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diff --git a/44063-0.txt b/44063-0.txt index 412a998..a951a4b 100644 --- a/44063-0.txt +++ b/44063-0.txt @@ -1,37 +1,4 @@ -Project Gutenberg's The Making of Species, by Douglas Dewar and Frank Finn - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: The Making of Species - -Author: Douglas Dewar - Frank Finn - -Release Date: October 29, 2013 [EBook #44063] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE MAKING OF SPECIES *** - - - - -Produced by Stephen Hutcheson, Marcia Brooks and the Online -Distributed Proofreading Canada Team at -http://www.pgdpcanada.net (This file was produced from -images generously made available by The Internet -Archive/American Libraries.) - - - - - +*** START OF THE PROJECT GUTENBERG EBOOK 44063 *** [Illustration: HEX CURASSOW FEEDING YOUNG BIRD, WITH PLUMAGE OF THE GLOBOSE CURASSOW] @@ -12489,362 +12456,4 @@ colours, and 20 in black and white. 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You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: The Making of Species - -Author: Douglas Dewar - Frank Finn - -Release Date: October 29, 2013 [EBook #44063] - -Language: English - -Character set encoding: ISO-8859-1 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE MAKING OF SPECIES *** - - - - -Produced by Stephen Hutcheson, Marcia Brooks and the Online -Distributed Proofreading Canada Team at -http://www.pgdpcanada.net (This file was produced from -images generously made available by The Internet -Archive/American Libraries.) - - - - - - -[Illustration: HEX CURASSOW FEEDING YOUNG BIRD, WITH PLUMAGE OF THE -GLOBOSE CURASSOW] - - - - - THE MAKING - OF SPECIES - - - BY DOUGLAS DEWAR, B.A. (Cantab), I.C.S., F.Z.S. - AND FRANK FINN, B.A. (Oxon), F.Z.S., M.B.O.U. - WITH FIFTEEN ILLUSTRATIONS - - - LONDON: JOHN LANE THE BODLEY HEAD - NEW YORK: JOHN LANE COMPANY MCMIX - - _Turnbull & Spears, Printers, Edinburgh_ - - - - - PREFACE - - -Post-Darwinian books on evolution fall naturally into four classes. I. -Those which preach Wallaceism, as, for example, Wallace's _Darwinism_, -Poulton's _Essays on Evolution_, and the voluminous works of Weismann. -II. Those advocating Lamarckism. Cope's _Factors of Evolution_ and the -writings of Haeckel belong to this class. III. The writings of De Vries, -forming a group by themselves. They advocate the theory that species -spring suddenly into being; that new species arise by mutations from -pre-existing species. IV. The large number of books of a more judicial -nature, books written by men who decline to subscribe to any of the above -three creeds. Excellent examples of such works are Kellog's _Darwinism -To-Day_, Lock's _Recent Progress in the Study of Variation, Heredity, and -Evolution_, and T. H. Morgan's _Evolution and Adaptation_. - -All four classes are characterised by defects. - -Books of the two first classes exhibit the faults of ardent partisanship. -They formulate creeds, and, as Huxley truly remarked, "Science commits -suicide when it adopts a creed." The books which come under the third -category have the defects of extreme youth. De Vries has discovered a new -principle, and it is but natural that he should exaggerate its -importance, and see in it more than it contains. But, as time wears on, -these faults will disappear, and the theory of mutations will assume its -true form and fall into its proper place, which is somewhere between the -dustbin, to which Wallaceians would relegate it, and the exalted pinnacle -on to which De Vries would elevate it. - -In the present state of our knowledge, books of Class IV. are the most -useful to the student, since they are unbiassed, and contain a judicial -summing-up of the evidence for and against the various evolutionary -theories which now occupy the field. Their chief defect is that they are -almost entirely destructive. They shatter the faith of the reader, but -offer nothing in place of that which they have destroyed. T. H. Morgan's -_Evolution and Adaptation_, however, contains much constructive matter, -and so is the most valuable work of this class in existence. - -Zoological science stands in urgent need of constructive books on -evolution--books with leanings towards neither Wallaceism, nor -Lamarckism, nor De Vriesism; books which shall set forth facts of all -kinds, concealing none, not even those which do not admit of explanation -in the present state of our knowledge.--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 speculation. We have followed up the exposure of the weak points of -the theories, which at present occupy the field, with certain -suggestions, which, we believe, throw new light on many biological -problems. - -Our aim in writing this book has been twofold. In the first place we have -attempted to place before the general public in simple language a true -statement of the present position of biological science. In the second -place, we have endeavoured to furnish the scientific men of the day with -food for reflection. - -Even as the British nation seems to be slowly but surely losing, through -its conservatism, the commercial supremacy it had the good fortune to -gain last century, so is it losing, through the unwillingness of many of -our scientific men to keep abreast of the times, that scientific -supremacy which we gained in the middle of last century by the labours of -Charles Darwin and Alfred Russell Wallace. To-day it is not among -Englishmen, but among Americans and Continentals, that we have to look -for advanced scientific ideas. - -Even as the Ultra-Cobdenites believe that Free Trade is a panacea for all -economic ills, so do most English men of science believe that natural -selection offers the key to every zoological problem. Both are living in -a 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 dissecting-room, that nature can best be -studied. Far be it from us to deprecate the study of morphology. We wish -merely to insist upon the fact, that the leaders of biological science -must of necessity be those naturalists who go to the tropics and other -parts of the earth where nature can be studied under the most favourable -conditions, and those who conduct scientific breeding experiments. -Natural 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 knowledge -second-hand to be the pioneers of biological science. - -We fear that this book will come as a rude shock to many scientific men. -By way of consolation we may remind such that they will find themselves -in much the same position as that occupied by theologians immediately -after the appearance of the _Origin of Species_. - -At that time theological thought was cramped by dogma. But the clergy -have since reconsidered their position, they have modified their views, -and thus kept abreast of the times. Meanwhile scientific men have lagged -behind. The blight of dogma has seized hold of them. They have adopted a -creed to which all must subscribe or be condemned as heretics. Huxley -said that the adoption of a creed was tantamount to suicide. We are -endeavouring to save biology in England from committing suicide, to save -it from the hands of those into which it has fallen. - -We would emphasise that it is not Darwinism we are attacking, but that -which is erroneously called Neo-Darwinism. Neo-Darwinism is a -pathological growth on Darwinism, which, we fear, can be removed only by -a surgical operation. - -Darwin, himself, protested in vain against the length to which some of -his followers were pushing his theory. On p. 657 of the new edition of -the _Origin of Species_ he wrote: "As my conclusions have lately been -much misrepresented, and as it has been stated that I attribute the -modification of species exclusively to natural selection, I may be -permitted to remark that in the first edition of this work, and -subsequently, I placed in a most conspicuous position--namely, at the -close of the Introduction--the following words: 'I am convinced that -natural selection has been the main but not the exclusive means of -modification.' This has been of no avail. Great is the power of steady -misrepresentation; but the history of science shows that this power does -not long endure." - -Notwithstanding this protest the Wallaceians continue on their course, -and give to the world a spurious Darwinism. It is our belief that were -Darwin alive to-day his sympathies would be with us, and not with those -who call themselves his followers. It was one of Darwin's strong points -that he never avoided facts. If new facts came to light which were -incompatible with a theory of his, he promptly modified his theory. Since -his death a number of new facts have come to light which, in our opinion, -plainly indicate that the theory of natural selection as enunciated by -Darwin needs considerable modification. - -We have in this book set forth certain of these facts and indicated the -directions in which the Darwinian theory seems to require modification. - -This volume originated as the result of several conversations we, the -joint authors, had last summer. We discovered that we had a great many -ideas in common on the subject of evolution. This seemed strange, seeing -that our education had not been on the same lines. One of us took a -degree in natural science at Cambridge, and subsequently entered His -Majesty's Indian Civil Service, but continued his zoological studies in -India as a hobby. The other, a naturalist from childhood, nevertheless -took a classical degree at Oxford, then received a technical zoological -training, adopted zoology as a profession, and held for some years a -position in the Natural History Museum at Calcutta. - -Our conversations revealed that we were both of opinion that biology is -in an unhealthy condition, especially in England, and that the science -sorely needs some fresh impetus. Neither of us had the time to attempt, -single-handed, to give the required impetus, but as one of us happened to -be home on eighteen months' leave, we thought we might undertake the task -in collaboration. - -We felt that we might collaborate the more successfully because the large -number of facts collected by the one of us form the necessary complement -to the philosophical studies of the other. - -We have endeavoured, so far as possible, to avoid technical terms, and -have made a special point of quoting, wherever practicable, familiar -animals as examples, in order that the work may make its appeal not only -to the zoologist but to the general reader. - -It may, perhaps, be urged against us that we have quoted too freely from -popular writings, including those of which we are the authors. Our reply -to this is that the study of bionomics, the science of living animals, -occupies so small a place in English scientific literature that we have -been compelled to have recourse to popular works for many of our facts; -and we would, moreover, point out that a popular work is not necessarily -inaccurate in its information. - -In conclusion, we would warn the reader against the danger of confounding -Inference with Fact. The failure to distinguish between the two has -vitiated much of the work of the Wallaceian school of biologists. - -Facts are always to be accepted. Inferences should be scrutinised with -the utmost care. - -In making our deductions, we have endeavoured to act without bias. We -shall, therefore, welcome any new facts, be they consistent with, or -opposed to, our inferences. - - D. D. - F. F. - - - - - CONTENTS - - - PAGE - - -CHAPTER I 1 - - Rise of the Theory of Natural Selection and its Subsequent Development - - Pre-Darwinian 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 30 - -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--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. - - -CHAPTER III 52 - - 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 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 "discontinuous - 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 111 - - 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. - - -CHAPTER V 133 - - 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--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 modification of the - generally-accepted Mendelian formulæ--Unit characters--Biological - isomerism--Biological molecules--Interpretation of the phenomena of - variation and heredity on the conception of biological - molecules--Correlation--Summary of the conception of biological - molecules. - - -CHAPTER VI 170 - - The Colouration of Organisms - - 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 - Müllerian 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--Illustrative 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--Objections 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 recognition 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 297 - - Sexual Dimorphism - - 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--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. - - -CHAPTER VIII 345 - - The Factors of Evolution - - 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 in a position to decide--_Modus operandi_ - of Natural Selection--Correlation an important factor--Examples of - correlation--Correlation is a subject that requires close - study--Isolation a factor in evolution--Discriminate - isolation--Indiscriminate 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 compared 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. - - -Footnotes 389 - - -Index 389 - - - - - LIST OF ILLUSTRATIONS - - - FACING PAGE - - -Heck'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._ - - -A Turbit belonging to Mr H. P. Scatliff 92 - -_From "The Modern Turbit," published by "The Feathered World," London._ - - -Yellow-Rumped and Chestnut-Breasted Finches, with Specimens in -Transitional State 98 - - On the left, the yellow-rumped finch; on the right, the - chestnut-breasted; birds in state of change in the middle. - _By permission of the Avicultural Society._ - - -Male Amherst Pheasant 122 - - The chief colours of this species (_Chrysolophus amherstiæ_) are - white and metallic green, so that it is very different in - appearance from its near ally the gold pheasant. - - -Harlequin Quail (_Coturnix delegorguei_) 124 - - _By permission of the Avicultural Society._ - - -Rain Quail (_Coturnix coromandelica_) 124 - - The markings on the throats of these quails are of the type usually - put down as "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._ - - -Bouru Friar-Bird 222 - - Like most of the group to which it belongs, this honey-eater - (_Tropidorhynchus bouruensis_) is a soberly coloured bird, but is - noisy, active, and aggressive. - _By permission of Messrs Hutchinson & Co._ - - -Bouru Oriole 222 - - This "mimicking" oriole (_Oriolus bouruensis_) is of the same tone - of colour as its supposed model the Friar-bird of the same island. - _By permission of Messrs Hutchinson & Co._ - - -King-Crow or Drongo 232 - - This very conspicuous black bird (_Dicrurus ater_), ranging from - Africa to China, is a striking feature of the landscape wherever it - occurs. - _By permission of Messrs Hutchinson & Co._ - - -Drongo-Cuckoo 232 - - The fork of the tail in this bird is unique among cuckoos, but is - nevertheless much less developed than in the supposed model, and - may be an adaptation for evolutions in flight, as such tails - usually appear to be. - _By permission of Messrs Hutchinson & Co._ - - -Shikra Hawk 236 - - The upper surface of the tail, not shown in this drawing, exactly - corresponds with that of the cuckoo "mimic." - _By permission of Messrs Hutchinson & Co._ - - -Hawk-Cuckoo 236 - - This species (_Hierococcyx varius_) is commonly known in India as - the "Brain-fever bird." - _By permission of Messrs Hutchinson & Co._ - - -Brazilian Troupial 284 - - This species (_Icterus vulgaris_) is that most frequently seen in - captivity; the pattern of colour is found in several other allied - forms. - _By permission of Messrs Hutchinson & Co._ - - -Indian Black-Headed Oriole 284 - - Several other orioles besides this (_O. melanocephalus_) have the - black head. - _By permission of Messrs Hutchinson & Co._ - - -Queen Whydah 298 - - This species (_Tetraenura regia_) is a typical example of seasonal - sexual dimorphism, the male being long-tailed and conspicuously - coloured only during the breeding season, and at other times - resembling the sparrow-like female. - _By permission of the Foreign Bird Club._ - - -Courtship of Skylark 314 - - Illustrating display by a species with no decorative colouring or - sex difference. - - - - - THE MAKING OF SPECIES - - - - - CHAPTER I - RISE OF THE THEORY OF NATURAL SELECTION AND ITS SUBSEQUENT DEVELOPMENT - - - Pre-Darwinian 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. - -Darwinism and evolution are not interchangeable terms. On this fact it is -impossible to lay too much emphasis. Charles Darwin was not the -originator of the theory of evolution, nor even the first to advocate it -in modern times. The idea that all existing things have been produced by -natural causes from some primordial material is as old as Aristotle. It -was lost sight of in the mental stagnation of the Middle Ages. In that -dark period zoological science was completely submerged. It was not until -men shook off the mental lethargy that had held them for many generations -that serious attention was paid to biology. From the moment when men -began to apply scientific methods to that branch of knowledge the idea of -evolution found supporters. - -Buffon suggested that species are not fixed, but may be gradually changed -by natural causes into different species. - -Goethe was a thorough-going evolutionist; he asserted that all animals -were probably descended from a common original type. - -Lamarck was the first evolutionist who sought to show the means whereby -evolution has been effected. He tried to prove that the efforts of -animals are the causes of variation; that these efforts originate changes -in form during the life of the individual which are transmitted to its -offspring. - -St Hilaire was another evolutionist who endeavoured to explain how -evolution had occurred. He believed that the transformations of animals -are effected by changes in their environment. These hypotheses were -considered, and rightly considered, insufficient to explain anything like -general evolution, so that the idea failed for a time to make headway. - - - Strength of 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 which afforded a plausible explanation of what they believed -to have occurred. - -Hence the rapturous welcome accorded to the theory of natural selection -by the more progressive biologists. - -Another point in 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 -something to take the part played among domesticated animals by the human -breeder. This he was able to do. As the numbers of species remain -stationary, it is evident that only a small portion of the animals that -are born can reach maturity. A child can see that the individuals most -likely to survive are those best adapted to the circumstances of their -life. Even as the breeder weeds out of his stock the creatures not suited -to his purpose, so in nature do the unfit perish in the everlasting -struggle for existence. - -In nature there is a selection corresponding to that of the breeder. - -It is useless to deny the existence of this selection in nature, this -natural selection. The only disputable point is whether such selection -can do all that Darwin demanded of it. - -The man in the street, then, was able to comprehend the theory of natural -selection. This was greatly in its favour. Men are usually well disposed -towards doctrines which they can readily understand. - -The nineteenth century was a superficial age. It liked simplicity in all -things. If Darwin could show that natural selection was capable of -producing one species, men were not only ready but eager to believe that -it could explain the whole of organic evolution. - -The simplicity of the Darwinian theory has its evil side. It has -undoubtedly tended to make modern biologists superficial in their -methods. It has, indeed, stimulated the imagination of men of science; -but the stimulation has not in all cases been a healthy one. - -So far from adhering to the sound rule laid down by Pasteur, "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 facts in -support of his hypothesis. He enunciated no crude theory, he indulged in -no wild speculations. He was content to marshal a great array of facts, -and to draw logical conclusions therefrom. He was as cautious in his -deductions as he was careful of his facts. He thus stood head and -shoulders above the biologists of his day. He was a giant among pigmies. -So well equipped was he that those who attempted to oppose him found -themselves in the position of men, armed with bows and arrows, who seek -to storm a fortress defended by maxim guns. - -Nor was this all. The majority of the best biologists of his time did not -attempt to oppose him. They were, as we have seen, ready to receive with -open arms any hypothesis which seemed to explain how evolution had -occurred. Some of them perceived that there were weak points in the -Darwinian theory, but they preferred not to expose these; they were -rather disposed to make the best of the hypothesis. It had so many merits -that it seemed to them but reasonable to suppose that subsequent -investigation would prove that the defects were apparent rather than -real. - - - Opponents of Darwin - -We hear much of the "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 obtained acceptance. We venture to say that statements such as -these are misleading. We think we may safely assert that scarcely ever -has a theory which fundamentally changed the prevailing scientific -beliefs met with less opposition. It would have been a good thing for -zoology had Darwin not obtained so easy a victory. - -Sir Richard Owen, a distinguished anatomist, certainly attacked the -doctrine in no unmeasured terms, but his attack was anonymous and so -cannot be considered very formidable. Far more important was the -opposition of Dr St George Mivart, whose worth as a biologist has never -been properly appreciated. His most important work, entitled the _Genesis -of Species_, might be read with profit even now by many of our modern -Darwinians. - -For some time after the publication of the _Origin of Species_ Mivart -appears to be almost the only man of science fully alive to the weak -points of the Darwinian theory. The great majority seem to have been -dazzled by its brilliancy. - -The main attack on Darwinism was conducted by the theologians and their -allies, who considered it to be subversive of the Mosaic account of the -Creation. Now, when one whose scientific knowledge is, to say the best of -it, not extensive, attacks a man who has studied his subject -dispassionately for years, and invariably expresses himself with extreme -caution, the onslaught can have but one 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 position of warriors who do not -know what it is against which they are fighting; they confounded natural -selection with evolution, and directed the main force of their attack -against the latter, under the impression that they were fighting the -Darwinian theory. - -It was the misfortune of those theologians that it is possible to prove -that evolution, or, at any rate, some evolution has occurred; they thus -kicked against the pricks with disastrous results to themselves. When -this attack had been repulsed men believed that the theory of natural -selection had been demonstrated, that it was as much a law of nature as -that of gravitation. What had really happened was that the fact of -evolution had been proved, and the theory of natural selection obtained -the credit. Men thought that Darwinism was evolution. Had the theologians -admitted evolution but denied the ability of natural selection to explain -it, the Darwinian theory, in all probability, would not have gained the -ascendency which it now enjoys. - - - Evolution and Natural Selection - -To us who are able to look back dispassionately upon the biological -warfare of the last century, Darwin's opponents--or the majority of -them--appear very foolish. We must, however, bear in mind that at the -time of the publication of the _Origin of Species_ both natural selection -and evolution were comparatively unknown ideas. Darwin had to fight for -both. He had to prove evolution as well as natural selection. Many of the -facts adduced by him supported both. It is, therefore, not altogether -surprising that many of his opponents failed to distinguish between them. - -A glance at the _Origin of Species_ will suffice to show how considerable -is the portion of the book that deals with the evidence in favour of -evolution rather than of natural selection. - -Of the fourteen chapters which make up the book no fewer than nine are -devoted to proving that evolution has occurred. It has been truly said, -that for every one fact biologists have found in support of the special -theory of natural selection they have found ten facts supporting the -doctrine of evolution. Darwin, then, was in the position of a skilled -barrister who has a plausible case and who knows the ins and outs of his -brief, while his opponents stood in the shoes of inexperienced counsel -who had but recently received their brief, and who had not had the time -to master the details thereof. In such circumstances it is not difficult -to predict which way the verdict of the jury will go. - -Darwin, moreover, had a charming personality. Never was a man with a -theory less dogmatic. Never was the holder of a theory more careful of -the expressions he used. Never was a scientific man more ready to give -ear to his opponents, to meet them half way, and, where necessary, to -compromise. Darwin was not afraid of facts, and was always ready to alter -his views when they appeared to be opposed to facts. The average -scientific man of to-day makes facts fit his theory; if they refuse to -fit it he ignores or denies them. - -Darwin continually modified his views; when he found himself in a tight -place he did not hesitate to resort to Lamarckian factors, such as the -inheritance of the effects of use and disuse and of the effects of -environment. He conceded that natural selection was insufficient to -account for all the phenomena of organic evolution, and advanced the -theory of sexual selection in order to account for facts which the major -hypothesis seemed to him incapable of explaining. - -Darwin, moreover, having ample private means, was not obliged to work for -a living, and was therefore able to devote the whole of his time to -research. The advantages of such a position cannot be over-estimated, -and, perhaps, have not been sufficiently taken into account in -apportioning the praise between Darwin and Wallace for their great -discovery. - - - Huxley - -To all these factors in Darwin's favour we must add his good fortune in -possessing so able a lieutenant as Huxley. - -Huxley was an ardent evolutionist, an able writer, and a brilliant -debater. A man of his mental calibre was able, like a clever barrister, -to make out a plausible case for any theory which he chose to take up. -While nominally a strong supporter of the Darwinian theory, he was in -reality fighting for the doctrine of descent. Had _any_ plausible theory -of evolution been enunciated, Huxley would undoubtedly have fought for it -equally earnestly. - -A firm believer in evolution, Huxley was, as Professor Poulton says, -confronted by two difficulties,--first, the insufficiency of the evidence -of evolution, and, secondly, the absence of any explanation of how the -phenomenon had occurred. The _Origin of Species_ solved both these -difficulties. It adduced much weighty evidence in favour of evolution, -and suggested a _modus operandi_. Small wonder, then, that Huxley became -a champion of Darwinism. But, as Poulton writes, on page 202 of _Essays -on Evolution_, "while natural selection thus enabled Huxley freely to -accept evolution, he was by no means fully satisfied with it." "He never -committed 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 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 adherents gathered round him, a herd of men to whom he -seemed an absolutely unquestionable authority. Darwinism became a creed -to which all must subscribe. It still retains this position in the -popular mind. - - - Growing Opposition to Darwinism - -The ease with which the theory of natural selection gained supremacy was, -as we have already said, a misfortune to biological science. It produced -for a time a considerable mental stagnation among zoologists. Since -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 -majority of biologists that they see everything through Darwinian -spectacles. The wish has been in many cases the father to the -observation. Zoologists are ever on the lookout for the action of natural -selection, and in consequence frequently imagine they see it where it -does not exist. Many naturalists, consciously or unconsciously, stretch -facts to make them fit the Darwinian theory. Those facts which refuse to -be so distorted are, if not actively ignored or suppressed, overlooked as -throwing no light upon the doctrine. This is no exaggeration. A perusal -of almost any popular book dealing with zoological theory leaves the -impression that there is nothing left to be explained in the living -world, that there is no door leading to the secret chambers of nature to -which natural selection is not an "open sesame." - -But the triumph of natural selection has not been so complete as its more -enthusiastic supporters would have us believe. Some there are who have -never admitted the all-sufficiency of natural selection. In the British -Isles these have never been numerous. In the United States of America and -on the Continent they are more abundant. The tendency seems to be for -them to increase in numbers. Hence the recent lamentations of Dr Wallace -and Sir E. Ray Lankester. Modern biologists are commonly supposed to fall -into two schools of thought--the Neo-Darwinian and the Neo-Lamarckian. - -The former are the larger body, and pin their faith absolutely to natural -selection. They deny the inheritance of acquired characters, and preach -the all-sufficiency of natural selection to explain the varied phenomena -of nature. The Neo-Lamarckians do not admit the omnipotency of natural -selection. Some of them allow it no virtue. Others regard it as a force -which keeps variation within fixed limits, which says to each organism, -"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 developments of Darwinism is -incomplete, for it fails to include those who occupy a middle position. -If it be possible to classify a large number of men of which scarcely any -two hold identical views, it is into three, rather than two, classes that -they must be divided. - -Speaking broadly, evolutionists of to-day may be said to represent three -distinct lines of thought. For the sake of classification we may speak of -them as falling into three schools, which we may term the Neo-Lamarckian, -the Wallaceian, and the Neo-Darwinian, according as their views incline -towards those held by Lamarck, Wallace, or Darwin. - - - The Neo-Lamarckian School - -As adherents of the Neo-Lamarckian school, we cite Cope, Spencer, Orr, -Eimer, Naegeli, Henslow, Cunningham, Haeckel, Korchinsky, and a number of -others. It may almost be said of these Neo-Lamarckians that each holds a -totally distinct theory of evolution. So heterogeneous are their views -that it is difficult to find a single article common to the evolutionary -belief of all. It is commonly asserted that all Neo-Lamarckians are -agreed, firstly, that acquired characters are transmissible; and, -secondly, that such transmission is an important factor in the production -of new species. This assertion is certainly true of the great bulk of -Neo-Lamarckians, but it does not appear to hold in the case of those who -believe that evolution is the result of some unknown inner force. So far -as we can see, a belief in the inheritance of acquired characters is not -necessary to the theories of orthogenesis held by Naegeli and Korchinsky. -For that reason it would possibly be more correct to place those who hold -such views in a fourth school. Since, however, a number of undoubted -Neo-Lamarckians, as, for example, Cope, believe in an inner growth-force, -it is convenient to regard Naegeli as a Neo-Lamarckian. His views need -not detain us long. Those who wish to study them in detail will find them -in his _Mechanisch-physiologische Theorie der Abstammungslehre_. - -Naegeli believes that there is inherent in protoplasm a growth-force, -which makes each organism in itself a force making towards progressive -evolution. He holds that animals and plants would have become much as -they are now even if no struggle for existence had taken place. "To the -believers in this kind of . . . orthogenesis," writes Kellog (_Darwinism -To-day_, p. 278), "organic evolution has been, and is now, ruled by -unknown inner forces inherent in organisms, and has been independent of -the influence of the outer world. The lines of evolution are immanent, -unchangeable, and ever slowly stretch toward some ideal goal." 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. - - - Orr's Views - -Spencer and Orr preach nearly pure Lamarckism. The former, while fully -recognising the importance of natural selection, considered that -sufficient weight has not been given to the effects of use and disuse, or -to the direct action of the environment in determining or modifying -organisms. - -The similarity of the views of Orr and Lamarck is best seen by comparing -their respective explanations of the long neck of the giraffe. Lamarck -thought that this was the direct result of continual stretching. The -animal continually strains its neck in the search for food, hence it -grows longer as the individual grows older, and this elongated neck has -been transmitted to the offspring. Orr writes, on page 164 of his -_Development and Heredity_: "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 animal are widely -different from the forces acting upon an animal which eats the grass at -its feet like an ox, or one which must run and climb like a goat or a -deer, and the resultant modifications of growth in the several cases must -also be different. The principle of increased growth in the direction of -the shock, resulting from superabundant repair of the momentary -compression, explains how the giraffe acquired the phenomenal length of -the bones of its forelegs and neck; and the absence of the shock in the -hind-quarters shows why they remained undeveloped and absurdly -disproportionate to the rest of the body." - - - Inheritance of Acquired Characters - -It seems to us that a fatal objection to all these Neo-Lamarckian -theories of evolution is that they are based on the assumption that -acquired characters are inherited, whereas all the evidence goes to show -that such characters are not inherited. In these days, when scientific -knowledge is so widely diffused, it is scarcely necessary to say that all -the characteristics which an organism displays are either congenital or -inborn, or acquired by the organism during its lifetime. Thus a man may -have naturally a large biceps muscle, and this is a congenital character; -or he may by constant exercise develop or greatly increase the size of -the biceps. The large biceps, in so far as it has been increased by -exercise, is said to be an acquired character, for it was not inherited -by its possessor, but acquired by him in his lifetime. We must bear in -mind that the period in the life history of an organism at which a -character appears, is not necessarily a test as to whether it is -congenital or acquired, for a great many congenital characters, such as a -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, -notwithstanding the fact that its ancestors have for generations had the -greater portion of their caudal appendage removed shortly after birth. - -We do not propose to discuss at any great length the vexed question of -the inheritance of acquired characters, for the simple reason that the -Neo-Lamarckians have not brought forward a single instance which -indubitably proves that such characters are inherited. - -Mr J. T. Cunningham, in a paper of great value and interest, entitled -"The Heredity of Secondary Sexual Characters in relation to Hormones: a -Theory of the Heredity of Somatogenic Characters," which appeared in vol. -xxvi., No. 3, of the _Archiv für Entwicklungsmechanik 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 _a -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 -inheritance of acquired characters does not play an important part in the -evolution of, at any rate, the higher animals, is based, not on the -ground of _a priori_ reasoning, but on facts. All the evidence seems to -show that such characteristics are not inherited. If, as Mr Cunningham -thinks, all secondary sexual characters are due to the inheritance of the -effects of use, etc., how is it that no Neo-Lamarckian is able to bring -forward a clear case of the inheritance of a well-defined acquired -character? If such characteristics are habitually inherited, countless -examples should be forthcoming. Fanciers in their endeavours are -constantly "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 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 characters are inherited, not on -evidence thereof, but because if such characters are not inherited it is -very difficult to account for many of the phenomena presented by the -organic world? - -In many of the lower animals, as, for example, the hydra, the germinal -material is diffused through the organism, so that a complete individual -can be developed from a small portion of the creature. In such -circumstances it seems not improbable that the external environment may -act directly on the germinal substance, and induce changes in it which -may perhaps be transmitted to the offspring. If this be so, it would seem -that some acquired characters may be inherited in such organisms. Very -many plants can be propagated from cuttings, buds, etc., so that we might -reasonably expect some acquired characters to be hereditary in them. The -majority of botanists appear to hold Lamarckian views; but on the -evidence at present available, it is doubtful whether such views are the -correct ones. - -Plants are so plastic, so protean, so sensitive to their environment that -their external structure appears to be determined by the external -conditions in which they find themselves quite as much as by their -inherited tendencies. In this respect they differ very considerably from -the higher animals. The peacock, for example, presents the same outward -appearance[1] whether bred and reared in Asia or Europe, in a hot or -cold, a damp or a dry climate. The same plant, on the other hand, differs -greatly in outward appearance according as it is grown in a dry or a damp -soil, a hot or a cold country. In his recent book _The Heredity of -Acquired Characters in Plants_, the Rev. G. Henslow cites several -examples of the celerity with which plants react to their environment. On -page 32 he writes: "The following is an experiment I made with the common -rest-harrow (_Ononis spinosa, L._) growing wild in a very dry situation -by a roadside. I collected some seeds, and also took cuttings. These I -planted in a garden border, keeping this well moist with a hand-light -over it, and a saucer of water, so that the air should be thoroughly -moist as well. Its natural conditions were thus completely reversed. They -all grew vigorously. The new branches of the first 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 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 experiment -affords strong evidence against the Lamarckian doctrine. Here we have a -plant which has, perhaps, for thousands of generations developed spines -owing to its dry environment. If acquired characters are inherited we -should have expected this spiny character to have become fixed and -persisted under changed conditions, for some generations 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 environment -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 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 inheritance 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 inheritance 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 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 Wallaceian School - -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 structures displayed by organisms cannot be explained on -the natural selection hypothesis. Those who 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 Theorie_ on the thriving and very healthy plant of Darwinism, -is a much more staunch Darwinian than either Dr Wallace himself, or the -two great authorities in biological science whom he mentions, Sir William -Thistleton Dyer and Professor Poulton." - - - Complexity of the Problem - -Having classified ourselves, it remains for us (the authors of the -present work) to define our position more precisely. Like Darwin we -welcome 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 recognise -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 necessary in the case of contracts between the weak and -the strong. Similarly the earlier economists considered 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 attributes 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. - - - The Aim of the Biologist - -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 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. - - - - - 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--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. - -"The 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. - - - 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 related 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 _The Origin of Species_ 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 -profitable to itself, under the complex and sometimes varying conditions -of life, will have a better chance of surviving, and thus be naturally -selected. From the strong principle of inheritance, 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 geometrical -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. - - - Various Anti-Darwinian Views - -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 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 evolution, 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 _nil_, 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. 