falc Fedli CORNELL UNIVERSITY LIBRARY <= Laboratory of Ornithology {159 Sapsucker Woods Road Cornell University Ithaca, New York 14850 All books are subject to recall after two weeks DATE DUE . GAYLORD PRINTED IN U.S.A. THE MAKING OF SPECIES OTHER WORKS BY THE SAME AUTHORS By DOUGLAS DEWAR BOMBAY DUCKS BIRDS OF THE PLAINS ANIMALS OF NO IMPORTANCE Ere. Etc. By FRANK FINN ORNITHOLOGICAL AND OTHER ODDITIES THE WORLD'S BIRDS WILD BEASTS OF THE WORLD GARDEN AND AVIARY BIRDS IN INDIA Etc. Etc. Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31924022547503 vicudlural Soctety At X CURASSOW By permission of the THE GLOBOSE WENS OF THE or PLUMAGE 29ECIES ITS FATHERS & THE WHICIL HAS CURASSOW, DING YOUNG BIRD, o FEE oy Ik 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 3% 3 LONDON: JOHN LANE THE BODLEY HEAD NEW YORK: JOHN LANE COMPANY MCMIX Onnth QH 3b6 ae Ti urnbull & Spears, Printers, Edinburgh PREFACE OST-DARWINIAN books on evolution fall naturally into four classes. I. Those which preach Wallaceism, as, for ex- ample, Wallace’s Darwzxzsm, Poulton’s Essays on Evolution, and the voluminous works of Weismann. II. Those advocating Lamarckism. Cope’s Factors of Evolutzon 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 Kellog’s Darwinism To-Day, Lock’s Recent Progress in the Study of Variation, Heredity, and Evolution, and T. H. Morgan’s Evolutzon 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, ‘“ Science commits suicide when it adopts a creed.” The Vv The Making of Species 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. Morgan’s Evolutzon 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 evolution— books with leanings towards neither Wallaceism, nor La- marckism, nor De Vriesism ; books which shall set forth facts of all kinds, concealing none, not even those which do not admit of explana- tion in the present state of our knowledge.— vi Preface It 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 specu- lation. 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 biologi- cal 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 un- willingness 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 b vii The Making of Species Russell Wallace. To-day it is not among Englishmen, but among Americans and Con- tinentals, 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 fool’s 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 dis- secting-room, that nature can best be studied. Far be it from us to deprecate the study of mor- phology. 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 con- ditions, and those who conduct scientific breeding experiments. Natural selection—the idea which has revolutionised modern biological science— came, 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 viii Preface 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 them- selves in much the same position as that occupied by theologians immediately after the appearance of the Origen of Spectes. At that time theological thought was cramped by dogma. But the clergy have since recon- sidered 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 push- ing his theory. On p. 657 of the new edition IX The Making of Species 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 en- deavoured to act without bias. We shall, there- fore, welcome any new facts, be they consistent with, or opposed to, our inferences. D. D. FF, xii CONTENTS CHAPTER I RIsE OF THE THEORY OF NATURAL SELECTION AND ITS SUBSEQUENT DEVELOPMENT . ‘ i I PAGE Pre-Darwinian Evolutionists—Causes which led to the speedy triumph of the theory of Natural Selection—Nature of the opposition which Darwin had to overcome—Post-Darwinian biology— Usually accepted classification of present-day biologists as Neo- Lamarckians and Neo-Darwinians is faulty—Biologists fall into three classes rather than two—Neo-Lamarckism : its defects— Wallaceism: its defects—Neo-Darwinism distinguished from Neo-Lamarckism and Wallaceism—Neo-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 SOME OF THE MORE IMPORTANT OBJECTIONS TO THE THEORY OF NATURAL SELECTION . , 30 Brief statement of Theory—Objections to the Theory fall into two classes—Those which strike at the root of the Theory—Those which deny the all-sufficiency of Natural Selection—Objections which strike at root of Theory are based on misconception— Objections to Wallaceism—The Theory fails to explain the origin of Variations—Natural Selection called on to explain too much—Unable to explain beginnings of new organs—The Theory of change of function—The co-ordination of variations —The fertility of races of domesticated animals—Missing links— Swamping effects of intercrossing—Small variations cannot have a survival value—Races inhabiting same area—Excessive specialisation—Chance and Natural Selection—Struggle for existence most severe among young animals—Natural Selection fails to explain mimicry and other phenomena of colour— Conclusion, 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. xiii The Making of Species CHAPTER III PAGE VARIATION. , . . ‘ z 52 The assumption of Darwin and Wallace that variations are haphazard in origin and indefinite in direction—If these assumptions be not correct Natural Selection ceases to be the fundamental factor in evolution—Darwin’s views regarding variation underwent modification—He eventually recognised the distinction between definite and indefinite variations, and between continuous and discontinuous variations—Darwin attached but little importance to either definite or discontinuous variations—Darwin’s views on the causes of variations—Criticism of Darwin’s views—Variations appear to occur along certain definite lines—There seems to be a limit to the extent to which fluctuating variations can be accumulated—De Vries’ experiments—Bateson on ‘‘discon- tinuous variation” — Views held by De Vries— Distinction between continuous and discontinuous variations—The work of De Vries—Advantages enjoyed by the botanist in experimenting on the making of species—Difficulties encountered by the animal breeder—Mutations among animals—The distinction between germinal and somatic variations—The latter, though not transmitted to offspring, are often of considerable value to their possessor in the struggle for existence. CHAPTER IV Hypripism 2 ‘ < a zs IIr The alleged sterility of hybrids a stumbling-block to evolutionists— Huxley’s views—Wallace on the sterility of hybrids—Darwin on the same—Wallace’s theory that the infertility of hybrids has been caused by Natural Selection so as to prevent the evils of intercrossing—Crosses between distinct species not necessarily infertile—Fertile crosses between species of plants—Sterile plant hybrids—Fertile mammalian hybrids—Fertile bird hybrids— Fertile hybrids among amphibia—Limits of hybridisation— Multiple hybrids—Characters of hybrids—Hybridism does not appear to have exercised much effect on the origin of new species. CHAPTER V INHERITANCE . ‘ : p : - 133 Phenomena which a complete theory of inheritance must explain— In the present state of our knowledge it is not possible to formulate a complete theory of inheritance—Different kinds of inheritance—Mendel's experiments and theory—The value and xiv Contents PAGE importance of Mendelism has been exaggerated—Dominance sometimes imperfect—Behaviour of the nucleus of the sexual cell ~—Chromosomes—Experiments of Delage and Loeb—Those of Cuénot on mice and Castle on guinea pigs—Suggested modifica- tion of the generally-accepted Mendelian formulze — Unit characters—Biological isomerism—Biological molecules—Inter- pretation of the phenomena of variation and heredity on the conception of biological molecules—Correlation—Summary of the conception of biological molecules. CHAPTER VI THE COLOURATION OF ORGANISMS . : . 170 The theory of protective colouration has been carried to absurd lengths—It will not bear close scrutiny—Cryptic colouring —Sematic colours — Pseudo-sematic colours — Batesian and Miillerian mimicry — Conditions necessary for mimicry — Examples—Recognition markings—The theory of obliterative colouration—Criticism of the theory—Objections to the theory of cryptic colouring—Whiteness of the Arctic fauna is exaggerated —lIlilustrative tables—Pelagic organisms—Objectors to the Neo- Darwinian theories of colouration are to be found among field naturalists—G. A. B. Dewar, Gadow, Robinson, F, C. Selous quoted—Colours of birds’ eggs—Warning colouration— Objec- tions to the theory—Eisig’s theory—So-called intimidating attitudes of animals—Mimicry—The case for the theory—The case against the theory—“ False mimicry ’—Theory of recogni- tion colours—The theory refuted—Colours of flowers and fruits —Neo-Darwinian explanations—Objections—Kay Robinson’s theory—Conclusion that Neo-Darwinian theories are untenable —Some suggestions regarding the colouration of animals— Through the diversity of colouring of organisms something like order runs—The connection between biological molecules and colour—Tylor on colour patterns in animals—Bonhote's theory of poecilomeres—Summary of conclusions arrived at. CHAPTER VII SExUAL DIMORPHISM . : . . . 297 Meaning of the term—Fatal to Wallaceism—Sexual Selection—The law of battle—Female preference—Mutual Selection — Finn’s experiments — Objections to the theory of Sexual Selection— Wallace’s explanation of sexual dimorphism stated and shown to be unsatisfactory—The explanation of Thomson and Geddes shown to be inadequate—Stolzmann’s theory stated and criticised XV The Making of Species —Neo-Lamarckian explanation of sexual dimorphism stated and criticised—Some features of sexual dimorphism—Dissimilarity of the sexes probably arises as a sudden mutation—The four kinds of mutations—Sexual dimorphism having shown itself, Natural Selection determines whether or not the organisms which display it shall survive. PAGE CHAPTER VIII THe Factors oF EVOLUTION : : 345 Variation along definite lines and Natural Selection are undoubtedly important factors of evolution—Whether or not sexual selection is a factor we are not yet ina position to decide—Modus operandi of Natural Selection—Correlation an important factor—Examples of correlation—Correlation is a subject that requires close study —lIsolation a factor in evolution—Discriminate isolation—Indis- criminate isolation—Is the latter a factor?—Romanes’ views— Criticism of these—Indiscriminate isolation shown to be a factor —Summary of the methods in which new species arise—Natural Selection does not make species—It merely decides which of certain ready-made forms shall survive—Natural Selection com- pared to a competitive examination and to a medical board— We are yet in darkness as to the fundamental causes of the Origin of Species—In experiment and observation rather than speculation lies the hope of discovering the nature of these causes, , INDEX ‘ : . : ‘ - 389 xvi LIST OF ILLUSTRATIONS HEcxk’s CURASSOW FEEDING YOUNG BIRD, WHICH HAS THE PLUMAGE OF THE HENS OF THE GLOBOSE Curassow, ITS FaTHER’s SPECIES . Frontispiece By permission of the Avicultural Society. FACING PAGE A TuRBIT BELONGING TO Mr H. P. ScatTLirr , From‘ The Modern Turbit,” published by‘ The Feathered World,” L ondon. YELLOW-RUMPED AND CHESTNUT-BREASTED FINCHES, WITH SPECIMENS IN TRANSITIONAL STATE < On the left, the yellow-rumped finch; on the right, the chest- nut-breasted ; birds in state of change in the middle. By permission of the Avicultural Society. MALE AMHERST PHEASANT . . ; . The chief colours of this species (Chrysolophus amherstie) are white and metallic green, so that it is very different in appear- ance from its near ally the gold pheasant. HARLEQUIN QuaAIL (Coturnix delegorguet) . By permission of the Avicultural Society. Rain Quait (Coturnix coromandelica) The markings on the throats of these quails are of the type usually put down as ‘‘recognition marks,” but as the Harlequin Quail is African and the Rain Quail Indian, the two species cannot possibly interbreed. The pattern, then, can have no ‘recognition ”’ significance. By permission of the Avicultural Society xvil g2 98 I22 124 124 The Making of Species FACING PAGE Bourvu FriAr-BirRD . F é F . 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 : P ‘ ; é This ‘‘ mimicking” oriole (Oriolus bouruensis) is of the same tone of colour as its supposed model the Friar-bird of the same island. By pernvission of Messrs Hutchinson & Co. Kinc-Crow or Dronco ‘ : ‘ : 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. Dronco-Cuckoo : , , : : 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 Hutchisson & Co. SHIKRA Hawk . ‘ 3 The upper surface of the tail, not shown in this drawing, exactly corresponds with that of the cuckoo ‘‘ mimic,” By permission of Messrs Hutchinson & Co. Hawk-Cuckoo ‘ This species (Hverococcyx varius) is commonly known in India as the ‘' Brain-fever bird.” By permission of Messrs Hutchinson & Co xvili 222 222 232 232 236 236 List of Ilustrations FACING PAGE BRAZILIAN TROUPIAL 5‘ This species (/cterus 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 Several other orioles besides this (0. me/anocephalus) have the black head, By permission of Messrs Hutchinson & Co. QUEEN WHYDAH 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 Illustrating display by a species with no decorative colouring or sex difference, xix 284 284 314 THE MAKING OF SPECIES CHAPTER I RISE OF THE THEORY OF NATURAL SELECTION AND ITS SUBSEQUENT DEVELOPMENT Pre-Darwinian Evolutionists—Causes which led to the speedy triumph of the theory of Natural Selection—Nature of the opposition which Darwin had to overcome—Post-Darwinian biology — Usually accepted classification of present-day biologists as Neo-Lamarckians and Neo-Darwinians is faulty—Biologists fall into three classes rather than two— Neo-Lamarckism: its defects—Wallaceism: its defects— Neo-Darwinism distinguished from Neo-Lamarckism and Wallaceism — Neo-Darwinism realises the strength and weakness of the theory of Natural Selection, recognises the complexity of the problems which biologists are endeavouring to solve. : ARWINISM 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 A 1 The Making of Species 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 en- deavoured 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. 2 Strength of Darwin’s 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 lion’s 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, Darwin’s 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 3 The Making of Species 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 pro- gressive biologists. Another point in Darwin’s 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 some- thing 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 circum- stances 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 selec- tion in nature, this natural selection. The only disputable point is whether such selection can do all that Darwin demanded of it. 4 Strength of Darwin’s Position The man in the street, then, was able to com- prehend 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 pro- ducing 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, ‘(never advance anything that cannot be proved in a simple and decisive manner,” many modern naturalists allow their imagination to run riot, and so formulate ill- considered theories, and build up hypotheses on the most insecure foundations. “A tiny islet of truth,” writes Archdale Reid, ‘is discovered, on which are built tremendous and totally illegitimate hypotheses.” Another source of Darwin’s strength was the vast store of knowledge he had accumulated. For twenty years he had been steadily amassing 5 The Making of Species facts in support of his hypothesis. He enunciated no crude theory, he indulged in no wild specula- tions. He was content to marshal a great array of facts, and to draw logical conclusions there- from. 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 pre- ferred 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 investiga- tion would prove that the defects were apparent rather than real. We hear much of the “ magnitude of the prejudices” 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 6 Opponents of Darwin 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 pre- vailing 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 Geneszs 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 Specces 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 know- ledge 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 7 The Making of Species extreme caution, the onslaught can have but one result—the 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 posi- tion 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. To us who are able to look back dispassionately upon the biological warfare of the last century, Darwin's opponents—or the majority of them— 8 Evolution and Natural Selection appear very foolish. We must, however, bear in mind that at the time of the publication of the Origin of Speczes both natural selection and evolu- tion 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, there- fore, not altogether surprising that many of his opponents failed to distinguish between them. A glance at the Origen 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 selec- tion 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 inex- “‘perienced counsel who had but recently received their brief, and who had not had the time to master the details thereof. In such circum- stances it is not difficult to predict which way the verdict of the jury will go. Darwin, moreover, had a charming personality. 9 The Making of Species 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 apportion- ing the praise between Darwin and Wallace for their great discovery. To all these factors in Darwin’s favour we Io Huxley 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, — first, the insufficiency of the evi- dence of evolution, and, secondly, the absence of any explanation of how the phenomenon had occurred. The Ovigin of Species solved both these difficulties. It adduced much weighty evi- dence in favour of evolution, and suggested a modus operandt. Small wonder, then, that Huxley became a champion of Darwinism. But, as Poulton writes, on page 202 of Lssays on Evolution, ‘while natural selection thus enabled | Huxley freely to accept evolution, he was by no means fully satisfied with it.” ‘He never com- mitted himself to a full belief in natural selection, and even contemplated the possibility of its ultimate disappearance.” To use Huxley’s own words: ‘‘ Whether the particular shape which the II The Making of Species doctrine of evolution, as applied to the organic world, took in Darwin’s hands, would prove to be final or not, was, to me, a matter of indifference.” 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. “At once,” writes Waggett, “the theory of development leapt from the position of an obscure guess to that of a fully-equipped theory and almost a certainty.” Darwin thus became a dictator whose authority none durst question. A crowd of slavish adher- ents 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. 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 Darwin’s day the science has not made the progress that might reasonably have been expected, because the theory has so captivated the minds of the 12 Growing Opposition to Darwinism 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 ex- plained in the living world, that there is no door leading to the secret chambers of nature to which natural selection is not an ‘“‘ open sesame.” But the triumph of natural selection has not been so complete as its more enthusiastic sup- porters 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 thought— the Neo-Darwinian and the Neo-Lamarckian. 13 The Making of Species 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, “thus far shalt thou vary and no farther.” 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 develop- ments 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 in- cline towards those held by Lamarck, Wallace, or Darwin. As adherents of the Neo-Lamarckian school, 14 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 hetero- geneous 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 Mechanztsch-phystologische Theorwe der Abstammungslehre. Naegeli believes that there is inherent in 15 The Making of Species protoplasm a growth-force, which makes each organism in itself a force making towards pro- gressive evolution. He holds that animals and plants would have become much as they are now even if no struggle for existence had taken place. “To the believers in this kind of . . . ortho- genesis,” writes Kellog (Darwinism To-day, p. 278), “organic evolution has been, and is now, ruled by unknown inner forces inherent in organ- isms, 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.” 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 Eimer’s 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. Spencer and Orr preach nearly pure Lamarck- ism. 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 16 Orr’s Views of the environment in determining or modifying organisms. The similarity of the views of Orr and Lamarck is best seen by comparing their re- spective 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 trans- mitted to the offspring. Orr writes, on page 164 of his Development and Heredity: “The 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 B 17 The Making of Species 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 super- abundant 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.” 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 18 Inheritance of Acquired Characters 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 man’s 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, notwith- standing 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 “The Heredity of Secondary Sexual Characters in relation to Hormones: a Theory of the Heredity of Somatogenic Characters,” which appeared in 19 The Making of Species vol. xxvi, No. 3, of the Avchw fir Ent- wicklungsmechanik des Organismen, states: “The dogma that acquired characters cannot be inherited ... is founded not so much on evidence, or the absence of evidence, as on @ priori reasoning, on the supposed difficulty or impossibility of conceiving a means by which such inheritance could be effected.” \ 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 in- heritance 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 forth- coming. Fanciers in their endeavours are con- stantly “doctoring” 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 20 Inheritance of Acquired Characters charged with refusing to believe that acquired characters are inherited because they ‘“ cannot conceive the means by which it could be effected,’ may it not be said with equal justice that many Neo-Lamarckians believe that acquired char- acters 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 con- ditions in which they find themselves quite as 21 The Making of Species 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! 