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 unfavourable, 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 environment, 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 conditions, 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 orthogenesis 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 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. - - - Darwinism does not explain Variation - -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 variations. 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 objection is that which points out -that it is a long journey from Amoeba to man. It is difficult to 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 objection 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? - - - Theory of Change of Function - -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, 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 connecting 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 unreasonable 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 explanations, 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: "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 -counterbalanced 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. - - - 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 emphasis 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 may indirectly be responsible for characteristics which in -themselves are injurious to the individual. 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 palæontology 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. - - - Missing Links - -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 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 -palæontology 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 -_Orohippus_, through the _Mesohippus_, the _Miohippus_, the -_Protohippus_, and the _Pliohippus_, until we reach the one-toed _Equus_. - -Wallace further points out that in order that the fossil of any organism -may be preserved, the "concurrence of a number of favourable conditions" -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. 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, palæontology 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 -pure ancestors and breed true _inter se_. Nor is this all. - - - Recurrent Mutations - -Experience shows that where a mutation, or sport, or discontinuous -variation occurs, it frequently 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 -priori_ 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. Therefore 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 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 advantage 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 similar habits, such as that -of the jaguar and puma in South America, and the five very -differently-coloured flycatchers in the Nilgiri Hills. - - - Leaf-butterflies - -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 _Darwinism 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. 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 concealment 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 culmination, 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 precariously 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? Kallima continues its way, specifically and absurdly -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. - - - A Dilemma - -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 existence, 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 value, -they are, as Kellog points out, in trouble over the close and detailed -resemblance which the Kallima butterflies bear to dead leaves. - -10. 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," 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 -conditions 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 therefore 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. - - - The Effects of Chance - -Writing of plants, Professor Henslow says, on page 16 of _The Heredity of -Acquired Characters 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 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. - - - The Origin of Mimicry - -12. Natural selection, as we shall see, fails to account for the origin -of what is known as protective 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." It is easy -to understand the profit that these mimics derive from their mimicry. -When once the disguise has been assumed we can comprehend 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 explanation of the phenomena -of sexual dimorphism. Why, for example, in some species of doves and -ducks, the sexes 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. - - - - - 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 - 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 "discontinuous 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. - - - Nature of Variation - -As 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 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 diversity of inheritable deviations of -structure . . . are endless" (page 14, ed. 1902). "The variations 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 domestication, 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 -_Darwinism_ 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 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 altogether new conceptions. Such being the case, his ideas were of -necessity somewhat hazy; they underwent considerable modification as -fresh facts came to his knowledge. - - - Definite and Indefinite Variability - -Towards the end of his life Darwin recognised that variability is of two -kinds--definite and indefinite. Indefinite variation is indiscriminate -variation in all directions around a mean, variation 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 direction 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 perceived that some variations are much more pronounced than -others. He recognised the distinction between what are now known as -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. - - - Monstrosities - -"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 produced 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 structures 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 depend 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 Species_, 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, if the varying individual did -not actually transmit to its offspring its newly acquired character, 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 individuals 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. - - - Minute Variations - -Again, we read (page 34): "Some variations useful to him (_i.e._ 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 arisen in a -seedling. This is known to be the case with the turnspit dog."[2] 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 complexity of -the coadaptations between all organic beings . . . which may have been -effected[3] 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. - -Although the theory of natural selection does not attempt to explain the -causes of variation, 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 domestication 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. Variability is, he stated, governed by unknown laws which -are infinitely complex. - - - Lines of Variation - -It will be convenient to deal with each of 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 variations do not always occur -equally in all directions. The results of many years of the efforts of -practical 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 _Genesis of Species_, "Not only -does it appear that there are barriers which oppose change in certain -directions, but that there are positive tendencies to development along -certain special lines. In a bird which has been kept and studied like the -pigeon, it is difficult to believe that any remarkable spontaneous -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 artificial -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 considerably 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 significant, -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. - - - Breeders' Boasts - -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 _Origin of -Species_, Darwin quotes, with approval, Youatt's description of selection -as "the magician's wand, by means of which he may summon into life -whatever 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 anything 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 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 -carefully 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 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. - - - Albinistic Variations - -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 (_Haliaetus albicilla_) the Nicobar Pigeon -(_Caloenas nicobarica_), 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 Linnæus, based on experience, 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 identification 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 -sport. Similarly, white animals appear not to give rise to colour -varieties. - -We are never surprised to find that an ordinary upright plant produces as -a sport or mutation 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 variation is furnished by what -Grant Allen calls the "Law of Progressive Colouration" of flowers. - -On pp. 20, 21 of _The 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." - - - Over-development - -So among animals there are many colour patterns and structures that -appear in widely different genera, as, for example, the magpie 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 inherited 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 palæontologists 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. "Palæontology," 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 unwieldiness -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 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 proportions 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. - - - Speed of Racehorses - -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 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 multiplication 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. - - - Experiments of De Vries - -De Vries has made some important experiments 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: their 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 -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 character as far as possible by a -very rigid and careful selection. . . . By this method I brought my -strain within two years up to an average of nearly 90 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 produce 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 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 -ameliorations are obtained, and the selection must be made in the same -manner every year. Moreover, the improvement is very limited, and does -not give any promise of further increase." Notwithstanding 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 circumstances 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 experiments, 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 differences not only can, but have actually been -produced by the selection of such variations. This objection is based -upon the assumption that breeders have in the past dealt only with -fluctuating variations. This assumption does not appear to be justified. -It is exceedingly probable that most, if not all, the varieties of -domesticated animals have originated in mutations. 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." - - - Bateson on Variation - -As long ago as 1894 Bateson published his _Materials for the Study of -Variation_, in which he set forth a large number of cases of -discontinuous 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 -continuous, 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 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 perfection 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." - - - Work of Bateson and De Vries - -But Bateson's views fell upon stony ground, because zoologists are mostly -men of theory and not practical breeders. They laboured under the -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 perpetuating 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 recognise the immense value of his work. Had his -statements in 1894 received the attention they merited, zoological theory -would to-day be considerably 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 -conclusions are applicable to animals. We are far from accepting his -theory of mutations _in toto_. We are, however, convinced that he, like -Bateson, 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. - - - Varieties and Elementary Species - -That eminent botanist, as we have already seen, insists on the -distinction between fluctuating 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. - -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 average comply with the same laws as the -deviations 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 -composite nature, being made up of a collection of varieties and -elementary species. His conception 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 consider (page 141 _Species and -Varieties_) the following as the principal difference between elementary -species and varieties: that the first arise by the 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 retrogression, while others have diverged from the -parental types in a line of digression or in the way of repetition. . . . -The system (of the vegetable kingdom) is built up of species; varieties -are only local and lateral, never of real importance 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 experiment which plants -are in the mutating state and which are not. The great majority, however, -are not at present in the mutating state. - - - Mutations - -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 fluctuating variation -in an organism. If, however, the block be tilted to such an angle that -when left to 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 sometimes 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 variations occur. - -As it is of considerable importance thoroughly to grasp the true nature -of mutations or discontinuous 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 individuals 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 individual 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 mean whether that departure is due to a -mutation or a fluctuating variation. - - - Law of Regression - -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 variation. -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 Müller and Galton conducted independently enquiries into the amount -of the regression shown by the progeny of parents which have deviated -from the average by fluctuating variation. - -Müller 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 average, a length of wing of only about 18-1/4 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 18-1/4 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's Dictum - -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 _inter se_, some of them 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 fluctuating 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 -experimental 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. - - - Mutating Plants - -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 _Species and Varieties_ (p. 525), "was found in a locality -near Hilversum, in the vicinity of Amsterdam, where it grew in some -thousands of individuals. Ordinarily 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 producing 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 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 observed 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, however, are, like their parent form, liable to mutations." 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 sometimes gives rise to -the wheat-ear form. "In this variety," writes De Vries (p. 228), "the -flower is suppressed, and the loss is attended by a corresponding -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 (_Linaria vulgaris 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 purple beech seems -to be a mutation which has originated at least three times over. - - - Mutation Theory Criticised - -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 agriculturist 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 variation 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 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 probability that it was produced by crossing various forms of -the polymorphic _Oenothera biennis_, which had been previously introduced -in Europe." - - - Definition of a Species - -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 Linnæan 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 a distinct race is produced. And, finally, -fresh mutations occur, so that a new species is eventually 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 characters, -which they transmit to their offspring. - -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 discontinuous 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 mutations 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. - - - "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_, "I 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 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 descended." - -[Illustration: A TURBIT BELONGING TO MR. H. P. SCATLIFF] - -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 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 -offspring 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 considerably over £100 in -purchases, and took eight years fixing the peculiarity in question. Had -"Ladybird" 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. - - - 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 -doubtless exercise much ingenuity in explaining how natural selection had -brought about the gradual disappearance of the horns; and -palæontologists, 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 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 mutating state" in that part of the world. - -The other classical examples of great and sudden variations are the Ancon -sheep of Massachusetts, 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 grandparents of Linus I. had exceptionally long -hair. - - - Mutations among Birds - -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. - -The Golden Pheasant (_Chrysolophus pictus_) produces, in domestication, -the dark-throated form (_C. obscurus_), 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 produces 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 _A. chiaradiæ_ in the wild state. In this the -irides are dark, instead of 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 exterminated by local ornithologists. - -The reed bunting (_Emberiza schoeniclus_) exists in two distinct -forms--one having a much stouter bill than the other (_E. pyrrhuloides_). -This probably is an example of a mutation. - -The rare yellow-rumped Finch (_Munia flaviprymna_), of Australia, has -displayed a tendency to change into the allied and far commoner -chestnut-breasted Finch (_M. castaneithorax_) during the lifetime of the -individual (_Avicultural Magazine_, 1907). 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. -russi_, 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 sometimes 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. - -[Illustration: YELLOW-RUMPED AND CHESTNUT-BREASTED FINCHES, WITH -TRANSITIONAL SPECIMENS] - -A well-marked mutation which appears regularly in nature is the -red-headed variety of the beautiful Gouldian Finch (_Pöephila 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 (_Ossifraga 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 pigment, 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 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.[4] 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 creatures are -less conspicuous than white ones. As examples of black mutations which -occur in nature, 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 sometimes brown, while the other bears, when not brown, are almost -invariably black. - - - Color Mutations - -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 giu_)--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, 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 -(_Palæornis torquatus_), 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 unfavourable 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 Cambridge, has long been known -to collectors as a habitat of a yellow-marked form of the six-spot Burnet -Moth (_Zygæna filipendulæ_). These lutinistic forms are not confined to -one genus of Butterflies. Moreover, in the Pin-tailed Nonpareil Finch -(_Eythrura prasina_) of the Eastern Archipelago the red tail and other -red parts of the plumage are not infrequently replaced by yellow in wild -individuals of either sex and of any age. In the blue-fronted Amazon -parrot (_Chrysotis æstiva_)--a most variable bird--the normally red edge -of the pinion is sometimes yellow. Bateson, in his _Materials for the -Study of Variation_, gives other examples of this kind of variation. - - - Mutations among Invertebrates - -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 (_Argynnis paphia_) and the _helice_ -form of the female Clouded-yellow Butterfly (_Colias 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 _Epenthesis 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." - - - Mutating Species - -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 likelihood that they have -suddenly arisen and managed to establish themselves alongside of the -parent species. - -The Curassows, _Crax grayi_, _C. hecki_, each of which is only known by a -very few specimens, appear to be mutations of the female of the globose -Curassow, _Crax globicera_. The fact that when a female _hecki_ bred in -the London Zoological Gardens with a male _globicera_, 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 (_Lophophorus impeyanus_), -the common species of the Himalayas. - -The Three-coloured Mannikin (_Munia malacca_) of South India is probably -simply a white-bellied form of the widely-ranging Black-headed Mannikin -(_M. atricapilla_), which has the abdomen chestnut like the back. -Intermediate wild-caught forms have been recorded. - -The African Cordon-bleu (_Estrelda phoenicotis_) and Blue-bellied Waxbill -(_E. 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 (_Stictoptera annulosa_) of Java, and Bicheno's Finch -(_S. bichenovii_) 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 -(_Chloëphaga magellanica_), 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 -(_Balearica chrysopelargus_) 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 convoluted brain or a mouse with -a peculiar pattern of molar teeth, have been come upon by anatomists. - -The above-cited mutations are all very considerable 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 hypothesis of De Vries that species -pass through alternate periods of comparative stability and periods when -swarms of mutations appear. We think it more probable that all species -throw off at greater or less intervals discontinuous variations, and that -it is upon these that natural selection acts. - -We further hope that we have succeeded in making clear what we believe to -be the very sharp distinction between continuous and discontinuous -variations, even when the latter are inconsiderable, as frequently -happens. - - - Somatic and Germinal Variations - -Before leaving the subject of variation it is necessary to notice the -distinction, which Weismann 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 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. - - - Somatic Variations - -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 organism 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 -is the result of a congenital variation or a somatic one. This will be -rendered clear by a hypothetical 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 -organism 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 -environment. 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 survival, 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 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 conspicuous 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 environment. -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. - -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 -environment. In so far as they are due to this latter they do not appear -to be inherited. - -Thus, although we cannot say of many variations 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 in a 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. - - - - - 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. - -The alleged sterility of the hybrids produced 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 useless 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. - -"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 permanent 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 -skilful physiologist, would very probably obtain the desired production -of mutually more or less infertile breeds from a common stock in a -comparatively few years; but still, as the case stands at present, this -little 'rift within the lute' is not to be disguised or overlooked." - - - Alleged Sterility of Hybrids - -Similarly Wallace writes, at the beginning of chapter vii. of his -_Darwinism_: "One of the greatest, or perhaps we may say the greatest, of -all the difficulties in the way of accepting the theory of natural -selection as a complete explanation 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 perfectly 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 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. - - - Fertile 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 _The 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 vaginalis_ and -_reevesii_, and from _Phasianus 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. -cygnoides_), 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 bred _inter 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 (grandchildren 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.[5] . . . 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, both in first crosses and in hybrids, is an -extremely 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 incidental on -unknown peculiarities of the reproductive 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." - - - A Biological Bogey - -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. - - - 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 perfectly -fertile plant hybrids cited by De Vries are the crosses between _Anemone -magellanica_ and _A. sylvestris_, between _Salix alba_ and _Salix -pentandra_, between _Rhododendron hirsutum_ and _R. ferrugineum_. - -He gives an instance of a hybrid--_Ægilops speltæformis_, 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 raspberry, which is not only fertile, but quite -popular as producing a novel fruit. - - - Sterile Plant Hybrids - -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 -"Gordon's currant," which is considered to be a hybrid between the -Californian and the Missouri species. He also gives _Cytisus adami_ 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. - - - Fertile Mammalian Hybrids - -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 specimen -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, however, succeed at all, which reminds us of -what happens in the case of finch-hybrids. - -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 constantly side by side in the -plains of India, never interbreed at all. - -Among wild ruminants of this hollow-horned family, the Himalayan Argali -(_Ovis ammon_) ram, a giant sheep of the size of a donkey, has been known -to appropriate a herd of ewes of the Urial (_O. vignei_), 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 sika_), 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 strong and useful, the three-quarter bred beasts are -apparently of little value. - - - Fertile Bird Hybrids - -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 recorded. Even among -birds so seldom bred, comparatively, as the parrot family, a fertile -hybrid has been produced, that between the Australian Rosella Parrakeet -(_Platycercus eximius_) and Pennant's Parrakeet (_P. elegans_). The -hybrid was first described as a distinct species, the Red-mantled -Parrakeet (_P. erythropeplus_). 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 (_Chrysolophus amherstiæ_) and the Gold Pheasant -(_C. pictus_) have long been known as producing hybrids which are fertile -either _inter se_ or with the parents. Here the species are still more -distinct; not only 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 descendants (_Anas 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 (_Motacilla lugubris_) and the Grey Wagtail (_M. -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 (_Ligurinus 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. - -[Illustration: MALE AMHERST PHEASANT] - -The Red Dove of India (_Oenopopilia tranquebarica_) has produced hybrids -with the tame Collared Dove (_T. 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 displaying 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 -_Molpastes_ bulbuls, and the Indian Roller (_Coracias indica_) and -Burmese Roller (_C. affinis_). 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 interesting experiment when, more than a century -ago, they introduced largely into their coverts the Chinese Ring-necked -Pheasant (_Phasianus torquatus_) and the Japanese _P. versicolor_. So -freely has the former bred with the common species already present there -(_Phasianus 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 Green Pheasant (_P. versicolor_) 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. - - - Fertile Hybrids among Amphibia - -Our Crested Newt (_Molge cristata_) and the Continental Marbled Newt (_M. -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 blasii_. 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. - -[Illustration: HARLEQUIN QUAIL (Coturnix delegorguei)] - -[Illustration: RAIN QUAIL (Coturnix coromandelica)] - - - Insects - -Among insects, M. de Quatrefages states that the hybrid progeny of the -silk-moths _Bombyx cynthia_ and _B. arrindia_ are fertile for eight -generations when bred _inter 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 -(_Phasianidae_), 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 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 frontalis_) 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 succeeded 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 (_Turtur 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 Darwin's view that domestication tends to -eliminate sterility; but it is doubtful if this can be upheld. The hybrid -between the Muscovy duck (_Cairina 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. - - - Characters of Hybrids - -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 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 a modified form in the hybrid; for instance, in that -between the blackcock (_Tetrao tetrix_) and the capercailzie (_T. -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 sheldrakes (_Tadorna cornuta_ and _Casarca cana_), now -in the British Museum, bear a distinct resemblance to the grey Australian -sheldrake (_C. tadornoides_). 