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 ora damp soil, a hot ora 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 theirenvironment. On page 32 he writes: “ The following is an experiment I made with the common rest-harrow (Oxonzs spznosa, 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 year’s 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 1 The white, pied, and “Japan” individuals are not more different from the type than some variations occurring in wild birds. 22 Inheritance of Acquired Characters blossomed, and, taken altogether, there was no appreciable difference from O. repens, L.” From this experiment Professor Henslow draws the inference that acquired characters tend to be inherited in plants. In our opinion the ex- periment 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 at any rate. But what do we find? By the second year the thorns have entirely disappeared. All the years during which the plant was exposed to a dry en- vironment have left no stamp upon it. The fact that the new branches of the first year’s growth bore small spines is not, as Professor Henslow asserts, proof of their hereditary character. It merely shows that the initial stimulus to their development occurred while the plant was still in its dry surroundings. In the same way all other so-called proofs of the heredity of acquired characters break down when critically examined. In our opinion “not proven” is the proper verdict on the question of the possibility of the inheritance of acquired characters in the higher animals, One thing is certain, and that is that 23 The Making of Species acquired characters are not commonly inherited in those organisms in which there is a sharp distinction between the germinal and the somatic cells. It is nothing short of a misfortune that Haeckel’s History of Creation, which seems to be so widely read in England, should be built on a fallacious foundation. It seems to us that this work is calculated to mislead rather than to teach. Our attitude is not quite that of the Wallaceian school, which denies the possibility of the in- heritance of acquired characters. In practice, however, the attitude we adopt is as fatal to Lamarckism in all its forms as the dogmatic assertions of the Wallaceians. It matters not whether acquired characters are very rarely or never inherited. In either case their inherit- ance cannot have played an important part in evolution. All those theories which rely on use- inheritance as a factor in evolution are therefore in our opinion worthless, being opposed to facts. Our attitude, then, is that the inheritance of acquired characteristics, if it does occur, is so rare as to be a negligible quantity in organic evolution. We may add that the position which we occupy will not be affected even if the Lamarckians do succeed eventually in proving that some acquired characters are really inherited. Such proof would 24 The Wallaceian School merely help to elucidate some of the problems which confront the biologist. Thus the question of the inheritance of acquired characters, while full of interest, has no very important bearing on the question of the making of species. The Wallaceians hold the doctrines which have been set forth above as those of the Neo- Darwinian school. It is incorrect to call those who pin their faith to the all-sufficiency of natural selection Neo-Darwinians, because Darwin at no time believed that natural selection explained everything. Darwin moreover was a Lamarckian to the extent that he was inclined to think that acquired characteristics could be inherited. His theory of inheritance by gemmules involved the assumption that such characters are inherited. It is Wallace who out-Darwins Darwin, who preaches the all-sufficiency of natural selection. For this reason we dub the school which holds this article of belief, and to which Weismann, Poulton, and apparently Ray Lankester belong, the Wallaceian school. Weismann has put forth a theory of inheritance, that of the continuity of the germ plasm, which makes this inheritance a physical impossibility. We believe that the Wallaceians have erred as far from the truth as the Lamarckians have, because, as we shall show hereafter, a great many of the organs and struc- tures displayed by organisms cannot be explained on the natural selection hypothesis. Those who 25 The Making of Species pin their faith to this, needlessly increase the difficulty of the problem which they have to face. There remains the third school, to which we belong, and of which Bateson, De Vries, Kellog and T. H. Morgan appear to be adherents. This school steers a course between the Scylla of use- inheritance and the Charybdis of the all-sufficiency of natural selection. It may seem surprising to some that we should class De Vries as a Neo- Darwinian, seeing that he is the originator of the theory of evolution by means of mutations, which we shall discuss in Chapter III. of this work. As a matter of fact the theory of mutations should be regarded, not as opposed to the theory of Darwin, but as a theory engrafted upon it. De Vries himself writes :—‘‘ My work claims to be in full accord with the principles laid down by Darwin.” Similarly Hubrecht writes in the Contemporary Review for November 1908: ‘Paradoxical as it may sound, I am willing to show that my colleague, Hugo de Vries, of Amsterdam, who a few years ago grafted his Mutations Theorte on the thriving and very healthy plant of Darwinism, is a much more staunch Darwinian than either Dr Wallace him- self, or the two great authorities in biological science whom he mentions, Sir William Thistleton Dyer and Professor Poulton.” Having classified ourselves, it remains for us 26 Complexity of the Problem (the authors of the present work) to define our position more precisely. Like Darwin we wel- come all factors which appear to be capable of effecting evolution. We have no axe to grind in the shape of a pet hypothesis, and consequently our passions are not roused when men come forward with new ideas seemingly opposed to some which already occupy the field. We re- cognise the extreme complexity of the problems that confront us. We look facts in the face and decline to ignore any, no matter how ill they fit in with existing theories. We recognise the strength and the weakness of the Darwinian theory. We see plainly that it has the defect of the period in which it was enunciated. The eighteenth century was the age of cocksureness, the age in which all phenomena were thought to be capable of simple explanation. This is well exemplified by the doctrines of the Manchester school as regards political and economic science. The whole art of legislation was thought to be summed up in the words laissez faire. The whole sphere of legitimate government was asserted to be the keeping of order and the enforcing of contracts. Experience has demonstrated that a State guided solely by these principles is wretchedly governed. A large proportion of recent Acts of Parliament limits the freedom of contract. Such limitations are neces- sary in the case of contracts between the weak and 27 The Making of Species the strong. Similarly the earlier economists con- sidered political economy a very simple affair. They asserted that men are actuated by but one motive—the love of money. All their men were economic men, men devoid of all attri- butes save an intense love of gold. Experience has shown that these premises are not correct. Love of family, pride of race, caste prejudices are more or less deeply implanted in men, so that they are rarely actuated solely by the love of money. Thus it is that the political economy of to-day as set forth by Marshall is far more complex and less dogmatic than that of Ricardo or Adam Smith. Similarly the political philosophy of Sidgwick is very different to that of Herbert Spencer. So is it with the theory of organic evolution. The theory of natural selection is no more able to explain all the varied phenomena of nature than is Ricardo’s assumption that all men are actuated solely by the love of money capable of accounting for the multifarious existing economic phenomena. Even as the love of wealth is an important motive of human actions, so is natural selection an important factor in evolution. But even as the majority of human actions are the resultant of a variety of motives, so are the majority of existing organisms the resultant of a complex system of forces. Even as it is the duty of the economist to discover the various 28 The Aim of the Biologist motives which lead to human actions, so is it the duty of the biologist to bring to light the factors which are operative in the making of species. 29 CHAPTER II SOME OF THE MORE IMPORTANT OBJECTIONS TO THE THEORY OF NATURAL SELECTION Brief statement of Theory—Objections to the Theory fall into two classes—Those which strike at the root of the Theory—Those which deny the all-sufficiency of Natural Selection—Objec- tions which strike at root of Theory are based on mis- conception—Objections to Wallaceism—The Theory fails to explain the origin of Variations—Natural Selection called on to explain too much—Unable to explain beginnings of new organs—The Theory of change of function—The co- ordination of variations—The fertility of races of domesticated animals—Missing links—Swamping effects of intercrossing —Small variations cannot have a survival value— Races inhabiting same area—Excessive specialisation—Chance and Natural Selection—Struggle for existence most severe among young animals—Natural Selection fails to explain mimicry and other phenomena of colour—Conclusion, 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. HE burden of proof is on him who asserts” is a rule of evidence which the man of science should apply as rigidly as does the lawyer. It is therefore incumbent upon us to prove our assertion that the theory of natural selection does not afford an adequate explanation of all the varied phenomena observed in the organic world. 30 Theory of Natural Selection The theory of natural selection is so generally understood, that to set it forth in detail in this place would be quite superfluous. Darwin, it will be remembered, based his great hypothesis on the following observed facts :— 1. No two individuals of a species are exactly alike. This is sometimes called the law of variation. 2. All creatures tend in a general way to resemble their parents in appearance more closely than they resemble individuals not re- lated to them. This may be termed the law of heredity. 3. Each pair of organisms produces in the course of a lifetime, on an average, many more than two young ones. 4. On an average the total number of each species remains stationary. From (3) and (4) follows the doctrine of Malthus, namely, that many more individuals are born than can reach maturity. Darwin applied this doctrine to the whole of the animal and the vegetable kingdoms. In his introduction to Zhe Origin of Spectes he writes :—‘‘ As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary, however slightly, in any manner pro- 31 The Making of Species fitable to itself, under the complex and some- times varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inherit- ance, any selected variety will tend to propagate its new and modified form.” In other words, the struggle for existence amongst all organic beings throughout the world, which inevitably follows from the high geometri- cal ratio of their increase, results in the survival of the fittest, that is to say, of those best adapted to cope with their enemies and to secure their food. Since organisms are thus naturally selected in nature, we may speak of a natural selection which acts in much the same way as the human breeder does. Darwin’s theory, then, is that all the variety of organisms which now exist have been evolved from one or more forms by this process of natural selection. The objections which have been urged against the theory of natural selection fall into two classes. I. Those which strike at its root, which either deny that there is any natural selection, or declare that it is not capable of producing a new species. II. Those which are directed against the all- sufficiency of natural selection to account for organic evolution. Those of the first class need not detain us 32 Various Anti-Darwinian Views long, although among those who formulate them are to be found some eminent men of science. Delage alleges that selection is powerless to form species, its function is, according to him, limited to the suppression of variations radically bad, and to the maintaining of a species in its normal character. It is thus an inimical factor in evolu- tion, a retarder rather than an accelerator of species-change. It merely acts by preserving the type at the expense of the variants, and so acts as a brake on evolution. Korschinsky, while possibly not denying that selection occurs in nature, declares that its influence on evolution is zz/, or, if it has any influence, that it is a hindering one. Eimer similarly denies any capacity on the part of natural selection to create species. Pfeffer urges a very different objection. He says that if such a force as natural selection existed it would transform species much more rapidly than it does! Now, in order that the above objections can carry any weight, one of two sets of conditions must be fulfilled. Either all organisms must be perfectly adapted to their environment, and this environment must never change, or there must be inherent in each species a kind of growth-force which impels the species to develop in certain fixed directions. c 33 The Making of Species In either of these circumstances natural selection will be an inhibitory force, for if the normal organism is perfectly adapted to its environment, all variations from the type must be unfavour- able, and natural selection will weed out the individuals that display them. No careful student of nature can maintain, either that all animals are perfectly adapted to their environ- ment, or that this never changes. Hence those who deny that natural selection is a factor in the making of species, assume the second set of con- ditions, that species develop in certain fixed directions, being impelled either by internal or external forces. How far these ideas are founded on fact we shall endeavour to determine when speaking of variation. It must suffice at present to say that even if any of these views of ortho- genesis be established, natural selection will have, so to speak, a casting vote, it will decide which series of species developing along preordained lines shall survive and which shall not survive. Thus we reach by a different line of argument the conclusion we arrived at in the last chapter : namely, there is no room for doubt that natural selection is a factor in the making of species. We must now pass on to the second class of objections, those which are urged against the all- sufficiency of natural selection. So numerous are these that it is not feasible to consider them all. A brief notice of the more important ones 34 Darwinism does not explain Variation should suffice to satisfy any unbiassed person ; firstly, that natural selection is an important factor in evolution; secondly, that the position taken up by Wallace and his followers, that natural selection, acting on minute variations, is the one and only factor in organic evolution, is untenable. 1. It has been urged that the Darwinian theory makes no attempt to explain variation, and that, until we know what it is that causes variations, we are not in a position to explain evolution. This of course is quite true, but the objection is scarcely a fair one, since, as we have seen, Darwin freely admitted that his theory made no attempt to explain the origin of varia- tions. It is not reasonable to object to a theory because it fails to explain phenomena with which it expressly states that it is not concerned. On the other hand, the objection is one that must be reckoned with, for, as we shall see, it makes a great difference to the importance of natural selection as a factor in evolution if variations appear indiscriminately in all directions, as Darwin tacitly assumed they do, or whether, as some biologists believe, they are determinate in direction, being the result of a growth-force inherent in all organisms. 2. Very similar to the above-mentioned objec- tion is that which points out that it is a long journey from Amoeba to man. It is difficult to 35 The Making of Species believe that this long course of development from the simple to the complex is due to the action of a blind force, to the survival of those whose fortuitous variations happen to be best adapted to the environment. The result seems out of all proportion to the cause. There must be some potent force inherent in protoplasm, or behind organisms, impelling them upwards. This objec- tion is as difficult to refute as it is to establish. It is purely speculative. 3. A very serious objection to the Darwinian theory is that the beginnings of new organs cannot be explained by the action of natural selection on fortuitous minute variations, and natural selection can act on an organ only when that organ has attained sufficient size to be of practical utility to its possessor. When once an organ has come into being it is not difficult to understand how it can be improved, modified and developed by natural selection. But how can we explain the origin of an organ such as a limb by the action of natural selection on minute variations ? The theory of the change of function goes some way towards meeting the difficulty, for by means of it we are able to understand how certain organs, as, for example, the lung of air-breathing animals, might have come into existence. This is said to have been developed from the swimming-bladder of fishes. This bladder is 36 Theory of Change of Function to use the words of Milnes Marshall, “a closed sac lying just underneath the vertebral column. In many fish it acquires a connection by a duct with some part of the alimentary canal. It then becomes an accessory breathing organ, especially in those fish which are capable of living out of water for a time, e.g. the Protopterus of America. An interesting series of modifications exists con- necting the air-bladder with the lung of the higher vertebrates, which is undoubtedly the same organ.” This theory, however, does not seem adequate to explain the origin of all organs. It does not explain, for example, how limbs developed in a limbless organism. Wallace tried to avoid the difficulty by asserting that it is un- reasonable to ask a new theory that it shall reveal to us exactly what took place in remote geological ages and how it took place. To this the obvious reply is, firstly, that we ought not to give unqualified acceptance to any theory of evolution until it does afford us such explana- tions, and, secondly, that the theory of the origin of species by means of natural selection is no longer a new one. Latterly, however, Wallace appears to have given up all hope of being able to account for the origin of new organs by means of natural selection, for he states on page 431 of the issue of the Fortnightly Review for March 1909: 37 The Making of Species “It follows—not as a theory but as a fact—that whenever an advantageous variation is needed, it can only consist in an increase or decrease of some power or faculty already existing.” Now, in order for an increase or decrease to occur, there must be something in existence to be increased or diminished. Wallace, it is true, speaks here only of powers and faculties; but it can scarcely be supposed that he believes that variations as to structure are intrinsically different from those relating to powers and faculties. 4. Herbert Spencer urges, as an objection to the theory of natural selection, that favourable variations in one organ are likely to be counter- balanced by unfavourable variations in some other organ. He maintains that the chances are enormous against the occurrence of the “ many coincident and co-ordinated variations” that are necessary to create a life or death determining advantage. This objection was urged by a writer in the Edinburgh Review in January 1909, and even by Wallace himself in the Fortnightly Review last March against the mutation theory. This objection, strong though it appears on paper, exists only in the imagination of the objector. Those who urge it display a misunderstanding of the manner in which natural selection acts, and ignorance of the phenomenon of the correlation of organs. 38 Correlation Natural selection deals with an organism as a whole. Its effect is to permit those creatures to survive which, taken as a whole, are best adapted to their environment. Physiologists insist with ever-increasing em- phasis that there is more or less correlation and inter-connection between the various parts of an organism. The several organs of an animal are not so many isolated units. It is impossible to act on one organ without affecting some or all of the others. Variations in a given direction of one organ are usually accompanied by correlated variations in some of the other organs. If strength be of paramount importance to an animal, natural selection will tend to preserve those individuals which exhibit strength to a marked degree, and this exhibition of strength may be accompanied by other peculiarities, such as short legs or a certain colour, so that natural selection will indirectly tend to produce individuals with short legs and having the colour in question, and it may happen that this particular colour is one that renders the animal more conspicuous than the normal colour does. Nevertheless, on account of the all-needful strength which accompanies it, those animals so coloured may survive while those of a more protective hue perish. Thus, paradoxical though it seems, natural selection 39 The Making of Species may indirectly be responsible for characteristics which in themselves are injurious to the in- dividual. This is probably the case as regards the decorative plumage of some male birds. The phenomenon of correlation was recognised by Darwin, and has, we believe, played an important part in the making of species. We shall deal more fully with the subject in a later chapter. 5. An oft-urged objection to the theory of natural selection, and one which weighed very strongly with Huxley, is that breeders have hitherto not succeeded in breeding a variety which is infertile with the parent species. If, Huxley asked, breeders cannot produce such a thing, how can we say we consider it proved that natural selection produces new species in nature? This objection, however, loses much of its force in view of the fact that many perfectly distinct species are quite fertile when bred together. We shall recur to this in Chapter IV. 6. The fact that paleontology has hitherto failed to yield links connecting many existing species is a classical objection to the theory of the origin of species by gradual evolution. Wallace states this objection as follows, on page 376 of his Darwinism: ‘‘Many of the gaps that still remain are so vast that it seems incredible to these writers that they could ever have been filled up by a close succession of 4o Missing Links species, since these must have been spread over so many ages, and have existed in such numbers, that it seems impossible to account for their total absence from deposits in which great numbers of species belonging to other groups are preserved and have been discovered.” Wallace’s reply is to the effect that in the case of many species paleontology affords abundant evidence of the gradual change of one species into another, the foot of the horse being a well-known case. The genealogy of this noble quadruped can be traced from the Eocene four-toed Ovohzp- pus, through the Mesohippus, the Miohippus, the Protohippus, and the Plohippus, until we reach the one-toed Zguus. Wallace further points out that in order that the fossil of any organism may be preserved, the “concurrence of a number of favourable condi- tions” is required, and against this the chances are enormous. Lastly, he urges the imperfection of our knowledge of the things that lie embedded in the earth’s crust. The objection based on the lack of “ missing links” loses some of its force if we accept the theory that species sometimes arise as sports. Thus, suppose a species with well-developed horns produces as a mutation a hornless variety, which eventually replaces the horned form, we should look in vain for any forms intermediate between the parent and the daughter species. 41 The Making of Species On the other hand, it is significant that just where the links are most needed they are missing. For example, the splint bones of the horse, taken in conjunction with the feet of existing tapirs, which have four toes in front and three behind, would have led us to infer, without the help of the geological record, that the horse was a descendant of a polydactyle ancestor. When, however, we come to the origin of birds, bats, and whales, paleontology fails to give us any assistance, so that we are in the dark as to the origin of such really important modifications. 7. The swamping effects of inter-crossing is an objection which has been repeatedly urged against the Darwinian theory. This objection is not so serious as it appears at first sight. Darwin and Wallace maintain, firstly, that natural selection acts by eliminating all individuals except those which present favourable variations. The favoured few alone survive and mate with one another, so that there is here no question of the swamping effects of inter-crossing, none but well-adapted individuals being left to mate with one another. The objection gains greater force when directed against the theory that evolution proceeds by sudden jumps. But in this connection we must bear in mind that the experiments of Mendel and his followers have demonstrated that some of the offspring of crosses may resemble their 42 Recurrent Mutations pure ancestors and breed true zuter se. Nor is this all. Experience shows that where a mutation, or sport, or discontinuous variation occurs, it fre- quently repeats itself; for example, the black- winged sport of the peafowl has occurred several times over and in different flocks of birds. The sport or mutation must have a definite cause. There must be something within the organism, something in the generative cells, which causes the mutation to arise; and hence, on a przore grounds, we should expect the same mutation to arise about the same time in many individuals. It seems legitimate to infer that things have been quietly working up to a climax. When this is reached there results a mutation. There- fore we should expect sudden mutations to appear simultaneously in a number of individuals. To this important subject we shall return. 8. An almost insuperable objection to the theory that species have originated by the action of natural selection on minute variations, is that such small differences cannot be of a life-or-death value, or, as it is usually called, a survival value to their possessor. But if evolution is the result of the preservation by natural selection of such slight variations, it is absolutely necessary that each of these should possess a survival value. As D. Dewar has pointed out, on page 704 of vol. ii. of The Albany Review, it is only when the 43 The Making of Species beast of prey and its victim are evenly matched as regards fleetness and power of endurance that small variations in these qualities can have a survival value. But in the rough and tumble of the struggle for existence the victim and its foe are but rarely well-matched. Take as an example the case of a flycatcher. ‘ This bird,” writes D. Dewar, ‘will sometimes take three or four insects in the course of one flight ; all are captured with the same ease, although the length of wing in each victim varies. So great is the superiority of the bird that it does not notice the difference in the flying powers of its puny quarry.” It is unnecessary to labour this point. 9. Species or varieties differing considerably in colour may exist side by side, as the hooded and carrion crows, the white and dark breasted forms of the Arctic skua, the pale and dark forms of the fulmar petrel, the grey and rufous forms of the American scops owl (Megascops asio). It is true that preponderance of one form or another in certain districts points to some advan- tage possessed by one over the other, but, for all we know, it may be due to heredity, and in any case the co-existence of the two types in part of their range, or at certain seasons, shows that selection is not at all rigorous. The same argument applies to the co-existence of very differently-coloured species with generally 44 Leaf-butterflies similar habits, such as that of the jaguar and puma in South America, and the five very differently-coloured flycatchers in the Nilgiri Hills. In short, there is abundant evidence to show that considerable differences in colour do not appear to have any effect on the chances of survival in the struggle for existence of those that display them. Yet this is precisely what the supporters of the Darwinian hypothesis cannot afford to admit, for they then find it impossible to account for the origin of such a form as Kallima, the leaf-butterfly, by the action of natural selection. As most people are aware, this creature displays a remarkable resemblance to a decaying leaf. ‘These butterflies” (there are several species which show the marvellous imitation), writes Kellog, on page 53 of Darwzutsm To-day, ‘‘have the under sides of both fore and hind wings so coloured and streaked that when apposed over the back in the manner common to butterflies at rest, the four wings combine to resemble with absurd fidelity a dead leaf still attached by a short petiole to the twig or branch. I say absurd, for it seems to me the resemblance is over-refined. Here for safety’s sake it is no question of mimicking some one particular kind of other organism or inanimate thing in nature which birds do not molest. It is simply to produce the effect of a dead leaf on a branch. 45 The Making of Species Leaf-shape and general dead-leaf colour-scheme are necessary for this illusion. But are these following things necessary ? namely, an extra- ordinarily faithful representation of mid-rib and lateral veins, even to faint microscopically-tapering vein tips; a perfect short petiole produced by the apposed ‘tails’ of the hind-wings; a conceal- ment of the head of the butterfly so that it shall not mar the outlines of the lateral margin of the leaf; and finally, delicate little flakes of purplish or yellowish brown to mimic spots of decay and fungus-attacked spots in the leaf! And, as culmin- ation, a tiny circular clear spot in the fore-wings (terminal part of the leaf) which shall represent a worm-eaten hole, or a piercing of the dry leaf by flying splinter, or the complete decay of a little spot due to fungus growth! A general and sufficient seeming of a dead leaf, object of no bird’s active interest, yes, but not a dead leaf modelled with the fidelity of the waxworkers in the modern natural history museums. When natural selection has got Kallima along to that highly desirable stage when it was so like a dead leaf in general seeming that every bird sweeping by saw it only as a brown leaf clinging pre- cariously to a half-stripped branch, it was natural selection’s bounden duty, in conformance to its obligations to its makers, to stop the further modelling of Kallima and just hold it up to its hardly won advantage. But what happens ? 46 , A Dilemma Kallima continues its way, specifically and ab- surdly dead-leafwards, until to-day it is a much too fragile thing to be otherwise than very gingerly handled by its rather anxious foster- parents, the Neo-Darwinian selectionists.” It is obvious that if natural selection has produced so highly specialised an organism as the dead- leaf butterfly, every minute variation must be of value and have been seized upon by natural selection. Thus the Wallaceians are on the horns of a dilemma. If they assert, as they appear to do, that every infinitesimal variation has a survival value, they find it difficult to explain the exist- ence, side by side of such forms as the hooded and carrion crows, to say why in some species of bird both sexes assume a conspicuous nuptial plumage at the very time when they stand most in need of protective coloration, why the cock paradise flycatcher is chestnut for the first two years of his life and then turns as white as snow. If, on the other hand, the Wallaceians assert that small variations are unimportant and have no survival they are, as Kellog points out, in trouble over the close and detailed resemblance which the Kallima butterflies bear to dead leaves. to. An objection to the Darwinian theory which has been advanced by Conn, Henslow, D. Dewar, and others, is that the selection theory fails to take into account the effects of chance. “If,” 47 The Making of Species writes D. Dewar on page 707 of The Albany Review, vol. ii., “the struggle for existence were of the nature of a race at a well-regulated athletic meeting, where the competitors are given a fair start, where there is no difference in the condi- tions to which the various runners are subjected, then indeed would every variation tell. I would rather liken the struggle for existence to the rush to get out of a crowded theatre, poorly provided with exits, when an alarm of fire is given. The people to escape are not necessarily the strongest of those present. Propinquity to a door may be a more valuable asset than strength.” Or again, we may take the imaginary case of some antelopes being pursued by wolves. The chase, being prolonged, brings the antelopes to a locality with which they are not familiar. The foremost of the herd, the most swift, and there- fore the individual which should stand the best chance of survival, suddenly finds himself on soft boggy ground, which, owing to the depth to which his feet sink into the soil, seriously impedes his progress. His fellow antelopes, now outdistanced, seeing his predicament, take another course and soon leave him behind, to fall an easy prey to his foes. Here we have a case of the perishing of the most fit as regards the important point of speed. Writing of plants, Professor Henslow says, on page 16 of The Heredity of Acquired Characters 48 The Effects of Chance in Plants: “ As the whole of the animal kingdom ultimately lives upon the vegetable, plants must supply the entire quantity of food supplied, not to add innumerable vegetable parasites as well, for both young and old. Myriads of germinating seeds perish accordingly, being destroyed by slugs and other mollusca, and ‘mildews,’ etc. But far more seeds and spores — about 50,000,000 of these it is calculated can be borne in a single male-fern — never germinate at all. They fall where the conditions of life are unfavourable and perish, This misfortune is not due to any inadaptiveness in themselves, but to the surrounding conditions which will not let them germinate. Thus thousands of acorns and other fruits, as of elder, drop upon the ground in and by our hedges, road-sides, copses, and elsewhere ; but scarcely any or even no seedlings are to be seen round the trees.” Every year thousands of birds perish in the great migratory flight, others succumb in a cyclone, a fierce tropical storm, a prolonged drought, a severe frost. Here death overtakes multitudes, all that dwell in a locality, the weak and the strong, the swift and the slow alike. This objection may be met by saying that in the long run it is the fittest that will survive. This is true. The objection is nevertheless of “importance in showing how exceedingly uncertain must be the action of natural selection if it have but D 49 The Making of Species small variations upon which to work. In such circumstances the mills of natural selection may grind surely, but they must grind very slowly. 11. We must bear in mind that the struggle for existence is most severe among young animals, among creatures that are not fully developed. Nature pays no attention to potentialities. The weak go to the wall in the conflict, even though, if allowed time, they might develop into prodigies of strength. Moreover, and this is an important point, death in the case of young creatures overtakes broods and families rather than individuals. The above-cited objections to the theory that species have originated by the action of natural selection on minute variations, are mostly of a general nature ; let us now notice briefly a few more concrete objections. We shall not devote much space to these in the present chapter, since we shall be continually confronted with them when dealing with the subject of animal colouring. 12. Natural selection, as we shall see, fails to account for the origin of what is known as pro- tective mimicry. Some insects look like inanimate objects, others resemble other insects which are believed or known to be unpalatable. Those creatures displaying this resemblance to other objects or creatures, and deriving profit therefrom, are said to “mimic” the objects or creatures they copy. They are also called ‘ Mimics.” 50 The Origin of Mimicry It is easy to understand the profit that these mimics derive from their mimicry. When once the disguise has been assumed we can compre- hend how natural selection will tend to improve it by eliminating those that mimic badly; but it seems to us that the theory fails utterly to account for the origin of the likeness. 13. Similarly, the Neo- Darwinian theory fails to explain the colours of the eggs of birds laid in open nests, why, for example, the eggs of the accentor or hedge-sparrow are blue and those of the doves are white. 14. The theory fails to give a satisfactory ex- planation of the phenomena of sexual dimorphism. Why, for example, in some species of doves and ducks, thesexes are alike, while in other species with similar habits they differ in appearance. 15. It fails to explain why the rook is black and why the jackdaw has a grey neck. These and many other objections we shall deal with more fully in the chapter on animal colouration. It must suffice here to mention them, and to say that our experience teaches us that scarcely a single species of bird or: beast exists which does not display some characteristic which is inexplicable on the theory that natural selection, acting on small variations, is the one and only cause of organic evolution. 51 CHAPTER III VARIATION The assumption of Darwin and Wallace that variations are haphazard in origin and indefinite in direction—If these assumptions be not correct Natural Selection ceases to be the fundamental factor in evolution—Darwin’s views regarding variation underwent modification—He eventually recognised the distinction between definite and indefinite variations, and between continuous and discontinuous variations—Darwin attached but little importance to either definite or discon- tinuous variations—Darwin’s views on the causes of variations —Criticism of Darwin’s views—Variations appear to occur along certain definite lines—There seems to be a limit to the extent to which fluctuating variations can be accumulated— De Vries’ experiments—Bateson on “discontinuous varia- tion ”—Views held by De Vries—Distinction between con- tinuous and discontinuous variations—The work of De Vries— Advantages enjoyed by the botanist in experimenting on the making of species—Difficulties encountered by the animal breeder— Mutations among animals—The distinction between germinal and somatic variations—The latter, though not transmitted to offspring, are often of considerable value to their possessor in the struggle for existence. S we have already seen, the Darwinian theory, unlike that of Lamarck, does not attempt to explain the origin of variations. It is content with the fact that variations do occur. Although Darwin did not try to explain how it is that variation occurs, and was very guarded 52 Nature of Variation in the expressions he used concerning it, he assumed that variations are indefinite in variety and occur indiscriminately in all directions, as the following quotations from the Origin of Species will show: “ But the number and diver- sity of inheritable deviations of structure . . are endless” (page 14, ed. 1902). ‘‘ The varia- tions are supposed to be extremely slight, but of the most diversified nature.” ‘I have hitherto sometimes spoken as if the variations so common and multiform with organic beings under domes- tication, and in a lesser degree to those under nature, were due to chance. This, of course, is a wholly incorrect expression, but it serves to acknowledge plainly our ignorance of the cause of each particular variation ” (page 164). Wallace is far less guarded in his expressions. On page 82 of his Darwznzsm he speaks of “the constant and large amount of variation of every part in all directions . . . which must afford an ample supply of favourable variations whenever required.” The double assumption that variations are for all practical purposes haphazard in origin and indefinite in direction is necessary if natural selection is to be the main factor in evolution. For if variations be not haphazard, if they are definite, if there be a directive force behind them, like fate behind the classical gods, then selection is not the fundamental cause of evolution. It 53 The Making of Species can at most effect, not the origin of species, but the survival of certain species which have arisen as the result of some other force. Its position is changed ; it is no longer a cause of the origin of new organisms, but a sieve determining which of certain ready-made forms shall survive. Evidently, then, we shall not be able to fully understand the evolutionary process until we have discovered how it is that variations are caused. In other words, we must go considerably farther than Darwin attempted to do. Before proceeding to inquire into the true nature of variations, it behoves us to set forth briefly the ideas of Darwin on the subject. We shall then be in a position to see how much progress has been made since the days of that great biologist. It is not at all easy to discover exactly what were Darwin’s views on the subject of variation. A perusal of his works reveals contradictions, and gives one the impression that he himself scarcely knew his own mind upon the subject. This should not be a matter for surprise. We must remember that Darwin had to do pioneer work, that he had to deal with alto- gether new conceptions. Such being the case, his ideas were of necessity somewhat hazy ; they underwent considerable modification as fresh facts came to his knowledge. Towards the end of his life Darwin recognised 54 Definite and Indefinite Variability that variability is of two kinds—definite and indefinite. Indefinite variation is indiscriminate variation in all directions around a mean, varia- tion which obeys what we may perhaps call the law of chance. Definite variation is variation in a determinate direction—variation chiefly on one side of the mean. Darwin believed that these determinate variations were caused by external forces, and that they are inherited. He thus accepted Lamarckian factors. ‘Each of the endless variations,” he writes, ‘‘ which we see in the plumage of our fowls, must have had some efficient cause, and if the same causes were to act uniformly during a long series of generations on many individuals, all probably would be modified in the same direction.” But Darwin was always of opinion that this definite variability, this variability in one direc- tion as the result of some fixed cause, is far less important, from an evolutionary point of view, than indefinite variability, that it is the exception rather than the rule, that the usual result of changed conditions is to let loose a flood of | indefinite variability, that it is almost exclusively upon this that natural selection acts. Darwin