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 -_inter se_, there seems to have been no reversion to the original pure -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." - - - Wild Hybrids - -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 offspring "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 _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 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 crossing 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. - - - - - 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--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 modification of the - generally-accepted Mendelian formulae--Unit characters--Biological - isomerism--Biological molecules--Interpretation of the phenomena of - variation and heredity on the conception of biological - molecules--Correlation--Summary of the conception of biological - molecules. - -We have seen that variations may be, firstly, either acquired or -congenital, and, secondly, fluctuating or discontinuous. We have further -seen that acquired variations--at all events in the higher animals--do -not appear to be inherited, 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 congenital variations, -although they do not appear to give rise directly to new species, may -play a 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 _inter 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 inheritance which differs more -or less greatly from the theory held by any other biologist. - -As regards the phenomena of heredity we may say _Tot homines tot -sententiæ_. - - - Phenomena of Inheritance - -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. - -2. Why they differ from their parents. - -3. Why the members of a family display individual 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 parthenogenesis 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. - -17. Why differences in the nature of the food administered to the larvæ -of ants determines whether these shall develop into sexual or neuter -forms. - -18. Why the application of heat, cold, etc., to certain larvæ 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 -appearance from the mule, etc. - -22. It must explain all the facts which constitute 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. - -26. It must render intelligible the effects of castration on animals. - - - Existing Theories Unsatisfactory - -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 critically 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 carefully 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 knowledge can be made. - -By inheritance we mean that which an organism 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--"all the qualities or characters which have their initial -seat, their physical basis, in the fertilised egg cell"--seems to cover -all cases except those where eggs are parthenogenetically developed. - -The first fact of heredity which we must notice is that inheritance may -take several forms. This is apparent from what was set forth in the -chapter dealing with hybrids. - - - Types of Crosses - -In considering the phenomena of inheritance it is convenient to deal with -crosses in which the parents do not closely resemble one another, because -by so doing we are able readily to follow the various characters -displayed by each parent. It may, perhaps, be urged that such crosses -occur but rarely in nature. This is true. But we should bear in mind that -any theory of inheritance must explain the various facts of -cross-breeding, so that, from the point of view of a theory of -inheritance, crosses are as important as what we may term normal -offspring. As inheritance is so much easier to observe in the former, it -is but natural that we should begin with them. Our deductions must, if -they be valid ones, fit all cases of ordinary inheritance, _i.e._ all -cases where the offspring results from the union of parents which closely -resemble one another. Now, when two unlike forms inter-breed, their -offspring will fall into one of six classes. - -I. They may exactly resemble one parent, or rather the type of one -parent, for, of course, they will never be exactly like either parent; -they must of necessity display fluctuating variations. The cases in which -the offspring exactly resemble one parent type in all respects are -comparatively few. They occur only when the parents differ from one -another in one, two, or at the most three characters. Thus when an -ordinary grey mouse is crossed with a white mouse the offspring are all -grey, that is to say, they resemble the grey parent type. Although they -are mongrels or hybrids, they have all the appearance of pure grey mice. -This is what is known as unilateral inheritance. - -II. The offspring may resemble one parent in some characters and the -other in other characters. They may have, for example, the colour of one -parent, the shape of the other, and so on. Thus if a pure, albino, -long-haired, and rough-coated male guinea-pig be crossed with a coloured, -short-haired and smooth-coated female, all the offspring are coloured, -short-haired, and rough-coated. That is to say, they take after the -father in being rough-coated, but after the mother in being pigmented and -short-haired. This form of inheritance is usually seen only in crosses -between two types which differ in but few of their characters. - -III. The offspring may display a blend of the characters of the two -parents. They may be intermediate in type. They are not of necessity -midway between the two parents; one of the parents may be prepotent. The -crosses between the horse and the ass show this well. Both the mule, -where the ass is the sire, and the hinny, where the horse is the sire, -are more like the ass than like the horse; but the hinny is less ass-like -than the mule. The offspring between a European and a native of India -furnishes a good case of blended inheritance; Eurasians are neither so -dark as the Asiatic nor so fair as the European. - -IV. The offspring may show a peculiarity of one parent in some parts of -the body and the peculiarity of the other parent in other parts of the -body. This is known as particulate inheritance. The piebald foal, which -is the result of a cross between a black sire and a white mare, is a good -example of such inheritance. This does not appear to be a common form of -inheritance. - -V. The usual kind of inheritance is perhaps a combination between the -forms II. and III. In such cases the offspring display some paternal -characters and some maternal ones, and some characters in which the -maternal and paternal peculiarities are blended. An example of -inheritance of this description is furnished by a cross between the -golden and the amherst pheasants. - -VI. The offspring may be quite unlike either parent. For example, Cuénot -found that sometimes a grey mouse when crossed with an albino produces -black offspring. - - - Mendel's Experiments - -The first two kinds of inheritance were carefully investigated by Gregor -Johann Mendel, Abbot of Brunn. The results of his experiments were -published in the Proceedings of the Natural History Society of Brunn, in -1854, but attracted very little notice at the time. - -Mendel experimented with peas, of which many varieties exist. He took a -number of varieties, or sub-species, which differed from one another in -well-defined characters, such as the colour of the seed coat, the length -of the stem, etc. He made crosses between the various varieties, being -careful to investigate one character only at a time. He found that the -offspring of such crosses resembled, in that particular character, one -only of the parents, the other parent apparently exerting no influence on -it. Mendel called the character that appeared in the off-spring dominant, -and the character which was suppressed, recessive. Thus when tall and -short varieties were crossed the offspring were all tall. Hence Mendel -said that tallness is a dominant character, and shortness a recessive -character. Mendel then bred these crosses among themselves, and found -that some of the offspring resembled one grandparent as regards the -character in question while some resembled the other, and he found that -those that showed the dominant character were three times as numerous as -those that displayed the recessive character. He further found that all -those of the second generation of crosses which displayed the recessive -character bred true; that is to say, when they were bred together all -their descendants exhibited this characteristic. The dominant forms, -however, did not all breed true; some of them produced descendants that -showed only this dominant character, others, when crossed, gave rise to -some forms having the dominant character and some having the recessive -character. - -It is thus evident that organisms of totally different ancestry may -resemble one another in external appearance. In other words, part of the -material from which an organism is developed may lie dormant. - - - Mendelism - -From the above results Mendel inferred, in the case of what he called -alternating characters, that only one or other of the pair can appear in -the offspring, that they will not blend. If both parents display one of -the opposing characters, the offspring will of course show it. But if one -parent display one character and the other the opposing character, the -hybrid offspring will display one only, and that which is dominant. The -other character is suppressed for the time being. When, however, these -hybrids are bred _inter se_, their gametes or sexual cells split up into -their component parts, and then the recessives are free to unite with -other recessives and thus produce offspring which show the recessive -character. - -His results can be set forth in symbols. - -Let T stand for the tall form and D for the dwarf form. Since the -offspring are composed of both the paternal and maternal gamete, we may -represent them as TD. But dwarfness is, as we have seen, recessive, so -that the offspring all look as though they were pure T's. When, however, -we come to breed these TD's _inter se_, the gamete or sex-cell of each -individual crossed breaks up into its component parts T and D, which -unite with other free T or D units to form TD's or TT's or DD's. What are -the possible combinations? A D of one parent may meet and unite with a D -of the other parent, so that the resulting cells will be pure D, _i.e._ -DD, and will give rise to pure dwarf offspring. Or the D gamete from one -parent may unite with a T gamete from the other parent, and the result -will be a TD cross, but this, as we have seen, will grow up to look like -a pure T, _i.e._ will become a tall organism. Similarly, a T gamete from -one parent may unite with a T gamete of the other, and produce a pure -tall form, or it may unite with a D and produce a hybrid TD, which gives -rise to a tall form. Thus the possible combinations of offspring are DD, -DT, TD, TT, but all these three last contain the dominant T gamete, and -so develop into tall offspring; therefore, _ex hypothesi_, we shall have -three tall forms produced to one dwarf form, but of these three tall -forms two are not pure, and do not breed true. Mendel's experimental -results accorded with what we should expect to obtain if the above -explanation were correct. Hence the inference that there is such a -splitting of the gametes in the sexual act seems a legitimate one. - -Mendel's experiments are of great importance, for they give us some -insight into the nature of the sexual act. But, as is usual in such -cases, Mendel's disciples have greatly exaggerated the value and -importance of his work. It is necessary to bear in mind that Mendel's -results apply only to a limited number of cases--to what we may call -balanced characters. In the case of characters which do not balance one -another, which are, so to speak, not diametrically opposed to one -another, Mendel's law does not hold. A second important point is, that -the dominance is in many cases not nearly so complete as it should be if -the Mendelian formula correctly represented what actually occurs in -nature. Further, the segregation of the gametes does not appear to be so -complete as the above hypothesis requires it to be. The phenomena of -inheritance seem to be far more complex than the thorough-going Mendelian -would have us believe. - -Let it be noted that it is not to the facts of Mendelism, but to some -portions of what we may call the Mendelian theory, that we take -exception. - - - Maturation of the Germ-cells - -Before passing on to consider some of the later developments of -Mendelism, it is necessary for us to set forth briefly certain of the -more important facts regarding the sexual act which the microscope has -brought to light. We propose to state these only in the merest outline. -Those who are desirous of pursuing the subject farther are referred to -Professor Thomson's _Heredity_. - -The germ cells, like all other cells, consist of a nucleus lying in a -mass of cytoplasm. The nucleus is composed of a number of rod-like -bodies, which are called chromosomes, because they are readily stainable. - -These chromosomes appear, under ordinary circumstances, to be joined -together end to end, and then look like a rope in a tangle. - -When a cell is about to divide into two, these chromosomes become -disjoined and can then be counted, and it is found that each cell of each -species of animal or plant has a fixed number of these chromosomes. Thus -the mouse and the lily have twenty-four chromosomes in each cell, while -the ox is said to have sixteen of them per cell. - -When a cell divides into two, each of these chromosomes splits by a -_longitudinal_ fissure into two halves, which appear to be exactly alike. -One-half of every chromosome passes into each of the daughter cells, so -that each of these is furnished with exactly half of each one of the -rod-like chromosomes. In the cell division, which takes place immediately -before the male gamete or generative cell meets the female gamete, the -chromosomes do not divide into equal halves, as is usually the case. In -this division half of them pass into one daughter cell and half into the -other daughter cell, so that, prior to fertilisation both the male and -the female gametes contain only half the normal number of chromosomes. In -the sexual act the male and the female chromosomes join forces and then -the normal number is again made up, each parent contributing exactly one -half. - - - Experiments of Delage and Loeb - -Biologists, with a few exceptions, seem to be agreed that these -chromosomes are the carriers of all that which one generation inherits -from another. Thus the cardinal facts of the sexual act are, firstly, -prior to fertilisation the male and the female gamete each part with half -their chromosomes; and, secondly, the fertilised cell is composed of the -normal number of chromosomes, of which one-half have been furnished by -each parent. Thus the microscope shows that the nucleus of the fertilised -egg is made up of equal contributions from each parent. This is quite in -accordance with the observed phenomena of inheritance. - -But Delage has shown that a non-nucleated fragment of the ovum in some of -the lower animals, as, for example, the sea-urchin, can give rise to a -daughter organism with the normal number of chromosomes when fertilised -by a spermatozoon. Conversely, Loeb showed that the nucleus of the -spermatozoon can be dispensed with. Thus it seems that either the egg or -the spermatozoon of the sea-urchin contains all the essential elements -for the production of the perfect larva of a daughter organism. We are, -therefore, driven to the conclusion that the fertilised ovum contains two -sets of fully-equipped units. Only one of these seems to contribute to -the developing organism. If this set happens to be composed of material -derived from one only of the parents, we can see how it is that we get -unilateral inheritance in the case of a cross. Where, however, the units -from the two parents intermingle, although only one set is active in -development, the result will be blended inheritance. Thus, we may regard -the fertilised egg as made up of two sets of characters--a dominant set, -which is active in the production of the resulting organism, and a -recessive set, which appears to take little or no part in the production -of the organism. - -This is quite in accordance with Mendelian conceptions. - -Let X be an organism having the unit characters A _B_ C D _E_ F _G_, and -let Y be another organism having the unit characters _a_ b _c_ _d_ e _f_ -g. - -Now suppose that these behave as opposed Mendelian units, and that the -unit characters in italics are dominant ones. Then the resulting -individual will resemble each parent in certain unit characters. It may -be represented by the formula a B c d E f G, but it will contain the -characters A b C D e F g in a recessive form, so that its complete -formula may be written - - a B c d E f G} - A b C D e F g - -When these hybrids are paired together it will be _possible_ to get such -forms as - - A B C D E F G - A B C D E F G - - and - - a b c d e f g - a b c d e f g - -which exactly resemble the -respective grandparents, and these should breed -absolutely true, if the segregation of the -gametes is as pure as the Mendel's law seems -to require. - - - Experiments of Cuénot and Castle - -There are, however, certain facts, which recent experimenters have -brought to light, that seem to show that the segregation is not so -complete as the law requires. For example, the so-called pure extracted -forms may be found, when bred with other varieties, to have some latent -characters. Thus Cuénot observed that extracted pure albino mice, that is -to say, those derived from hybrid forms, did not all behave alike when -paired with other mice. Those which had been bred from grey x white -hybrids behaved, on being crossed, differently to those that had been -bred from black x white hybrids; and further, those derived from yellow x -white hybrids yielded yet other results on being intercrossed. Castle -records similar phenomena in the case of guinea-pigs, and accordingly -draws a distinction between recessive and latent characters. Recessive -characters are those which disappear when they come into contact with a -dominant character, but reappear whenever they are separated from the -opposing dominant character. Latency is defined by Castle as "a condition -of activity in which a normally dominant character may exist in a -recessive individual or gamete." - -The ordinary Mendelian pictures a unit character in a cross that obeys -Mendel's law, as follows:-- - - D - R, - - the dominant character only -showing. It seems to us that each unit character -should be represented as a double entity, thus -D(D), the portion within the bracket being -latent. The cross would appear to be represented -by the formula - - D(R) - R(D), - - since the union -appears to take the form of the transfer of -the dormant latent characters. Now an extracted -pure recessive will, on this hypothesis, -bear the formula - - R(D) - R(D). - - When such recessives -are crossed the two dormant portions will -ordinarily change places, and never appear, so -that these extracted recessives will, under -ordinary circumstances, appear to be as pure -as the true pure recessives, which are represented -by the formula - - R(R) - R(R). - -Now, suppose that, from some cause or other, -it is possible for the latent D to change places -with the visible R, it is obvious that the impure -nature of the extracted and hitherto apparently -pure recessives will become manifest. This -seems to be what happens under certain circumstances -to the extracted albino mice. They -possess latent the character of their dominant -ancestor. - - - Unit Characters - -Mendelian phenomena force upon us the conclusion that organisms display a -number of unit characters, each of which behaves in much the same way as -a radicle does in chemistry, inasmuch as for one or more of these -characters others can be substituted without interfering with the -remaining unit characters. For example, it is possible to replace the -chemical radicle NH_{3} by the radicle Na_{2}; _e.g._ (NH_{3})_{2}SO_{4} -(ammonium sulphate) may be transformed into Na_{2}SO_{4} (sodium -sulphate). - -The conclusion that each organism is composed of a number of unit -characters, which sometimes behave more or less independently of one -another, is one which most biologists who have studied the phenomena of -inheritance appear to have arrived at. Zoologists are mostly of opinion -that these characters, or rather their precursors, exist as units in the -fertilised egg. Very varied have been the conceptions of the nature of -these biological units. Almost every biologist has given a name to his -particular conception of them. Thus we have the gemmules of Darwin, the -unit characters of Spencer, the biophors of Weismann, the micellæ of -Naegeli, the plastidules of Haeckel, the plasomes of Wiesner, the -idioblasts of Hertwig, the pangens of De Vries, and so on. It is -unnecessary to extend this list. It must suffice that almost every -investigator of the phenomena of inheritance believes in these units, and -calls them by a different name. Moreover, each clothes them with -characteristics according to his taste or the fertility of his -imagination. - - - Chemical Molecules - -These units behave in such a way as to suggest to us an analogy between -them and the chemical molecules. The sexual act would appear to resemble -a chemical synthesis in some respects. One of the most remarkable -phenomena of chemistry is that of isomerism. It not infrequently happens -that two very dissimilar substances are found, upon analysis, to have the -same chemical composition, that is to say, their molecules are found to -be composed of the same kind of atoms and the same number of these. Thus -chemists are compelled to believe that the properties of a molecule are -dependent, not only on the nature of the atoms which compose it, but also -on the arrangement of these within the molecule. To take a concrete -example: Analysis shows that both alcohol and ether are represented by -the chemical formula C_{2}H_{6}O. In other words, the molecule of each of -these compounds is made up of two atoms of the element Carbon, six of the -element Hydrogen, and one of the element Oxygen. Now, every chemical atom -possesses the property which chemists term valency, in other words, the -number of other atoms with which it can directly unite is strictly -limited. All atoms of the same element have the same valency. Monovalent -atoms are those which can, under no circumstances, unite with more than -one other atom. The Hydrogen atom is an example of such an atom. Divalent -atoms, as, for example, that of Oxygen, can unite with one other atom of -similar valency or with two monovalent atoms. Similarly, a trivalent -atom, such as that of Nitrogen, can unite with three monovalent atoms. A -tetravalent atom, such as that of Carbon, can combine with four -monovalent atoms. There are also pentavalent and hexavalent atoms. Now, -by indicating the valency of any given atom by a stroke for each -monovalent atom with which it is able to combine, chemists have been able -to represent the molecule of every compound, or, at any rate, of every -inorganic compound, by what is known as a graphic or structural formula. -Thus, ethylic alcohol is represented by the formula:-- - - H H - | | - H--C--C--O--H = C_{2}H_{6}O, - | | - H H - -and methylic ether by the structural formula:-- - - H H - | | - H--C--O--C--H = C_{2}H_{6}O. - | | - H H - -The formulæ indicate a very different arrangement of the nine atoms which -compose the molecule in each case. And to this different arrangement the -differing properties of the two compounds are supposed to be due. A rough -illustration of the phenomenon of isomerism is furnished by written -language. Thus, three different words can be made from the letters t, a, -and r, _e.g._ tar, art, and rat. They also form tra, which does not -happen to be an English word, although it might have been one. - - - Experiments of Gräfin von Linden - -Among organisms we sometimes observe a phenomenon which looks very like -isomerism. The classical example of this is furnished by the butterflies -_Vanessa prorsa_ and _Vanessa levana_. - -At one time these were supposed to belong to different species, since -they differ so greatly in appearance. _Vanessa levana_ is red, with black -and blue spots. _Vanessa prorsa_ is deep black, with a broad -yellowish-white band across both wings. It is now known that the _levana_ -is the spring form and the _prorsa_ the summer and autumn form of the -same species. The pupæ of _levana_ produce the _prorsa_ form, but -Weismann found that after being placed in a refrigerator they emerged, -not as _prorsa_, but partly as _levana_ and partly as another form -intermediate in many respects between _levana_ and _prorsa_. Weismann -also succeeded, by exposing the winter pupa to a high temperature, in -making it give rise to the _prorsa_ form, and not to the _levana_ form, -as it would ordinarily do. - -Similar results have been obtained with the seasonally dimorphic _Pieris -napi_. Standfuss, the Gräfin von Linden, and others have obtained like -results in the case of other seasonally dimorphic butterflies. In some -instances it has been proved that the change in the pigment is a purely -chemical one; a similar transformation can be effected in the extracted -pigment. But, we must bear in mind that the changes which are induced in -this way are not confined to colour; they occur in the marking and shape -of the wing. - -Even more remarkable is the fact that in some sexually dimorphic species -a change of temperature alters the female, so as to cause her to have the -outward appearance of the male. For example, it has been found that -warmth changes the colours of the female _Rhodocera rhamni_ and -_Parnassius apollo_ into the colours of the male. - -By applying rays of strong light, electric shock, or centrifuge, the -Gräfin von Linden was able to change the colours of the butterflies to -which the caterpillars gave rise. Pictet experimented on twenty-one -species of butterflies, or rather on their caterpillars, and found that -in nearly all cases when the caterpillars ate unusual food, they -developed into butterflies with abnormal colouring. Schmankewitsch made -the discovery that, in the case of the crustacean _Artemia_, he could -produce either of two species according to the amount of salt in the -water in which these creatures were placed. He declared that the -anatomical differences between the species _Artemia salina_ and _Artemia -milhausenii_ depended solely on the percentage of the salt in the -surrounding water. He further stated that by adding still more salt he -could change the _Artemia_ into a new genus--_Branchipus_. More recent -observers have cast doubt upon these results of Schmankewitsch. They, -however, admit that the degree of salinity of the water has some effect -on the form of the _Artemia_, although they suggest that factors other -than concentration affect the result. In any case, it is now well-known -that changes in the environment effect changes in the colouring of many -crustacea. Pictet has shown that the alternating wet and dry seasons in -some tropical countries are the cause of, or stimulus that induces, -seasonal dimorphism in some butterflies. He was able to effect changes in -the colouring of certain species by means of humidity. - -The most important cases, from our point of view, are those in which the -application of heat or cold to a pupa has affected the colour, shape, -etc., of the emerging butterfly. Here we have but one factor, that of -temperature. All the material for the formation of the butterfly is -already stored up in the pupa. The unit characters, or their precursors, -are all there, and they take one form or another according to the -stimulus applied. - - - Biological Isomerism - -Phenomena of this kind can, we think, be accounted for only on the -assumption that the unit characters affected are each developed from a -definite portion of the fertilised egg, that each of these portions, -these precursors of the unit characters, is, like a chemical molecule, -made up of a number of particles, and that upon the arrangement of these -particles in its precursor in the egg depends the form that the unit -character derived from it will take. One arrangement of these particles -gives rise to one form of unit character, while another arrangement will -give rise to a totally different form of unit character. - -Thus, some organisms seem to display a biological isomerism akin to -chemical isomerism, save that the particles which in organisms take the -place of chemical atoms are infinitely more complex. - -In other words, the precursors in the fertilised egg of each of these -unit characters behave in some respects like chemical molecules. - -In order to avoid the manufacture of fresh terms we may speak -figuratively of the germ cells as being composed of biological molecules, -which in their turn are built up of biological radicles and atoms. These -behave in some ways like chemical molecules, radicles, and atoms, as the -case may be. - - - Biological Molecules - -It seems legitimate to regard each unit character in the adult as the -result of the development of one or more of the biological molecules -which compose the nucleus of the fertilised egg. These biological -molecules are, of course, a million-fold more complex than chemical -molecules. Each biological atom must contain within itself a number of -the very complex protoplasmic molecules. This view of the structure of -the germ cell seems to force itself upon the observer. Notwithstanding -this, the conception will have no value unless it seems to throw light on -the various phenomena of heredity, variation, etc. - -Let us then try to interpret some of these. - -Each chemical element is made up of atoms which are all of the same kind, -but no two elements are made up of the same kind of atoms, although -chemists are now inclined to conceive of all the various kinds of atoms -as made up of varying amounts of some primordial substance. In any case, -the molecules of chemical compounds are made up of various kinds of -atoms. With biological atoms the case would seem to be different. All -would appear to be made up of the same kind of substance, and the -differences shown by the various unit characters that go to make up an -organism would seem to be due to the different numbers and the varying -arrangement of the biological atoms which compose the molecules from -which unit characters are derived. This would be quite in accordance with -the chemical notion of allotropy. Thus, the graphite and the diamond -molecules are both made up of the same kind of atoms. - -But the biological atoms are living, that is to say, they are continually -undergoing anabolism and katabolism, growth and decay. They exhibit all -the phenomena of life, they must grow and divide, and they must absorb -nourishment; hence it is not surprising that they should differ slightly -among themselves, that they should exhibit the phenomenon of variation. -Although probably all are composed of the same living material, no two -are exactly alike, hence the molecules formed by them will also differ -from one another. Thus we can see why it is that all organisms exhibit -fluctuating variations. - -Very different are the discontinuous variations or mutations. These would -seem to be due to either a rearrangement of the biological atoms in the -biological molecule or the splitting up of the latter into two or more -molecules. This, of course, is pure hypothesis. Let us take an imaginary -example. Suppose that a biological molecule contains eighteen biological -atoms, and that these are arranged in the form of an equilateral -triangle, six of them going to each side. Suppose now, that from some -cause or other they rearrange themselves to form an isosceles triangle, -so that only four form the base and seven go to each of the remaining -sides. Such an arrangement would give rise to a mutation. Suppose now -that, from some cause or other, this triangular biological molecule were -to split up into two triangles, each having three atoms to each side, we -should obtain a still more marked mutation. We are far from saying that -the atoms in the organic molecule ever take such forms. We have merely -attempted to give rough but simple illustrations of the kind of processes -which on this hypothesis might be expected to take place in the germ -cells or the fertilised eggs. - -Let us now consider the sexual act from this aspect. The various -molecules (we speak, of course, of biological molecules) of the male -parent meet those of the female parent, and a synthesis occurs, which -results in the formation of a new organism. When these two sets of -gametes meet one another, one of several events may happen. The gametes -may refuse to combine. This will occur whenever they are of very -different constitution; thus it is that widely differing species will not -interbreed. But it may even happen that gametes of individuals of the -same species may refuse to coalesce on account of some peculiarity in the -composition of one or other of them. Secondly, they may be able to form -some sort of a union, but, owing to their diverse nature, the resulting -molecules may be so complex that they cannot be broken up into equal -halves, and as this seems to be necessary for the sexual act, the -resulting organism will be sterile. Thirdly, the two sets of gametes may -enter into a proper union, that is to say, form new molecules, but these -may be of such different structure to the molecules of the gametes, that -the resulting offspring will be quite unlike their parents in appearance. -Fourthly, some or all the groups of radicles in each gamete may be united -so closely that in the sexual act they do not break up, but enter bodily -into the new resulting organism. In these circumstances the inheritance -of the offspring will follow Mendel's law. Fifthly, there may be some -slight disturbance of the molecule, perhaps one or only a few atoms will -be replaced by those of the other gamete. This would give us impure -dominance. - -Thus this hypothesis appears to be compatible with the various modes of -inheritance. - -The curious phenomenon known as prepotency would seem also to be quite in -accordance with the conception. - -In chemical reactions the tendency is for the most stable combinations to -be formed, so in nature. - -We may probably go farther and say, not only will the most stable -biological molecules be formed, but the most stable radicles will -dominate the molecule. Hence, if any two animals are crossed and the -offspring show alternate inheritance, the resulting organism will, in the -case of each unit character, display the most stable of the pair; in -other words, it will take after the parent which happens to have the -greater stability as regards that particular character. The difference -between the mule and the hinny would seem to be explicable on this -supposition. If the union were like a simple chemical synthesis it should -not make any difference which way the cross were made. But if the species -crossed are of varying stability, and if their respective degrees of -stability vary with the sex, it is easy to see that it will make a -difference how the animals are crossed. - -In the cases of creatures that obey Mendel's law, the most stable form of -a unit character will presumably be the dominant one. - -One of the most curious of the phenomena of inheritance is that of -correlation. We shall deal with this more fully in Chapter VIII. It will -suffice here to say that certain characters appear to be linked together -in organisms. Such seem to be transmitted in pairs. The offspring never -exhibits one of such a correlated couple without exhibiting the other -also. - -It would thus seem that certain combinations of biological atoms, certain -molecules, can only exist in conjunction with certain other combinations. -This is quite in accordance with the teaching of physiologists regarding -the interdependence of the various organs of the body. We have now -reached the stage of the fertilised ovum. According to our conception it -is a series or conglomeration of the precursors of the unit characters of -the adult. These precursors we call biological molecules. Each is of a -very complex nature. Each seems to be composed of several portions, only -one of which will take part in the building up of the body of the -offspring, the other portions remaining latent. We further conceive that -it is possible for the various radicles which compose these molecules to -arrange themselves in various manners, and with each new arrangement a -different form of unit character will be developed. These molecules, -then, are built up from radicles derived from both parents, the most -stable combinations being formed and one portion of the molecule -dominating the whole. Under normal circumstances this dominant portion of -the molecule will give rise to a character of a definite type. But it -seems that other factors may come into play and cause a rearrangement of -the radicles which compose it, and this will result in the formation of a -unit character different from that to which it would ordinarily give -rise. - -But, it may be objected, if the colour of an organism be derived from one -of these so-called biological molecules, how is it that it affects the -whole organism, or, at any rate, several of the other unit characters? -The objection may be met in several ways. In the first place, the -colour-forming molecules may split up into as many portions as there are -units which it affects, and each portion may attach itself to a unit. Or -the property which we call colouration may not be derived from a -molecule, it may be an expression in the relative positions of the -various molecules in the fertilised egg. Or the colour-determining -molecule may secrete a ferment or a hormone, and this may be the cause of -the particular colouring of the resulting organism. We do not pretend to -say which (if any) of these alternative suppositions is the correct one. -But it seems to us that some such conception as that which we have set -forth is forced upon us by observed facts. This conception should be -regarded not as a theory, but rather as an indication of the lines along -which we believe the study of inheritance could best be made. - -The fertilised ovum has nothing of the shape of the creature to which it -will give rise. It is merely a potential organism, a something which -under favourable conditions will develop into an organism. - - - Phenomenon of Sex - -In the higher animals each individual is either of the male or the female -sex. A vast amount of ingenuity has been expended by zoologists in the -attempt to ascertain what it is that determines sex. Many theories have -been advanced, but no one of them has obtained anything like general -acceptance, because its opponents are able to adduce facts which appear -to be incompatible with it. - -It is tempting to try to interpret the phenomenon of sex on the -assumption that the female-producing biological molecule or unit is an -isomeride of the male-producing cell. Certain facts, however, seem to -negative the idea, as, for example, the occasional appearance in an -individual of one sex of characteristics of the other sex. - -Possibly the attempts to explain the phenomena of sex-production on a -Mendelian basis may prove to be more successful. It seems not impossible -that each fertilised egg contains material which is capable of developing -into male generative organs and material which is capable of developing -into female generative organs, but that only one kind of material, that -which dominates, succeeds in developing. The number of what are known as -"X-elements" that happen to be present in the fertilised egg appear to -decide which kind of material is to be dominant. - -But the problem of the determination of sex, fascinating though it be, is -not one that can be discussed adequately in a general work on evolution. -Those interested in the subject are referred to Professor Thomson's -_Heredity_, and to the address given by Professor E. B. Wilson, of -Columbia University, before the American Association for the Advancement -of Science, which was fully reported in the issue of _Science_, dated -January 8, 1909. - -Stated briefly, then, our conception is, that the fertilised egg is -composed of a number of entities, to which we have given the name -"biological molecules," because in certain respects their behaviour is -not unlike that of chemical molecules. - -The units which compose these molecules, being made up of protoplasm, are -endowed with all the properties of life, including the inherent -instability which characterises all living matter. - -We suggest that the continuous or fluctuating variations that appear in -the adult organism may be the result of individual differences in the -biological "atoms" that compose the molecule. - -Discontinuous variations, or mutations, on the other hand, may be the -result of a rearrangement of the atoms within the biological molecule. -Upon what causes this rearrangement it would not be very profitable