also recognised that variations differ in degree, even as they do in kind. He per- ceived that some variations are much more pronounced than others. He recognised the distinction between what are now known as 55 The Making of Species continuous and discontinuous variations. The former are slight departures from the normal ; the latter are considerable deviations from the mean or mode; great jumps, as it were, taken by nature, as, for example, the pea and the rose combs of fowls, which were derived from the normal single comb. “At long intervals of time,” wrote Darwin, “out of millions of individuals reared in the same country and fed on nearly the same food, deviations of structure so strongly pronounced as to deserve to be called monstrosities arise, but monstrosities cannot be separated by any distinct line from slighter variations.” Therefore it is evident that he regarded the difference between continuous and discontinuous variations as not one of kind, but merely of degree. To the discontinuous variations Darwin attached very little importance from an evolutionary point of view. He looked upon them as something abnormal. “It may be doubted,” he wrote, ‘whether such sudden and _ considerable deviations of structure such as we occasionally see in our domestic productions, more especially with plants, are ever permanently propagated in a state of nature. Almost every part of every organic being is so beautifully related to its complex conditions of life that it seems as improbable that any part should have been suddenly pro- 56 Monstrosities duced perfect, as that a complex machine should have been invented by a man in a perfect state. Under domestication monstrosities sometimes occur which resemble normal struc- tures in widely different animals. Thus pigs have occasionally been born with a sort of proboscis, and if any wild species of the same genus had naturally possessed a proboscis, it might have been argued that this had appeared as a monstrosity; but I have as yet failed to find, after diligent search, cases of monstrosities resembling normal structures in nearly allied forms, and these alone bear on the question. If monstrous forms of this kind ever do appear in a state of nature and are capable of reproduction (which is not always the case), as they occur rarely and singly, their preservation would de- pend on unusually favourable circumstances. They would, also, during the first and succeeding generations cross with the ordinary form, and thus their abnormal character would almost inevitably be lost.” But, in a later edition of the Origin of Spectes, Darwin seems to contradict the above assertion: ‘It should not, however, be overlooked that certain rather strongly marked variations, which no one would rank as mere individual differences, frequently recur owing to a similar organisation being similarly acted on— of which fact numerous instances could be given with our domestic productions. In such cases, 57 The Making of Species if the varying individual did not actually trans- mit to its offspring its newly acquired char- acter, it would undoubtedly transmit to them, as long as the existing conditions remained the same, a still stronger tendency to vary in the same manner. There can also be little doubt that the tendency to vary in the same manner has often been so strong that all the individuals of the same species have been similarly modified without the aid of any form of selection. Or only a third, fifth, or tenth part of the indi- viduals may have been thus affected, of which fact several instances could be given. Thus Graba estimates that about one-fifth of the guillemots in the Faroe islands consist of a variety so well marked, that it was formerly ranked as a distinct species under the name Uria lacrymans. In cases of this kind, if the variation were of a beneficial nature, the original form would soon be supplanted by the modified form, through the survival of the fittest.” Here we seem to have a plain statement of the origin of new forms by mutation. Again, we read (page 34): ‘Some variations useful to him (ze. man) have probably arisen suddenly, or by one step; many botanists, for instance, believe that the fuller’s teasel, with its hooks, which cannot be rivalled by any mechanical contrivance, is only a variety of the wild Dipsacus; and this amount of change may have suddenly 58 Minute Variations arisen in a seedling. This is known to be the case with the turnspit dog.” But, as we have already said, Darwin at no time attached much importance to these jumps made by nature as a factor in evolution. He pinned his faith to the minute, indefinite variations which he believed could be piled up, one upon another, so that, if allowed sufficient time, either nature or the human breeder could, by a continued selection of these minute variations, call into being any kind of organism. The importance of selection, he writes, ‘‘consists in the great effect produced by the accumulation in one direction, during successive generations, of differences absolutely inappreciable by an uneducated eye” (page 36). On page 132 he writes: ‘I can see no limit to the amount of change, to the beauty and com- plexity of the coadaptations between all organic beings . . . which may have been effected? in the long course of time by nature’s power of selection.” He expressly states, on page 149, that he sees no reason to limit the process to the formation of genera alone. Athough the theory of natural selection does not attempt to explain the causes of variation, 1 This short-legged type of dog is sometimes seen among the ownerless and unselected pariah dogs of Indian towns ; and a short- legged variety of the fowl may occur sporadically in Zanzibar, where the long-legged Malay is the prevalent breed. 2“ Effected” appears in the earlier editions, but in the later editions has given place to “affected,” probably a printer’s error. 59 The Making of Species Darwin paid some attention to the subject. He believed that both internal and external causes contribute to variation, that variations tend to be inherited whether the result of causes within the organism or outside it. He believed that the inherited effect of use and disuse was a cause of variation, and cited, as examples, the lighter wing-bones and heavier leg-bones of the domestic duck and the drooping ears of some domestic animals. He supposed that animals showed a greater tendency to vary when under domestica- tion than when in their natural state, attributing the supposed greater variability to the excess of food received, and the changed conditions of the life of domestic animals. Nevertheless, he was fully alive to the fact that ‘nearly similar variations sometimes arise under, as far as we can judge, dissimilar conditions; and, on the other hand, dissimilar variations arise under conditions which appear to be nearly uniform.” In other words, the nature of organisms appeared to Darwin to be a more important factor in the origin of variations than external conditions. Evidence of this is afforded by the fact that some animals are more variable than others. Finally, he frankly admitted how great was his ignorance of the causes of variability. Varia- bility is, he stated, governed by unknown laws which are infinitely complex. It will be convenient to deal with each of 60 Lines of Variation Darwin’s main ideas on variation separately, and to consider to what extent they seem to require modification in the light of later research. Firstly, Darwin believed that variations arise in what appears to be a haphazard manner, that they occur in all directions, and seem to be governed by the same laws as chance. It is our belief that we are now in a position to make more definite statements regarding variation than Darwin was able to. Biologists can now assert definitely that varia- tions do not always occur equally in all directions. The results of many years of the efforts of practi- cal breeders demonstrate this. These men have not been able to produce a green horse, a pigeon with alternate black and white feathers in the tail, or a cat with a trunk, for the simple reason that the organisms upon which they operated do not happen to have varied in the required direction. It may perhaps be objected that breeders have no desire to produce such forms; had they wished to do so, they would probably have succeeded. To this objection we may reply that they have not managed to produce many organisms, which would be highly desirable from a breeder’s point of view, as, for example, a blue rose, hens that lay brown eggs but do not become broody at certain seasons of the year, or a cat that cannot scratch. As Mivart well says, on page 118 of his Geneszs of Species, ‘‘ Not only does it appear that there are 61 The Making of Species barriers which oppose change in certain directions, but that there are positive tendencies to develop- ment along certain special lines. In a bird which has been kept and studied like the pigeon, it is difficult to believe that any remarkable spontane- ous variations would pass unnoticed by breeders, or that they would not have been attended to and developed by some fancier or other. On the hypothesis of indefinite variability, it is then hard to say why pigeons with bills like toucans, or with certain feathers lengthened like those of trogons, or those of birds of paradise, have never been produced.” There are certain lines along which variation seems never to occur. Take the case of the tail of a bird. Variable though this organ be, there are certain kinds of tail that are seen neither in wild species nor domesticated races. A caudal appendage, of which the feathers are alternately coloured, occurs neither in wild species nor in arti- ficial breeds. For some reason or other, variations in this direction do not occur. Similarly, with the exception of one or two of the ‘‘ Noddy” terns, whenever a bird has any of: its tail feathers con- siderably longer than the others, it is always the outer pair or the middle pair that are so elongated. It would thus appear that variations in which the other feathers are especially lengthened do not usually occur. The fact that they are elongated in two or three wild species is the more signifi- 62 Breeders’ Boasts cant, because it shows that there is apparently nothing inimical to the welfare of a species in having, say, the third pair of tail feathers from the middle exceptionally prolonged. This is a most important point, and one which seems to be ignored by the majority of scientific men, who appear to be misled by the boastful talk of certain successful breeders. Thus, on page 29 of the Ovigen of Speczes, Darwin quotes, with approval, Youatt’s descrip- tion of selection as ‘‘the magician’s wand, by means of which he may summon into life what- ever form and mould he pleases.” Darwin further cites Sir John Sebright as saying, with regard to pigeons, that he would “ produce any given feather in three years, but it would take him six years to obtain head and beak.” If it were possible absolutely to originate any- thing by selection, horticulturists would almost certainly ere this have produced a pure black flower. The fact that not a single mammal exists, either in nature or under domestication, with scarlet, blue, or green in its hair, appears to show that, for some reason or other, mammals never vary in any of these directions. The fact that so few animals have developed prehensile tails seems to indicate that variation does not often occur in that direction, for obviously a prehensile tail is of the very greatest utility to its possessor; so that there can be 63 The Making of Species little room for doubt that it would be seized upon and preserved by natural selection, whenever it occurred. As E. H. Aitken very truly says, “so early and useful an invention should, one would think, have been spread widely in after time; but there appears to be some difficulty in developing muscles at the thin end of a long tail, for the animals that have turned it into a grasping organ are few and are widely scattered. Examples are the chameleon among lizards, our own little harvest mouse, and, pre-eminent among all, the American monkeys” (Strand Magazine, Nov. 1908). Even as there are many variations which seem never to occur in nature, so are there others which occur so frequently that they may be looked for in any species. Albinistic forms appear now and again in almost every species of mammal or bird; while melanistic sports, although not so common, are not by any means rare. Every complete manual on poultry gives for each breed a note of the faults which constantly appear, and which the fancier has to watch care- fully for and guard against. The fact that these “faults” occur so frequently in each breed shows how strong is the tendency to vary in certain definite directions. It is true that some of these faults are in the nature of reversions, as, for 64 Albinistic Variations example, the appearance of red hackles in the cocks of black breeds of poultry. On the other hand, some certainly are not reversions, such as the appearance of a white ring in the neck of the female of the Rouen duck, which should resemble the Mallard as regards the plumage of the neck. Again, the tendency of Buff Orpingtons to assume white in the wings and tail must be regarded as a variation which is not in the nature of a reversion. In short, the efforts of all breeders are largely directed to fighting against the tendencies which animals display towards variation in certain directions. This tendency to vary in the direction of whiteness may account for many of the white markings which occur in nature, as, for example, the white tails of the Sea Eagle (Hakaetus albicella) the Nicobar Pigeon (Caloenas nico- barica), and many hornbills. Provided that such variations are not too great a handicap to their possessors in the struggle for existence, natural selection will allow them to persist. It was the belief of Linnzus, based on experi- ence, that every blue or red-coloured flower is likely to produce a white variety, hence he held that it is not safe to trust to colour for the identi- fication of a botanical species. ‘On the other hand, white flowers are not likely to produce red varieties, and we believe we may positively assert that they never produce a blue E 65 The Making of Species sport. Similarly, white animals appear not to give rise to colour varieties. We are never surprised to find that an ordi- nary upright plant produces as a sport or muta- tion a pendulous, or fastigiate form. These aberrant varieties, be it noted, occur in species which belong to quite different orders. De Vries points out that laciniated leaves appear in such widely separated trees and shrubs as the walnut, the beech, the hazel-nut, and the turnip. Another example of the definiteness of varia- tion is furnished by what Grant Allen calls the “Law of Progressive Colouration ” of flowers. On pp. 20, 21 of Zhe Colours of Flowers, he writes, “ All flowers, as we know, easily sport a little in colour. But the question is, do their changes tend to follow any regular and definite order? Is there any reason to believe that the modification runs from any one colour toward any other? Apparently there is. . .. All flowers, it would seem, were in their earliest form yellow ; then some of them became white; after that a few of them grew to be red or purple ; and finally a comparatively small number acquired the various shades of lilac, mauve, violet, or blue.” So among animals there are many colour patterns and structures that appear in widely different genera, as, for example, the magpie 66 Over-development colouring in birds. With this phenomenon we shall deal more fully when speaking of animal colouration. There is certainly no small amount of evidence which seems to indicate that, from some cause or other, an impetus has been given to certain organs to develop along definite lines, The reduction of the number of digits in several mammalian families which are not nearly related is a case in point. This phenomenon is, as Cope points out, observed in Marsupials, Rodents, Insectivores, Carnivores, and Ungulates. He, being a Lamarckian, ascribes this to the in- herited effects of use. Wallaceians attribute it solely to the action of natural selection. The assumption of a growth-force or tendency for the development of one digit at the expense of the others, would explain the phenomenon equally well. And it is significant that many paleonto- logists are believers in some kind of a growth- force. In the case of certain extinct animals we seem to have examples of the over-development of organs. “ Paleontology,” writes Kellog on p. 275 of his Darwinism To-day, “reveals to us the one-time existence of animals, of groups of animals, and of lines of descent, which have had characteristics which led to extinction. The un- wieldiness of the giant Cretaceous reptiles, the fixed habit of life of the crinoids, the coiling of the ammonities and the nautili, the gigantic antlers of the Irish stag—all these are examples 67 The Making of Species of development along disadvantageous lines, or to disadvantageous degrees. The statistical studies of variation have made known numerous cases where the slight, as yet non-significant (in a life-and-death struggle) variation in pattern of insects, in dimensions of parts, in relative pro- portions of superficial non-active areas, are not fortuitous, that is, do not occur scattered evenly about a mean or mode according to the law of error, but show an obvious and consistent tendency to occur along certain lines, to accumulate in certain directions.” It seems to us that the only proper attitude to adopt in the present state of our knowledge is, not to call in to our aid an unknown growth- force, but simply to say that there is evidence to show that variations frequently occur along certain definite lines only. Darwin’s second assumption was that there is no limit to which variations may be accumulated in any direction; that by adding one minute variation to another through countless generations new species, new genera, new families may arise. This assumption, if applied to continuous or fluctuating variations, seems opposed to facts. All the evidence available goes to show that there is a definite limit to which minute variations can be accumulated in any given direction. No one has succeeded in breeding a dog as large as a horse, or a pigeon with a beak as long as that 68 Speed of Racehorses of a snipe. In the case of racehorses, which have been selected so carefully through a long period of time, we seem to have reached the limit of speed which can be attained by the mul- tiplication of insignificant variations. We do not wish to dogmatise, but we believe that of late years there has not been any material increase in the speed of our racehorses. Mr S. Sidney says, on page 174 of Cassell’s Book of the Horse: “ As far as form went (pace Admiral Rous), the British racehorse had reached perfection in 1770, when ‘ Eclipse’ was six years old.” He quotes the measurements of the skeleton of “Eclipse” in the Museum of the Royal College of Surgeons as evidence of this. All the efforts of breeders, then, have failed appreciably to improve the form of the British racehorse in the course of over a century and a quarter. De Vries has made some important experi- ments with a view to determining whether or not there is a limit to the amount of change which can be induced by the selection of fluctuating or continuous variations as opposed to mutations. “I accidentally found,” he writes, on page 345 of Species and Varieties: ther Origin by Mutation, “two individuals -of the ‘five-leaved’ race (of clover); by transplanting them into my garden I have isolated them and kept them free from cross-fertilisation with the 69 The Making of Species ordinary type. Moreover, I brought them under such conditions as are necessary for the full development of their character; and last, but not least, I have tried to improve their char- acter as far as possible by a very rigid and careful selection. . . . By this method [| brought my strain within two years up to an average of nearly go per cent. of the seedlings with a divided primary leaf (such seedlings averaging five leaves in the adult)... . This condition was reached by the sixth generation in the year 1894, and has since proved to be the limit, the figures remaining practically the same through all the succeeding generations... . I have cultivated a new generation of this race nearly every year since 1894, using always the strictest selection. This has led to a uniform type, but has not been adequate to produce further improvement.” Similarly, De Vries found in the bulbous buttercup (Ranunculus bulbosus) a strain varying largely in the number of petals; therefore he tried by means of continuous selection of those flowers having the largest number of petals to pro- duce a double flower, but was not able to do so. He succeeded in evolving a strain with an average number of nine petals, some individuals having as many as twenty or thirty; but even by breeding only from these last he could not increase the average number of petals in any 70 Experiments of De Vries generation beyond nine. This was the limit to be obtained by the most rigorous selection of fluctuating variations. Selection, based on fluctuating variation, does not, asserts De Vries, conduce to the production of improved races. ‘‘Only temporary ameliora- tions are obtained, and the selection must be made in the same manner every year. More- over, the improvement is very limited, and does not give any promise of further increase.” Not- withstanding prolonged efforts, horticulturists have not yet succeeded in breeding a biennial race of either beetroots or carrots that does not continually give rise to useless annual forms. Writing of the beet, De Vries says useless annual varieties “are sure to return each year. They are ineradicable. Every individual is in the possession of this latent quality, and liable to convert it into activity as soon as the circum- stances provoke its appearance, as is proved by the increase of annuals in the early sowings ”— that is to say, in circumstances favourable to the annual variety. It will be urged perhaps that these experi- ments, which seem to show that there is a limit to which a species can be modified by the accumulation of fluctuating variations, cannot have been properly carried out, because all the various breeds of pigeons and other domestic animals clearly show that extraordinary differ- 71 The Making of Species ences not only can, but have actually been pro- duced by the selection of such variations. This objection is based upon the assumption that breeders have in the past dealt only with fluc- tuating variations. This assumption does not appear to be justified. It is exceedingly prob- able that most, if not all, the varieties of domesticated animals have originated in muta- tions. Take, for instance, the modern turbit pigeon; this has been derived from the old Court-bec, described and figured over two centuries ago by Aldrovandus. De Vries goes so far as to assert that the various races of pears are all mutations; that each distinct flavour is a mutation, and that it is impossible to produce a new flavour by selecting fluctuating variations. Thus it would appear that in every case of the production of a new breed a mutation has occurred which has attracted the fancy of some breeder, and he has seized upon this and perpetuated it. All the evidence available tends to show that there is a limit—and one which is quickly reached—to the amount of change that can be produced by the selection of fluctuating or continuous variations. We, therefore, seem driven to the belief that evolution is based on the kind of variation which Professor Bateson terms “discontinuous variation” and Professor De Vries calls “ mutation.” 72 Bateson on Variation ' As long ago as 1894 Bateson published his Materials for the Study of Varzatzon, in which he set forth a large number of cases of discon- tinuous variation which he had collected. He pointed out that species are discontinuous, that they are sharply separated one from another, whereas ‘“‘environments often shade into one another and form a continuous series.” How, then, he asked, if variations are minute and con- tinuous, have these discontinuous species arisen? May not variation prove to be discontinuous, and thus make it clear why species are discontinuous? On page 15 of the above-cited work we find: “The preliminary question, then, of the degree of continuity with which the process of evolution occurs has never been decided. In the absence of such a decision, there has nevertheless been a common assumption, either tacit or expressed, that the process is a continuous one. The immense consequence of a knowledge of the truth as to this will appear from a consideration of the gratuitous difficulties which have been introduced by this assumption. Chief among these is the difficulty which has been raised in connection with the building up of new organs in their initial and imperfect stages, the mode of transformation of organs, and, generally, the selection and perpetuation of minute variations. Assuming, then, that variations are minute, we are met by this familiar difficulty. We know 73 The Making of Species that certain devices and mechanisms are useful to their possessors ; but from our knowledge of natural history we are led to think that their usefulness is consequent on the degree of per- fection in which they exist, and that if they were at all imperfect, they would not be useful. Now it is clear that in any continuous process of evolution such stages of imperfection must occur, and the objection has been raised that natural selection cannot protect such imperfect mechanisms so as to lift them into perfection. Of the objections which have been brought against the theory of natural selection this is by far the most serious.” Bateson further pointed out that chemical compounds are not continuous, that they do not merge gradually each into the next, and suggested that we might expect a similar phenomenon in the organic world. Elsewhere he says: ‘‘ Let the believer in the efficacy of selection operating on continuous fluctuations try to breed a white or a black rat from a pure strain of black-and-white rats, by choosing for breeding the whitest or the blackest; or to raise a dwarf sweet pea from a tall race by choosing the shortest. It will not work. Variation leads and selection follows.” But Bateson’s views fell upon stony ground, because zoologists are mostly men of theory and not practical breeders. They laboured under the 74 Work of Bateson and De Vries delusion that mutations or “sports” are rare in nature, and that when these do happen to occur they must of necessity be swamped by inter- crossing. However, the discovery of the Abbé Mendel’s account of his experiments on breeding mongrel sweet peas has opened the eyes of many zoologists, so that they have at last learned what practical breeders have known for untold years—namely, that sports have a way of per- petuating themselves. Moreover, Mendel was able to give a theoretical explanation of his discoveries, with the result that the believers in discontinuous variation have largely increased in number of late. While we are unable to see eye to eye with Professor Bateson in all things, we gladly recog- nise the immense value of his work. Had his statements in 1894 received the attention they merited, zoological theory would to-day be con- siderably more advanced than it actually is. Professor De Vries has gone farther than Bateson, having engrafted upon the Darwinian hypothesis the theory of mutations. He has done no small amount of experimental work, and has undoubtedly thrown much new light on the ways in which species arise. He is purely a botanist, so that he argues only from plants. Nevertheless, we believe that some of his con- clusions are applicable to animals. We are far 75 The Making of Species from accepting his theory of mutations 2% éofo. We are, however, convinced that he, like Bate- son, is on the right track. There can be no doubt that a great many new forms have originated suddenly, by jumps, and not by imperceptibly slow degrees. Before giving a list of the names of some of the races, both plant and animal, which appear to have come into existence suddenly, it will be of advantage to consider for a little some of the more important conceptions of De Vries. That eminent botanist, as we have already seen, insists on the distinction between fluc- tuating variations and mutations. The former correspond, for all practical purposes, to the continuous variations of Bateson, and the latter seem to be equivalent to his discontinuous variations, According to De Vries, all plants display fluctuating variation, but only a small percentage exhibit the phenomenon of mutation. The most daring of his conceptions is, that the history of every species is made up of alternating periods of inactivity, when only fluctuating variations occur, and of activity when “ swarms of species” are produced by mutation, and of these only a few at the most survive; natural selection, which De Vries likens to a sieve, determining which shall live and which shall perish. 76 Varieties and Elementary Species As we have seen, De Vries does not believe that new species can arise by the accumulation of fluctuating variations. By means of these the race may be greatly improved, but nothing more can be accomplished. These variations follow Quetelet’s law, which says that, for biological phenomena, deviations from the aver- age comply with the same laws as the devia- tions from the average in any other case, if ruled by chance alone. Very different in character are mutations. By means of these, new forms, quite unlike the parent species, suddenly spring into being. Mutations are said by De Vries to be of two kinds—those that produce varieties and those which result in new elementary species. According to De Vries, those species of plants which are in a state of mutation (he refers to the species of the systematic botanists) are of a com- posite nature, being made up of a collection of varieties and elementary species. His concep- tion of a variety is a plant that differs from the parent plant in the loss or suppression of one or more characters, while an elementary species differs from the parent form in the possession of some new and additional character. But we will allow him to speak for himself: ‘“ We can con- sider (page 141 Sfeczes and Varretzes) the follow- ing as the principal difference between elementary species and varieties: that the first arise by the 77 The Making of Species acquisition of entirely new characters, and the latter by the loss of existing qualities, or by the gain of such peculiarities as may already be seen in other allied species. If we suppose elementary species and varieties originated by sudden leaps and bounds, or mutations, then the elementary species have mutated in the line of progression, some varieties have mutated in the line of retro- gression, while others have diverged from the parental types in a line of digression or in the way of repetition. . . . The system (of the vege- table kingdom) is built up of species ; varieties are only local and lateral, never of real import- ance for the whole structure.” De Vries asserts that these elementary species, when once they arise, breed true, and show little or no tendency to revert to the ancestral form. We can, says De Vries, ascertain only by experi- ment which plants are in the mutating state and which are not. The great majority, however, are not at present in the mutating state. The distinction between fluctuating variation and mutation has been roughly illustrated by the case of a solid block of wood having a number of facets, on one of which it stands. If the block be tilted slightly it will, when the force that has tilted it is removed, return to its old position. Such a gentle tilt may be compared to a fluctu- ating variation in an organism. If, however, the block be tilted to such an angle that when left to 78 Mutations itself the block does not return to its old position, but tips over and comes to rest on another facet, we have a representation of the kind of change indicated by a mutation. The analogy is far from perfect, for it makes it appear that the smallest mutation must of necessity involve a departure from the normal type more considerable than that of the largest fluctuating variation. Now, although mutations ordinarily consist in considerable deviations from the mean or mode of the type, while continuous variations are usually minute deviations, it some- times happens that the extreme fluctuations are more considerable than some mutations. Hence “fluctuating” describes this latter kind of variation more accurately than “continuous” does. The test, then, of a mutation is not so much the amount of deviation as the degree in which it is inherited. Mutations show no tendency to a gradual return to the mean of the parent species ; fluctuating variations do display such a tendency. A mutation consists, as M. E. East says, in the production of a new mode or centre for linear fluctuation ; it is, as it were, a shifting of the centre of gravity ; the centre about which those fluctuations which we call continuous varia- tions occur. As it is of considerable importance thoroughly to grasp the true nature of mutations or discon- 79 Laboratory of Ornithology 159 Sapsucker Vigeds Roe Cartel University Utiaca, New York fassh The Making of Species tinuous variations, and as some writers do not appear to realise wherein lies the essential difference between the two kinds of variation, we will, at the risk of appearing tedious, give a further illustration. Let A be a species of bird of which the average length of the wing is 20 inches, and let us suppose that individuals belonging to that species occur in which the length of the wing varies as much as 3 inches each side of the mean ; thus it is possible to find individuals of this species with a wing as short as 17 inches, or as long as 23 inches. Let B be another species of which the average length of the wing is 17 inches, and let us suppose that a 3-inch variation on each side of the mean be found to occur. Individuals belonging to species B will occur which have a wing as short as 14 inches, or as long as 20 inches. Thus some individuals of the short-winged species will have longer wings than certain individuals of the long- winged species. Similarly, certain individuals of a species which display a mutation may show less deviation from the mean than some indi- viduals showing a very pronounced fluctuating variation. In other words, even as by measuring the length of wing in the above example it was not always possible to say whether a given indi- vidual belonged to species A or B, so is it not always possible to say by looking at an individual that shows a considerable departure from the 80 Law of Regression mean whether that departure is due to a mutation or a fluctuating variation. It is only by watching the effect of the peculiarity on the offspring of its possessor that we are able to determine the nature of the varia- tion. Where the peculiarity is due to a fluctuating variation the offspring will display the peculiarity in a diminished degree ; but if the peculiarity be due to a mutation, the offspring are likely to display it in as marked a degree as the parent. Fritz Miller and Galton conducted inde- pendently enquiries into the amount of the regression shown by the progeny of parents which have deviated from the average by fluctuating variation. Miller experimented with Indian corn; Galton with the sweet pea. Each found that where the deviation of the parents is represented by the figure 5, that of their offspring is usually 2, that is to say, the deviation they display is, on the average, less than half that of their parents. Applying this rule to the hypothetical case given above, if two individuals of species A having a length of wing of 20 inches be bred together, their offspring will, on an average, have a length of wing of 20 inches, since neither parents showed any deviation from the mean. On the other hand, the offspring of 20-inch-wing individuals of species B would show, on an F 81 The Making of Species average, a length of wing of only about 138} inches. They tend to return to that mode from which their parents had departed. But suppose that the deviation of the parents in this case had been due, not to fluctuating variation, but to a mutation; this would mean that, owing to some internal change in the egg that produced each parent, 20 inches became the normal length of wing; that the normal length of wing had suddenly shifted from 17 inches to 20 inches. The result of this would be that their offspring would have on an average a wing-length of 20 inches instead of 18} inches, that the centre of variation as regards length of wing had suddenly shifted from 17 to 20, that, in future, all fluctuating variations would occur on either side of 20 inches, instead of on either side of 17 inches as heretofore. Thus a variation is a fluctuating one or a mutation according as it does or does not obey Galton’s Law of Regression. De Vries says that it is of the essence of mutations that they are completely inherited. This statement, although substantially true, fails to take into consideration the factor of fluctuating variation. For example, in the above instance if the two individuals of species B had mutated into forms with a 20-inch wing, their offspring will nevertheless vary zuter se, some of them 82 De Vries’s Dictum will have wings shorter than 20 inches and others wings more than 20 inches in length. But the average wing-length of the offspring of the two mutating individuals will be 20 inches. So much, then, for the practical difference between a mutation and a fluctuating variation. In Chapter V. we shall discuss the possible causes of the difference. By way of anticipation we may say that the suggestion we shall make is that a mutation is due to some rearrangement in the particles which represent that part of the organism in the fertilised egg, whereas a fluctu- ating variation is caused by variations in the particles themselves. De Vries, it should be noted, bases his theory largely on experimental evidence. His dictum is ‘‘the origin of species is an object of experi- mental observation.” He has, we consider, proved conclusively that among plants mutations sometimes occur, and, further, that in a mutating plant the same mutation tends to occur again and again. This latter is a most important fact, because it goes some way towards overcoming the difficulty urged by Darwin that isolated sports must be swamped by continual crossing with the normal type. If mutations arise in swarms, as De Vries asserts they do, then any particular mutation is likely, sooner or later, to cross with a similar mutation and so be able to perpetuate itself. ; 83 The Making of Species The classical example of a mutating plant is the evening primrose of the species Oenothera lamarckiana. This is described by De Vries as a stately plant, with a stout stem, attaining often a height of 1.6 metres or more. The flowers are large and of a bright yellow colour, attracting immediate attention, even from a distance. “This striking species,” he writes, in Speczes and Varieties (p. 525), ‘was found in a locality near Hilversum, in the vicinity of Amsterdam, where it grew in some thousands of individuals. Or- dinarily biennial, it produces rosettes in the first, and stems in the second year. Both the stems and the rosettes were seen to be highly variable, and soon distinct varieties could be distinguished among them. The first discovery of this locality was made in 1886. Afterwards I visited it many times, often weekly or even daily, and always at least once a year up to the present time. This stately plant showed the long-sought peculiarity of pro- ducing a number of new species every year. Some of them were observed directly in the field, either as stems or rosettes. The latter could be transplanted into my garden for further observation, and the stems yielded seeds to be sown under like control. Others were too weak to live a sufficiently long time in the field. They were discovered by sowing seed from indifferent plants of the wild locality in the garden. A third 84 Mutating Plants and last method of getting still more new species from the original strain was the repetition of the sowing process, by saving and sowing the seed which ripened on the introduced plants. These various methods have led to the discovery of over a dozen new types, never previously ob- served or described.” Some of these De Vries regards as varieties, in the sense in which he uses the words; others, he maintains, are real progressive species, some of which are strong and healthy, others weaker and apparently not destined to be successful. All these types proved absolutely constant from seed. ‘‘ Hundreds of thousands of seedlings may have arisen, but they always come true and never revert to the original O. lamarckiana type. But some of them, how- ever, are, like their parent form, liable to muta- tions.” The case of the evening primrose is by no means an isolated one. De Vries cites several other instances of plants in a mutating state. “The common poppy,” he says (p. 189), ‘‘ varies in height, in colour of foliage and flowers; the last are often double or laciniated. It may have white or bluish seeds, the capsules may open themselves or remain closed, and so on. But every single variety is absolutely constant, and never runs into another when the flowers are artificially pollinated and the visits of insects excluded.” Similarly the garden carnation some- times gives rise to the wheat-ear form. ‘‘In this 85 The Making of Species variety,” writes De Vries (p. 228), ‘‘ the flower is suppressed, and the loss is attended by a corres- ponding increase in the number of pairs of bracts. This malformation results in square spikes, or somewhat elongated heads, consisting only of the greenish bracts. As there are no flowers, the variety is quite sterile, and, as it is not regarded by horticulturists as an improvement on the ordinary bright carnations, it is seldom multiplied by layering. Notwithstanding this it appears from time to time, and has been seen in different countries and at different periods, and what is of great importance for us, in different strains of carnations. Though sterile, and obviously dying out as often as it springs into existence, it is nearly two centuries old. It was described in the beginning of the eighteenth century by Volckamer, and afterwards by Jaeger, De Candolle, Weber, Masters, Magnus, and many other botanists. I have had it twice at different times and from different growers.” Similarly, the long-headed green dahlia arose twice over some years ago in the nursery of Messrs Zocher & Co. Further, the peloric Toad-flax (Zzxarza vul- garis peloria) is, De Vries informs us, ‘‘ known to have originated from the ordinary type at different times and in different countries under more or less divergent conditions.” And, as this variety is wholly barren, it must in each instance have had an independent origin. Lastly, the 86 Mutation Theory Criticised purple beech seems to be a mutation which has originated at least three times over. Every one interested in biological theory should read both Species and Varieties and Plant Breeding by De Vries, works which are of incalculable value to the horticulturist and agri- culturist as well as to the biologist. While not wishing to detract in any way from the truly splendid work done by De Vries, we feel constrained to bring several charges against him. Firstly, he suffers from the complaint that seizes nine out of ten originators of new theories. He pushes his theory to extreme lengths; he allows his imagination to run away with him. We do not think that on the evidence available he is justified in asserting that every species passes through alternating periods of comparative quiescence and periods in which it throws off, as mutations, swarms of elementary species. He is justified in asserting that discontinuous varia- tion is by no means an uncommon phenomenon, but further than this it does not seem safe to go at present. Secondly, he ought to lay more stress on the fact that Oenothera lamarckiana is a plant which does not appear to be known in the wild state, and that it is therefore possibly a hybrid plant, and the so-called elementary species which it gives off may be merely the varieties out of 87 The Making of Species which it has been built up. Boulenger and Bailey have both studied this plant, and they have not been able to witness all the mutations of which De Vries speaks, so that the former says, “ The fact that Oenothera lamarckiana was originally described from a garden flower, grown in the Paris Jardin des Plantes, and that, in spite of diligent search, it has not been discovered wild anywhere in America, favours the prob- ability that it was produced by crossing various forms of the polymorphic Oenothera bcennis, which had been previously introduced in Europe.” It has further been objected that, even if these various forms which Lamarck’s evening primrose throws off are true mutations, they ought not to be called new species, for they do not differ sufficiently from the parent species to deserve the name of new species. The reply to this criticism is that De Vries asserts that mutations produce new elementary species, which are not the same things as new species in the ordinary sense of the term. Most Linnzan species differ from one another to a far greater extent than do elementary species. It seems to us quite plain that new species arise, not by a single mutation, but by two or three successive mutations which occur in various parts of an organism. First arises a well-marked variety, by a single mutation. Subsequent mutations follow, so that 83 Definition of a Species a distinct race is produced. And, finally, fresh mutations occur, so that a new species is eventu- ally produced. What De Vries calls an elementary species the majority of systematists would call a well- marked variety. We may take this opportunity of remarking that the definition of a species is one on which naturalists seem unable to agree. So vast is the field of biology, that now-a-days biologists are compelled to specialise to some extent. Thus we have botanists, ornithologists, those who devote themselves to the study of mammals, those who confine themselves to reptiles, or insects, or fishes, or crustaceans, or bacteria, etc. Now each class of systematists has its own particular criterion of what constitutes a species. Ornithologists do not seem very exacting. Most of them appear to consider a constant difference of colour sufficient for the formation into a species of the birds that display such a variation. Those who study reptiles, on the other hand, do not allow that a mere difference in colour is sufficient to promote its possessor to specific rank. Into these nice questions we cannot enter. For our purpose a species is a group of individuals that differ from all other individuals in displaying certain well-marked and tolerably constant charac- ters, which they transmit to their offspring. 