to -speculate in the present state of our knowledge. To do this would be to -inquire into the cause of a re-grouping of entities of the existence of -which we are not certain! For aught we know there may be an intracellular -struggle for nourishment among the various molecules and among the atoms -which compose the molecules. If one molecule enjoys any special advantage -over the others the result may be an unusual degree of development of the -resulting unit character; in other words, the result will be a variation -in the organism. This variation may prove favourable or unfavourable to -its possessor. - - - Struggle for Nourishment - -Certain phenomena seem to point to a struggle for nourishment between the -germinal and the somatic portions of the egg, between the parts from -which the sexual cells of the resulting organism are produced and those -which give rise to the body of the organism. Each molecule may strive, so -to speak, to increase at the expense of the others. Thus, great size in -an organism is likely to be produced at the expense of the germinal -cell-forming molecules. In other words, great size in an organism would -be incompatible with excessive fecundity. This is what we observe in -nature. On the other hand, poor development of bodily tissue, as in the -case of intestinal parasites, would be correlated with great fecundity. -Some organisms are mere sacs full of eggs. - -Success in the struggle for nourishment of one molecule might be shared -by the other molecules near to it, hence the phenomena of correlation. - -It is thus conceivable that, in a brood consisting of several -individuals, a particular molecule or set of molecules in one of the -individuals may receive more than its share of nourishment, and this will -result in the organs of that individual which spring from the -well-nourished molecules being exceptionally well developed. Thus arises -the phenomenon of differences between the members of a litter or brood. - -Natural selection will tend to eliminate those individuals in which the -resulting variation is an unfavourable one. If the environment is such, -as in the case of an internal parasite, that the production of germ cells -is the most necessary function of the organism, then those individuals in -which the germ-forming molecules increase at the expense of the -body-forming ones will tend to be preserved. This would cause the -phenomenon which biologists term degeneration. The nourishment of the -various biological molecules may possibly depend on their relative -positions in the egg. Those in a favourable position will then tend to -develop at the expense of the others. This will result in variation along -definite lines. Each succeeding generation will tend to an increased -development of that particular organ to which the favourably-situated -molecule gives rise. This process may continue, as in the case of the -horns of the Irish elk, until the development of that particular organ -becomes so excessive as to be positively injurious; then natural -selection will step in and eliminate the species. But before this -happens, something may cause a rearrangement of the biological molecules -in the fertilised egg, and thus a mutation may arise, which, so to speak, -strikes out a new line. - - - Origin of Mutations - -Finally, on this conception there may be some sort of connection between -fluctuating variations and mutations. We can picture the fluctuating -variations being piled up, one upon the other, until there results a -rearrangement of the atoms in one or more of the biological molecules -which, in turn, causes a mutation. - -Occasionally this remodelling, as it were, of one biological molecule may -affect certain of the other molecules, and thus lead to correlated -mutations. - - - - - CHAPTER VI - THE COLOURATION OF ORGANISMS - - - 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 Müllerian - 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--Illustrative 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--Objections 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 - recognition 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. - -Since the publication of _The Origin of Species_, naturalists have paid -much attention to the colouration of animals and plants, with the result -that a large majority of scientific men to-day hold the belief that all, -or nearly all, the colours displayed by animals are of direct utility to -them, and are therefore the direct result of natural selection; a few -would add, "and of sexual selection." - -"Among the numerous applications of the Darwinian theory," writes -Wallace, "in the interpretation of the complex phenomena, none have been -more successful than those which deal with the colours of animals and -plants." - - - Robinson on Protective Colouring - -We readily admit that the Darwinian theory has thrown a great deal of -light on the phenomenon of animal colouration; it has reduced to -something like order what was before Darwin's time chaos. While admitting -this we feel constrained to say that many naturalists, especially Dr -Wallace and Professor Poulton, have pushed the various theories of animal -colouration to absurd lengths. As Dr H. Robinson truly says (_Knowledge_, -January 1909), "It seems to have been taken for granted, and some even of -Dr Wallace's writings may be interpreted in this sense, that protective -colouring is necessary to the continued existence of every species, and -that, sexual colouration apart, it is incumbent on naturalists to offer -ingenious speculations in this sense to account for the appearance even -of the most bizarre and conspicuous beasts. Thence it has been but a -short step to the announcement of those speculations as further evidence -in favour of natural selection, and of various assumptions made in the -speculative process as indisputable facts." - -The result of this is that men have ceased to regard the Neo-Darwinian[6] -theories of protective colouration, mimicry, and recognition markings as -mere hypotheses which seem to throw light on certain phenomena in the -organic world. These theories have assumed the rank of laws of nature. To -dispute them would seem to be as futile as to assert that the earth is -flat. To take exception to them would appear to be as ridiculous as to -object to Mont Blanc. To dare to criticise them is heresy of the worst -type. - -Be this as it may, scientific dogma or no scientific dogma, scientific -opinion or no scientific opinion, we have dared to weigh these theories -in the balance of observation and reason, and have found them wanting. We -have examined these mighty images of gold, and silver, and brass, and -iron, and found that there is much clay in the feet. - -We shall devote this chapter to lifting the hem of the garment of -sanctity that envelopes each of these images, and so expose to view the -clay that lies concealed. - -We propose, first, to set forth in outline what we trust will be -considered a fair statement of the various theories of animal colouration -which are generally accepted to-day, then to show up the various weak -points in these, and lastly, to endeavour to ascertain whether there are -not some alternative explanations in certain cases to which the -generally-accepted theory does not apply. - - - Cryptic Colouring - -Neo-Darwinians divide the various forms of colouration into three great -classes:--(1) Cryptic colouring, or protective and aggressive -resemblances; (2) sematic colours, or warning and recognition colours; -and (3) pseudo-sematic colours, or mimicry. A tabular statement of this -scheme of colouring will be found on pp. 293-7 Professor Poulton's -_Essays on Evolution_. - -As regards class (1), Neo-Darwinians point out that the great majority of -animals are so coloured as to make them very difficult to see in their -natural environment, hence the whiteness of the creatures which inhabit -the snow-bound Arctic regions, the sandy colour of desert animals, the -spotted coats of creatures which live among trees, the striped markings -of animals which spend their lives amid long grass, and the transparent -blueness of pelagic animals. The theory is that all kinds of animals, -whether those that hunt or those that are hunted, derive much advantage -from being coloured like their environment. The hunted creatures are -thereby the better able to elude the vigilance of their foes, while those -that hunt are in a position to take their quarry by surprise; so that -natural selection has caused them all to assimilate to the hues of their -surroundings. Neo-Darwinians point to the fact that some Arctic animals -are brown in the summer to match the ground from which the snow has -melted, and turn white in winter to assimilate with their snowy -background. Naturalists further cite, as evidence in favour of this -theory, the case of those creatures which imitate inanimate objects, such -as leaves and twigs, and thereby escape the observation of their foes. - -Thus, the great majority of animals are supposed to be cryptically -coloured, that is to say, coloured so as to be, if not quite invisible, -at least very inconspicuous in their natural habitat. - - - Warning Colouration - -It is, however, generally admitted that many creatures are not -cryptically coloured. Some, indeed, seem to be coloured in such a way as -to render them as conspicuous as possible. The Neo-Darwinians declare -that there is a reason for this. "If," writes Professor Milnes Marshall -(page 133 of his _Lectures on the Darwinian Theory_), "an animal, -belonging to a group liable to be eaten by others, is possessed of a -nauseous taste, or if an animal, such as a wasp, is specially armed and -venomous, it is to its advantage that it should be recognised quickly, -and so avoided by animals that might be disposed to take it as food. - -"Hence arises warning colouration, the explanation of which is due to -Wallace. Darwin, who was unable to explain the reason for the gaudy -colouration of some caterpillars, stated his difficulty to Wallace, and -asked for suggestions. Wallace thought the matter over, considered all -known cases, and then ventured to predict that birds and other enemies -would be found to refuse such caterpillars if offered to them. This -explanation, first applied to caterpillars, soon extended to adult forms, -not only of insects, but of other groups as well. . . . Insects afford -many admirable examples of warning colours, and many well-known instances -occur among butterflies. The best examples of these are found in three -great families of butterflies--the _Heliconidæ_, found in South America, -the _Danaidæ_, found in Asia and tropical regions generally, and the -_Acræidæ_ of Africa. These have large but rather weak wings, and fly -slowly. They are always very abundant, all have conspicuous colours or -markings, and often a peculiar form of flight, characters by which they -can be recognised at a glance. The colours are nearly always the same on -both upper and under surfaces of the wings; they never try to conceal -themselves, but rest on the upper surfaces of leaves and flowers. -Moreover, they all have juices which exhale a powerful scent; so that, if -they are killed by pinching the body, a liquid exudes which stains the -fingers yellow, and leaves an odour which can only be removed by repeated -washing. This odour is not very offensive to man, but has been shown by -experiment to be so to birds and other insect-eating animals. - -"Warning colours are advertisements, often highly coloured -advertisements, of unsuitability as food. Insects are of two kinds--those -which are extremely difficult to find, and those which are rendered -prominent through startling colours and conspicuous attitudes. Warning -colours may usually be distinguished by being conspicuously exposed when -the animal is at rest. Crude patterns and startling contrasts in colour -are characteristically warning, and these colours and patterns often -resemble each other; black combined with white, yellow, or red, are the -commonest combinations, and the patterns usually consist of rings, -stripes, or spots." - -We trust that we shall be forgiven for this lengthy quotation. Our object -in reproducing so large an extract is to allow the Neo-Darwinians to -speak for themselves. Were we to state their theory in our own words, we -might perhaps be charged with stating it inaccurately. We should add -that, even as natural selection is supposed to have been the cause of -conspicuous colouring in some organisms, so has it caused others to -assume intimidating attitudes or emit warning sounds, such as a hiss, -when attacked. - - - Batesian Mimicry - -We now come to the third great class of animal colours--mimetic colours. -Mimicry is of two kinds, known respectively as Batesian and Müllerian -mimicry, after their respective discoverers. - -It has been found that some apparently warningly coloured butterflies and -other creatures are palatable to insectivorous animals. The explanation -given of this is that these showy but edible butterflies "mimic," that is -to say, have the appearance of, show a general resemblance to, species -which are unpalatable. This is known as Batesian mimicry. "Protective -mimicry," writes Professor Poulton (_Essays on Evolution_, p. 361), "is -here defined as an advantageous superficial resemblance of a palatable -defenceless form to another that is specially defended so as to be -disliked or feared by the majority of enemies of the groups to which both -mimic and model belong--a resemblance which appeals to the senses of -animal enemies . . . but does not extend to deep-seated characters, -except when the superficial likeness is affected thereby." - -As Wallace has pointed out, five conditions must be satisfied before such -protective mimicry can occur:-- - -"1. That the imitative species occur in the same area and occupy the same -station as the imitated. 2. That the imitators are always the more -defenceless. 3. That the imitators are always less numerous in -individuals. 4. That the imitators differ from the bulk of their allies. -5. That the imitation, however minute, is external and visible only, -never extending to internal characters or to such as does not affect the -external characters." (_Darwinism_, Chap. ix.) - -Thus the mimic is supposed to deceive his enemies by deluding them into -the belief that he is the inedible species which they once tried to eat -and vowed never again to touch, so nasty was it. The mimic, then, may be -compared to the ass in the lion's skin. Needless to say, this mimicry is -quite unconscious. It is supposed to have been developed by natural -selection. Every popular book on Evolution cites many examples of such -mimicry. We may therefore content ourselves with mentioning but a few. - - - Examples of Mimicry - -Our common wasps are copied by a beetle (_Clytus arietis_), active in -movement and banded black and yellow, and by several yellow-barred -hover-flies (_Syrphidæ_); and the bumble-bee by a clear-winged moth -(_Sesia fuciformis_). There is, indeed, a whole group of these -clear-winged moths, resembling bees, wasps, and other stinging -hymenoptera. The common Indian Danaid butterfly, _Danais chrysippus_, is -marvellously reproduced by the female of _Hypolimnas misippus_, a form -allied to our Purple Emperor. The male of this is black, with white -blue-bordered patches, the female chestnut, edged with black and with -white spots at the tips of the wings, as in the _Danais_. Finn has shown -experimentally that this species is liked by birds. - -Another common Indian Danaid (_D. limniace_), black, spotted with pale -green, is imitated, though not very closely, by the female of one of the -"white" group, _Nepheronia hippia_. Finn found that this insect was eaten -freely by birds, and that the common jungle-babbler (_Crateropus -canorus_) was deceived by the mimicry of the female. The very nauseous -Indian swallow-tail (_Papilio aristolochiæ_) is closely imitated by -another swallow-tail (_P. polites_), both having black wings marked with -red and white; _P. aristolochiæ_, however, has a red abdomen. This -difference was not noticed by two species of Drongo-shrikes (_Dicrurus -ater_ and _Dissemurus paradiseus_), to which the butterflies were -offered; but the Pekin robin (_Liothrix luteus_)--a very intelligent -little bird--did not fail to pick out and eat the mimic, though it was -deceived by the marvellously perfect imitation of _Danais chrysippus_, by -the female of the _Hypolimnas_. - -Such resemblances can therefore be effective. - -The cases of mimicry usually quoted include very few among mammals, -probably, as Beddard suggests, because the species of that class are -relatively few. - -The insectivorous genus _Tupaia_ is supposed to mimic the squirrels, -which it much resembles as regards form in all respects save the long -muzzle; the idea being that squirrels are so active that carnivorous -animals find it hopeless to pursue them. - -On the other hand, there is a squirrel (_Rhinosciurus tupaioides_) which -is supposed to mimic the tupaias! It has a similar long muzzle, and the -light shoulder-stripe which is a common marking in tupaias. But why the -squirrel, one of the group imitated, should in turn become an imitator is -not explained. - -The true interpretation of the resemblance is probably that both -squirrels and tupaias are adapted to a life in trees. Like profession -begets like appearance: the ground-living shrews much resemble mice, and -the moles find representatives in mole-like rodents. - -Another case, however, wherein true mimicry may have come into play is -that of the South American deer (_Cervus paludosus_) which singularly -resembles in colouration the long-legged wolf or _Aguara-guazu_ (_Canis -jubatus_). Both these species are chestnut in colour, with the front of -the legs black, and the ears lined with white hair; both inhabit the same -regions in South America. - - - Müllerian Mimicry - -The second kind of mimicry--Müllerian mimicry--is where one unpalatable -creature resembles another. This form of mimicry is named after Fritz -Müller, who suggested the explanation now usually accepted, namely, that -"Life is saved by a resemblance between the warning colours in any area, -inasmuch as the education of young inexperienced enemies is facilitated, -and insect life saved in the process." "It is obvious," writes Poulton -(p. 328 of _Essays on Evolution_), "that the amount of learning and -remembering, and consequently of injury and loss of life involved in -these processes, are reduced when many species in one place possess the -same aposematic colouring, instead of each exhibiting a different danger -signal. . . . The precise statement of advantage was made by Mr Blakiston -and Mr Alexander, of Tokio. 'Let there be two species of insects equally -distasteful to young birds, and let it be supposed that the birds would -destroy the same number of individuals of each before they were educated -to avoid them. Then if these insects are thoroughly mixed and become -undistinguishable to the birds, a proportionate advantage accrues to each -over its former state of existence. These proportionate advantages are -inversely in the duplicate ratio of the respective percentages that would -have survived without the mimicry.'" - -This is rather a cumbrous method of saying that if there are in a -locality a number of young birds, and each of these has to learn by -experience which insects are edible and which are not, each will, if it -learns by one example, devour one insect of any given pattern. Now, if -two species of inedible insects have this pattern, they will between them -lose only one member in the educating process of each bird, whereas if -each species of insect had a colouration peculiar to itself, each species -would lose a whole individual instead of half a one. There can be no -doubt that such a livery of unpalatability is of some advantage to its -possessors. - -It has been shown experimentally that hand-reared young birds have to -acquire their knowledge of flavours and colours by experiment. - -It is well known that in many species the male and the female are not -coloured alike. Such species are said to exhibit sexual dimorphism. In -these cases it is usually the male that is more conspicuously coloured. -Darwin felt that the theory of natural selection could not satisfactorily -account for this phenomenon, so put forward the supplementary theory of -sexual selection. On this hypothesis the females are supposed to be able -to pick and choose their mates, and to select the most beautiful and -ornamental ones, hence the greater showiness of these in most sexually -dimorphic species. Wallace does not accept this theory. He thinks it -unnecessary. He looks upon the brilliant colouring of the males as due to -their superior vigour; moreover, he says that it is the hen that sits -upon the eggs, and so requires a greater degree of protection than the -male, and therefore natural selection has not permitted her to develop -all the ornaments displayed by the cock. With the phenomenon of sexual -dimorphism we shall deal at length in the next chapter. - - - Danger Signals - -Dr Wallace recognizes yet another exception to the rule that animals are -cryptically coloured. Many creatures possess on the body markings which -tend to render them conspicuous rather than difficult to see. Where such -markings occur on gregarious animals, Wallace believes that they have -been evolved by natural selection, either to enable their possessors to -recognize one another, or to act as a danger signal to their fellows. The -white tail of the rabbit is believed by Wallace to serve as a danger -signal. The first member of the company to espy the approaching foe takes -to his heels, and, as he moves, his white tail catches the eye of his -neighbour, who at once follows him, so that, in less time than it takes -to tell, the whole company of rabbits is scampering towards the burrow, -thanks to the white under-surface of the tail. - -Even as Wallace out-Darwin's Darwin, so does Mr Abbott Thayer, an -American naturalist and artist, out-Wallace Wallace. That gentleman seems -to be of opinion that _all_ animals are cryptically or, as he calls it, -concealingly or obliteratively coloured. Even those schemes of colour -which have hitherto been called conspicuous are, he asserts, "purely and -potently concealing" when looked at properly, that is to say, with the -eye of the artist. - -Lest it be thought unnecessary to criticize a hypothesis which appears to -be based upon the assumption that animals see with the eye of the artist, -we may say that Professor Poulton writes approvingly of Thayer's theory. -He frequently alludes to it in his _Essays on Evolution_, and he -published an account of it in the issue of _Nature_, dated April 24, -1902. Moreover the hypothesis has been enunciated in such scientific -journals as _The Auk_ (1896) and _The Year-Book of the Smithsonian -Institution_ (1897). - -Thayer asserts that all animals, or at any rate the great majority, -including many that are usually supposed to be conspicuously coloured, -are in reality obliteratively coloured--that is to say, coloured in such -a way that the effects of light and shade are completely counteracted, -with the result that they are invisible. - - - Obliterative Colouring - -It is possible, says Mr Thayer, to almost obliterate a statue in a -diffused light, by putting white paint on the surfaces in darkest shadow -and dark paint on the most brightly lighted parts, all in due proportion. -Now this is precisely what nature is supposed by Mr Thayer to have done -for all her creatures. - -It is well known that a great many animals, as for example the Indian -black-buck and the hare, are coloured on the upper side and white below. -This is called by Mr Thayer the principle of the gradation of colour. It -runs, he declares, all through the animal world, and is "the main -essential step toward making animals inconspicuous under the descending -light of the sky." - -Animals, he contends, are not protectively coloured to look like clods or -stumps or like surrounding objects, they are simply obliteratively -coloured--coated, as it were, with invisible paint. - -To quote from _The Century Magazine_ (1908): "Whales, lions, wolves, -deer, hares, mice; partridges, quails, sandpipers, larks, sparrows; -frogs, snakes, fishes, lizards, crabs; grasshoppers, slugs, -caterpillars--all these animals, and many thousands more, crawl, crouch, -and swim about their business, hunting and eluding, under cover of this -strange obliterative mask, the smooth and perfect balance between shades -of colour and degrees of illumination." - -Nature having thus visually unsubstantialized the bodies of animals, so -that, if seen at all, they look flat and ghostly, does not stop there. -From solid-shaded bodies they have been converted, as it were, into flat -cards or canvases, and, to complete the illusion of obliteration, -pictures of the background--veritable pictures of the more or less -distant landscape--have been painted on their canvases! Such in effect -are the elaborate "markings of field and forest birds." - -Again he writes: "Brilliantly changeable or metallic colours are usually -supposed to make the birds that wear them conspicuous, but nothing could -be further from the truth. Iridescence is, indeed, one of the strongest -factors of concealment. The quicksilver-like intershifting of many lights -and colours, which the slightest motion generates on an iridescent -surface, like the back of a bird or the wing of a butterfly, destroys the -visibility of that wing or back as such and causes it to blend -inextricably with the gleaming and scintillating labyrinthine-shadowed -world of wind-swayed leaves and flowers." - -According to Thayer, the skunk, which for years has been an important -item of the stock-in-trade of the advocates of the theory of warning -colouration, is an excellent example of obliterative colouring, since its -enemies are supposed to mistake for the sky-line the line of junction -between the white fur of the back and the dark fur of the sides. -Similarly the crocodiles are supposed to mistake a flamingo for the sky -at sunrise or at sunset! - -There is doubtless something in this theory of obliterative colouration. - -Any one can see, by paying a visit to the South Kensington Museum, that -an animal which is of a lighter colour below than above, is less -conspicuous in a poor light than it would be were it uniformly coloured. -There is then no doubt that this scheme of colour, which is so common in -nature, has some protective value. - -To this extent has Mr Thayer made a valuable contribution to zoological -science. But when he informs us that obliterative colouring is a -"universal attribute of animal life," we feel sorely tempted to poke fun -at him. - -We would ask all those who believe in the universality of obliterative -colouring to observe a flock of rooks wending their way to their -dormitories at sunset. - -Let us now pass on to the examination of the more orthodox theories of -animal colouration. - - - Objections to the Theory of Cryptic Colouring - -Before criticising the theory of cryptic colouring, we desire to state -distinctly that we admit that, where other things are equal, it is of -advantage to all creatures which hunt or which are preyed upon to be -inconspicuous. If difficult to distinguish amid their natural -surroundings, the former are likely to secure their prey readily, and the -latter have a chance of escaping from their enemies. Our quarrel is with -the theory of cryptic colouring as it is enunciated by many -Neo-Darwinians, with the theory that every hue, every marking, every -device displayed by an organism is of utility to the organism and has -been directly developed by natural selection. - -The extreme advocates of the theory of cryptic colouring have greatly -exaggerated the degree in which animals are assimilated to their natural -environment. - - - Fauna of Polar Regions - -We grant that a great many creatures, which when seen in a menagerie -appear very conspicuous, are the reverse of conspicuous when standing -motionless amid their natural surroundings. As Beddard has pointed out, -it is often not easy to find a sixpenny piece which has been dropped on -the carpet, but the reason for this is, not that the coin is protectively -coloured, but that any small object, no matter how coloured, is difficult -to distinguish amid a variegated environment. The assumption of a white -winter coat by many organisms that live in northern latitudes has been -cited, again and again, as showing how important it is for an animal to -be protectively coloured. If, it is urged, those creatures that live in -lands which are covered in snow for half of the year have become white in -winter by the action of natural selection in order to escape their foes, -it is obviously of paramount importance to all creatures that they should -be cryptically coloured. Popular books on natural history convey the -impression that during winter the snow-clad, ice-bound Arctic regions are -peopled by a fauna whose fur or hair rivals in whiteness the snowy mantle -of the earth. The impression thus conveyed is misleading. It is true that -an unusually large percentage of the animals that inhabit the polar -regions are white in winter, but the majority of the creatures which -dwell there do not assume the white garb of winter. - -As the fauna of the polar regions is a small one, we are able to give -lists of all the birds and mammals which dwell in the Arctic and the -Antarctic regions. We have arranged these in in three columns. In the -first are placed those creatures which are white throughout the year, in -the third those that retain their colour through the winter, while the -middle column contains those forms which change their colouring with the -season. - - ARCTIC FAUNA. - Mammals. - White. - Polar Bear. - Arctic Fox (some individuals). - White Whale or Beluga. - Changing with the Seasons. - Arctic Fox (most individuals). - Arctic Lemming. - Stoat. - Weasel. - Blue Hare. - Coloured. - Arctic Fox (sometimes). - Reindeer. - Musk-ox. - Glutton. - Moose. - Sable. - Seals. - Walrus. - Narhwal. - Greenland Whale. - Birds. - White. - Ivory Gull. - Snowy Owl. - Gyrfalcon. - Snow Goose. - Changing with the Seasons. - Black Guillemot. - Ptarmigans. - Snow Bunting (whitest in summer!) - Razorbill. - Little Auk (throat only becomes white). - Coloured. - Sea Eagle. - Greenland Redpoll (very pale). - All Arctic Geese and Ducks other than Snow Goose. - Raven. - Cormorant. - Brunnich's Guillemot. - Puffin. - Fulmar Petrel. - Ross's Gull. - Glaucous Gull (very pale). - Sandpipers. - - ANTARCTIC FAUNA. - Mammals. - White. - Antarctic White Seal (_Lobodon carcinophaga_), in some cases. - Changing with the Seasons. - None. - Coloured. - Other Seals than _Lobodon._ - Whales. - Birds. - White. - Sheathbill. - Snowy Petrel. - Giant Petrel (some individuals). - Chick of Emperor Penguin. - Changing with the Seasons. - None. - Coloured. - Penguins. - Cormorant. - Skua Gull. - Giant Petrel (usually). - Other Petrels. - -It will be observed that the third column contains the largest number of -forms. It is thus evident that the whiteness of the Arctic and Antarctic -faunas in winter has been greatly exaggerated. - -The Arctic fox appears in all three columns, as the creature seems to -fall into three races--a permanently white race, a permanently coloured -race, and a seasonally dimorphic race. - -Of the creatures set forth in the middle column of the above tables all -are whiter in winter than in summer with the exception of the snow -bunting, who sets at naught the theory of cryptic colouring by turning -darker in winter! The same may be said of the Alpine chamois. - -The advocates of the theory of protective colouring assert that the -creatures which do not turn white in winter are strong and active animals -which have no enemies to fear. - -This contention is met by F. C. Selous as follows (_African Nature Notes -and Reminiscences_, p. 9): "According to the experience of Arctic -travellers, large numbers of young musk oxen are annually killed by -wolves. . . . Nothing, I think, is more certain than that a far smaller -percentage of so-called protectively coloured giraffes are killed -annually by lions in Africa than of musk oxen by wolves in Arctic -America." - -Another difficulty which confronts the Neo-Wallaceian school is that, _ex -hypothesi_, the assumption of the white coat was gradual. Hence the -change in the direction of whiteness cannot, in its first beginning, have -been of perceptible utility to an organism. How then can natural -selection have operated on it? - - - Pelagic Organisms - -The transparency of pelagic organisms is frequently cited as exemplifying -cryptic colouring. We all know that the common jelly-fish is as -transparent as glass. Floating on the surface of the ocean are millions -of tiny organisms, so transparent as to be invisible to the human eye. At -first sight this certainly appears to be a remarkable case of protective -colouring. Unfortunately, nearly all the more highly developed forms -display conspicuous pigment (as in most jelly-fish) in some part of the -body. - -"An animal floating about in the sea," writes Beddard, "perfectly -transparent, but decked with dense black patches, of the size of saucers, -would betray its whereabouts even to the least observant; if the observer -were stimulated by hunger or fear, the conspicuousness would not be -lessened. . . . Besides the internecine warfare which is continually -going on amongst the smaller surface organisms, they are devoured -wholesale by the larger pelagic fish, and by whales and other Cetacea. A -whale, rushing through the water with open mouth and gulping down all -before him, is not the least inconvenienced by the invisibility of the -organisms devoured in such enormous quantities; nor do a solid phalanx of -herring or mackerel stop to look carefully for their food: they take what -comes in their way, and get plenty in spite of 'protective absence of -colouration.' - -"If the transparency of the pelagic organisms be due entirely to natural -selection, it is remarkable that there is so little modification in this -direction among the species inhabiting the bottom at such depths as are -accessible to the sun's rays; the advantage gained by this transparency -and consequent invisibility would be equally great. And yet this is not -the case; the bulk of the bottom fauna of the coasts are brilliantly -coloured animals, and those that show any protective colouring at all -appear to be coloured so as to resemble stones or sea-weeds."