89 The Making of Species Our contention, then, is that new species, in the ordinarily-accepted use of the term, do not arise as a rule by one sudden bound (although they may sometimes do so), but are the result of the accumulation of several mutations or dis- continuous variations. Some of these mutations are exceedingly well marked, while others are so small as to be indistinguishable from the more extreme fluctuating variations. Before passing on to consider some cases of well-marked muta- tions which have occurred among animals and plants, we should like to take this opportunity of pointing out that as regards experiments in evolution the botanist is far more favourably situated than the zoologist. The botanist is able to reproduce many species vegetatively, e.g. by cuttings, and is thus easily able to multiply examples of mutation. He can also reproduce the great majority of plants by self-fertilisation, and so experiences no difficulty in “fixing” a new form. Again, plants are far easier to control than animals; as a rule they can be transplanted without any impairment of their capacity for breeding. Moreover, they produce a greater number of offspring than the most prolific of the higher animals. The animal breeder is thus at an obvious disadvantage as compared with the horticulturist. It is only with great difficulty that he can fix the mutations which appear in his stock. go “ Scatliff Strain” of Turbit The history of the production of the “ Scatliff strain” of turbit affords a good example of the kind of difficulties that confront the breeder. Pigeon fanciers require that the ideal turbit shall have, among other things, an unbroken “sweep,” that is to say the line of the profile from the tip of the beak to the back of the head should be the arc of a circle. As a rule this line is broken by the overgrowth of the wattle at the base of the beak. Mr Scatliff, however, has succeeded in breeding a strain which possesses the required description of profile. “In the year 1895,” writes Mr H. P. Scatliff on page 25 of The Modern Turbit, ‘1 visited Mr Houghton’s lofts and purchased three or four extra stout and short-beaked stock birds... . The following year I mated one of these to one of my own black hens, and reared one of the most successful show birds ever bred, viz. ‘Champion Ladybird,’ a black hen. . . . Most of _the leading judges and many turbit breeders remarked upon this hen’s wonderful profile, which seemed to improve as she got older instead of getting worse, as is usual in rather coarse-wattled birds. I, too, had remarked this, and it opened my eyes to a point in turbit breeding which I had never heard mentioned by any turbit judges or breeders, and which I believe I am now pointing out for the first time in print, viz. that the feathers over her beak wattle which formed gr The Making of Species her front grew from the top and right to the front of her wattle, and not from slightly behind, as in almost every other turbit of her day; thus, as the wattle developed and grew coarser, the front became more developed, and made her head larger without in any way spoiling the sweep of the profile. “The same year ‘ Ladybird’ was bred I bred eight others from the same pair, and with one exception all turned out to be hens. There was only one other hen, however (a dun), that had this same point, but in a lesser degree than ‘Ladybird,’ and from these two hens nearly all my blacks, and several of my blues are de- scended.” Mr Scatliff, having “spotted” this point, looked about him for another bird having the peculiarity, with the object, if possible, of fixing the same in his strain. He discovered this point in a pigeon belonging to Mr Johnston of Hull, and purchased the bird for £20. But it died in the following spring without producing for Mr Scatliff a single young one. The next year Scatliff found that a bird belonging to a Mr Brannam had the required peculiarity and so purchased him for £20. But that cock, too, died before anything was bred from him. Nothing daunted, Scatliff found that another of Brannam’s cocks displayed the same peculiarity, so purchased him in 1899 for £15, but he also died before the g2 Pa Lepouny| PMO at i yt , {ihe If Wily A TURBIT BELONGING TO MR. H. P. SCATLIFF Fron “The Modern Turbit,” published by “ The Feathered World,’ London. “ Scatliff Strain” of Turbit year was out. Meanwhile Scatliff had, by mating up “ Ladybird” with the most likely of his own cocks, succeeded in producing one or two young cocks with the desired point. By breeding these with their mother “Ladybird” and their off- spring again with “ Ladybird,” Scatliff eventually succeeded in breeding some turbits, both blacks and duns, with the required peculiarity fully developed, but not before he had spent a further sum of £55 on two other cocks, both of which died before they could be mated with the famous “Ladybird.” However, amid all his misfortunes, Scatliff informs us that he bought one bird, by name “Amazement,’ which did assist him in fixing his strain. Thus Scatliff spent consider- ably over £100 in purchases, and took eight years fixing the peculiarity in question. Had “ Lady- bird” been a flower, the peculiarity could probably have been fixed in one generation by self- fertilisation. This furnishes an excellent example of the trouble which breeders will take, and the expense to which they will go in order to produce a desired result. Nevertheless, it appears to be the fashion for scientific men to decry the work of the breeder. Let us now pass on to consider the cases of mutations which are known to have occurred among animals. 93 The Making of Species MuTATIONS AMONG ANIMALS Some instances of great and sudden variation in domesticated animals have become classical, and been detailed in almost every work on evolution. These are, firstly, the celebrated hornless Paraguay cattle. This hornless breed, or rather the ancestor of the breed, arose quite suddenly. Many domestic horned breeds of animals, especially sheep and goats, throw off hornless sports. Were a hornless breed of buffalo found in nature, it would undoubtedly be ranked a new species, and the Wallaceians would doubt- less exercise much ingenuity in explaining how natural selection had brought about the gradual disappearance of the horns ; and paleontologists, being baffled in their search for intermediaries between the hornless species and their horned ancestors, would complain of the imperfection of the geological record. It may, perhaps, be argued that this hornless mutation was a direct result of the unnatural conditions to which the Paraguay cattle were subjected, it may be asserted that since there are no species of hornless cattle in nature, such mutations have never occurred under natural conditions, and hence the Paraguay cattle prove nothing. As a matter of fact, we know that in Nature a great many mutations occur which are 94 Mutations among Mammals not perpetuated because not beneficial to the species. A hornless individual in the wild state would stand but little chance in fighting for females against his horned brethren. We must keep clearly in mind that the theory of mutation does not seek to abolish natural selection; it merely affords that force something substantial to work upon. The second classical example of a leap taken by nature is furnished by the Franqueiro breed of long-horned cattle in Brazil. These’ furnish us with an example of a mutation in the other direction. Then there is the Niata or bull-dog breed of cattle, which are also South American. These instances would seem to indicate that cattle are what De Vries would call “in a mutat- ing state” in that part of the world. The other classical examples of great and sudden variations are the Ancon sheep of Massa- chusetts, the Mauchamp breed of Merino sheep, the tufted turkeys, and the long-haired race of guinea-pigs. The “wonder horses,” whose manes and tails grow to an extraordinary length, so as to trail on the ground, may perhaps be cited as a race which originated in a sudden mutation. They are all descendants of a single individual, Linus I., whose mane and tail were respectively eighteen and twenty-one feet long. But in this case it is important to note that the parents and 95 The Making of Species grandparents of Linus I. had exceptionally long hair. Coming now to birds we find several undoubted examples of mutations, or new forms which have come suddenly into being. The black-winged peafowl, whose peculiarities were commented on by Darwin, afford a striking example of this phenomenon. These birds breed true when mated together, and are known to have arisen from common peafowl in no less than nine instances. The cocks have the wings (except the primary quills), black glossed with blue and green, and have the thighs black, whereas, in the ordinary peacock, the same part of the wing is nearly all mottled black and pale buff, and the thighs are drab. The black-winged hen, on the other hand, is nearly white, but has a black tail and black speckling on the upper surface of the body, while her primary quills are cinnamon coloured as in male peafowl, not drab as in the normal hens. The young are white when hatched, the young cock gradually assuming the dark colour as he matures. This mutation, which, in one case quoted by Darwin, increased among a flock of peafowl until the black-winged supplanted the ordinary kind, is so distinct in appearance in all stages that it was formerly supposed to be a true species (Pavo nigripennis), of which the wild habitat was unknown. 96 Mutations among Birds The Golden Pheasant (Chrysolophus pictus) produces, in domestication, the dark-throated form (C. odscurus), in which the cock has the throat sooty-black instead of buff, and the scapulars or shoulder feathers black instead of red. Moreover, the two middle-tail-feathers are barred with black and brown like the lateral ones, while in the ordinary form they are spotted with brown on a black ground. The hens have a chocolate-brown ground-colour instead of yellow-ochre as in the normal type. The chicks are likewise darker. The common duck, in domestication, when coloured like the wild mallard, sometimes pro- duces a form in which the chocolate breast and white collar of the drake are absent, the pencilled grey of the abdomen reaching up to the green neck. In this mutation the duck has the head uniformly speckled black and brown, and lacks the light eye-brow and cheek-stripes found in the normal duck. Both sexes have the bar on the wing dull black instead of metallic blue. The ducklings which ultimately bear this plumage are sooty-black throughout, not black and yellow like normal ones. The phenomenon of mutation is not confined to animals in a state of domestication. The common Little Owl of Europe (Athene noctua) has produced the mutation 4. chiaradie in the wild state. In this the irides are dark, instead of G 97 The Making of Species yellow as in the normal type, and the plumage of the back of the wings is longitudinally streaked with white instead of barred. Several examples of this form were found, along with normal young, in the nest of one particular pair of little owls in Italy, but the whole family were foolishly ex- terminated by local ornithologists. The reed bunting (Eméberiza schoentclus) exists in two distinct forms—one having a much stouter bill than the other (Z. Ayrrhulocdes). This prob- ably is an example of a mutation. The rare yellow-rumped Finch (Munza flavt- prymna), of Australia, has displayed a tendency to change into the allied and far commoner chestnut - breasted Finch (JZ. castanezthorax) during the lifetime of the individual (Avicultural Magazine, 907). Conversely, the male of the common Red-billed Weaver (Quelea quelea) of Africa has been found in its old age to assume the characters of the comparatively rare Q. russz, its black throat becoming pale buff as in that form. Everyone is familiar with the chequered variety of the common blue-rock pigeon, in which the wings are regularly mottled with black instead of being barred. This form some- times occurs among wild birds, so that it has been described as a distinct species. It is important to note that there are red, dun, and silver chequers as well as blue ones. 98 Mutations among Birds A well-marked mutation which appears regu- larly in nature is the red-headed variety of the beautiful Gouldian Finch (Péephila mirabilis ) of North Australia. Normally the head of the cock is black, but in about ten per cent. of the individuals the cock has a crimson head, while that of the hen is dull crimson and black. | Mutations which occur with such regularity are certainly rare. On the other hand, there are certain mutations which we may expect to see appear in any species of plant or animal. Albinistic forms are a case in point, and less frequently we see white varieties which are not pure albinos, because the eye retains some at least of the normal pigment. As examples, we may cite white dogs, cats, fowls, horses, ducks, geese, and Java sparrows among domesticated animals, and the white forms of the Amazonian dolphin and of the giant Petrel of the South seas (Osstfraga gigantea) among wild creatures. In a white mutation the eye may lose all its pigment, and then we have a true albino, Such forms on account of their imperfect vision cannot survive in a state of nature, hence no wild pink- eyed species are known. Or the eye may display a partial loss of pig- ment, as, for example, in the white domestic forms of the common goose, the Chinese goose, and the Muscovy duck. Finn saw a case in which the eyes of a pink-eyed rabbit changed 99 The Making of Species after death into this type of eye—that is, with the pupil black and the iris blue. It is to be observed that this kind of eye sometimes occurs in coloured horses, rabbits, and dogs. Finally, we have white mutations in which the eye loses none of the pigment. These are abundant in nature, and probably most of the white species of birds—as, for example, some egrets, swans, etc.—arose in this way. Pure white species are comparatively uncommon in nature, because, except in snow-clad regions, white creatures are easily seen by their adversaries. Most white birds are of considerable size, and well able to look after themselves. Similarly black mutations occur frequently among animals, both under domestication and in a state of nature. All are familiar with black dogs, cats, horses, fowls, ducks, pigeons. Black mutations, however, do not occur nearly so frequently as white ones. So far as we are aware no black mutation has been recorded among canaries, geese, guinea-fowl, ferrets, Java sparrows or doves, all of which produce white mutations. On the other hand, in the wild state black species occur more frequently than normal-eyed white forms. This is probably because such 1 Some egrets, such as the rock-egrets (Demzegretta) of eastern tropical coasts, are normally grey, but may be white, and this whiteness may be confined in individuals to the young or adult states. 100 Colour Mutations creatures are less conspicuous than white ones. As examples of black mutations which occur in Mature, we may cite black leopards, water rats, squirrels, foxes, barking deer (Cervulus muntjac), hawk-eagles, harriers, peppered moth (Amphidasys betularia), etc. That many black species have arisen as sudden mutations from lighter-coloured animals seems tolerably certain from the facts that in Malacca the black leopard forms a local race; that some of the Gibbon apes are as often black as light coloured ; that the American black bear is some- times brown, while the other bears, when not brown, are almost invariably black. Not uncommon, although rarer than black or melanistic forms, are reddish or chestnut varieties. These occur both among tame and wild animals. Among domesticated creatures, sandy cats, ‘‘red” pigeons, buff fowls, chestnut horses, red guinea pigs afford examples of this mutation. Among wild animals many of the species of squirrel, not naturally red, produce red mutations ; and some of the grey owls—as, for example, the Indian race of the Scops (Scops gzu)—throw off a red or chestnut form. As everyone knows, some species are normally red. Green or olive species not unfrequently throw off yellow mutations. As examples of these we may cite yellow canaries, yellow budgerigars (Melopsittacus undulatus), goldfish, golden tench, Iol The Making of Species and the golden form of the common carp among captive animals; and among animals in a state of nature, yellow forms have been recorded of the rose-ringed Paroquet (Paleornis torguatus), the green woodpecker, the pike, and the eel. These lutinistic forms usually have normally coloured eyes. Sometimes, but only very rarely, these yellow forms throw off white sports—as, for example, the “silver” form of the goldfish. Finn has seen a white variety of the common carp. White canaries are excessively rare, while white budgerigars are unknown. It is worthy of note that entirely yellow species of birds and fish are unknown. We would suggest that the explanation of this is that yellowness is correlated with some physical characteristic un- favourable to an organism exposed to the struggle for existence; hence individuals which are yellow are not permitted to survive. In some species of moths individuals occur in which the parts normally red are yellow. According to Bateson, a chalk pit at Madingly, near Cam- bridge, has long been known to collectors as a habitat of a yellow-marked form of the six-spot Burnet Moth (Zygena filipendule). These lutinistic forms are not confined to one genus of Butterflies. Moreover, in the Pin-tailed Non- pareil Finch (Zythrura prasina) of the Eastern Archipelago the red tail and other red parts of the plumage are not infrequently replaced by 102 Mutations among Invertebrates yellow in wild individuals of either sex and of any age. In the blue-fronted Amazon parrot (Chrysotts @steva)—a most variable bird—the normally red edge of the pinion is sometimes yellow. Bateson, in his Materials for the Study of Variatzon, gives other examples of this kind of variation. As further instances of mutations among animals which have been observed in nature, we may mention the valezina form of the female of the Silver-washed Fritillary Butterfly (4zzynnzs paphia) and the helice form of the female Clouded- yellow Butterfly (Colas edusa). The common jelly-fish is an organism which frequently throws off sports, and some zoologists are of opinion that the medusoid Pseudoclytia pentata arose by a discontinuous variation from LEpentheses folleata or a closely allied form. Thomson discusses this particular case at some length on pages 87-89 of his Heredity, and gives it as his opinion that the evidence in favour of this latter having arisen as a mutation is “exceedingly strong.” It is our belief that many species of birds which occur in nature have been derived from other species which still exist, but as no one has ever seen the mutation take place, we cannot furnish any proof thereof. We merely rely on the fact that the species in question differ so slightly from one another that there seems every 103 The Making of Species likelihood that they have suddenly arisen and managed to establish themselves alongside of the parent species. The Curassows, Crax grayt, C. heckz, each of which is only known by a very few specimens, appear to be mutations of the female of the globose Curassow, Crvax globicera. The fact that when a female ekz bred in the London Zoological Gardens with a male g/odicera, the solitary young one which lived to grow up was a pure globicera, renders the assumption almost certain. The