[7] - -Before leaving the subject of marine animals, we may point out that the -majority of the creatures that live in the everlasting blackness of the -depths of the ocean display exceedingly conspicuous colouring, and this -colouring seems to be constant. In such cases the colouring cannot be -useful as such to its possessors. The same may be said of the colour of -blood, or of the colouring of the internal tissues of all organisms. We -must not lose sight of the fact that every organism, and every component -part thereof, must of necessity be either of some colour or perfectly -transparent. It seems to us that since the appearance of _The Origin of -Species_ zoologists have tended to exaggerate the importance of colouring -to organisms; they frequently speak of it as though it were the one and -only factor in the struggle for existence. It is on this account that -they feel it incumbent upon them to find ingenious explanations for every -piece of colouring displayed by every plant or animal. - - - Unimportance of Colour - -The tendency to exaggerate the importance to an animal of its colouring -is doubtless in large part due to the fact that many zoologists are -content to study nature in museums rather than in the open. Some of those -who observe organisms in their natural surroundings, especially in such -favourable localities as the tropics, seem to be of opinion that natural -selection has but little influence on the colouration of organisms. - -Thus D. Dewar writes (_Albany Review_, 1907): "Eight years of -bird-watching in India have convinced me that, so far as the struggle for -existence is concerned, it matters not to a bird whether it be -conspicuously or inconspicuously coloured, that it is not the necessity -for protection against raptorial foes which determines the colouring of a -species; in short, that the theory of protective colouration has but -little application to the fowls of the air." - -Similarly, F. C. Selous writes, on page 13 of _African Nature Notes and -Reminiscences_: "Having spent many years of my life in the constant -pursuit of African game, I have certainly been afforded opportunities -such as have been enjoyed by but few civilised men of becoming intimately -acquainted with the habits and life-history of many species of animals -living in that continent, and all that I have learned during my long -experience as a hunter compels me to doubt the correctness of the now -very generally accepted theories that all the wonderfully diversified -colours of animals--the stripes of the zebra, the blotched coat of the -giraffe, the spots of the bushbuck, the white face and the rump of the -bontebok, to mention only a few--have been coloured either as means of -protection from enemies or for the purpose of mutual recognition by -animals of the same species in times of sudden alarm." - -So also G. A. B. Dewar--a very close observer of nature in -England--writes, in _The Faery Year_: "Few theories in natural history -have received more attention of late years than protective or aggressive -colour, 'mimicry,' and harmony with environment. . . . To doubt this use -of colour to animals seems like inviting back chaos in place of -cosmos--for abandon the theory, and a world of colour is straightway void -of purpose, a muddle of chance. So we all like the theory. Some, however, -perceive plans to aid the wearer in every colour, tint, shade, and -pattern. We may be sceptical of a good many of the cases they cite in -support of colour aid, though attracted by the main idea." - -Writing of the commoner British butterflies, he says: "After a little -practice, any man furnished with good eyesight can easily distinguish -these butterflies--blues, coppers, small heaths, and meadow browns--from -their perches; and so we may be sure that the small beast, bird, or -insect of prey, with sense of colour or form, could also distinguish -them. . . . Quite often, without even searching for them, I can see -cabbage whites and other butterflies asleep on perches to which they by -no means assimilate." Mr G. A. B. Dewar suggests that the safety of the -resting butterfly lies in "the position, the couch on high, . . . not the -mask of colour or marking." - - - Gadow on Coral Snakes - -Two short visits to Southern Mexico sufficed to show Dr Hans Gadow that -some of the commonly accepted explanations of colour phenomena are not -the correct ones. - -Thus writing of coral snakes, he says, on page 95 of _Through Southern -Mexico_: "They are usually paraded as glaring instances of warning -colouration, but I am not at all sure whether this is justifiable. -Certainly these _Elaps_ are most conspicuous and beautiful objects. Black -and carmine or coral red, in alternate rings, are the favourite pattern; -sometimes with narrow golden-yellow rings between them, as if to enhance -the beautiful combination. But these snakes are inclined to be nocturnal -in their habits, and, except when basking, spend most of their time under -rotten stumps, in mouldy ground, or in ants' nests in search of their -prey, which must be very small, to judge from the size of the mouth." - -Dr Gadow goes on to show that although black and red are very strong -contrasts in the day-time, the combination ceases to be effective in the -dark. He suggests that red and black is a self-effacing rather than a -warning pattern. He further points out that several kinds of harmless -snakes have the same colouring and pattern. "There seems," he says, "to -be no reason why we should not call these cases of mimicry; and yet this -is most likely a wrong interpretation, since such harmless snakes are -also found in districts where the _Elaps_ does not occur, not only in -Mexico, but likewise in far-distant parts of the world, where neither -elapines nor any other similarly coloured poisonous snakes exist. To -interpret this as an instance of 'warning colours' in a perfectly -harmless snake, which has no chance of mimicry, amounts in such cases to -nonsense, and we have to look for a different explanation upon -physiological and other grounds." - -It is, to say the least of it, significant that all the opposition to the -theory of protective colouration comes from those who observe nature -first hand, while the warmest supporters of the theory are cabinet -naturalists and museum zoologists. - -In the case of nocturnal creatures, as Dr H. Robinson very sagely points -out (_Knowledge_, January 1909), the value for protective purposes of any -given colouration must depend very largely on the state of the moon. "It -was," he writes, "a common experience in the South African War that on -overcast or moonless nights the nearly black army great-coat made a -picquet sentry invisible at a distance of a few feet. In strong moonlight -this garb could be seen at a great distance, whereas a khaki pea jacket, -useless on a dark night, answered the requirements of invisibility very -well." It is thus evident that the dark colour of the buffalo and sable -antelope cannot be protective on both dark and moonlight nights. - -The theory of protective colouration is based on the tacit assumption -that beasts of prey rely on eyesight for finding their quarry. Raptorial -birds certainly do use their eyes as the means of discovering their -victims; but the great majority of predaceous mammals trust almost -entirely to their power of smell as a means for tracking down their prey. - - - F. C. Selous Quoted - -"Nothing," writes F. C. Selous, on page 14 of _African Nature Notes and -Reminiscences_, "is more certain than that all carnivorous animals hunt -almost entirely by scent until they have closely approached their quarry, -and usually by night, when all the animals on which they prey must look -very much alike as far as colour is concerned." - -The herbivora--the quarry for the beast of prey--too, have a keen sense -of smell, so that they trust their noses rather than their eyes for -safety. - -No observer of nature can have failed to remark how the least movement on -the part of an animal will betray its whereabouts, even though in -colouring it assimilates very closely to the environment. So long as the -hare squats motionless in the furrow, it may remain unobserved, even -though the sportsman be searching for it; but the least movement on its -part at once attracts his eye. Thus, in order that protective colouration -can be of use to its possessor, the latter must remain perfectly -motionless. But, in tropical countries, where flies, gnats, etc., are a -perfect scourge, no large animal is, when awake, motionless for ten -seconds at a time. The tail is in constant motion, flicking off the flies -that attempt to settle on the quadruped. The ears are used in a similar -manner. Thus the so-called protective colouring of herbivora cannot -afford them much protection. It is further worthy of note that the -brush-like tip to the tail of many mammals is not of the same colour as -the skin or fur. It is very frequently black. Thus we have the spectacle -of a protectively coloured creature continually moving, as if to attract -attention, almost the only part of its body that is not protectively -coloured! - - - Sexual Dimorphism - -Many species of birds display what is known as seasonal dimorphism, still -more display sexual dimorphism. - -Seasonally dimorphic birds very often assume a bright livery at the -breeding season; this nuptial plumage is by no means invariably confined -to the cock, so that we are brought face to face with the fact that some -hen birds, that are normally inconspicuously coloured, become showy and -easy to see at the nesting time, that is to say, precisely at the season -when they would seem to be most in need of protection. - -In the great majority of cases of sexual dimorphism among birds the cock -is the more showily coloured. Now, if it be a matter of life-and-death -importance to a bird to be protectively coloured, we should expect the -showily coloured cock birds to be far less numerous than the -dull-plumaged hens, since the former are, _ex hypothesi_, exposed to far -greater danger than the inconspicuous hens. As a matter of fact, cock -birds in practically all species appear to be at least as numerous as the -hens. Nor can it be said that this is due to their more secretive habits. -As a general rule, cock birds show themselves as readily as the hens; -indeed, in the case of the familiar blackbird, the conspicuous cock is -less retiring in his habits than the more sombre hen. It may, perhaps, be -thought that the greater danger to which the sitting bird is exposed -accounts for the fact that hens, notwithstanding their protective -colouration, are not more numerous than the cocks. Unfortunately for the -supposition, in many sexually dimorphic hens, as, for example, the -paradise fly-catcher (_Terpsiphone paradisi_), the showy cock shares the -burden of incubation equally with the hen. - -It frequently happens that allied species of birds are found in -neighbouring countries. The Indian robins, for example, fall into two -species. The brown-backed robin (_Thamnobia cambayensis_) occurs north of -Bombay, while the black-backed species (_T. fulicata_) is found south of -Bombay. The hens of these two species are almost indistinguishable, but -the cocks differ, in that one has a brown back, while the other's back is -glossy black. The Wallaceian theory of colouration seems quite unable to -explain this phenomenon--the splitting up of a genus into local -species--which is continually met with in nature. Equally inimical to the -theory of protective colouration is the existence, side by side, of -species which obtain their living in much the same manner. On every -Indian lake three different species of kingfisher pursue their profession -cheek by jowl; one of these--_Ceryle rudis_--is speckled black and white, -like a Hamburg fowl; the second is the kingfisher we know in England; and -the third is the magnificent white-breasted species--_Halcyon -smyrnensis_--a bright-blue bird with a reddish head and a white wing bar. -It is obvious that all three of these diversely plumaged species cannot -be protectively coloured. It may perhaps be objected that the piscatorial -methods of these kingfishers differ in detail. We admit that this is the -case, but would maintain, at the same time, that these comparatively -slight differences in habit do not account for the very striking -differences in plumage. We may also cite the yellow and pied wagtails of -our own country, which may be seen feeding in the same meadows. Most -familiar and striking of all is the everyday sight of a blackbird and -thrush plying their respective avocations within a few yards of each -other on the same lawn, differently coloured though they be. - -Another weighty objection to the generally accepted theory of protective -colouration is that some of the creatures which assimilate most closely -to their environment are those which appear to be the least in need of -such protection. - - - Precis Artexia - -The butterfly _Precis artexia_, writes F. C. Selous, "is only found in -shady forests, is seldom seen flying until disturbed, and always sits on -the ground amongst dead leaves. Though handsomely coloured on the upper -side, when its wings are closed it closely resembles a dead leaf. It has -a little tail on the lower wing, which looks exactly like the stalk of a -leaf, and from this tail a dark-brown line runs through both wings (which -on the under side are light brown) to the apex of the upper wing. One -would naturally be inclined to look upon this wonderful resemblance to a -dead leaf in a butterfly sitting with closed wings on the ground amongst -real dead leaves as a remarkable instance of protective form and -colouration. And of course it may be that this is the correct -explanation. But what enemy is this butterfly protected against? Upon -hundreds of different occasions I have ridden and walked through forests -where _Precis artexia_ was numerous, and I have caught and preserved many -specimens of these butterflies, but never once did I see a bird -attempting to catch one of them. Indeed, birds of all kinds were scarce -in the forests where these insects were to be found." - -Similarly D. Dewar writes (_Albany Review_, 1907): "If a naturalist be -asked to cite a perfect example of protective colouring, he will, as -likely as not, name the sand grouse (_Pteroclurus exustus_). This species -dwells in open, dry, sandy country, and its dull brownish-buff plumage, -with its soft dark bars, assimilates so closely to the sandy environment -as to make the bird, when at rest, practically invisible, at any rate to -the human eye. Unfortunately for the theory, this bird stands less in -need of protective colouration than any other, for it has wonderful -powers of flight. Even a trained falcon is unable to catch it, because it -can fly upwards in a straight line as though it were ascending an -inclined plane, with the result that the pursuing hawk is never able to -get above it to strike." - - - Striped Caterpillars - -Lord Avebury, who is a typical Wallaceian, points out the connection that -exists between longitudinal stripes on caterpillars and the habit of -feeding either on grass or low-growing plants among grass. The inference, -of course, is that birds mistake these caterpillars for leaves, or, at -any rate, fail to observe them when feeding, not only because they are -green in colour, but because their longitudinal stripes look like the -parallel veins on the blades of grass. But the butterflies of the family -_Satyridæ_, as Beddard points out, _all_ possess striped larvæ, and these -feed chiefly by night, when neither their colouring nor marking is -visible, while during the day many of them lie up under stones; other -caterpillars of this family feed inside the stems of plants. "Now," -writes Beddard (_Animal Colouration_, p. 101), "in these cases the colour -obviously does not matter: if, therefore, the longitudinal striping is -kept up by constant selection on account of its utility, and has no other -signification, we might expect that in these two species (_Hipparchia -semele_ and _Oenis_), and in others with similar habits, the cessation of -natural selection would have permitted the high standard required in the -other cases to be lowered--perhaps, even, as has been suggested in the -case of cave animals, the colours being useless to their possessors, -might have disappeared altogether--but they have not." - -Many exceedingly conspicuous birds--as, for example all the crow-tribe, -the egrets, the kingfishers--flourish in spite of their showy plumage. -Such creatures, while scarcely constituting a valid objection to the -theory of protective colouration, serve to show that protective colouring -is not a necessity. An animal otherwise able to take care of itself can -afford to dispense with cryptic colouration. "An ounce of good solid -pugnacity is a more effective weapon in the struggle for existence than -many pounds of protective colouration." - -There used to live in the gardens of the Zoological Society of London a -black cat belonging to the manager of one of the restaurants. This animal -used to catch birds on the lawn. We believe that not even Mr Thayer will -maintain that a black cat is cryptically coloured when stalking on a -well-watered lawn! Nevertheless the nigritude of that cat did not prevent -it securing a meal. - - - Colours of Eggs - -The case of birds' eggs furnish an excellent example of the lengths to -which Wallace and his followers have pushed the theory of protective -colouration. - -D. Dewar maintains that it is possible to divide birds' eggs that are -coloured, as opposed to those that are white, into two classes--those -which are protectively coloured and those which are not. The former class -includes all those which are laid in shingle or on the bare ground, as, -for example, the eggs of the ring-plover and the lap-wing.[8] He -maintains that the variously coloured and speckled eggs that are laid in -cup-shaped nests are not protectively coloured at all; he declares that -they are usually very conspicuous when in the nest, and, moreover, it -would be futile for them to be cryptically coloured, for a bird or lizard -that habitually sucks eggs will examine carefully the interior of each -nest it discovers. - -Needless to say, this view does not appeal to the so-called -Neo-Darwinians. Wallace writes, on page 215 of _Darwinism_: "The -beautiful blue or greenish eggs of the hedge-sparrow, the song-thrush, -the blackbird, and the lesser redpole seem at first sight especially -calculated to attract attention, but it is very doubtful whether they are -really so conspicuous when seen at a little distance among their usual -surroundings. For the nests of these birds are either in evergreen, or -holly, or ivy, or surrounded by the delicate green tints of early spring -vegetation, and may thus harmonise very well with the colours around -them. The great majority of the eggs of our smaller birds are so spotted -or streaked with brown or black on variously tinted grounds that, when -lying in the shadow of the nest and surrounded by the many colours and -tints of bark and moss, of purple buds and tender green or yellow -foliage, with all the complex glittering lights and mottled shades -produced among these by the spring sunshine and sparkling rain-drops, -they must have quite a different aspect from that which they possess when -we observe them torn from their natural surroundings." - -The obvious comment on this is that it is very fine and poetic English, -but it is not science. It is futile to deny what should be obvious to -every field naturalist, namely, that the majority of eggs laid in open -nests are most conspicuous. - -D. Dewar thus summarises the main facts which show that eggs in nests (as -opposed to those laid on the bare ground) are not protectively -coloured:-- - -"1. Allied species of birds, even though their nesting habits are very -different, as a rule lay similarly coloured eggs. - -"2. Eggs laid in domed nests certainly do not need protective colouring, -yet many of these are coloured. - -"3. The same is true of many eggs laid in holes in trees or in buildings. - -"4. The protective resemblances of eggs which are laid in the open are -apparent to everyone, which certainly is not true of those deposited in -nests. - -"5. Many birds lay eggs which exhibit very great variations. - -"6. Some birds lay eggs of different types, and these sometimes differ -from one another so greatly that it is difficult to believe that they -could have been laid by the same species."[9] - -7. It not infrequently happens that one species lays in the disused nest -of another, and the eggs of the latter are often very different in -colouring from those of the former. - -We have up to the present considered the theory of general cryptic -colouration, which declares that the majority of creatures are so -coloured as to be inconspicuous. We have still to deal with the -hypothesis of special cryptic colouring. - -Certain animals look, when resting, very like an inanimate object, such -as a dead leaf or a twig. This resemblance is said to be the result of -natural selection, since it enables its possessors to escape destruction; -they are seen, but mistaken for something else. - -The classical examples of this kind of protective colouring are furnished -by the _Kallimas_ or leaf-butterflies, which display an extraordinary -resemblance to dead leaves. - -Other examples are the stick-insects and the lappet moth, which looks -like a bunch of dry leaves. It is needless to multiply instances. In -every work on animal colouration numbers of such cases are cited. - -We may grant that in some cases, at any rate, the resemblance is of value -to its possessor, in that it deceives predatory creatures. But it does -not follow from this that the likeness has originated through the action -of natural selection. In order that there can be selection there must be -varying degrees of a tolerable resemblance to select from. How did the -initial similarity arise? This is a matter upon which Wallaceians are -silent. As Poulton truly says, in discussing the degree of protection -afforded by such resemblances, we tacitly endow animals with senses -exactly similar to our own. Are we justified in so doing? Most certainly -not in the case of the invertebrate animals, especially as regards the -arthropods, of which the eyes are constructed very differently from those -of human beings. - -D. Dewar has often seen a toad shoot out its tongue and touch a lighted -cigarette end, apparently mistaking it for an insect. Similarly, he has -again and again induced a gecko lizard to chase and try to swallow a -piece of black cotton, one end of which was rolled up into a ball. It is -only necessary to take hold of the unrolled end of the cotton and place -the rolled-up end a few inches from the lizard, and gradually draw it -away in order to induce the lizard to attempt to seize it. - - - Eyesight of Birds - -It would therefore seem that all these elaborate "protective" devices are -unnecessary refinements if regarded as a protection against invertebrate, -reptilian, and amphibian foes. Birds, on the other hand, appear to have -exceedingly sharp eyesight, so that in order to deceive them the -resemblance requires to be very close. Indeed, as regards those birds -which systematically hunt for their prey among leaves and grass, it seems -doubtful whether the alleged "protective" resemblances of caterpillars to -twigs, etc., are sufficient to be of much use to them. Thus Beddard -writes (on page 91 of _Animal Colouration_): "Judging of birds by our own -standard--which is the way in which nearly all the problems relating to -colour have been approached--does it seem likely that we should fail to -see a caterpillar, perhaps as long or longer than the arm, of an -obviously different texture from the branches, and displaying in many -cases through its semi-transparent skin the pulsation of the heart, for -which we were particularly searching?" - -Now, birds certainly feed very largely on caterpillars, while they are -but rarely seen to eat butterflies. If, therefore, the aim and object of -these special resemblances is the protection of the species, we should -expect to see them in a nearly perfect state in caterpillars on which -birds feed very largely, and poorly developed in butterflies, which do -not appear to be greatly preyed upon by birds, but have to fear chiefly -the comparatively dull-eyed lizards and mammals, of which the latter hunt -mainly by scent. As a matter of fact, the most striking cases of -resemblance to inanimate objects are seen among butterflies, which seem -to stand least in need of them. - -We have already cited the case of the butterfly _Precis artexia_. Even -more marked does the unnecessary elaboration of the likeness seem to be -in the Kallima butterflies. - - - The Theory of Warning Colouration - -All biologists admit that there exist some organisms which are not -coloured so as to be inconspicuous. Indeed, the colouring of certain -species is such as to render them particularly conspicuous. Such species -are said to be warningly coloured. They are supposed to be inedible, or -to have powerful stings or other weapons of defence, or to resemble in -appearance organisms which are thus protected. In the first two cases -they are said to be warningly coloured, and in the last they are cited as -examples of protective mimicry. With the theory of mimicry we shall deal -shortly. We must first discuss the hypothesis of warning colouration. - -When animals are unpalatable, or when they possess a sting or -poison-fangs, it is, to use the words of Wallace, "important that they -should not be mistaken for defenceless or eatable species of the same -class or order, since in that case they might suffer injury, or even -death, before their enemies discovered the danger or the uselessness of -the attack. They require some signal or danger-flag which shall serve as -a warning to would-be enemies not to attack them, and they have usually -obtained this in the form of conspicuous or brilliant colouration, very -distinct from the protective tints of the defenceless animals allied to -them" (_Darwinism_, page 232). - - - Examples of Warning Colouration - -For examples of so-called warningly coloured animals, we may refer the -reader to Wallace's _Darwinism_, Poulton's _Essays on Evolution_, or -Beddard's _Animal Colouration_. An instance familiar to all is our -English ladybird. "Ladybirds," says Wallace, "are another uneatable -group, and their conspicuous and singularly spotted bodies serve to -distinguish them at a glance from all other beetles." - -In order to establish the theory of warning colouration, it is necessary -to prove that all, or the great majority of conspicuously-coloured -organisms, are either unpalatable or mimic unpalatable forms. If this be -so, we are able to understand that the possession of gaudy colouring may -be of advantage to the individual. But even if this be satisfactorily -proved, we must bear in mind that it does not necessarily follow that -these warning colours can be accounted for on the theory of natural -selection. For, in order to explain the existence of any organ by the -action of natural selection, we must be able to demonstrate the utility, -not only of the perfected organ, but of the organ at its very beginning, -and at each subsequent stage of development. This, as we shall show, is -precisely what the Neo-Darwinians are unable to do. We shall have no -difficulty in proving that it would be more advantageous even to a highly -nauseous creature to have remained inconspicuously coloured rather than -to have gradually become more and more conspicuous. - -In the first place, let us briefly examine the evidence on which rests -the assertion that all gaudily-coloured insects, etc., are unpalatable, -or possess stings, or mimic forms which are thus armed. - -In England wasps, bees, and ladybirds are familiar examples of -conspicuous insects. - -The banded black and yellow pattern of the common wasp and the humble bee -are regarded as advertisements or danger signals of the powerful sting. - -The red-coat with its black spots is similarly believed to be a warning -that the ladybird is not fit to be eaten. - -Caterpillars are usually coloured grey or brown, so as to be -inconspicuous; but numerous exceptions occur which are brightly coloured, -and of these individuals many have been experimentally proved to be -objectionable as food to most insect-eating animals, being either -protected by an unpleasant taste, or covered with hairs or spines. - -Familiar cases are those of the abundant and conspicuous black and yellow -mottled caterpillars of the European Buff-tip Moth (_Pygæra bucephala_), -which are much disliked by birds; and the gaily--coloured Vapourer Moth -caterpillar (_Orgyia antiqua_), with its conspicuous tufts of hair. -Readers will remember that a few years back these caterpillars were a -perfect plague in London, in spite of the abundance of sparrows, which -feed freely on smooth green and brown caterpillars. - -Oft-cited examples of warning colouration, are the three great groups of -mainly tropical butterflies--the _Heliconidæ_ of America, the _Acræidæ_ -of Africa, and the _Danainæ_ found all over the world. In all of these -the sexes are alike. They are, every one, strikingly coloured, displaying -patterns of black and red, chestnut, yellow, or white. In most -butterflies the lower surface of the wings is of a quiet hue, in order to -render the organism inconspicuous when at rest, but in these warningly -coloured groups the under surface of the wings is as gaudy as the upper -surface. Their flight is slow. They are tough, and exhale a -characteristic odour. - -Belt showed that, in Nicaragua, birds, dragonflies, and lizards seem to -avoid the Heliconine butterflies, as the wings of these last are not -found lying about in places where insectivorous creatures feed, whereas -wings of the edible forms are to be found. Moreover, a Capuchin monkey, -kept by Belt, always refused to eat Heliconine butterflies. - -Finn investigated the palatability of a number of Indian insects. He -found that most of the birds with which he experimented objected to the -Danaine butterflies; but they disliked still more intensely two -butterflies belonging to groups not universally protected--a swallowtail -(_Papilio aristolochiæ_) and a white (_Delias eucharis_). - -Finn further experimented with the tree-shrew or Tupaia (_Tupaia -ellioti_), which feeds largely on insects. He found that this creature -refused most emphatically all these warningly-coloured butterflies. It -would under no circumstances eat the _Danainæ_, whereas the birds would -do so if no more palatable insects were offered to them at the time. - -Colonel A. Alcock found that a tame Himalayan bear indignantly refused to -eat a locust (_Aularches militaris_) gaily coloured with black, red, and -yellow, and exhaling an unpleasant-smelling froth; but this bear readily -devoured ordinary brown or green species. - -Among cold-blooded vertebrates the common European salamander, with its -bright black and yellow markings, is a striking example of warning -colouration; its skin exudes, on pressure, a very poisonous secretion. - -Colonel A. Alcock has described a small siluroid sea-fish, brightly -banded with black and yellow, and armed with poison spines. - -A well-known Indian poisonous snake, the banded Krait (_Bungarus -coeruleus_), is conspicuously barred with wide bands of black and yellow; -and in South America there occur numerous species of coral snakes, in -which red is added to these conspicuous colours. - -The only known poisonous lizard--the Heloderm of Mexico--is conspicuously -blotched with black and salmon-colour. - -Among birds, no instances of warning colouration have been recorded, -though Professor Poulton has suggested that possibly the striking and -contrasted tints of many tropical species may be due to this cause. The -suggestion is an ingenious one, but is at present totally unsupported by -evidence. - -The skunks are often cited as an excellent example of warning colouration -among mammals. Skunks are most conspicuously arrayed in black and -white--the latter above, not below, as is usual--and have bushy tails, -which they carry erect. Although less powerful and ferocious than other -members of the weasel family, to which they belong, skunks are -notoriously protected by their abundant secretion of a very fetid liquid. - -For further examples of warning colouration we would refer the reader to -Beddard's illuminating book, entitled _Animal Colouration_. - -It should be noticed that in all the cases which we have cited the -colouration is not only conspicuous, but is found in both sexes, whereas -in many undefended animals the male may be just as strikingly coloured, -but the female is not. - -We may take it as proved that there is a very general relation between -gaudy colouring and inedibility, or rather unpalatability, among insects. -It may safely be said that any species of insect which lives, either as -an adult or as a larva, in the open will perish in the struggle for -existence if, being conspicuously coloured, it is neither inedible nor -armed with a weapon such as sting, nor provided with a thick cuticle, nor -resembles in appearance some creature which is protected. - - - Warning Colouring a Drawback - -But from this it is not legitimate to conclude, as Neo-Darwinians do, -that these brilliant colours have been slowly brought into being by -natural selection. - -Why should any creature, having by the "luck" of variation and heredity -acquired some quality--be it strength, pugnacity, sting, or unpleasant -taste--which renders it comparatively immune from persecution, proceed to -advertise the fact by assuming a gaudy or striking colour? It would -surely be better for such an organism to remain inconspicuous. By -becoming showy it is visible to every young bird who, not having yet -learned that the creature in question is unfit for food, seizes and -perhaps kills it. It is true that the young bird vows that never again -will it touch another such organism. But of what avail to the dying -example of warning colouration is the resolution of the young bird? -Moreover, the organism in question, by being conspicuous, also advertises -itself to those few enemies which will eat it. There are always, as -Professor Poulton justly remarks, animals which are enterprising enough -to take advantage of prey which has at least the advantage of being -easily seen and caught. - - - Conspicuous Animals Attacked - -It is possible to cite cases where animals, notwithstanding the fact that -they possess natural defences, become the prey of others in some -exceptional cases. - -The salamander can be eaten with comparative impunity by the toad, a -creature very likely to meet with it. - -The toad itself may be eaten; Finn saw the Indian toad (_Bufo -melanostictus_) eat another of its own kind. He further observed that the -Indian water-snake (_Tropidonotus piscator_) and the "Crow pheasant" -cuckoo (_Centropus sinensis_), in the free state, and the Indian Roller -(_Coracias indica_) and the Pied Hornbill (_Anthracoceros_), in -captivity, eat the warningly-coloured toad. On the other hand, a captive -Racket-tailed drongo rejected toads when offered to it. The common cuckoo -is well known to feed on hairy and "warningly-coloured" caterpillars. - -Finn has also seen the glossy cuckoo in Zanzibar devouring -black-and-yellow caterpillars. Moreover, in America crows are found to -select deliberately highly polished and strongly flavoured beetles. Yet -again, wasps are preyed upon by bee-eaters, and also eaten by our common -toad. In India, Finn found, by many experiments, that the common garden -lizard, or "bloodsucker" (_Calotes versicolor_), would eat, both in -captivity and in freedom, all "warningly-coloured" butterflies, not only -the _Danainæ_, but even _Delias eucharis_ and the pre-eminently nauseous -_Papilio aristolochiæ_. That this reptile is a great enemy to butterflies -is rendered probable by the frequent occurrence of specimens of these -insects with its semicircular bites in their wings. - -Further, Finn found that bulbuls, the commonest garden birds in India, -ate the _Danainæ_ readily in captivity, even when other butterflies could -be had, which was not the case with most other birds. Bulbuls did, -however, usually refuse the _Delias_ and _Papilio_ mentioned above. - -The Skunk is preyed upon in America by the Eagle-owl (_Bubo virginianus_) -and the Puma. - -Thus, animals provided with natural defences are not immune from attack. - -Hence natural selection cannot have encouraged the survival of -individuals which displayed a conspicuous colour, for the sake of the -"warning." - -We must not forget that many creatures armed with powerful weapons -possess the unobtrusive drab, brown, or green colouration which is -associated with concealment from foes. - -There can be little doubt that, but for the fact that the hive-bee can -inflict a sting more severe than that of the wasp, this useful insect -would have been cited as a case of a protectively coloured creature. -Notwithstanding its sober brown colouring, the hive-bee is recognised and -avoided. - -Professor Poulton records that the dull inconspicuous caterpillar of the -moth (_Mænia typica_) is rejected by reptiles. It must be admitted, -however, that these cases among insects are very rare. - -The smooth newt (_Molge vulgaris_), a relation of the salamander, is -protected by a poisonous skin; nevertheless the creature has a dark brown -back and spends most of its time on land. Its black-spotted, yellow -under-surface may have some protective value in the water. Neither the -pike nor the common European water-tortoise will eat this newt. - -Toads are nearly all very inconspicuous; nevertheless they are well -protected by the acrid secretion from the skin glands; moreover, they are -both recognised and avoided by those predacious creatures to whom they -are distasteful. Hawks, although as a rule plainly coloured, are -certainly recognised by all other birds. It would seem, therefore, that -"warning colours," like the similar striking hues of many domestic -animals, are incidental attributes. It has been possible for their owners -to develop them, because for the most part let alone. - -Eisig, long ago, pointed out that the brightly coloured pigment in the -skin of these warningly coloured insects is in certain cases of an -excretory nature. Therefore the inference which should be drawn is, as -Beddard points out on page 173 of his _Animal Colouration, "that the -brilliant colours_ (i.e. _the abundant secretion of pigment_) _have -caused the inedibility of the species, rather than that the inedibility -has necessitated the production of bright colours as an advertisement_." -In other words, Neo-Darwinians put the cart before the horse! - -[Illustration: BOURU FRIAR-BIRD] - -[Illustration: BOURU ORIOLE] - -In some cases these brilliantly coloured insects may be survivals of an -age in which there were no birds. When these came into being and began to -prey upon insects, the conspicuously coloured species which were not -inedible or very unpalatable would soon become extinct, while those that -were inedible would survive as warningly-coloured insects. In other cases -it is not improbable that these warningly-coloured creatures have arisen -by mutations from more soberly-hued insects. It is conceivable that every -now and again a mutation occurs which renders its possessor conspicuous. -This will result in the early destruction of these aberrant individuals -unless their newly-acquired gaudiness is either correlated with, or the -result of, distastefulness. - - - Aposematic Sounds - -In the case of warning colouration, the Neo-Darwinians have, as usual, -pursued their theory to absurd lengths. Professor Poulton, for example, -extends it to sounds and attitudes. "Sound," he writes, on page 324 of -_Essays on Evolution_, "may be employed as an Aposematic character, as in -the hiss of some snakes and some lizards. Certain poisonous snakes when -disturbed produce by an entirely different method a far-reaching sound -not unlike the hiss. Thus the rattle-snake (_Crotalus_) of America -rapidly vibrates the series of dry, horny, cuticular cells, movably -articulated to each other and to the end of the tail. The stage through -which the character probably arose is witnessed in another genus which -vibrates its tail among dry leaves, and thus produces a warning sound. -The deadly little Indian snake (_Echis carinata_) ('the Kuppa') makes a -penetrating swishing sound by writhing the coils of its body one over the -other. Special rows of the lateral scales are provided with serrated -keels which cause the sound when they are rubbed against each other. -Large birds, when attacked, often adopt a threatening attitude, -accompanied by an intimidating sound which usually suggests more or less -closely the hiss of a serpent, and thus includes an element of mimicry. . -. . The cobra warns an intruder chiefly by attitude and by the broadening -of its flattened neck, the effect being heightened in some species by the -'spectacles.' In such cases we often witness a combination of cryptic and -Aposematic methods, the animal being concealed until disturbed, when it -instantly assumes a warning attitude. - -"The benefit of such intimidating attitudes is clear: a venomous snake -gains far more advantage by terrifying than by killing an animal it -cannot eat. By striking, the serpent temporarily loses its poison, and -with this a reserve of defence. Furthermore, the poison does not cause -immediate death, and the enemy would have time to injure or destroy the -snake." - - - Intimidating Attitudes - -At first sight this reasoning may seem very convincing. But consider for -a moment the process by which the hiss originated and gradually increased -by natural selection. We must suppose that the rattle-snake was formerly -incapable of making any sound. One day a variety appeared in which the -skin was slightly hardened, so that when the creature moved its body -rapidly there issued a slight sound. This must have caused an enemy to -refrain from attack; it thus lived to transmit this peculiarity to its -offspring, and those which made more noise than their ancestors escaped, -while those that made less succumbed to their enemies. For ourselves, we -find it quite impossible to believe that the rattle was thus gradually -evolved by means of natural selection. Indeed, we are inclined to think -that neither the hiss of the cobra nor its "intimidating attitude" has -any terrifying effect on its adversary. In the case of the cobra we are -able to cite positive evidence that dogs and cattle show no alarm at the -attitude. - -"Dogs," writes D. Dewar of this display, "regard it as a huge joke. Of -this I have satisfied myself again and again, for when out coursing at -Muttra we frequently came across cobras, which the dogs used invariably -to chase, and we sometimes had great difficulty in keeping the dogs off, -since they seemed to be unaware that the creature was venomous." - -Colonel Cunningham writes, on page 347 of _Some Indian Friends and -Acquaintances_: "Sporting dogs are very apt to come to grief where cobras -abound, as there is something very alluring to them in the sight of a -large snake when it sits up nodding and snarling; and it is often -difficult to come up in time to prevent the occurrence of irreparable -mischief." - -Colonel Cunningham also states that many ruminants have a great animosity -to snakes, and are prone to attack any that they may come across. - -We may therefore well be sceptical as to the value of intimidating -attitudes to those creatures which are in the habit of striking them. - - - Mimicry - -In a work of this kind it is neither possible nor necessary to consider -in great detail the mass of evidence which has been advanced in favour of -the theory of mimetic resemblance. - -Chapters vii. and viii. of Professor Poulton's _Essays on Evolution_ -contain an up-to-date statement of the facts in favour of the theory. -Professor Poulton believes that in all cases mimetic resemblance is the -result of the action of natural selection. - -He admits that there is no direct evidence in its favour, but asserts -that "the facts of the cosmos, so far as we know them, are consistent -with the theory, and none of them inconsistent with it" (page 271). - - - Theory of Protective Mimicry - -We are not at all sure that no facts are against the theory of protective -mimicry. We shall presently set forth some which to us seem, if not -actually inconsistent with the theory, at least to point to the -conclusion that the phenomenon may be explained otherwise than as a -product of natural selection. - - - Evidence for the Theory - -Let us first briefly state the case for the theory of protective mimicry. - -1. It is asserted that the mimicking species and that which is mimicked -are often not nearly related. For example, the unpalatable larva of the -Cinnabar Moth (_Euchelia jacobaeæ_) is said to mimic a wasp, because it -has black and yellow rings round its body. - -"The conclusion which emerges most clearly," writes Poulton (p. 232), "is -the entire independence of zoological affinity exhibited by these -resemblances." This is supposed to be proof that Darwin was wrong when he -asserted that the original likeness was due to affinity. Says Poulton: -"The preservation of an original likeness due to affinity undoubtedly -explains certain cases of mimicry, but we cannot appeal to this principle -in the most remarkable instances." - -2. It is asserted that species which are mimicked are invariably either -armed with a sting, well defended, or unpalatable, so that it is against -the interest of insectivorous creatures to attack them. It is further -asserted that the species imitated are "even more unpalatable than the -generality of their order." - -3. It is pointed out that the most distasteful groups of butterflies--the -_Danaidæ_, the _Acræinæ_, the _Ithomiinæ_, and the _Heliconinæ_--consist -of large numbers of species which closely resemble one another. This is -said to be due to Müllerian mimicry. Mayer states that in South America -there are 450 species of inedible _Ithomiinæ_ which display only 15 -distinct colours, while the 200 species of _Papilio_, which are edible, -exhibit 36 distinct colours. Nevertheless, he says, there is no lack of -individual variability among the former hence their conservatism as -regards colour cannot be attributed to their having but little tendency -to vary. - -4. It is asserted that although in many cases the mimetic resemblances -extend to the minutest detail, nevertheless they are not accompanied by -any changes in the mimetic species except such as assist in the -production or strengthening of a superficial likeness. - -Pictures illustrating such cases of mimicry are figured on pp. 241, 247, -and 251 of Wallace's _Darwinism_ (1890 edition). - -5. It is stated that mimetic resemblance is not confined to colour, but -extends to pattern, form, attitude, and movement; that deep-seated organs -are affected when the superficial resemblance is intensified, but not -otherwise. Poulton cites _Clytus arietis_, the "wasp-beetle," as an -example of this. - -6. It is asserted that mimetic resemblances are produced in the most -diverse ways; that the modes whereby the similarity in appearance is -brought about are varied, but the result is uniform. - -"A lepidopterous insect," writes Poulton (p. 251), "requires above all to -gain transparent wings, and this, in the most striking cases that have -been studied, is produced by the loose attachment of the scales, so that -they easily and rapidly fall off and leave the wing bare except for a -marginal line and along the veins (_Hemaris_, _Trochilium_)." - -7. It is alleged that the imitator and imitated are always found in the -same locality. If they did not do so no advantage would be derived from -the resemblance. It is further alleged that where the mimicking species -is edible it is invariably less abundant where it occurs than the species -it imitates. - -8. It is pointed out that it sometimes happens that where in the mimic -the sexes differ in appearance, the male copies one species, the female -quite a different one. This is said to be because the deception would be -liable to be detected if the mimicking species became common relatively -to that which is imitated. "We therefore find that two or more models are -mimicked by the same species" (_Essays on Evolution_, p. 372). - -Occasionally the female mimics two other species, _i.e._ she occurs in -two forms, each like a different species. - -It sometimes happens that the female alone mimics. This is said by -Wallace to be due to her greater need of protection. When she is laden -with eggs her flight is slow, and therefore she requires a special degree -of protection. - -9. It is said that in some species we find a non-mimetic ancestor -preserved on islands where the struggle for existence is less severe, -while on the adjacent continent mimicry has been developed. - -10. It is alleged that in the cases where moths resemble butterflies the -former are either as diurnal as the butterflies or are species which -"readily fly by day when disturbed." - -11. It is asserted that some seasonally dimorphic forms are examples of -mimicry only in one state, in the form that comes into being at the time -when the struggle for existence is most severe; that is to say, in the -dry season, in Africa, when insect life is far less abundant than in the -rainy season. - -In other cases the mimicry of the dry-weather form is said to be far more -perfect. - -Instances of this phenomenon are set forth in Professor Poulton's _Essays -on Evolution_. - - - Alternative Theories - -It will be observed that we have quoted very largely from Professor -Poulton's work. Our reason for so doing is that he appears to be the most -prominent advocate of the theory of protective mimicry, and his work, -which was published in 1908, may be taken as the latest Neo-Darwinian -pronouncement on the subject. - -Hence if we can show, as we believe we can, that his arguments are not -sound, we may take it that we have demonstrated that the theory in its -present form is untenable. - -It is worthy of notice that Professor Poulton sets forth three other -suggestions which have been proposed as substitutes for natural selection -as an explanation of the phenomena of mimicry. - -The first is the theory of External Causes, namely, that the resemblance -is due to some external cause, such as food or climate. - -The second is the theory of Internal Causes, which states that mimetic -resemblance is due to internal developmental causes. - -The third is the suggestion that sexual selection has caused the origin -of these resemblances. - -He then proceeds to demolish these to his own satisfaction, and adds -triumphantly, "The conclusion appears inevitable that under no theory, -except natural selection, do the various resemblances of animals to their -organic and inorganic environments fall together into a natural -arrangement and receive a common explanation" (p. 228). - -To reasoning of this description there is an obvious reply. Even if it be -granted that the alternatives to the theory of natural selection as set -forth by Professor Poulton are untenable, it does not follow that natural -selection affords an adequate explanation. If A, B, C and D are charged -with theft and the prosecutor proves that neither A nor B nor C committed -the theft, this will not suffice to secure the conviction of D. It is -quite possible that a fifth person, E, may be the culprit. - -Much of the popularity of the theory of natural selection is due to the -fact that biologists have not yet been able to discover a substitute for -it. - -It seems to us that the proper method of making progress in science is -not to bolster up natural selection by ingenious speculations, but to -look around for other hitherto undiscovered causes. - -[Illustration: KING-CROW OR DRONGO] - -[Illustration: DRONGO-CUCKOO] - - - Objections to the Theory that the so-called Cases of Mimicry owe their - Origin to Natural Selection - -It is obvious that for one creature to resemble another can be of little -or no benefit to either until the resemblance is tolerably close. It is, -therefore, insufficient to prove the utility of the perfected -resemblance. We may readily grant this and yet maintain that the origin -of the resemblance cannot be due to the action of natural selection. - -The Drongo-cuckoo (_Surniculus lugubris_) displays so great a likeness to -the King Crow (_Dicrurus ater_) that it is frequently held up by -Neo-Darwinians as an excellent example of mimicry among birds. But D. -Dewar writes, on page 204 of _Birds of the Plains_: "I do not pretend to -know the colour of the last common ancestor of all the cuckoos, but I do -not believe that the colour was black. What then caused _Surniculus -lugubris_ to become black and assume a king-crow-like tail? - -"A black feather or two, even if coupled with some lengthening of the -tail, would in no way assist the cuckoo in placing its egg in the -drongo's nest. Suppose an ass were to borrow the caudal appendage of the -king of the forest, pin it on behind him, and then advance among his -fellows with loud brays, would any donkey of average intelligence be -misled by the feeble attempt at disguise? I think not. Much less would a -king-crow be deceived by a few black feathers in the plumage of a cuckoo. -I do not believe that natural selection has any direct connection with -the nigritude of the drongo-cuckoo." - -Darwin was fully alive to this difficulty when he wrote: "As some writers -have felt much difficulty in understanding how the first step in the -process of mimicry could have been effected through natural selection, it -may be well to remark that the process probably commenced long ago -between forms not widely dissimilar in colour" (_Descent of Man_, 10th -Ed., p. 324). Such a statement is of course quite inconsistent with the -Neo-Darwinian position. "The conclusion which emerges most clearly," -writes Poulton (_Essays on Evolution_, p. 232), "is the entire -independence of zoological affinity exhibited by these resemblances; and -one of the rare cases in which Darwin's insight into a biological problem -did not lead him right was when he suggested that a former closer -relationship may help us to a general understanding of the origin of -mimicry. The preservation of an original likeness due to affinity -undoubtedly explains certain cases of mimicry, but we cannot appeal to -this principle in the most remarkable instances." - -It is unnecessary to labour this point. It is surely evident to everyone -with average intelligence that, until the resemblance between two forms -has advanced a considerable way, the likeness cannot be of utility to -either, or at any rate of sufficient utility to give its possessor a -survival advantage in the struggle for existence. Until it reaches this -stage, natural selection cannot operate on it. It is therefore absurd to -look upon natural selection as the direct cause of the origin of the -likeness. When once a certain degree of resemblance has risen, it is -quite likely that in some cases natural selection has strengthened the -likeness. - -The second great objection to the Neo-Darwinian explanation of the -phenomenon known as mimicry is that in many cases the resemblance is -unnecessarily exact. Even as we saw how the Kallimas, or dead-leaf -butterflies, carried their resemblance to dead leaves to such an extent -as to make it appear probable that factors other than natural selection -have had a share in its production, so do we see in certain cases of -mimetic resemblance an unnecessarily faithful likeness. - - - The Brain-fever Bird - -The common Hawk Cuckoo of India (_Hierococcyx varius_) furnishes an -example of this: "The brain-fever bird," writes Finn, on page 58 of -_Ornithological and Other Oddities_, "is the most wonderful feather copy -of the Indian Sparrow-hawk or Shikra (_Astur badius_). All the markings -in the hawk are reproduced in the cuckoo, which is also of about the same -size, and of similar proportions in the matter of tail and wing; and both -hawk and cuckoo having a first plumage quite different from the one they -assume when adult, the resemblance extends to that too. Moreover, their -flight is so much the same that unless one is near enough to see the -beak, or can watch the bird settle and note the difference between the -horizontal pose of the cuckoo and the erect bearing of the hawk, it is -impossible to tell them apart on a casual view." Moreover, the tail of -the cuckoo sometimes hangs down vertically, thus intensifying the -likeness to the hawk. - -It is quite possible that the brain-fever bird derives some benefit from -the resemblance; indeed, it has been seen to alarm small birds, even as -the hawk-like common cuckoo frightens its dupes, but, as D. Dewar pointed -out, on page 105 of vol. 57 of the _Journal of the Society of Arts_, -"this is not sufficient to explain a likeness which is so faithful as to -extend to the marking of each individual feather. When a babbler espies a -hawk-like bird, it does not wait to inspect each feather before fleeing -in terror; hence all that is necessary to the cuckoo is that it should -bear a general resemblance to the shikra. The fact that the likeness -extends to minute details in feather marking, points to the fact that in -each case identical causes have operated to produce this type of -plumage." This conclusion is still further strengthened by the fact that -the likeness extends to the immature plumage, that is to say, exists at a -time when it cannot assist the cuckoo in its parasitical work. - -Poulton meets this objection as follows: - -[Illustration: SHIKRA HAWK] - -[Illustration: HAWK-CUCKOO] - - - Hypertely - -"All such criticism is founded on our imperfect knowledge of the struggle -for existence. The impressions and judgments of man are immensely -influenced by the 'corroborative detail,' giving 'artistic verisimilitude -to a bold and unconvincing narrative.' Indeed, the laughter which is -invariably raised by this passage from _The Mikado_ is, I have always -thought, not only or chiefly due to the humour of the application, but to -the way in which a great and familiar truth breaks in upon the listener -with all the pleasing surprise which belongs to epigram. Birds, the chief -enemies of insects, are known to have powers of sight far superior to -those of man, and, from our experience of them in captivity, it may be -safely asserted that their attention is attracted by excessively minute -detail. Until our knowledge of the struggle for life is far more -extensive than at present, the argument founded on Hypertely may be left -to contend with another argument often employed against the explanation -of cryptic and mimetic resemblance by natural selection. Hypertely -assumes that there are unnecessary details in the resemblance, that the -resemblance is perfect beyond the requirements of the insect; the second -argument maintains that birds are so supremely sharp-sighted that no -resemblance, however perfect, is of any avail against them. In the -meantime the majority of naturalists will probably reject both extremes, -and believe that the enemies are certainly sharp-sighted and successful -in pursuit, but that perfection in detail makes their task a harder one, -and gives to the individuals possessing it in a higher degree than -others, increased chances of escape, and of becoming the parents of -future generations." (_Essays on Evolution_, p. 302.) - -This long quotation requires careful consideration, since to us it -appears to be typical of the kind of reasoning resorted to by -Neo-Darwinians. - -Note the reference to our "imperfect knowledge of the struggle for -existence." This is almost invariably the last refuge of the -Neo-Darwinian when worsted in argument. We fully admit that there is -still much to be learned of the nature of the struggle for existence, but -such a statement sounds very curious when uttered to those who pin their -faith to the theory which sees in the principle of natural selection an -explanation of all the phenomena of the organic world. Natural selection, -be it remembered, is but a name for the struggle for existence. - - - Birds capturing Butterflies - -"Birds," says Professor Poulton, "are the chief enemies of insects." This -may be so. But we greatly doubt whether they are the chief enemies of -butterflies and moths, among which the most perfect examples of mimicry -are supposed to occur. - -We have watched birds closely for some years, but believe that we could -almost count on our fingers the cases in which we have seen a bird chase -a butterfly. - -Professor Poulton, being aware of this objection, sets forth, on pp. -283-292 of _Essays on Evolution_, the evidence he has gathered in favour -of the view that birds are the chief enemies of butterflies and other -lepidoptera. - -As the result of five years' observation in S. Africa, Mr G. A. K. -Marshall was able to record some eight cases of birds capturing -butterflies. In three cases the butterfly seized was warningly coloured, -or, at any rate, conspicuous! In two of these eight cases the bird failed -to capture its quarry! - -Says Mr Marshall, "the fact that birds refrain from pursuing butterflies -may be due rather to the difficulty in catching them than to any -widespread distastefulness on the part of these insects." - -During six years' observation in India and Ceylon, Colonel Yerbury -records some half dozen cases of birds capturing, or attempting to -capture, insects. He writes: "In my opinion an all-sufficient reason for -the rarity of the occurrence exists in the fact that in butterflies the -edible matter is a minimum, while the inedible wings, etc., are a -maximum." - -Colonel C. T. Bingham in Burma states that between 1878 and 1891 he on -two occasions witnessed the systematic hawking of butterflies by birds, -although he observed on other occasions some isolated cases. - -This appears to be the sum total of the evidence adduced by Professor -Poulton as regards the capture of butterflies by birds. This seems to us -an altogether insufficient foundation upon which to build the theory that -the cases of resemblance between unrelated species have been effected by -natural selection. - -It is, however, to be noted that probably among birds the most dangerous -enemies of butterflies are not those that habitually catch insect prey on -the wing. Such are experts in the art of fly-catching, and would despise -the comparatively meatless butterfly. One often comes across butterflies -with an identical notch in each wing, which leaves little room for doubt -that those particular butterflies had been snapped at, _while resting_, -by a bird. Among birds the chief enemies of butterflies and moths are -probably to be found in those that hunt for their food in bushes and -trees. - -Thus, what we do know of the nature of the struggle for existence offers -but poor support to the Neo-Darwinian explanations of the cases of -so-called mimicry in nature. - - - Observing-powers of Birds - -Professor Poulton's idea of pitting the argument of Hypertely against -that of the alleged supreme sharp-sightedness of birds is ingenious, but -is not likely to satisfy very many people save those content to live in a -fools' paradise. If birds are supremely sharp-sighted, and pay attention -to excessively minute detail, the difficulty of accounting for the -_origin_ of protective mimicry on the natural selection hypothesis -becomes all the greater. - -The question whether or not birds are good observers is a most -interesting one. Unfortunately, hitherto, but little attention has been -paid to the subject. The evidence available seems to point to the fact -that birds, like savages, have sharp eyes only for certain objects--that -is to say, for the things they are accustomed to look out for. All -observers of nature must have noticed how quick a butcher-bird is to -catch sight of a tiny insect upon the ground at a distance of some yards -from his perch. - -On the other hand, it is said that when there is snow upon the ground -wood pigeons will approach quite close to a man wearing white clothes and -a white hat, provided he keep perfectly still. Finn once witnessed in -Calcutta a sparrow pick up a very young toad, obviously by mistake, for -it dropped it at once with evident distaste. Birds of prey are supposed -to have remarkably good eyesight; yet they can readily be caught by a net -stretched out before their quarry. They are not trained to be on the -watch for such things as nets, and so do not appear to notice one when -erected. - -It is thus our belief that the very perfection and detail of some -so-called mimetic resemblances are a very serious objection to the theory -of protective mimicry as enunciated by Professor Poulton and other -Neo-Darwinians. - -There is yet a further objection to this theory, one which, in our -opinion, is fatal to the hypothesis in its generally accepted form. - -A number of cases occur where two species, in no way related, show close -resemblance to one another under such circumstances that neither can -possibly derive any benefit from the likeness. The theory of protective -mimicry is quite unable to explain these cases. This fact leads to a -suspicion that, in the instances where the theory does at first sight -appear to offer an explanation, the resemblance may also be due to mere -coincidence. - -We may perhaps call the cases which the theory of mimicry is unable to -account for "false mimicry," but in so doing we must bear in mind the -possibility that some, at any rate, of the examples of so-called mimicry -may, on further investigation, prove to be nothing of the kind. - - - "False" Mimicry among Mammals - -The Cacomistle of Mexico (_Bassaris astuta_), one of the raccoon family, -has a grey body and long black-and-white ringed tail, just like the -ring-tailed Lemur of Madagascar (_Lemur catta_); both are arboreal and -about the same size, and this lemur's colouration is exceptional in its -family. - -The banded Duiker-buck of West Africa (_Cephalophus doriae_), has the -same very unusual colouration as the thylacine or marsupial wolf of -Tasmania, light brown, with bold black bands across the hinder part of -the back, and the animals are about the same size. - -The dormouse of Europe closely resembles a small American Opossum -(_Didelphys murina_), and a larger opossum (_D. crassicaudata_) is very -like the Siberian Mink (_Mustela sibirica_). - -The Flying Squirrel of North America (_Sciuropterus volucella_) is -closely copied by the Flying Phalanger (_Petaurus breviceps_) of -Australia. - -It will be readily seen that in no one of these cases can the likeness be -of utility to either the "model" or the "copy." - - - False Batesian Mimicry among Birds - -There are many instances of this phenomenon among birds. The New Zealand -Cuckoo (_Urodynamis tritensis_) shows a far closer resemblance to the -American Sparrow-hawk (_Accipiter cooperi_) than to any New Zealand hawk, -and in fact closely mimics this quite alien bird. - -The stormy petrel, a purely oceanic bird, closely resembles in size, -colour, and style of flight the Indian Swift (_Cypselus affinis_), a -purely inland creature; both are sooty black, with a conspicuous white -patch on the lower back. - -The Pied Babbling Thrush (_Crateropus bicolor_) of Africa is singularly -like the Pied Myna (_Græulipica melanoptera_) of Java, both being of -about the same size, with white body and black wings and tail quills. -This, we may add, is a very unusual colouration among small birds. - -The black-headed Oriole (_Oriolus melanocephalus_) of India is very -similar in appearance to the common Troupial (_Icterus vulgaris_) of -Brazil; indeed, the troupials, a purely American group, are so like the -old world orioles in colour that they usurp their name in America. - -The little insectivorous Iora (_Ægithina tiphia_) of India strongly -resembles in size and colour a Siskin (_Chrysomitris colambiana_) from -South America, the males in both being black above and yellow below, -while in the females the black is replaced by olive-green. - -Another Indian babbler (_Cephalopyrus flammiceps_), yellowish-green, with -orange forehead, is closely copied by, or copies, the well-known -Brazilian Saffron-finch (_Sycalis flaveola_). - -In Fergusson Island, near New Guinea, there is a ground pigeon -(_Otidiphaps insularis_) which is black with chestnut wings, like several -of the powerful ground cuckoos of the genus _Centropus_, but no species -of these cuckoos so coloured appears to inhabit the island. - -In Africa there is a tit (_Parus leucopterus_) which has the same very -unusual colouration as an East-Indian bulbul (_Micropus melanoleucus_), -both being black with a white patch on the wing-coverts. These two birds -are about the same size. As showing the purely coincidental character of -such resemblances, we may mention that this same rare pattern occurs -again in our Black Guillemot (_Uria grylle_) and in the Muscovy Duck -(_Cairina moschata_). - - -We have already quoted Gadow (p. 198) on "false mimicry" among snakes. He -also gives, on p. 110 of _Through Southern Mexico_, an example of this -phenomenon among amphibia. It is, he writes, "impossible to distinguish -certain green tree-frogs of the African genus _Rappia_ from a _Hyla_, -unless we cut them open. If they lived side by side, which they do not, -this close resemblance would be extolled as an example of mimicry." - -We should be very greatly surprised if abundant examples of "false -mimicry" are not found among insects. We trust that this remark will -stimulate some entomologist to pay attention to the subject. - -It is the essence of Müllerian mimicry that both model and copy are -immune from attack from enemies. Unfortunately for the theory, similar -resemblances occur among birds of prey, where neither party can benefit -from the association. This gives rise to what we may perhaps call false -Müllerian mimicry. Thus the goshawk and peregrine falcon resemble each -other in being brown above and streaked below in immature plumage, and -having barred underparts and a grey upper plumage when adult. - - - Theory of Mimicry Criticised - -Having stated the more important objections to the theory of protective -mimicry, it now remains for us to deal specifically with each head of -evidence offered in its favour. - -1. With regard to the assertion that the model and its copy are often not -nearly related, we have shown that among mammals and birds instances of -resemblance between widely-separated groups occur under such -circumstances that neither party can derive any benefit therefrom. - -2. As regards the assertion that species which are mimicked are either -well-defended or unpalatable, this certainly does not hold good with -regard to some at any rate of the coincidental resemblances among birds -which we have pointed out; even if these pairs of similar species lived -in the same country it would require considerable ingenuity to say why -one should mimic the other. - -3. As regards the argument that the inedible species of _Ithomiinæ_, -etc., display only fifteen colours, while the less numerous edible -_Papilios_ display more than double this number of colours, we may draw -attention to the fact that those birds which are most immune from attack -are precisely those which display the smallest range as regards colour, -e.g., hawks, owls, crows, gulls, storks, and cranes. As we have already -submitted, no question of Müllerian association comes in here. - -On the other hand, the eminently edible families of game-birds and ducks -display great variety of colour, in the males at all events. - -4. As regards the statement that although in many cases the mimetic -resemblances extend to the minutest detail, they are not accompanied by -any structural changes except such as assist in the production of a -superficial likeness, we may refer to the case we have already cited of -the New Zealand cuckoo, which, though it so closely copies an American -hawk, is typically cuculine in structure. Here, of course, there can be -no question of advantage to the "mimicking" cuckoo in the resemblances. - -5. In answer to the argument that mimetic resemblance extends to form, -attitude, and movement, as well as colour, and that deep-seated organs -are affected only when the superficial resemblance is thereby -intensified, we may draw attention to such cases as the following:-- - -(_a_) The harmless Indian Snake (_Lycodon aulicus_) is closely similar to -the well-known Krait (_Bungarus coeruleus_), also Indian; but the -resemblance extends to a structural detail which can hardly have mimetic -value--namely, the harmless snake has long, fang-like front teeth, though -these are unconnected with poison-glands. Animals which come into contact -with the krait and its mimic are hardly likely to inspect their teeth. - -(_b_) A considerable number of birds of the shrike group--known as -Cuckoo-Shrikes (_Campophaga_)--closely resemble cuckoos in plumage; but -even if they derive any benefit from mimicking birds which are credited -with being mimics already, they cannot profit by the fact that the shafts -of the rump-feathers in both groups are stiffened; this being a -peculiarity which would not be perceptible until the bird was in the -grasp of an aggressor. - -(_c_) As a third case of coincidence we may refer to the tubercle in the -nostril of the Brain-fever-bird (_Hierococcyx varius_), as a minute -detail of hawk-like appearance, though not present in the particular -species imitated. - -6. The argument that mimetic resemblances are produced in the most -diverse ways, but the result is uniform, loses much of its force when we -consider the various methods by which short-tailed birds appear to have -long caudal appendages. - -In the peacock it is the upper tail coverts which are elongated; in the -Stanley Crane (_Tetrapteryx paradisea_) it is the innermost or tertiary -quills of wing; in one of the egrets some of the feathers of the upper -back grow to a great length and form a train; in the Bird of Paradise -(_Paradisea apoda_) the long flank plumes are commonly mistaken for the -tail. - -In these cases there can be no question of mimicry. - -7. We have shown that the idea that imitator and imitated are always -found in the same area is absolutely fallacious. In birds, for example, -the most striking resemblances appear to occur between species that dwell -far apart. - -8. We can cite, as parallel to the case of a mimicking species of which -the male copies one model and the female another, the strange similarity -between the barred brown plumage of the female blackcock and that of the -female eider-duck. The males of these species, although both black and -white, differ greatly in appearance; but the male blackcock is admittedly -very like the male of another species of sea-duck--the scoter. - -9. Against the supposed ancestral non-mimetic forms existing on islands -we can pit the "mimetic" orioles in small islands and their non-mimetic -cousins on the mainland. In Australia an oriole of what appears to be an -ancestral style lives beside, but declines to mimic, a friar bird of a -very pronounced type. - -10. The case of certain diurnal moths mimicking butterflies appears to be -explicable without the aid of the theory of protective mimicry. When two -species adopt the same method of obtaining food, it not infrequently -happens that a professional likeness springs up between them. Of this the -swifts and swallows afford a striking illustration. - -11. As a set-off to the cases where the alleged mimicry is confined to -certain seasons of the year, we may cite the case of the pheasant-tailed -Jaçana (_Hydrophasianus chirurgus_), which in its winter plumage might -easily be mistaken, when on the wing, for the paddy bird or Pond Heron -(_Ardeola grayii_), both being of like size and having a brown back, long -green legs, and white wings. Moreover, they are to be found in the same -localities in India. At the breeding season, however, they are absolutely -different in plumage. - -Yet another argument commonly adduced in favour of the theory of -protective mimicry is that local variations of the imitated species are -sometimes followed by the imitator; thus the butterfly _Danais -chrysippus_ shows a white patch on the hind wings in Africa, and this is -followed by its mimic. - -But the same thing occurs, quite irrationally, so to speak, among birds. -The peregrine falcon and hobby of Europe are only winter migrants to -India, where they are replaced as residents by the Shaheen (_Falco -peregrinator_) and Indian Hobby (_F. severus_). Both these differ from -the migratory forms by being blacker above and chestnut below, instead of -cream colour. Thus the resemblance occurs in each race. A similar -distinction, as noted by Blyth, exists between the Common Swallow -(_Hirundo rustica_) and the Swallow (_H. tytleri_) of Eastern Asia, the -latter having the whole ventral surface rufous instead of only the -throat. Yet no one will suggest that swallows mimic falcons, or that -there is mimicry between the peregrine and hobby. It is obvious that such -parallel changes occur independently of mimicry. - -The Water-rail (_Rallus aquaticus_) and Baillon's Crake (_Porzana -bailloni_) of Europe are distinguished from their allies of Eastern Asia -by having the sides of the head plain grey, whereas the Eastern Asiatic -forms (_R. indicus_ and _P. pusilla_) have a brown streak along each side -of the face. Here, again, we have an instance of birds of the same family -varying together with geographical distribution. - - - "Recognition" Colours - -One of the prettiest conceits of the Wallaceian school of zoologists is -the theory of recognition markings. - -"If," writes Wallace, on page 217 of _Darwinism_, "we consider the habits -and life-histories of those animals which are more or less gregarious, -comprising a large proportion of the herbivora, some carnivora, and a -considerable number of all orders of birds, we shall see that a means of -ready recognition of its own kind, at a distance or during rapid motion, -in the dusk of twilight or in partial cover, must be of the greatest -advantage and often lead to the preservation of life. Animals of this -kind will not usually receive a stranger in their midst. While they keep -together they are generally safe from attack, but a solitary straggler -becomes an easy prey to the enemy; it is therefore of the highest -importance that, in such a case, the wanderer should have every facility -for discovering its companions with certainty at any distance within the -range of vision. - -"Some means of easy recognition must be of vital importance to the young -and inexperienced of each flock, and it also enables the sexes to -recognise their kind and thus avoid the evils of infertile crosses; and I -am inclined to believe that its necessity has had a more widespread -influence in determining the diversities of animal colouration than any -other cause whatever. To it may probably be imputed the singular fact -that whereas bilateral symmetry of colouration is very frequently lost -among domesticated animals, it almost universally prevails in a state of -nature; for if the two sides of an animal were unlike, and the diversity -of colouration among domestic animals occurred in a wild state, easy -recognition would be impossible among numerous closely allied forms." - -As examples of recognition colouration, Wallace cites, among others, the -white upturned tail of the rabbit--a "signal flag of danger," the -conspicuous white patch displayed by many antelopes, the white marks on -the wing- and tail-feathers of the British species of butcher-birds, the -stone-chat, the whin-chat, and the wheat-ear. - -Wallace therefore asserts, firstly, that recognition marks not only help -herbivorous animals to keep together, but act as a danger signal; the -member of a flock which first catches sight of the enemy takes to its -heels, displaying its white flag, which is the signal of danger to the -other members of the flock. Secondly, that recognition marks prevent the -evils of infertile crosses. Thirdly, that the necessity of being able to -recognise one another has rigidly preserved bilateral symmetry among -animals in a state of nature. - -As regards assertion number one, we would point out that where a flock of -herbivora is being stalked by a beast of prey, the member of the flock -nearest to the enemy--that is to say, the hindmost member--will probably -be the first to observe him. As that creature will be more unfavourably -situated for escape than the rest of the herd, it will not be to their -advantage to follow the line it has taken. Moreover, being at the rear of -the flock, it is not in a good position to take the lead, and its pursuer -is likely to see the danger signal before its friends do. It would thus -seem that "danger signals," while possibly sometimes of service to their -possessors, are on the whole ornaments which might profitably be -dispensed with. Natural