Chamba Monaul (Lophophorus chambanus) _ seems to be a mutation of the male of the common Monaul or Impeyan Pheasant (Lopho- phorus impeyanus), the common species of the Himalayas. The Three-coloured Mannikin (Junta malacca) of South India is probably simply a white-bellied form of the widely-ranging Black-headed Man- nikin (JZ. atricapilla), which has the abdomen chestnut like the back. Intermediate wild- caught forms have been recorded. The African Cordon-bleu (Zstrelda pheenicotzs) and Blue-bellied Waxbill (4. cyanogastra) would also seem to be mutations, as almost the only difference between them lies in the fact that the male of the former has a crimson cheek- patch, which is wanting in the latter. The Ringed Finch (Stzctoptera annulosa) of 104 Mutating Species Java, and Bicheno’s Finch (S. dechenovii) of Australia, only differ in the former having the rump black, while in the latter it is white, and this difference appears to be of the nature of a mutation. So, it might be urged, is the pure white breast of the male Upland Goose (Chloéphaga magel- fanica), which part, in the very similar C. dispar, is barred as in the females, the latter form being probably the ancestor. The differences between the silver-grey-necked Crowned Crane of the Cape (Bakarica chryso- pelargus) and the dark-necked species of West Africa (B. regulorum) seem also to be not more than could be accounted for by mutation. Peculiar forms, such as a rabbit with a con- voluted brain or a mouse with a peculiar pattern of molar teeth, have been come upon by anatomists. The above-cited mutations are all very con- siderable ones, and we do not profess to have mentioned a tenth part of those which have actually been recorded. We trust that we have collected and set forth sufficient evidence to show that the phenomenon of discontinuous variation is a very general one, and this would seem to tell against the hypo- thesis of De Vries that species pass through alternate periods of comparative stability and periods when swarms of mutations appear. We 105 The Making of Species think it more probable that all species throw off at greater or less intervals discontinuous varia- tions, and that it is upon these that natural selec- tion acts. We further hope that we have succeeded in making clear what we believe to be the very sharp distinction between continuous and dis- continuous variations, even when the latter are inconsiderable, as frequently happens. Before leaving the subject of variation it is necessary to notice the distinction, which Weis- mann was the first to emphasise, between somatic and germinal variations. Every adult organism must be regarded as the result of two sets of forces ; inherited tendencies or internal forces, and the action of environment or external forces. The differences which the various members of a family show are due in part to the initial differences in the germinal material of which they are composed, and in part to the differences of their environment. The former differences are the result of what we may call germinal variations, and the latter the result of somatic variations. It is scarcely ever possible to say of any particular variation that it is a germinal or a somatic one, because even before birth a developing organism has been subjected to environmental influences. One of a litter may have received more nourishment than the others. Nevertheless, any marked variation which appears 106 Somatic and Germinal Variations at birth is probably largely germinal. According to Weismann and the majority of zoologists, there is a fundamental difference between these germinal and somatic variations, in that the former tend to be inherited, while the latter are never inherited. Weismann believes that very early in the formation of the embryo the cells which will form the generative organs of the developing organism are separated off from those cells which will go to build up the body, and become as much isolated from them as if they were contained in a hermetically-sealed flask, so that they remain totally unaffected by any changes which the environment effects in the somatic cells. Therefore, says Weismann, acquired characters cannot be inherited. While the majority of zoologists believe that acquired characters are not inherited, probably not many will go so far as Weismann and declare that the environment cannot exercise any effect whatever on the germ cells. Even though acquired characters or variations are not inherited, it does not follow that they do not play an important part in evolution. Acquired variations are the result of the way in which an organism reacts to its environment. If an organ- ism is unable to react to its environment it must inevitably perish. If it is able to react, it matters not, so far as the chances of survival of the organism are concerned, whether the adaptation ; 107 The Making of Species is the result of a congenital variation or a somatic one. This will be rendered clear by a hypotheti- cal example. Let us suppose that a certain mammal is forced, owing to the intensity of the struggle for existence, to migrate into the Arctic regions. Let us further suppose that this organ- ism is preyed upon by some creature that hunts by sight rather than by scent. Let us yet further imagine that this predacious species is swifter than our animal, on which it preys. It is obvious that, other things being equal, the more closely the creature preyed upon assimilates to its surroundings the more likely is it to escape the observation of its foes, and so to survive and give birth to offspring. Now suppose that the glare from the snow-covered ground bleaches its coat. This whitening of the fur is a somatic variation, one which is induced by the environ- ment. Such an animal will be as difficult to see, if the bleaching is such as to render it snow- white, as if its whiteness were due to a germinal variation. ‘Thus, as regards its chances of sur- vival, it matters not whether its whiteness be the result of germinal or somatic variation. But if the whiteness is due to a somatic variation, its offspring will show no tendency to inherit the variation ; they will have in turn to undergo the bleaching process. If, on the other hand, the whiteness is due to a germinal variation, the offspring will tend to inherit this peculiarity and 108 Somatic Variations to be born white. In such a case, it is unlikely that the fur of an organism which is naturally coloured will be completely bleached by the snow, and, even if it be, the bleaching process will take time, meanwhile the creature will be comparatively conspicuous. So that those which are naturally whiter than the average, that is to say, those in which the tendency to whiteness appears as a germinal variation, will be less con- spicuous than those which tend to be the ordinary colour. Thus the former will enjoy a better chance of survival, and will be likely to transmit their whiteness to their offspring in so far as it is due to a germinal or congenital variation. Thus, although none of the whiteness due to somatic variations is transmitted to the offspring, such variations are of considerable importance to the species, as they enable it to survive and allow time for the germinal variations in the required direction to appear. That this case need not be purely hypothetical is shown by the fact that dun domestic pigeons, which are of an earthy-brown colour when fresh moulted, soon fade in the sun to a dull creamy hue. Thus a coloration adapted to an ordinary soil could soon be suited to a desert environ- ment. The ruddy sheldrake also, normally a bright chestnut-coloured bird, and one that haunts exposed sunny places, in many cases fades very much, becoming almost straw-coloured, 109g The Making of Species Many variations which organisms display are of a mixed kind, being in part the result of inner forces and in part due to the action of the en- vironment. In so far as they are due to this latter they do not appear to be inherited. Thus, although we cannot say of many varia- tions whether they are germinal, or somatic, or of a mixed kind, it is of great importance to keep continually in mind the fundamental differences between the two kinds. Some somatic variations are due to the direct action of the environment; they are merely the expression of the manner in which an organism responds to external stimuli. What is the cause of germinal variations? This is a question to which we are not yet ina position to give a satisfactory answer, The attempt to explain their origin plunges us into the realm of theory. This doubtless is a realm full of fascination, but it is an unexplored region of extreme darkness, in which, we believe, it is scarcely possible to take the right road until more of the light of fact has been shed upon it. In the chapter dealing with inheritance we shall indicate the lines along which it is likely that future progress will be made. TIo CHAPTER IV HYBRIDISM The alleged sterility of hybrids a'stumbling-block to evolutionists— Huxley’s views— Wallace on the sterility of hybrids—Darwin on the same—Wallace’s theory that the infertility of hybrids has been caused by Natural Selection so as to prevent the evils of intercrossing—Crosses between distinct species not necessarily infertile—Fertile crosses between species of plants —Sterile plant hybrids—Fertile mammalian hybrids—Fertile bird hybrids—Fertile hybrids among amphibia—Limits of hybridisation—Multiple hybrids—Characters of hybrids— Hybridism does not appear to have exercised much effect on the origin of new species. HE alleged sterility of the hybrids pro- duced by crossing different species has long proved a great stumbling- block to evolutionists. Huxley, in particular, felt the force of this objection to the Darwinian theory. If the hybrids between natural species are sterile, while those of all the varieties which the breeder has produced are perfectly fertile, it is obviously quite use- less for evolutionists to point with pride to the results obtained by the breeder, and to declare that his products differ from one another to a greater extent than do many well-recognised species. Tit The Making of Species “ After much consideration, and with no bias against Mr Darwin’s views,” wrote Huxley to the Westminster Review in 1860, ‘it is our clear conviction that, as the evidence now stands, it is not absolutely proven that a group of animals having all the characters exhibited by species in nature, has ever been originated by selection, whether natural or artificial. Groups having the morphological nature of species, distinct and per- manent races, in fact, have been so produced over and over again; but there is no positive evidence at present that any group of animals has, by variation and selective breeding, given rise to another group which was in the least degree infertile with the first. Mr Darwin is perfectly aware of this weak point, and brings forward a multitude of ingenious and important arguments to diminish the force of the objection. We admit the value of these arguments to the fullest extent; nay, we will go so far as to express our belief that experiments, conducted by a skil- ful physiologist, would very probably obtain the desired production of mutually more or less in- fertile breeds from a common stock in a com- paratively few years; but still, as the case stands at present, this little ‘rift within the lute’ is not to be disguised or overlooked.” Similarly Wallace writes, at the beginning of chapter vii. of his Darwinism: “One of the greatest, or perhaps we may say the greatest, of Il2 Alleged Sterility of Hybrids all the difficulties in the way of accepting the theory of natural selection as a complete expla- nation of the origin of species, has been the remarkable difference between varieties and species in respect of fertility when crossed. Generally speaking, it may be said that the varieties of any one species, however different they may be in external appearance, are per- fectly fertile when crossed, and their mongrel offspring are equally fertile when bred among themselves; while distinct species, on the other hand, however closely they may resemble one another externally, are usually infertile when crossed, and their hybrid offspring absolutely sterile. This used to be considered a fixed law of nature, constituting the absolute test and criterion of a species as distinct from a variety; and so long as it was believed that species were separate creations, or at all events had an origin quite distinct from that of varieties, this law could have no exceptions, because if any two species had been found to be fertile when crossed and their hybrid offspring to be also fertile, this fact would have been held to prove them to be not species but varieties. On the other hand, if two varieties had been found to be infertile, or their mongrel offspring to be sterile, then it would have been said—These are not varieties, but true species. Thus the old theory led inevitably to reasoning in a circle, and what might be H 113 The Making of Species only a rather common fact was elevated into a law which had no exceptions.” Thus the sterility of hybrids was a zoological bogey which had to be demolished. The plan of campaign adopted by Darwin and Wallace was, firstly, to try to disprove the assertion that the hybrids between different species are always sterile, and secondly, to find a reason for the alleged sterility of these hybrids. Darwin succeeded in obtaining some examples of crosses between botanical species which were said to be fertile. These he quotes in chapter viii. of Zhe Origin of Species. As regards animals, he met with less success. “‘ Although,” he writes, ‘I do not know of any thoroughly well-authenticated cases of perfectly fertile hybrid animals, I have some reason to believe that the hybrids from Cervulus vagenalis and veeveszz, and from Phastanus colchicus and P. torquatus and with P. versicolor are perfectly fertile. There is no doubt that these three pheasants, namely, the common, the true ring- necked, and the Japan, intercross, and are becoming blended together in the woods of several parts of England. The hybrids from the common and Chinese geese (A. cygnozdes), species which are so different that they are generally ranked in distinct genera, have often been bred in this country with either pure parent, and in one single instance they have 114 Fertile Hybrids bred znter se. This was effected by Mr Eyton, who raised two hybrids from the same parents but from different hatches; and from these two birds he raised no less than eight hybrids (grand- children of the pure geese) from one nest. In India, however, these cross-bred geese must be far more fertile; for I am assured by two eminently capable judges, namely, Mr Blyth and Captain Hutton, that whole flocks of these crossed geese are kept in various parts of the country ; and as they are kept for profit, where neither pure parent species exists, they must certainly be highly fertile... . So again there is reason to believe that our European and the humped Indian cattle are quite fertile together ; and from facts communicated to me by Mr Blyth, I think they must be considered as distinct species.” Darwin does not seem to have been very satisfied with the evidence he had collected, for he said: “ Finally, looking to all the ascertained facts on the intercrossing of plants and animals, it may be concluded that some degree of sterility, 1 After years of observation of these Indian geese, Finn is convinced they are now, at all events, pure Chinese ; it is possible that they really were hybrids in Blyth’s time, but that fresh im- portations of geese from China, such as still occur, may have ultimately swamped the blood of the common goose. The fertility of the hybrid geese was, however, known to such early writers as Pallas and Linnzus. Darwin himself, at a later date, bred five young from a pair of such hybrids (WVa¢ure, Jan. 1, 1880, p. 207). 115 The Making of Species both in first crosses and in hybrids, is an ex- tremely general result; but that it cannot, under our present state of knowledge, be considered as absolutely universal.” Similarly Wallace writes : ‘‘ Nevertheless, the fact remains that most species which have hitherto been crossed produce sterile hybrids, as in the well-known case of the mule; while almost all domestic varieties, when crossed, produce offspring which are perfectly fertile among themselves.” Darwin resorted to much ingenious argument in his attempt to explain what he believed to be the almost universal sterility of hybrids, as opposed to mongrels or crosses between varieties. He pointed out that changed conditions tend to produce sterility, as is evidenced by the fact that many creatures refuse to breed in confinement, and believed that the crossing of distinct wild species produced a similar effect on the sexual organs. He expressed his belief that the early death of the embryos is a very frequent cause of sterility in first crosses. Wallace thus summarises Darwin's conclusions as to the cause of the sterility of hybrids: “The sterility or infertility of species with each other, whether manifested in the difficulty of obtaining first crosses between them or in the sterility of the hybrids thus obtained, is not a constant or necessary result of species difference, but is in- 116 A Biological Bogey cidental on unknown peculiarities of the repro- ductive system. These peculiarities constantly tend to arise under changed conditions owing to the extreme susceptibility of that system, and they are usually correlated with variations of form or of colour. Hence, as fixed differences of form and colour, slowly gained by natural selection in adaptation to changed conditions, are what essentially characterise distinct species, some amount of infertility between species is the usual result.” But Wallace has not been content to let the matter remain where Darwin left it. He has boldly tried to make an ally of this bogey of the infertility of hybrids. On page 179 of Darwinism he argues, most ingeniously, that the sterility of hybrids has been actually produced by natural selection to prevent the evils of the intercrossing of allied species. We will not reproduce his argument for the simple reason that it is now well-known, or should be well-known, that hybrids between allied species are by no means always sterile. The doctrine of the infertility of hybrids seems to have been founded on the fact that the hybrids best known to breeders, namely the cross between the ass and the horse, and those between the canary and other finches, are sterile. 117 The Making of Species FERTILE CROSSES BETWEEN SPECIES OF PLANTS In the case of plants the number of fertile hybrids between species is so large that we cannot attempt to enumerate them. De Vries cites several instances in Lecture IX of his Species and Varieties: Their Origin by Mutation. One of these—the hybrid between the purple and the yellow species of Lucerne which is known to botanists as Medicago media is, writes De Vries, “cultivated in some parts of Germany on a large scale, as it is more productive than the ordinary lucerne.” Other examples of per- fectly fertile plant hybrids cited by De Vries are the crosses between Anemone magellanica and A. sylvestris, between Salix alba and Sahx pentandra, between Rhododendron hirsutum and Rk. ferrugineum. He gives an instance of a hybrid—Zgzlops spelteformts, which, though fertile, is not so fertile as a normal species would be. It is worthy of note that Burbank of California has obtained a hybrid between the blackberry and the rasp- berry, which is not only fertile, but quite popular as producing a novel fruit. STERILE Ptanr Hysrips De Vries does not cite nearly so many examples of sterile hybrids, presumably because they are not so easy to find. He mentions the sterile 118 Fertile Mammalian Hybrids ‘“‘Gordon’s currant,” which is considered to be a hybrid between the Californian and the Missouri species. He also gives Cytzsus adamz as an absolutely sterile hybrid, this being a cross between two species of Labernum—the common and the purple. In the case of animals the known hybrids are so much less numerous that we are able to furnish a list which may be taken as fairly exhaustive. FertitE Mammatian Hysrips Taking the mammals first, we find that, in addition to those cited by Darwin, there are several recorded cases of crosses between well- defined species which are fertile. There is the hybrid between the brown bear and the polar bear, which is perfectly fertile. In the London Zoological Gardens there is a speci- men of this hybrid, also one of this individual’s offspring by a pure polar bear. The stoat has been crossed with the domestic ferret, a descendant of the polecat, a very distinct species; the resulting hybrids have nevertheless proved fertile. The bull American bison produces with the domestic cow hybrids known as “cataloes,” which are fertile. The reverse cross of the domestic bull with the bison cow does not, how- ever, succeed at all, which reminds us of what happens in the case of finch-hybrids. 