selection can scarcely be charged with the -production of a character of such doubtful utility to the organism. - -Moreover, flourishing species of many gregarious animals do not possess -any "signal flag of danger," while, on the other hand, a great many -solitary species display markings that render them very conspicuous when -in motion. Take the case of the famous Indian Paddy Bird (_Ardeola -grayii_). This, when at rest, is coloured so as to be very difficult to -distinguish from its surroundings, but flight transforms it, for it then -displays its milk-white pinions, which would make a perfect danger -signal, if only it were not peculiarly solitary in its habits. Its -gregarious brethren, the Cattle Egrets (_Bubulcus coromandus_), on the -other hand, display no danger signal. - - - Interbreeding of Allied Species - -That these recognition marks prevent the intercrossing of allied species -and the production of infertile hybrids appears to be pure fiction. As we -have already shown, hybrids between allied species are by no means always -infertile. Moreover, species which differ only in colour seem usually to -interbreed in those parts where they meet. - -"This interbreeding," writes Finn, on page 14 of _Ornithological and -Other Oddities_, "occurs where the carrion crow (_Corvus corone_) meets -the hooded crow (_Corvus cornix_), where the European and Himalayan -goldfinches (_Carduelis carduelis_ and _C. caniceps_) encounter each -other, and where the blue rollers of India and Burma (_Coracias indicus_ -and _C. affinis_) come into contact, to say nothing of other cases." - -Of these other cases, the Indian bulbuls of the genus _Molpastes_ form a -very remarkable one. In all places where two of the so-called species -meet they appear to interbreed, and so freely do they interbreed that at -the points where the allied species run into one another it is not -possible to refer the bulbuls to either species. Thus William Jesse -writes of the Madras Red-vented Bulbul (_Molpastes hæmorrhous_) (page 487 -of _The Ibis_ for July 1902): "This bird, although I have given it the -above designation, is not the true _M. hæmorrhous_. I have examined -numbers of skins and taken nests and eggs time after time, and have come -to the conclusion that our type is very constant, and at the same time -differs from all the red-vented bulbuls hitherto described. The -dimensions tally with those given by Oates for _M. hæmorrhous_, while the -black of the crown terminates rather abruptly on the hind neck, and is -not extended along the back, as is the case with _M. intermedius_ and _M. -bengalensis_. On the other hand, as in the two last species, the ear -coverts are chocolate. Furthermore, I may add--although I attach little -importance to this--that the eggs of the Lucknow bird which I have seen -are, without exception, far smaller than my eggs of genuine _M. -intermedius_ from the Punjab. My own opinion is that the Lucknow race is -the result of a hybridisation between the other three species." - -Further, in Bannu, Mr D. Donald saw _M. intermedius_ and _M. leucogenys_ -paired at the same nest. That gentleman could not possibly be mistaken on -the point, as the latter species has white cheeks and yellow under -tail-coverts, while the cheeks of the former species are dark-coloured -and the patch of feathers under the tail is red. Similarly, Whitehead and -Magrath, writing of the birds of the Kurram Valley (_Ibis_, January -1909), record that the former shot no fewer than twelve bulbuls, which -undoubtedly appear to be hybrids between these two species. As these -hybrids differ considerably _inter se_, there seems no room for doubt -that they breed with one another and with the parent species. - - - Symmetry in Nature - -Wallace's third statement, that if the two sides of animals in a state of -nature were alike, easy recognition would be impossible among numerous -closely allied forms, reminds us forcibly of the sad case of the boy -whose tailor was his mother. _Humanum est errare_: she made her son one -pair of trousers that fastened up behind, so that the poor boy when -wearing them never knew whether he was going to or coming home from -school! If animals are able to recognise their mates, their bilateral -symmetry does not seem necessary to enable them to distinguish their -fellows from allied species. - -It is, indeed, true that asymmetrically marked animals are very rarely -seen in the wild state, while they are the rule rather than the exception -among domesticated species. But this appears to be due, not to the -necessity of recognition markings in nature, but to the fact that those -animals that display a tendency to massed pigment perish in the struggle -for existence, since this massing of pigment appears to be correlated -with weakness of constitution. In other words, this massing of pigment is -an unfavourable variation, which under natural conditions dooms its -possessor. In the easier circumstances of domestication, animals which -are irregularly pigmented are able to survive, so that, among them, the -almost universal tendency to the massing of pigment can be followed -without let or hindrance. - -It is unnecessary to say more upon this subject. The few facts we have -set forth suffice to destroy this particular excrescence on the Darwinian -theory. - - - The Colouring of Flowers and Fruits - -Extremely interesting though the subject be, we are unable to consider at -length the generally accepted theory that the colour markings and -perfumes of wild flowers are the result of the unconscious selection -exercised by insects. - -While not denying that many flowers profit by their colouring, that these -colours may sometimes serve to attract the insects, by means of which -cross-fertilisation is effected, we are not prepared to go to the length -of admitting that all the colours, etc., displayed by flowers and floral -structures are due to the unconscious selection exercised by insects. It -is one thing to admit that the colour of its flowers is of direct utility -to a plant; it is quite another to assert that the colour in question -owes its origin and development to natural selection. Our attitude -towards the generally accepted explanation of the colours of flowers is -similar to that which we adopt towards the theory of protective mimicry -among animals. In certain cases we are prepared to admit that the -mimicking organism derives benefit from the likeness; but this, we -assert, is no proof that natural selection has originated the likeness. - - - Cross- versus Self-fertilisation - -The theory that flowers have developed their colours in order to attract -insects to them, and thus secure cross-fertilisation, is based on the -assumption that cross-fertilisation is advantageous to plants. It is -questionable whether this assumption is justified. True it is that -numbers of experiments have been performed, which show that, in many -cases, flowers which are artificially self-fertilised yield comparatively -few seeds. But experiments of this kind do not prove very much. - -To place on the stigma pollen from the anthers of the same flower, in -case of a plant which for many generations has been cross-fertilised, is -to subject the plant in question to a novel experience--an experience -which may be compared to transplanting it to another soil. The immediate -effect may appear to be unfavourable, although, if the experiment be -persisted in, the ultimate results may prove beneficial to the plant. - -That this is the case with some flowers that are artificially fertilised -is asserted by the Rev. G. Henslow. This observer states, that had Darwin -pursued his investigations further, he would probably have modified his -views regarding the benefits of self-fertilisation. Darwin's statement -that "Nature abhors perpetual self-fertilisation" seems to be as far from -the truth as that which declares "Nature abhors a vacuum." - -From the mere fact that cross-fertilised flowers yield a greater quantity -of seed than they do when self-fertilised, it does not necessarily follow -that cross-fertilisation is advantageous. The amount of seed produced is -probably not always a criterion as to the advantages of the crossing to -the plant. Some flowers yield most seed when fertilised by the pollen -from flowers belonging to a different species! - -It is significant that some plants produce cleistogamous flowers, that is -to say, flowers which invariably fertilise themselves. Such flowers never -open; so that the visits of insects are precluded. - -According to Bentham, the Pansy (_Viola tricolor_) is the only British -species of _Viola_ in which the showy flowers produce seeds. The other -species are all propagated by their cleistogamous flowers. The genus -_Viola_ is an advanced species: it would therefore seem that the -production of cleistogamous flowers is an advance on the production of -entomophilous flowers. Cleistogamous blossoms are obviously more -economical. - - - Insects and Flowers - -In the case of the malvas, epilobias and geraniums, where we see, side by -side, races of which the individuals produce insect-fertilised flowers -and those that are characterised by self-fertilised flowers, the latter -are quite as thriving as the former. - -The common groundsel, which, according to Lord Avebury, is "rarely -visited by insects," flourishes like the green bay tree, as many -gardeners know to their cost. The same may be said of the pimpernels. In -this connection it is important to bear in mind that the anemophilous, or -wind-fertilised, angiosperms, as, for example, the grasses, are believed -to be descendants of insect-fertilised or entomophilous forms. - -A weighty objection to the theory that the colours of flowers have been -developed because they attract insects has been urged by Mr E. Kay -Robinson, namely, that among wild flowers the most highly coloured ones -are the least attractive to insects. - -"Show me," writes he, on page 222 of _The Country-Side_ for March 20, -1909, "the insect-collector who will seek for specimens among the -brilliant scarlet poppies. Of what use is the dog rose, with its large -discs of pinky-white, to him? On the other hand, does he not find that by -far the most attractive flowers are the almost invisible spurge laurel -blossoms in February and March, the fuzzy sallow catkins in March and -April, the bramble blossom in midsummer, and the ivy's small green -flowers in autumn? Of these only the bramble has any pretensions to -colour, and if you try, as I have tried, the experiment of picking off -every petal from sprays of bramble blossoms you will find that its -attraction to moths does not appear diminished. - -"The fact that insects do visit many conspicuously coloured flowers does -not show that the colour attracts them, when the fact is borne in mind -that they neglect others which are equally coloured, while the flowers -which they particularly haunt are inconspicuous. Conspicuous flowers -_which have abundance of nectar_ attract insects, of course, but so do -inconspicuous flowers which have nectar. If they have no nectar, neither -the conspicuous nor the inconspicuous flowers attract insects other than -pollen or petal eaters, whose visits are not good for the plant. This -shows that the nectar attracts the insects and that the colour of the -flowers makes no difference." - -In autumn many leaves assume bright and beautiful tints. These are not -believed to be in any way useful to the plant. The autumnal hues and -shades are regarded, and rightly regarded, as the garb of death and -decay. Such colours are the result of the oxidation of the chlorophyll or -green colouring matter of the leaves. Why should not the colours of the -petals of the flowers, which wither and fade long before the green leaves -do, be due to a similar cause? The bright colours of fruits are supposed -to have been effected by natural selection in order to attract -fruit-eating animals. Surely a hungry animal does not require that its -food be brightly coloured in order to find it! We must remember that -during the greater part of the year most animals have no occupation save -that of finding their food. Inconspicuously coloured fruits, like those -of the ivy, are frequently eaten by birds. The bright colours of some -ripening fruits are undoubtedly the colours of decay. Many fungi and -seaweeds have bright colours. It is never hinted that these are of any -direct utility to their possessor. - -Every flower, every plant, every organism must be of some colour. - - - Honey - -Many flowering plants produce honey. This is said by some botanists to -have been directly caused by natural selection, because the honey -attracts insects. Possibly those who take up this attitude are putting -the cart before the horse. It is probable that honey, like oxygen, is an -ordinary product of the metabolism of the plant, and that the visits of -bees and other insects to such plants are the result rather than the -cause of the honey being there. Boisier found that some plants, for -example, _Potentilla tormentilla_ and _Geum urbanum_, gave honey in -Norway, but very little near Paris. - -He further discovered that by supplying certain plants copiously with -water he could induce them to produce more than their normal output of -honey. - -As is their habit, Neo-Darwinians have pushed their pet theory to absurd -lengths in its application to flowers. They assert that the visits of -insects are responsible for not merely the general colour of every -flower, but also the various lines, spots, and other markings of flowers. -The lines that frequently occur on the petals are supposed to guide the -insects to the honey! This particular refinement of Neo-Darwinism, to -quote Kay Robinson, "needs little discussion. Insects have very poor -sight. You can see this when a bee or a butterfly flies bang against a -whitewashed wall; when a wasp pounces upon a black spot on a sunlit -floor, mistaking it for a fly; or when a settled dragon-fly will allow -you to poke it in the face with the end of a walking-stick, although it -will be off like a flash if you raise your arm. There is, therefore, -large reason to doubt whether insects can even see the fine lines in the -throats of flowers which are supposed to guide them to the nectar. It is -rather absurd, too, to suppose that such lines can be needed, since -insects come in swarms to inconspicuous and apparently scentless flowers -or to 'sugared' tree-trunks in the dark. Where there is nectar, insects -which have come to the feast from a distance need no pencilled lines to -guide them over the last quarter of an inch of their journey." - - - Scents of Flowers - -Neo-Darwinians further assert that the scents of flowers have been -developed by natural selection because they serve to attract insect -visitors to the flowers. In support of this contention it is urged that -the most highly scented flowers are not usually the most conspicuous -ones, since it is not necessary for a flower to be both highly coloured -and strongly scented. Again, those flowers which open at night are -usually very highly scented. - -Plausible though this view seems, there are weighty objections to it. -These are so admirably summarised by Kay Robinson in the issue of _The -Country-Side_ for March 27, 1909, that we feel we cannot do better than -reproduce his words:-- - -"It is true that many flowers which are strongly scented are visited by -insects, but these flowers have abundance of nectar, and the insects come -in spite of the scent, and not on account of it. They visit unscented -flowers, provided that they have nectar, equally freely; and they do not -visit flowers which have scent without nectar. - -"Moreover, fruits are more generally scented even than flowers; but what -explanation have those, who attribute the scents of flowers to the tastes -of insects, for the scents of fruits? Insects which visit fruits are only -robbers. Therefore, if we say that plants have scents for the purpose of -attracting insects, we accuse all plants which have scented fruits of -attempted suicide. - -"There are hosts of plants, again, with scented leaves. Here also the -insects are only robbers, and it is quite clear that the scent is not -useful in attracting insects. If, therefore, you adopt the insect theory -to explain the scents of flowers, you must invent entirely new theories -to explain the scents of fruits and leaves." - -It is thus evident that the ordinarily accepted explanation of the -colours, scents, and markings of flowers is far from satisfactory. - - - Kay Robinson's Theory - -Mr E. Kay Robinson has put forth in recent issues of _The Country-Side_ -(March 20, 27, and April 3, 1909) quite a new explanation of the -phenomena, and one which deserves careful consideration. He maintains -that "the real, primary, and original meaning of the colours, markings, -nectar and scents of flowers is not to attract insects, but to deter -grazing and browsing animals." - -"I say," he writes, "that grazing and browsing animals avoid eating -conspicuous flowers. I have watched a flock of five hundred sheep pass -across a yard-wide strip of close-nibbled turf on the Norfolk coast, -grazing as they passed, and the number of open daisy blossoms after they -had passed seemed the same as before they came. Every one of five hundred -sheep had eaten something from that yard of grass, and not one had eaten -any of the hundred and thirty odd daisies. - -"Every summer the farm horses are turned into the same old pasture, and -as the summer wanes the field always presents the same appearance--the -green grass close-grazed, the tall buttercups left standing high. - -"Once, leaning over a gate with friends, I pointed out that a flock of -sheep grazing in a sainfoin field were nibbling the greenstuff close, but -were not eating the flowery stalks, when one sheep near us accidentally -pulled up a whole sainfoin plant by the roots and proceeded to munch it -upwards. Inch by inch the stem passed into its jaws, and I began to be -afraid that it was going to establish an 'exception' to my rule. But, -just when the bright cluster of pink sainfoin blossom was within two -inches of its teeth, it gave an extra nip, and the flower head fell to -the ground, and the sheep resumed its search for greenstuff. - -"I do not say that this would always happen--I should be sorry for any -theory which depended upon the intelligence of a sheep--but it was a very -striking object-lesson to my two companions; and any one who looks around -during this summer with an inquiring mind will find plenty of evidence -that grazing, browsing, and nibbling animals avoid flowers, and stick to -greenstuff when they can get it. - -"I do not say that all animals avoid the same flowers. Horses, for -instance, may dislike large flowers like roses and conspicuous yellow -flowers like buttercups, but they will bite off flat clusters of minute -white or pale yellow flowers, such as yarrow or wild parsnip. These -distinctions made by certain kinds of beasts will probably in the future -be found to afford valuable evidence as to the regions of origin of our -flowers and animals. Such plants as the yarrow and the wild parsnip, for -instance, probably did not originate in the home of the wild horse, -because they are not protected against it. - -"As a general rule, however, there is abundance of evidence that plants -with conspicuous flowers gain a large advantage in the struggle for -existence, because grazing and browsing animals avoid them; while there -is no real evidence at all that conspicuous flowers attract insects." - -Kay Robinson extends this explanation to the shape, the scent, and the -nectar of flowers. He admits that many flowers are adapted to the visits -of insects, but this is, he asserts, but a secondary result. The "real, -primary meaning" of the shapes of flowers of curious configuration is, he -insists, "a deterrent to grazing or browsing animals." - -According to him plants, like the snap-dragon, which have "blossoms in -the semblance of a mouth," are avoided by grazing animals, because they -mistake such flowers for mouths, and have no wish to be bitten! Orchids, -he asserts, "are strongly deterrent to grazing and browsing animals, -which are looking for greenstuff, and regard these gaudy, spidery, winged -blossoms as live creatures." "If this is not the truth," he asks, "will -any adherent of the theory that we owe the shapes of flowers to insects -explain why some of our common British orchids are so like bees, spiders, -etc.? Some which have no particular resemblance to any insect still -exhibit weird shapes, suggestive to the human mind of living things, such -as lizards, etc. The reason why they look like bees, spiders, lizards, -and various unclassed creatures is quite simple. Grazing animals are -looking for greenstuff, and do not wish to eat living creatures which may -bite or sting or taste nasty. Thus the orchids have acquired the power of -looking like creatures. - -"Every one," he continues, "who is familiar with the blossom of the wild -carrot--a flat head of minute, dull-white blossoms--must have noticed how -very often the centre blossom in each head is purplish or reddish-black. -This makes it very conspicuous in the middle of the flat white flower -head. Now what conceivable use can this barren little blackish -blossom--scarcely bigger than a pin's head--be to the wild carrot plant -if we regard the flat head of white flowers as an attraction to the sight -of insects? If, on the other hand, we rightly regard the flat head of -white blossoms as an advertisement to grazing animals that it is not -wholesome greenstuff, but innutritious blossoms liable to be infested -with ants and other stinging insects, we see at once the great use of -this small blackish flower in the middle. It looks like an insect, and -possibly in the home of the wild carrot there is some minute blackish -insect with a peculiarly villainous smell or taste--or perhaps a potent -sting--which grazing animals carefully avoid whenever they can see it. -Thus the wild carrot flourishes; though here in Britain--where the wild -carrot has established itself now--we may fail at first to see the exact -meaning of the trick. I think, however, that, when we understand it, it -fits admirably into the theory that the shapes and colours of flowers are -primarily useful as deterrents to grazing and browsing animals and not as -attractions to insects. - -"Thus we see," he concludes, "that the queer shapes of these orchids, -which are a great stumbling-block in the way of those who preach that we -owe the shapes of flowers to the tastes of insects, become a strong -confirmation of my theory that we owe the shapes of flowers to grazing -and browsing animals." - -Of the nectar of flowers, Kay Robinson writes: "Since this is eagerly -sought for by hosts of insects, whose visits are in most cases useful to -the flowers, it seems only natural to suppose that we see cause and -effect in this connection. - -"Here, however, I will outline my theory of the origin of nectar and of -flowers in general. - -"I think there is no doubt whatever that all the parts of a flower are -modified leaves. The original type of flowering plant--I think we may -safely assume--had a single stem and produced its seed at the summit, as -the crown of its year's endeavour. The flower, before it became what we -would recognise as a flower, was a cluster of protecting leaves round the -seed-making parts of the plant. To the production of the seed the whole -energies of the plant were devoted, and into the cluster of leaves at the -top of the stem all the essences of the plant were concentrated. If -during the coming spring you handle and examine the leaves at the end of -the strong shoots of thorns or fruit bushes, you will find that the -surface of the young leaves is quite sticky. If you observe browsing -animals also, you will discover that--contrary to expectation--they do -not like strong-growing, juicy shoots, evidently preferring mature leaves -lower down the branch. This shows, I think, that plants have the power of -protecting their new shoots by crowding into them the volatile oils and -essences which they produce as a protection against animals. Now nectar -appears always to be distasteful to grazing and browsing animals; and -they also dislike scented flowers. I think, therefore, that it is -reasonable to suppose that the nectar and scents which now distinguish so -many flowers were first produced as an exudation of concentrated sap upon -the surfaces of the protecting leaves round the seed-making parts of the -original flowers. As these leaves became more efficiently protective by -assuming colours, shapes, and markings which warned animals of their -character, so their apparatus for producing scent and honey became -specialised; and at this point the insect appeared upon the scene as a -factor in the life's success of the plant." - -Such, then, is Kay Robinson's bold and original theory. In some respects -it seems far-fetched. The natural inclination is to ask, "Is it possible -that cattle can be so stupid, so blind, as to really believe that a -snap-dragon is the mouth of an animal, or that an orchid is a spider?" - -At present we know so little of animal psychology that we are not yet in -a position to give an answer to this question. Horses, we know, are apt -to be frightened by the most harmless things, such as a piece of brown -paper lying on the road. Mr Robinson's theory should give a stimulus to -the study of the mind of animals--a study which, if properly undertaken, -will probably throw a flood of light upon some of the problems of -evolution. Mr Robinson's theory equally with the ordinarily-accepted -hypothesis, utterly fails to explain the first origins of colours, -scents, etc. When once a flower has acquired a certain amount of colour, -it is easy to understand how that flower may attract insects or repel -grazing animals. But how can the origin of the colour or other -characteristic be explained? - -We asked Mr Kay Robinson how he would account for the great success in -the struggle for existence of some species of grasses on which -herbivorous animals feed so largely. He replied, in the issue of _The -Country-Side_, dated April 3, 1909:-- - -"The grass has a manner of growth which defies the grazing animal. Its -long, thin leaves are constantly pushing upwards from the ground, and, if -they are grazed down one day, they will have pushed up again the next. -Moreover, when the outside blade of grass has exhausted its power of -growing, there is another blade inside it with many inches still to grow, -and another inside that which has scarcely begun to grow, and yet another -further in which has not yet seen daylight; and so on. In a state of -nature grazing animals are nowhere so numerous on any given patch of -ground from day to day as to keep down the grass. If they were, -carnivorous animals would stay there to eat the grazing animals, and grow -fat and multiply. Thus the grazing herds are scattered and wandering, -followed wherever they go by the beasts of prey; and in their absence the -grass pushes ahead, so that when the grazing animals return its clump is -larger and its roots are stronger, and it is better able to survive -attack than before. - -"The method of the clovers and trefoils is quite different. When -circumstances are favourable and enemies few, they will form large-leaved -luxuriant clumps, with fine heads of blossom; but where grazing animals -abound they have the power of adapting themselves to altered -circumstances. They creep so closely along the ground that the teeth of -the grazing animal cannot pick them up between the surrounding grass, and -they produce leaves so small and short-stalked that to eat them would be -like nibbling the pile off velvet. Any clover or trefoil thus growing in -self-defence is accepted as the 'shamrock' of Ireland; and it is -certainly a fine emblem for a race which regards itself as surviving in -spite of incessant oppression. - -"These are the reasons, however, why the grasses and clovers or trefoils -continue to enrich old pastures when most of the other plants disappear, -with the exception of daisies and buttercups, and the acid sorrels." - -We should be glad to hear how Mr Robinson accounts for the conspicuous -flowers in the species of "prickly pear" (_Euphorbia_), which is so -abundant in India, and which is not browsed upon by animals. - -We regret that we are not able to devote more space to this most -interesting theory. We can only add that, even if it fail to become -widely accepted, it is of great value as showing that it is possible to -offer a plausible explanation of a large number of phenomena, which nine -out of ten botanists explain in a very different way. - -So satisfied are the majority of naturalists with the "insect theory," -that they seem of late years to have paid but little attention to the -subject of floral colouration. This affords a striking instance of the -pernicious influence which Neo-Darwinism is exercising on the minds of -men to-day. It tends to stifle research instead of stimulating it. - - - Accepted Theories Unsatisfactory - -We have now dealt with the theory of protective colouration, the theory -of warning colouration, the theory of mimicry, and the theory of -recognition markings. We have shown that although many organisms -undoubtedly derive profit from the fact that they are difficult to see in -their natural surroundings or from their resemblance to other organisms, -the hypothesis that this inconspicuousness or the mimicry of these -animals has been caused by the natural selection of small variations is -untenable. - -Warning colours, we have shown, although a disadvantage to their -possessors, are sometimes seen in nature because they are accompanied by -unpalatability. The theory of recognition markings must, we fear, be laid -to rest in the burial ground of exploded hypotheses. - -The extreme popularity of the existing theories regarding animal -colouration and their very general acceptance are to be attributed, -firstly, to their simplicity; secondly, to the fact that they have thrown -light on many phenomena which previously had seemed inexplicable; -thirdly, that if we assume, as the great majority of biologists do, that -evolution has been effected by the accumulation of numerous variations, -small in degree and indefinite in direction, we seemed forced either to -accept Neo-Darwinism or admit that the whole subject of animal -colouration baffles us, in other words, to reject what appears like -cosmos and substitute for it chaos. - -With a few exceptions, books that deal with the colours of organisms, -while emphasising the evidence in favour of the generally-accepted -theories, seem almost entirely to ignore the host of facts that do not -appear to fit in with them. - -This is largely due to the almost unavoidable bias of the human mind when -obsessed by a pet theory. There are none so blind as those who will not -see. It is also, in part, the consequence of the prevalent neglect of the -scientific method of comparison which leads men to theorise on -insufficient evidence. This, of course, is a natural result of -specialisation in biology. Naturalists are in the habit of confining -their study to the habits of the animals of one particular country and -then making far-reaching generalisations therefrom. - -As an example of the kind of theorising to which this method leads, we -may cite the often-quoted theory which ascribes the green colouring of -some arboreal fruit-eating pigeons to adaptation to an existence among -tropical foliage, and ignores the fact that in America tree-haunting -pigeons are never of this colour, and that it is not by any means -universal even among the old-world pigeons. - - - White Down of Nestlings - -Similarly, a theory has been advanced (W. P. Pycraft, _Knowledge_, 1904, -p. 275) that the white down of some nestling birds, is an adaptation to -resisting the heat of the sun in open nests. This is at once negatived by -the fact that young owls, usually hatched in shaded places, are also -generally white, while young cormorants, living in open nests, are black; -yet the allied darters, with the same breeding haunts in some cases, have -white young. Lest it should be thought that black has some especial value -in a nestling living exposed, we may mention that young petrels, which -are born in holes, have black or dark down. - -As we have already pointed out, naturalists in too readily accepting the -theory that variation is minute in degree and indefinite in direction, -have raised quite unnecessary difficulties, even for the selection -hypothesis. We have cited certain facts, which seem to show that -variations, as a rule, are not indefinite in direction; of these the most -striking is furnished by birds in which the tail feathers are greatly -elongated. Were variations indeterminate, we might reasonably expect to -find that the elongation occurred in one particular feather or pair of -feathers in one species, in another pair in a second species, in a third -pair in a third species, and so on. But this is not the case; no bird has -one _single_ long feather in its tail, and when two are elongated, as is -so commonly the case, these are almost invariably the middle or the -outside pair; _e.g._, in the European bee-eater and pheasant it is the -former, in the swallow and blackcock, the latter. - -Exceptions are so rare that they may almost be said to prove the rule; -_e.g._, although most terns have the outer-tail feathers elongated, in -some of the Noddy Terns (_Anous_, _Gygis_) the third pair, in others the -fourth pair, of tail feathers are the longest. This must mean one of two -things, either that the variation, as regards length in tail feathers, -other than middle or outer, does not ordinarily occur, or that it occurs, -but is, in some way, inimical to the welfare of the species. The latter -hypothesis does not seem probable, as the Noddies are particularly -abundant birds where they occur, that is to say, in the tropical seas; -therefore, we can only conclude that that particular variation has not -occurred in birds as a whole. - -We have adduced abundant evidence to show that mutations or discontinuous -variations occur in nature; and as these afford much more favourable -material on which natural selection can act, it is reasonable to suppose -that they have played a considerable part in evolution. - -When discussing the phenomena of inheritance, we attempted to show that, -not improbably, these discontinuous variations are due to some -re-arrangement in the constituent parts of the unit characters, or -biological molecules, as we have called them. - - - Cranes - -In this connection we may mention the apparently singular phenomenon of -different species in the same natural group, exhibiting either a definite -excess or deficiency of plumage on the head. Among cranes, most species -are more or less bald; but the Demoiselle (_Anthropoides virgo_) has a -fully-feathered head with long side-plumes, while the head of the Stanley -Crane (_A. paradisea_) appears to be swollen, so abundantly is it -feathered. The crowned cranes, although bare-cheeked, have double crests, -the two parts of which have been respectively compared to a pen-wiper and -a bunch of toothpicks! - -Among the guinea-fowls, several species are crested, while others, as, -for example, the domestic one, are bare-headed. Now, on the theory of -evolution, by accumulation of minute variations, phenomena such as these -are difficult of explanation; but, on the assumption that a slight -rearrangement of the biological atoms in the molecule may produce very -diverse results, as we see in the case of chemical molecules, and of -seasonally dimorphic butterflies, there is no particular ground for -surprise at such a phenomenon. - -In this connection we may cite the significant fact, so well known to -canary breeders, that two crested birds when mated tend to produce a -bald-headed one. - -If the colour of any part of an organism be due to the internal -arrangement of the constituent parts of the biological molecule from -which it is derived, we should expect any rearrangement of the component -parts to produce quite a different colour. In other words, we should -expect occasionally to see colour-mutations. These are precisely what we -do see. Similarly, if the scheme of colouring of an organism be due to a -certain grouping of biological molecules, we should expect the same -scheme of colouring to occur in organisms which are not nearly related. -This, too, we observe in nature. - -Many of the phenomena of mimicry, and all the cases which we have cited -as pseudo-mimicry, seem to us to be referable to this. - - - Magpie Colouring - -Take, for example, the magpie colouration in birds--that is to say, a -scheme of colouring in which the body is white, and head, wings, and tail -black. This occurs in the following birds belonging to the most diverse -groups:-- - -The Magpie. - -The Magpie Tanager (_Cissopis leveriana_). - -The Magpie Robin (_Copsychus saularis_), cock only; in the hen the black -is replaced by brownish grey. - -The Pied Honeyeater (_Entomophila picata_). - -The Chaplain Crow (white-bodied form of the hoodie crow). - -The New Ireland Swallow Shrike (_Artamus insignis_). - -The Magpie Goose (_Anseranas melanoleucus_). - -Combinations of this kind, in which the black is replaced by brown or -grey, are excessively rare. - -On the other hand, we see in several birds the combination in which the -white is replaced by yellow:-- - -The Common Troupial (_Icterus vulgaris_). - -The Black-headed Oriole (_Oriolus melano cephalus_). - -The Black-and-yellow Grosbeak, male only. - -What we may call imperfect magpie colouration, _i.e._ where the head -becomes white, occurs in several species of birds. The head of a black -species sometimes becomes white as a mutation; in the domestic Muscovy -duck, for example, an individual is sometimes produced having a white -head, although the black of the remainder of the plumage remains -unchanged. - -As examples of this scheme of colouration we may cite-- - -Black-and-white Fruit Pigeons (_Myristicivoræ_). - -Several Gannets (_Sula capensis_, _S. serrator_, etc.) - -Swallow-tailed Kite (_Elanoides furcatus_). - -Several Storks (_Euxenura maguari_, _Anastomus oscitans_, _Pseudotantalus -cinereus_). - -Moreover, a common variety of the barn-door fowl has also a white body -and black primaries and tail, showing that this scheme of colour may -arise as a mutation. - -A further elimination of black in the tail and body leads us to white -birds with more or less black wings:-- - -White Storks (_Ciconia