119g The Making of Species Bird fanciers when crossing the canary with wild species of finch, almost invariably use a hen canary as the female parent, because domesticated female animals breed more readily than do captive wild ones. The domestic yak breeds frequently in the Himalayas with the perfectly distinct zebu or humped cow of India, and the hybrids are fertile. Yet the zebu and the Indian buffalo, living con- stantly side by side in the plains of India, never interbreed at all. Among wild ruminants of this hollow-horned family, the Himalayan Argali (Ovzs ammon) ram, a giant sheep of the size of a donkey, has been known to appropriate a herd of ewes of the Urial (O. vignez), a very distinct species of the size of a domestic sheep. Many hybrids were born, and these, in turn, bred with the pure urials of the herd. In our parks the little Sika deer of Japan (Cervus stka), a species about the size of the fallow-deer, with an even more marked seasonal change of colouration and antlers having only three tines, breeds with the red deer, and the hybrids are fertile. In certain parts of Asia Minor the natives cross the female one-humped camel with the male of the bactrian or two-humped species. The hybrids (which are one-humped) will breed with the pure species; but, although the hybrids are 320 Fertile Bird Hybrids strong and useful, the three-quarter bred beasts are apparently of little value. FerTILE Birp Hysrips Coming to birds, we are confronted by a longer list of fertile hybrids. This is the natural outcome of the fact that a greater number of bird species have been kept in captivity. The oldest known fertile hybrid is that between the common and Chinese geese above cited, but many others have since been re- corded. Even among birds so seldom bred, comparatively, as the parrot family, a fertile hybrid has been produced, that between the Aus- tralian Rosella Parrakeet (Platycercus eximius) and Pennants Parrakeet (P. elegans). The hybrid was first described as a distinct species, the Red-mantled Parrakeet (P. evythropeplus). These two parrakeets, though nearly allied, are very distinct ; Pennant’s being coloured red, blue, and black, with a distinct young plumage of uniform dull green ; the rosella in addition to the above colours displays much yellow and some white and green. It is, moreover, considerably smaller and has no distinct youthful dress. The Amherst Pheasant (CArysolophus amher- stig) and the Gold Pheasant (C. Jzctus) have long been known as producing hybrids which are fertile either zzter se or with the parents. Here the species are still more distinct ; not only y2t The Making of Species are the leading colours of the Amherst white and green, instead of red and gold, but it is a bigger bird with a larger tail and smaller crest, and a bare patch round the eyes. The Pintail Duck (Dafila acuta) and the Mallard or Wild Duck and its domestic descen- dants (Aas boscas), when bred together, produce hybrids which have been proved fertile between themselves and with the pure pintail. Any sportsman or frequenter of our parks can see for himself the distinctness of the species concerned. The Pied Wagtail (Motaczlla lugubris) and the Grey Wagtail (JZ. melanope) have produced hybrids in aviaries, which have proved fertile. The two species are distinct in every way, as all British ornithologists know. The Cut-throat Finch (Amadina fasciata) and Red-headed Finch (A. erythrocephala) of Africa have hybridised in aviaries, and the produce has proved fertile. The red-headed finch, among other differences, is far larger than the cut-throat, and the males have the head all red, not merely a throat-band of that colour. The Japanese Greenfinch (Lzgurinus sinicus) which is not green, but brown and grey, with bolder yellow wing- and tail-markings than our larger European greenfinch, has produced fertile hybrids with this latter bird. The Red Dove of India (Oenopopztia trangue- barica) has produced hybrids with the tame 122 MALE AMHERST PHEASANT The chief colours of this species (Chrysolophus antherstia), are white and metallic green, so that it is very different in appearance from its near ally the gold pheasant. Fertile Bird Hybrids Collared Dove (7. risorius) and these have bred again when paired with the red species. O. tranquebarica, although presenting a general similarity to the collared dove, is truly distinct, being much smaller, with a shorter tail, and dis- playing a marked sex-difference (the male only being red, and the female drab). Its voice is also utterly unlike the well-known penetrating and musical coo of the Collared Dove. There is a large class of fertile wild hybrids produced between forms differing only in colour, such as those between the Hooded Crow (Corvus cornix) and Carrion Crow (Corvus corone), the various species of JZolpastes bulbuls, and the Indian Roller (Covaczas indica) and Burmese Roller (C. affinzs). Indeed, it may be said that wherever two such colour-species meet they hybridize and become more or less fused. In this connection sportsmen, as mentioned by Darwin, performed unconsciously a most in- teresting experiment when, more than a century ago, they introduced largely into their coverts the Chinese Ring-necked Pheasant (Phaszanus torguatus) and the Japanese P. versicolor. Sofreely has the former bred with the common species already present there (Phastanus colchicus) that nowadays nearly all our English pheasants show traces of the cross in the shape of white feathers on the neck, or the green tinge of the plumage of the lower back. The influence of the Japanese 123 The Making of Species Green Pheasant (P. versecolor) has been very slight. It is, of course, open to anyone to assert that such crosses are not true hybrids, as the species are not fully distinct, but mere colour-mutations. The fact of the intermingling, however, is a fatal blow to the theory of recognition marks, since it demonstrates that merely distinctive colouring is not a preventative of cross-breeding. To this matter we shall return later. FertTite Hysprips AMONG AMPHIBIA Our Crested Newt (Molge cristata) and the Continental Marbled Newt (JZ marmorata) interbreed in France, in the wild state, and the resulting hybrid was at first described as a distinct species, under the name of Molge déaszz. These two newts differ greatly in appearance. In the Marbled Newt the colouration is brilliant green and black above, and shows no orange below, thus differing much from that of the Crested Newt, which is black above and mottled with orange beneath, while the crest of the breeding-male of this species lacks the notches which are so conspicuous in that of the Crested Newt. INSECTS Among insects, M. de Quatrefages states that the hybrid progeny of the silk-moths Bombyx 124 By permission of the Avwultural Society HARLEQUIN QUAIL RAIN QUAIL (Coturnix delegorguer) (Coturnix coromandelica) The markings on the throats of these quails are of the type usually put down as ‘recognition marks,” but as the Harlequin Quail is African and the Rain Quail Indian, the two species cannot possibly interbreed. ‘The pattern, then, can have no “‘ recognition” significance. Limits of Hybridisation cynthia and B. arrindia are fertile for eight generations when bred znder se. LimITs To THE PossIBILITIES OF HyBRIDISATION Hybrids can apparently only be produced between species of the same natural family. The stories of cat-rabbits, deer-ponies, fowl- ducks, and similar distant crosses invariably break down on close examination. A belief in such remote crosses characterized the ancient “bestiaries,” and still lingers, as witness the falsely-reputed crosses alluded to above. This belief has no doubt arisen from the fact that the domestic breeds of dogs, fowls, etc., are popularly confounded with truly distinct species. Mongrels are well known to be readily produced, and hence the notion arises that hybrids between the most widely - separated species are possible. In practice, the most remote cross of which authenticated specimens exist is that between the red grouse and the domestic fowl (bantam cock). It is true that the grouse are commonly ranked by ornithologists as a family distinct (Tetraonidae) from that of the pheasants and partridges (Pkhaszanidae), to which the fowl belongs ; but the relationship is admittedly very close, and we doubt if general zoologists would countenance the maintenance of the families as distinct. Ornithologists are notoriously apt to 125 The Making of Species over-rate small differences when drawing up a classification. It would be therefore safe to say, in the present state of our knowledge, that species belonging to different natural families cannot hybridize. In some cases multiple hybrids have been produced. Thus, at the London Zoological Gardens, many years ago, a hybrid between the Gayal of India (Bos frontahs) and the Indian humped cow mentioned above was put to an American bison, and produced a double hybrid calf. M. G. Rogeron of Angers bred many hybrids from a male pochard and a duck bred from a Mallard and a Gadwall. More recently, Mr J. L. Bonhote has suc- ceeded in combining the blood of five wild species of ducks in one individual. Mr J. T. Newman has also bred turtle-doves containing the blood of three distinct species. A cross, which usually results in sterile offspring, may in very rare cases produce a fertile individual ; thus, Mr A. Suchetet once succeeded in obtaining a three-quarter-bred bird from the not uncommon hybrid of the tame pigeon and tame collared dove (Zurtur risorius), which is usually barren, by pairing it with a dove; but the bird thus produced, when again paired with a dove, was itself sterile. Some of the cases here given seem to encourage 126 Characters of Hybrids Darwin’s view that domestication tends to elimi- nate sterility; but it is doubtful if this can be upheld. The hybrid between the Muscovy duck (Cazrena moschata) and common duck is usually, at all events, sterile, like that between the pigeon and dove; yet all these birds have been long domesticated. The hybrid between the fowl and the guinea-fowl is likewise barren, nor has the long domestication of the horse and ass lessened the sterility of the mule. Some facts may be noted respecting the characters of hybrids. In the first place, it is important to notice that the characters of the hybrid vary according to the sexes of the species concerned ; thus, the “hinny,’ which is bred from a horse and a she-ass, is a different animal from the true ‘“‘mule,” which is bred from the jackass and mare, and is inferior to it. Similarly, Mr G. E. Weston, a great authority on British cage-birds and their hybrids, informs us that when hybrids are bred from a male canary and a hen goldfinch or siskin—contrary to the almost universal practice of using the hen canary for crossing—the progeny are inferior in size and colour to the hybrids obtained in the ordinary way. Hybrids, in animals at all events, differ from crosses between mutations or colour-variations in not exhibiting the phenomenon of alternative inheritance ; they do not follow one parent or 127 The Making of Species the other exclusively, but always exhibit some blending of the characters of both, which is, after all, what might have been expected, since well-defined species usually differ in more than one character. Thus, the cross between the Amherst and gold pheasants chiefly resembles the latter, but has the ruff white as in the Amherst, while the crest, though in form it resembles that of the gold species, is not yellow as in that species, nor red as in the Amherst, but of an intermediate tint, brilliant orange. The mule between the horse and ass, as all know, combines the shapes of the two parents, though in colour it follows the horse rather than the ass. When two remote species, one or each of which possesses some distinctive structural peculiarity, are crossed, the hybrid does not inherit such points. The guinea-fowl has a helmet, and a pair of wattles on the upper jaw ; the common fowl a comb, and a pair of wattles on the lower jaw; but in the hybrid no comb, helmet, or wattles are present. The Muscovy drake has a bare red eye-patch, and the male of the common duck curled middle- tail feathers; in the hybrid neither of these peculiarities is reproduced. In a cross between nearly-related forms, the peculiarity of one species may be reproduced in 128 Characters of Hybrids a modified form in the hybrid; for instance, in that between the blackcock (Ze¢rao t¢etrix) and the capercailzie (7. urogallus), the forked tail of the former reappears to a small extent in the hybrid. Very interesting are those cases in which the hybrid resembles neither parent, but tends to be like an altogether distinct species, or to have a character of its own. Thus the hybrids between the pied European and chestnut African shel- drakes (Zadorna cornuta and Casarca cana), now in the British Museum, bear a distinct resem- blance to the grey Australian sheldrake (C. ¢ador- nozdes). In pheasants, also, the crosses between the common and gold, common and Amherst, gold and Japanese, and gold and Reeves’ pheasants, widely different as all these birds are in colouration, are remarkably alike, being all chestnut-coloured birds with buff median tail- feathers. These may be seen in the British Museum. This phenomenon, together with the above-noted disappearance of specialised features in hybrids, is possibly comparable to the “reversion” observed when widely - distinct domestic breeds are crossed, and so may give us an idea of the appearance of the ancestors of the groups of species concerned. In the few cases wherein several generations of hybrids have been bred zuter se, there seems to have been no reversion to the original pure I 129 The Making of Species types, such as happens when colour-forms are crossed, M. Suchetet bred hybrid gold = Amherst pheasants for four generations, and they retained the hybrid character. The young bred by Darwin from a pair of common = Chinese geese hybrids “resembled,” he says, “in every detail their hybrid parents.” When hybrids have been—as has far more usually been the case — bred back to one of the pure stocks, the hybrid characters have shown, as might be expected, a tendency quickly to disappear. The three-quarter-bred polar bear now in the London Zoological Gardens is a pure polar save for a brown tinge on the back. A three-quarter Amherst = gold pheasant in the British Museum is a pure Amherst save for the larger crest, and a patch of red on the abdomen. When three-quarter-bred pintail = common duck hybrids were bred back to the pintail, the off- spring “lost all resemblance to the common duck.” In the case of the Argali-urial herd of wild sheep above-mentioned, after the usurping Argali ram had been killed by wolves, the hybrids bred with the urials, with the result that the herd renewed the appearance of pure urial. Thus, except in the very improbable case of a family of hybrids going off and starting a colony by themselves, the effect of hybridism on the evolution of species seems likely to have been 130 Wild Hybrids nil, It is, however, curious that three-quarter- bred animals have rarely, if ever, been recorded in a state of nature, though a good many wild- bred hybrids are on record. This points to some unfitness for the struggle for existence even in a fertile hybrid. It is necessary to emphasise the fact that wild hybrids are always exceedingly rare as individuals, in spite of what has been said as to the number of recorded crosses. More hybrid unions have been noted among the duck family than anywhere else in the animal kingdom. Nevertheless Finn never once saw a hybrid duck for sale in the Calcutta market, although for seven years he was constantly on the look-out for such forms; nor does Hume record any such specimen in his Game Birds and Wild Fowl of India. The hybrid which occurs most commonly as an individual is that between the blackcock and capercailzie, which is recorded yearly on the Continent; but it appears to be sterile, and so has no influence on the species. Wild hybrids between mammals are far rarer even than bird hybrids, the only ones which seem to be on record being those between the Argali and Urial above alluded to ; those between the brown and blue hares and the common and Arctic foxes. A consideration of the phenomena of hybridism 131 The Making of Species thus leads us to the conclusion that, although many hybrids are fertile, the crossing of distinct species has exercised little or no effect on the origin of species. Even where allied species, like the pintail and the mallard ducks, whose hybrid offspring is known to be fertile, inhabit the same breeding area and occasionally interbreed in nature, such crossing does not, for some reason or other, appear to affect the purity of the species. Very different, of course, is the effect of cross- ing a mutation within a species with the parent form ; the offspring are, as we shall see, likely to resemble one or other of the parents; so that, if the mutation occur frequently enough and be favourable to the species, the new form may in course of time replace the old one. 132 CHAPTER V INHERITANCE Phenomena which a complete theory of inheritance must explain —In the present state of our knowledge it is not possible to formulate a complete theory of inheritance—Different kinds of inheritance—Mendel’s experiments and ‘theory—The value and importance of Mendelism has been exaggerated—Domi- nance sometimes imperfect—Behaviour of the nucleus of the sexual cell—Chromosomes—Experiments of Delage and Loeb —Those of Cuénot on mice and Castle on guinea pigs—Sug- gested modification of the generally-accepted Mendelian formulae—Unit characters—Biological isomerism—Biologi- cal molecules—Interpretation of the phenomena of variation and heredity on the conception of biological molecules— Correlation — Summary of the conception of biological molecules. E have seen that variations may be, firstly, either acquired or con- genital, and, secondly, fluctuating or discontinuous. We have further seen that acquired variations—at all events in the higher animals—do not appear to be in- herited, and therefore have not played a very important part in the evolution of the animal world. Discontinuous congenital variations or mutations are the usual starting points of new species. It is not unlikely that fluctuating con- genital variations, although they do not appear to give rise directly to new species, may play a 133 The Making of Species considerable part in the making of new species, inasmuch as they may, so to speak, pave the way for mutations. We are now in a position to consider the exceedingly difficult question of inheritance. We know that offspring tend to resemble their parents, but that they are always a little different both from either parent and from one another. How are we to account for these phenomena? What are the laws of inheritance, whereby a child tends to inherit the peculiarities of its parents, and what are the causes of variation which make children differ zz¢er se and from their parents? Scores of theories of inheritance have been advanced. It is scarcely exaggerating to assert that almost every biologist who has paid much attention to the subject has a theory of inherit- ‘ ance which differs more or less greatly from the theory held by any other biologist. As regards the phenomena of heredity we may say Zot homznes tot sententia. For this state of affairs there is a good and sufficient reason. We are not yet in possession of a sufficient number of facts to be in a position to formulate a satisfactory theory of inheritance. A complete theory of heredity must explain, among other things, the following phenomena :— 1. Why creatures show a general resemblance to their parents. 134 Phenomena of Inheritance 2. Why they differ from their parents. 3. Why the members of a family display indi- vidual differences. 4. Why the members of a family tend to resemble one another more closely than they resemble individuals belonging to other families. 5. Why “sports ” sometimes occur. 6, Why some species are more variable than others, 7. Why certain variations tend to occur very frequently. 8. Why variations in some directions seem never to occur. 9. Why a female may produce offspring when paired with one male of her species and not when paired with another male of the species. 10. Why organisms that arise by partheno- genesis appear to be as variable as those which are sexually produced. 11. Why certain animals possess the power of regenerating lost parts, while others have not this power. | 12. Why most plants and some of the lower animals can be produced asexually from cuttings. 13. Why mutilations are not inherited. 14. Why acquired characters are rarely, if ever, inherited. 15. Why the ovum puts forth the polar bodies. 16. Why the mother-cell of the spermatozoa produces four spermatozoa. 135 The Making of Species 17. Why differences in the nature of the food administered to the larve of ants determines whether these shall develop into sexual or neuter forms. 18. Why the application of heat, cold, etc., to certain larve affects the nature of the imago, or perfect insect, to which they will give rise. 19. Why the females in some species lay eggs which can produce young without being fertilised. 20. Why some species exhibit the phenomena of sexual dimorphism, while others do not. 21. In addition to all the above, a satisfactory theory of inheritance must account for all the varied phenomena which are associated with the name of Mendel. It must explain the various facts with which we have dealt in the chapter on hybridism, why some species produce sterile hybrids when intercrossed, while others give rise to fertile hybrids, and yet others form no offspring when crossed ; why the hinny differs in appear- ance from the mule, etc. 22. It must explain all the facts which consti- tute what is known as atavism. 23. It must account for the phenomenon of prepotency. 24. It must explain the why and the wherefore of correlation. 25. It must tell us the meaning of the results of the experiments of Driesch, Roux, and others. 136 Existing Theories Unsatisfactory 26. It must render intelligible the effects of castration on animals. Now, no existing theory of heredity can give anything approaching a satisfactory explanation of all these phenomena. It is for this reason that we refrain from criti- cally examining, or even naming, any of them. We are convinced that in the present state of our knowledge it is not possible to formulate anything more than a provisional hypothesis. It must not be thought that we consider the various theories that have been enunciated to be of no value. Erroneous hypotheses are often of the greatest utility to science, for they set men thinking and suggest experiments by means of which important additions to knowledge are made. We now propose to set forth certain facts of inheritance, and from these to make a few deductions—deductions which seem to be forced upon us. We would ask our readers to distinguish care- fully between the facts we set forth, and the conclusions we draw therefrom. The former, being facts, must be accepted. The interpretations we suggest should be rigidly examined, we would say regarded with suspicion, and all possible objections raised. It is only by so doing that any advance in know- ledge can be made. 137 The Making of Species By inheritance we mean that which an organ- ism receives from its parents and other ancestors —all the characteristics, whether apparent or dormant, it inherits or receives from its parents. Professor Thomson’s definition—“