alba_, _C. boyciana_, and _Euxenura maguari_). - -The White Crane (_Grus leucogeranus_). - -The Snow Geese (_Chen nivalis_, _C. rossi_). - -The Common Gannet (_Sula bassana_). - -The White Buzzard (_Leucopternis_). - -The Scavenger Vultures (_Neophron_). - -A recurring combination in mammals is black, with a white marking on the -breast. - -Most of the bears, even young brown bears, show a tendency to this. It is -also found in the Tasmanian devil, and in varieties of our domestic cats, -rats, and dogs; also in the domestic duck. - -The white-spotted pelage, not uncommon in deer, especially fawns, is -curiously repeated in the Australian carnivorous marsupials, known as -Native Cats (_Dasyurus_). - -In domestic animals we frequently find the following localisation of -white--white socks, collar, breast, and muzzle. The arrangement occurs in -cats, dogs, rabbits, guinea-pigs and mice, also in the horse and pig, but -without the collar. The arrangement is not seen in goats, cattle, or -sheep, nor in wild animals of any kind. This would lead to the conclusion -that the combination is correlated with some character unfavourable to -survival under natural conditions. - -Many variations which frequently occur among both wild and domestic -animals do not persist in nature. - - - Albinos - -As instances of such variations we may mention pure albino forms, that is -to say those in which pigment does not occur in the eyes. - -It is easy to see why this variation is not allowed to persist in nature. -Its possessors are handicapped by bad eyesight, and so have no chance of -surviving in the struggle for existence. It is thus that natural -selection acts. On the other hand, white species with pigmented eyes are -fairly numerous. These enjoy normal eyesight, but labour under the -disadvantage of being easily seen by their foes. Hence we find that white -species generally either occur in a snowy habitat, or are powerful and -both able and ready to defend themselves. In this connection it is -interesting to notice that in New Zealand all birds, whether introduced -or indigenous, are particularly liable to albinism. Owing to the fewness -of their enemies these albinistic forms are able to persist. - -A variation, or rather a mutation, that frequently occurs among -domesticated birds, but which is seen in very few wild species, is that -which takes the form of white primary feathers on the wing. This -variation must often occur in nature, but it rarely establishes itself, -apparently because white feathers do not resist wear so well as coloured -ones do. - - - Biological Molecules and Colour - -Black-and-yellow colouration occurs in several widely separated species -of birds. The arrangement of the two colours follows to some extent the -same rules as the black-and-white combination. - -Several birds have a yellow body with black head, wings, and tail, such -as-- - -The Black-headed Oriole (_Oriolus melanocephalus_). - -The Black-and-Yellow Grosbeaks (_Pycnorhamphus icteroides_, _P. affinis_) -(cock). - -The Common Troupial (_Icterus vulgaris_). - -In others the black on the head is nearly or quite suppressed, that on -the tail remaining to a greater or less extent; such are-- - -The Golden Orioles (_Oriolus galbula_, _O. kundoo_, etc.). - -Several species of _Icterus_. - -Several fly-catchers of the genus _Piezorhynchus_ (males only). - -[Illustration: BRAZILIAN TROUPIAL] - -[Illustration: INDIAN BLACK-HEADED ORIOLE] - - -We have said sufficient to show that certain combinations of colours -recur in nature in species which are neither nearly related to one -another nor subjected to similar environment. For such phenomena it is -difficult, if not impossible, to account on the theory that natural -selection, acting on minute variations, is responsible for all the varied -colouring of the animal kingdom. The facts, however, are in accordance -with the supposition that the organism is the result of the growth and -development of a number of units or biological molecules which exist in -the fertilised egg. - -If there be any truth in the supposition, the colouration of every animal -must be due to the development of one or more of these molecules. -Colouration may be expression of the arrangement of all the molecules in -the fertilised egg, or it may be due to the development of a number of -molecules whose function is to determine the colouring of an organism, or -it may be the result of the development of one such molecule, which -perhaps splits up in such a way that a portion attaches itself to each of -the other molecules. - -But it is idle to speculate on this point. As we have already insisted, -the tendency to build up elaborate theories on very slender foundations -is a too frequent failing of zoologists. We desire merely to emphasise -the fact that the phenomena of animal colouration almost force us to the -conclusion that the colouring of each organism is the result of the -development of a number of units. - -It may be objected that, if this be the case, the number of the units -which contribute to the colour of any organism must be exceedingly large, -since we see in nature an almost limitless number of different schemes of -colouring. If the colour of each animal be the result of the development -of a few units, it might be thought, firstly, that the diversity of -schemes of colouration which we observe in nature could not possibly -occur; and secondly, that, under such circumstances, the colour pattern -of a bird or beast should be of the nature of a mosaic, each colour being -sharply defined and separated from every other colour, instead of the -colours shading one into the other, as is so frequently the case. - -Such objections would be based on a misconception as to the nature of the -units which combine to produce the colouration of an organism. _These -units show themselves as centres of development of colour_, as points -from which the colour or colouring they represent spreads, until it meets -and mingles with other patches of colour which are being developed from -other centres. The colour produced at one centre may spread more rapidly -than that which forms at another; this, of course, will result in a -preponderance in the organism of the colour which is produced at the -former centre. - -Further, we must bear in mind that the development of each -colour-producing unit is largely affected by conditions external to it, -as we shall see when dealing with Sexual Dimorphism. - -More than one naturalist, who has paid careful attention to the subject -of animal colouration, has perceived that through the apparently endless -diversity of the colouring of organisms something like order runs. - - - Mr Tylor Quoted - -Over thirty years ago Mr Alfred Tylor called attention to this important -fact. That observer, whose views met with the approval of Wallace, was of -opinion that colour follows structure, and that in a many-hued animal it -changes at points where the function changes. - -"If," writes Mr Tylor, "we take highly decorated species--that is, -animals marked by alternate dark or light bands or spots, such as the -zebra, some deer, or the carnivora, we find, first, that the region of -the spinal column is marked by a dark stripe; secondly, that the regions -of the appendages, or limbs, are differently marked; thirdly, that the -flanks are striped or spotted, along or between the regions of the lines -of the ribs; fourthly, that the shoulder and hip regions are marked by -curved lines; fifthly, that the pattern changes, and the direction of the -lines, or spots, at the head, neck, and every joint of the limbs; and, -lastly, that the tips of the ears, nose, tail, and feet, and the eyes are -emphasised in colour." - -More recently Mr J. Lewis Bonhote has devoted much attention to this -important subject. The results of his researches are summarised on page -185 of vol. xxix. of the _Proceedings of the Linnæan Society_, and on -page 258 of the _Proceedings of the Fourth International Ornithological -Congress_, 1905. Mr Bonhote states that the presence or absence of colour -tends almost invariably to make its appearance, first of all, on certain -definite tracts, common to mammals and birds alike, which he calls -_poecilomeres_. - - - Poecilomeres - -"Poecilomeres," he writes, "are situated on the following parts, viz., -chin, malar stripe, maxillary stripe, a spot above and slightly in front -of the eye, a spot below or slightly behind the eye, the ear, crown of -the head, occiput, fore-end of sternum, vent, rump, thighs, wrist, -shoulders (above and below). - -"Now, there is hardly any species of bird on which one or more of these -poecilomeres is not 'picked out' (to use a painter's expression) in some -colour different from that of the surrounding parts, and, in fact, most -of the so-called recognition or protective markings will be found on -these patches. - -"On the other hand, among many species the differentiation of colour on -the poecilomeres is not so conspicuous as to attract the eye or to serve -in any way for protection or mimicry, _yet we still find them marked by -differences of colour so slight that, unless especially looked for, they -would never be noticed_. - -"Or, again, some species occasionally, but not invariably, show a few -white feathers on certain parts of their body, and, when such is the -case, it will be found that these white feathers appear on the -poecilomeres. . . . There is hardly a species in which examples of these -poecilomeres may not be found. . . . The Kingfisher (_Alcedo ispida_) -shows the various head poecilomeres very clearly, and as examples of -inconspicuous differences on these tracts, the rump of the hen sparrow -(_Passer domesticus_) and hen chaffinch (_Fringilla coelebs_), the malar -stripe and dark ear-patch of the hen Yellow Bunting (_Emberiza -citrinella_), and the dark ante-orbital patch of the Barn Owl (_Strix -flammea_) are familiar examples. And, lastly, as an instance of the class -where a few white feathers frequently, but not invariably, appear, the -young of the cuckoo (_Cuculus canorus_) forms a good example. - -"These spots may, however, appear in a transitory manner, as, for -instance, where a change of plumage (not necessarily moult) is -occurring." - -As an instance of this, Bonhote cites the case of a young male Shoveler -(_Spatula clypeata_), "in which the metallic colour on the head first -showed itself on the post-orbital and auricular poecilomeres, gradually -meeting and joining up across the head with the crown and occipital -poecilomeres, and then finally spreading forwards. And it may be well to -note that the joining up of the auricular and post-orbital poecilomeres -formed a metallic patch similar in size and position to that found in the -male Teal (_Querquedula crecca_), and, further, in the last stage, when -the whole head, except the portion round the beak, was metallic, the -markings are similar to those found permanently in the hen Scaup -(_Fuligula marila_). - -"Now, these resemblances taking place in the normal pure-bred wild -shoveler, the question of reversion does not come in, and no one would -suppose these resemblances due to anything more than transitional -variation, and it is the object of this portion of the paper to show that -variation in colour follows along definite lines." - - - Biological Molecules - -Mr Bonhote continues: "As a further illustration of how widely spread -these lines are throughout the mammalian and avian kingdoms, we may note -the assumption of the brown head in the case of the Black-headed Gull -(_Larus ridibundus_), which invariably follows each year on lines similar -to those related in the case of the shoveler, and . . . the method by -which, on the approach of winter, the stoat assumes his white dress, is -(although the change is from brown to white) again conducted along -precisely similar lines." Mr Bonhote argues with great force that, as the -process occurs in two animals so widely separated, the fundamental cause -must be a deep-seated one. There can be no doubt that these poecilomeres -of Bonhote are connected with our biological molecules. Each of these -poecilomeres is the result of the development of one of these unit -characters; each is to be regarded as the centre of activity, the sphere -of influence of a biological molecule, or the portion of one, which -controls the colouring of a definite region of the organism. In the case -of creatures which display the same colour throughout, these molecules -all give rise to the same kind of colouring; in the case of animals which -display a variety of colours and markings the various molecules give -origin to various colours. But we must bear in mind that the final colour -to which each colour-producing molecule gives rise depends to some extent -on circumstances other than the constitution of the molecule. Thus it is -that the young in most organisms differ in colour and marking from the -adults. On this also depends the phenomena of seasonal and sexual -dimorphism. The same colour-producing molecule may give rise to one -colour under one set of conditions and to a totally different colour -under another set of conditions. - -It is a significant fact that under abnormal conditions the feathers of -birds tend to disappear precisely on those spots where the poecilomeres -of Bonhote occur. - -Thus in a sickly cage bird the feathers frequently show a tendency to -fall off on the following spots: crown of head, lores, jaws, head -generally, rump, vent and thighs. - -Many wild birds--as, for example, the cranes--display patches of naked -skin on the head, and these are usually situated on poecilomeres. -Similarly, natural excessive developments of plumage tend to occur on the -poecilomeres, or, rather, the spots characterised by poecilomeres--for -example, the train of the peacock. Loral plumage, it is true, is seldom -long, but is often of a peculiar nature. - -Colour mutations tend to occur on the poecilomeres. Thus it is that these -poecilomeres often form the distinctive characters and markings of allied -species. This is precisely what we should expect if the poecilomeres -correspond to biological molecules and mutations are the result of the -rearrangement of the constituent parts of these molecules. - -Still more significant is the fact that the colour-markings in hybrids -tend to follow poecilomeres. - -Bonhote has performed a large number of experiments in hybridising ducks. -Some of his hybrids were produced from three pure ancestors, as, for -example, the pintail, the spotbill, and the mallard; others from two -ancestors. Some of these hybrids were crossed with other hybrids, and -others with the parent forms, hence Bonhote secured a number of hybrids, -each of which had a distinctive appearance; but _all_ the variations -appearing among the hybrids were found to start on one or more of the -poecilomeres. - -Certain of the hybrids showed a resemblance to one or other of the parent -species, others were unlike either parent, and resembled either no known -species or species other than their parents. - -When a hybrid shows a resemblance to a species other than that to which -either parent belongs, it is said to exhibit the phenomenon of atavism or -reversion,--the individual is supposed to have been "thrown back" to an -ancestral form. - -The true explanation of the phenomenon would seem to be that, as the -result of the crossing, biological molecules in the fertilised egg have -been formed which, on development, give rise to combinations of colour -like those seen in other species. - -Thus the phenomena of "mimicry" and "reversion" are, we believe, due to -the fact that in the fertilised egg of both the pattern and its copy a -similar arrangement of biological molecules obtains. If we regard the -sexual act as resembling in many respects a chemical synthesis, the -phenomenon need not surprise us. - -To sum up, the observed facts of animal colouration seem to indicate that -there are in each organism some twelve or thirteen centres of colouring, -which we suggest may correspond with portions of the fertilised egg. From -each of these centres the colour develops and spreads, so that every part -of the organism is eventually coloured. These centres of colouring are -not altogether independent of one another. Sometimes they all give rise -to the same hue, in which case we have a uniformly-coloured organism, -such as the raven. More often from some one colour develops, and from -others another colour; if these two colours happen to be black and white, -the result is a pied organism, which displays a definite pattern due to -the correlation of the various colour-producing biological molecules. - -Thus it occasionally happens that two widely different organisms exhibit -very similar markings, and therefore resemble one another. When this -resemblance is believed to be of advantage to one or other of the -similarly-coloured species, naturalists call it mimicry, and assert that -the likeness is due to the action of natural selection; but where neither -organism can profit by the resemblance, zoologists make no attempt to -explain it. What we suggest is that the colouration of an animal depends -upon the structure, or, at any rate, the nature, of the parts of the egg -which produce these centres of colour. But this is not by any means the -only cause that determines the colouration of the organism. If it were, -young creatures in their first plumage would invariably resemble the -parents, the two sexes would always be alike, and there would be no such -phenomenon as seasonal dimorphism. - -As a matter of fact, the portions of the egg (we call them, for the sake -of clearness, colour-producing biological molecules) which give rise to -the poecilomeres exhibit themselves merely in the shape of tendencies; -the ultimate form the colouring will take depends to a large extent upon -other and extraneous circumstances, such as the secretion of hormones. - -Thus it is that organisms seem to display an almost endless diversity of -colouration. But beneath all this diversity we see something like order. -It occasionally happens (_why_, we do not know) that one, or more, of the -biological molecules which make up the nucleus of the fertilised ovum -becomes altered in the sexual act, with the result that a discontinuous -variation or mutation appears in the resulting organism. The mutation may -be a favourable one, or one which does not affect in any way the chances -of an organism in the struggle for existence, or an unfavourable one. In -the last of the three cases the organism will perish early and not leave -behind any offspring exhibiting its peculiarity. - -It is thus that natural selection acts. Natural selection weeds out -relentlessly all organisms which display unfavourable variations. It is -thus obvious that many species may, and we believe do, exist which -possess characters of no direct utility to them, or even slightly harmful -ones. For this reason Wallace and his followers fail in their attempts to -prove that every patch of colour in every organism is of direct utility. -Natural selection has to take an animal as it finds it--the good with the -bad. If an organism as a whole is not wanting--that is to say, if it is -able to hold its own against other organisms, and is fitted to fill any -place in nature--that organism will probably survive, although it may be -defective in many respects. As its name implies, natural selection is a -mere selecting agency. It has to choose from what is presented to it. It -is not, as many seem to think, a manufacturer or inducer of variations. -Natural selection can no more _make_ an animal vary in any given -direction than the human breeder can. Its power is limited to the -destroying of all variations which do not pass the test prescribed by it. - - - - - CHAPTER VII - SEXUAL DIMORPHISM - - - 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--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. - -In some species the sexes are so similar in appearance that it is not -possible to tell by mere outward inspection to which sex a given -individual belongs. - -In other species the sexes differ so widely in external appearance that -it is difficult to believe that the male and the female belong to the -same species. Between these two extremes are a great number of species in -which the sexes are more or less dissimilar. Those species in which the -sexes differ in appearance are said to be sexually dimorphic. The -phenomena of sexual dimorphism are fatal to that form of Neo-Darwinism -which sees in natural selection an explanation of all the peculiarities -of animal structure and colouration. - -It is not easy to understand how natural selection can have caused marked -sexual dimorphism in a species where the habits of the sexes are the -same, in the Paradise Flycatcher (_Terpsiphone paradisi_), for example, -where the cock and the hen obtain their food in the same way, and share -equally the duties of nest-building, incubation, and feeding the young. - -Of course, in all species where each individual carries only one of the -two kinds of sexual organs, there must of necessity be some slight -difference between the individuals that carry the male organ, which -performs one function, and those that carry the female organ, which -performs another function. - -But in many species the sexes display differences which have no direct -connection with the generative organs--for example, the deer, where the -stag alone has horns. - -Those characters which differ with the sex, but are not directly -connected with the organs of reproduction, are known as secondary sexual -characters. - -[Illustration: QUEEN WHYDAH] - - - Theory of Sexual Selection - -In nearly all species where the male and female differ in beauty, it is -the male who surpasses the female. Natural selection is, in many cases, -not able to explain the origin of these differences, or why, when they -occur, the male should be more beautiful than the female. This Darwin -saw. In order to account for the phenomena of sexual dimorphism, he -formulated the theory of sexual selection. This hypothesis is based on -the assumption that there is, in all species of animals, a competition -among the males to secure females as mates. It is not difficult to -understand how this competition arises in polygamous species. Assuming -that approximately equal numbers of males and females are born (an -assumption which appears to be justified as regards the majority of -species), it is clear that for every male who secures more than one wife, -at least one male will be obliged to live in a state of single -blessedness. - -But how can there be competition in the case of monogamous species? The -sexes being approximately equal in number, there are sufficient females -to allow of a mate for every male. - - - The Law of Battle - -Such is the nature of things, said Darwin, that, even under these -circumstances, there is competition among the males for females. - -"Let us take any species," he writes, on page 329 of _The Descent of Man_ -(Ed. 1901), "a bird for instance, and divide the females inhabiting a -district into two equal bodies, the one consisting of the more vigorous -and better-nourished individuals, and the other of the less vigorous and -healthy. The former, there can be little doubt, would be ready to breed -in the spring before the others; and this is the opinion of Mr Jenner -Weir, who has carefully attended to the habits of birds during many -years. There can also be no doubt that the most vigorous, best nourished, -and earliest breeders would on an average succeed in rearing the largest -number of fine offspring. The males, as we have seen, are generally ready -to breed before the females; the strongest, and with some species the -best armed of the males, drive away the weaker; and the former would then -unite with the more vigorous and better-nourished females, because they -are the first to breed. Such vigorous pairs would surely rear a larger -number of offspring than the retarded females, which would be compelled -to unite with the conquered and less powerful males, supposing the sexes -to be numerically equal; and this is all that is wanted to add, in the -course of successive generations, to the size, strength, and courage of -the males, or to improve their weapons." - -From this competition among the males there arise, firstly, contests -between the males for mates; secondly, the preference of the females for -favoured males. - -It is a matter of common knowledge that at the breeding season the males -of nearly all, if not all, species are very pugnacious. Two males often -engage in desperate fights for one or more females; the victor drives -away his foe and secures the harem. In such contests the stronger male -wins, and thus emerges that particular form of sexual selection which -Darwin termed "the law of battle." - -"There are," writes Darwin, on page 324 of _The Descent of Man_, "many -other structures and instincts which must have developed through sexual -selection--such as the weapons of offence and the means of defence of the -males for fighting with and driving away their rivals--their courage and -pugnacity--their various ornaments--their contrivances for producing -vocal or instrumental music--and their glands for emitting odours." The -former characters have, according to Darwin, been developed by the law of -battle, and the latter, since they serve only to allure or excite the -female, by the preference of the female. - -"It is clear," continues Darwin, "that these characters are the result of -sexual and not of ordinary selection, since unarmed, unornamented, or -unattractive males would succeed equally well in the battle for life and -in leaving a numerous progeny, but for the presence of better-endowed -males. We may infer that this would be the case, because the females, -which are unarmed and unornamented, are able to survive and procreate -their kind. . . . Just as man can improve the breed of his game-cocks by -the selection of those birds which are victorious in the cockpit, so it -appears that the strongest and most vigorous males, or those provided -with the best weapons, have prevailed under nature, and have led to the -improvement of the natural breed or species." - - - Selection by Females - -"With mammals," says Darwin (_loc. cit._, p. 763), "the male appears to -win the female much more through the law of battle than through the -display of his charms." - -In the case of birds, however, feminine preference comes more into play. -It is well known that cocks display their charms to the hens at the -breeding season, and Darwin believed that the hen selected the most -beautiful of her rival suitors. - -"Just as man," he writes (p. 326 of _The Descent of Man_, new edition, -1901), "can give beauty, according to his standard of taste, to his male -poultry, or, more strictly, can modify the beauty originally acquired by -the parent species, can give to the Sebright bantam a new and elegant -plumage, an erect and peculiar carriage, so it appears that female birds -in a state of nature have, by a long selection of the more attractive -males, added to their beauty or other attractive qualities." - -Thus the theory of sexual selection is based on three assumptions. -Firstly, that there is in all species competition among the males for -females with which to mate. Secondly, that this results in either "the -law of battle" among the males, or selection by the female of one among -several admirers. Thirdly, that the female selects, as a rule, the most -attractive of her suitors. - -The evidence upon which Darwin founds this theory may be thus -summarised:-- - -1. In cases where the sexes differ in appearance, or power of song, it is -almost invariably the cock who is the more beautiful or the better -singer, as the case may be. - -2. All male birds that possess accessory plumes or other attractions, -make a most elaborate display of these before the females at the mating -season, hence "it is obviously probable that these appreciate the beauty -of their suitors." - -3. Darwin was able to cite specific instances in which the hens showed -preference. - -In the case of polygamous species there can be no doubt that there is -considerable competition among males for their wives. It cannot be said -that the contention is so well established in the case of monogamous -species. D. Dewar suggests that circumstances may occur in which the hens -have to fight for the cock, or in which the male is in the happy position -of being able to select his mate. He states his belief that in many cases -the selection is mutual, as in the case of human beings. - -"I have seen," he writes, on page 13 of _Birds of the Plains_, "one hen -Paradise Flycatcher (_Terpsiphone paradisi_) drive away another and then -go and make up to a cock bird. Similarly, I have seen two hen orioles -behave in a very unladylike manner to one another all because they both -had designs on the same cock. He sat and looked on from a distance at the -contest." - -Darwin quotes, on page 500 of _The Descent of Man_, a case of a male -exercising selection: "It appears to be rare when the male refuses any -particular female, but Mr Wright of Geldersley House, a great breeder of -dogs, informs me that he has known some instances: he cites the case of -one of his own deerhounds who would not take any notice of a particular -female mastiff, so that another deerhound had to be employed." - -Similarly, Finn records, in _The Country-Side_ for August 29th, 1908, -that the male Globose Curassow (_Crax globicera_) in the London -Zoological Gardens, which bred with the female Heck's Curassow (_C. -hecki_), as related on p. 104, selected the hen of this very distinctly -coloured form or species in preference to any of the typical hens of his -own kind. - - - Male Attractiveness - -The cases on record of cocks being in a position to select their mates -are comparatively rare, while instances of selection on the part of the -hens are far more numerous. - -Hence it would seem that the sex, which is in a minority, and so has the -opportunity of selecting a mate, does exert a choice and prefer one -particular individual; and that, for the reasons pointed out by Darwin, -it is in most cases the female who is in the position of being able to -pick and choose her mate. It is, as Darwin truly said, far more difficult -to decide what qualities determine the choice of the female. He believed -that it is "to a large extent the external attractions of the male, -though no doubt his vigour, courage, and other mental qualities come into -play." - -Darwin argued that it is the love of hen birds for "external attractions" -in cock birds that has brought into being all the wonderful plumes that -characterise such birds as the peacock. "Many female progenitors of the -peacock," he writes, on page 661 of _The Descent of Man_ (ed. 1901), -"during a long line of descent, have appreciated this superiority, for -they have unconsciously, by the continued preference of the most -beautiful males, rendered the peacock the most splendid of living birds." - -This conclusion has been vigorously attacked. It is argued, with some -show of reason, that it is absurd to credit birds with æsthetic tastes -equal, if not superior, to those of the most refined and civilised of -human beings. - -Is it likely, it is asked, that a bird, which will nest in an old shoe -cast off by a tramp, can appreciate beauty of plumage? - -As Geddes and Thomson say (page 29 of _The Evolution of Sex_), "When we -consider the complexity of the markings of the male bird or insect, and -the slow gradations from one step of perfection to another, it seems -difficult to credit birds or butterflies with a degree of æsthetic -development exhibited by no human being without special æsthetic -acuteness and special training. Moreover, the butterfly, which is -supposed to possess this extraordinary development of psychological -subtlety, will fly naively to a piece of white paper on the ground, and -is attracted by the primary æsthetic stimulus of an old-fashioned -wall-paper, not to speak of the gaudy and monotonous brightness of some -of our garden flowers. Thus we have the further difficulty, that we must -suppose the female butterfly to have a double standard of taste, one for -the flowers which she and her mate both visit, the other for the far more -complex colourings and markings of the males. And even among birds, if we -take those unmistakable hints of real awakening of the æsthetic sense -which are exhibited by the Australian bower-bird or by the common jackdaw -in its fondness for bright objects, how very rude is his taste compared -with the critical examination of infinitesimal variations of plumage on -which Darwin relies. Is not, therefore, his essential supposition too -glaringly anthropomorphic? - -"Again, the most beautiful males are often extremely combative; and on -the conventional view this is a mere coincidence, yet a most unfortunate -one for Mr Darwin's view. Battle thus constantly decides the question of -pairing, and in cases where, by hypothesis, the female should have most -choice, she has simply to yield to the victor." - -Darwin, with characteristic fairness, quotes some instances which appear -to be opposed to the theory that the hen selects the most beautiful of -her suitors. He informs us that Messrs Hewitt, Tegetmeier, and Brent, who -have all had a long experience of domesticated birds, "do not believe -that the females prefer certain males on account of the beauty of their -plumage. . . . Mr Tegetmeier is convinced that a game-cock, though -disfigured by being dubbed and with his hackles trimmed, would be -accepted as readily as a male retaining all his natural ornaments. Mr -Brent, however, admits that the beauty of the male probably aids in -exciting the female; and her acquiescence is necessary. Mr Hewitt is -convinced that the union is by no means left to mere chance, for the -female almost invariably prefers the most vigorous, defiant, and -mettlesome male"; and, in consequence, when there is a game-cock in the -farmyard, the hens will all resort to him in preference to the cock of -their own breed. Darwin thinks that "some allowance must be made for the -artificial state in which these birds have long been kept," and cites in -his favour the case of Mr Cupples' female deerhound that thrice produced -puppies, and on each occasion showed a marked preference for one of the -largest and handsomest, but not the most eager, of four deerhounds living -with her, all in the prime of life. - -The question what is it that determines the choice of the female is -obviously one of considerable importance, and it was to be expected that -many zoologists would have conducted experiments with a view to deciding -it. This legitimate expectation has not been realised. - -The matter of sexual selection remains to-day practically where Darwin -left it. Wallace rejects the whole theory, and believes that natural -selection alone can explain all the phenomena of sexual dimorphism. To -such an extent does the enticing idea of the all-puissance of natural -selection dominate the minds of scientific men that but few of them have -paid any attention to the question of sexual selection. This neglect of -the subject affords an example of the baneful results of the too-ready -acceptance of an enticing theory, "Natural selection explains everything, -why then investigate further?" seems to be the general attitude of our -present-day naturalists. - -Edmund Selous and D. Dewar have made some observations on birds, and the -Peckhams on spiders, in a state of nature. Such observations demonstrate -that selective mating occurs in nature, but, for the most part, fail to -show what it is that determines the choice. - -D. Dewar, however, states (_Birds of the Plains_, p. 42) that the -coloured peahens in the Zoological Gardens at Lahore show a decided -preference for the white cocks, which are kept in the aviary along with -normally coloured cocks. He gives it as his opinion that "the hens select -the white cocks, not because they are white, but because of the strength -of the sexual instincts of these latter. The white cocks continually show -off before the hens; the sexual desire is developed more highly in them -than in the ordinary cocks, and it is this that attracts the hens." - - - Pearson's Investigations - -The only zoologists who have investigated experimentally the question of -sexual selection appear to be Karl Pearson and Frank Finn. The former -tried to determine, by actual measurements, whether there is any -preferential mating among human beings as regards physical -characteristics. "Our statistics," he writes, on page 427 of _The Grammar -of Science_, "run to only a few hundreds, and were not collected _ad -hoc_. Still, as far as they go, they show no evidence of preferential -mating in mankind on the basis of stature, or of any character _very_ -closely correlated with stature. Men do not appear, for example, to -select tall women for their wives, nor do they refuse to mate with very -tall or very short women." As regards eye-colour, Pearson seems to have -arrived at somewhat more definite results. "We conclude," he writes (p. -428), "that in mankind there certainly exists a preferential mating in -the matter of eye-colour, or of some closely allied character in the -male; in the case of the female there also appears to be some change of -type due to preferential mating. . . . The general tendency is for -lighter-eyed to mate, the darker-eyed being relatively less frequently -mated." - -But Pearson's experiments seem to show that as regards stature and -eye-colour there is "a quite sensible tendency of like to mate with -like." "In fact," writes Pearson, "husband and wife for one of these -characters are more alike than uncle and niece, and for the other more -alike than first cousins." He adds, "Such a degree of resemblance in two -mates, which we reasonably assume to be not peculiar to man, could not -fail to be of weight if all the stages between like and unlike were -destroyed by differential selection." - -Two obvious criticisms of the results obtained by Prof. Pearson occur to -us. The first is that his conclusions do not seem to be in accordance -with the popular notion that fair-haired men prefer dark hair in a woman, -while dark-haired men prefer fair-haired women, and _vice versa_. The -second is that the human animal is not a typical one. Husbands and wives -are selected for mental and moral qualities rather than physical ones. -The same may, of course, be to some extent true of animals, but in these -there must of necessity be far less variation as regards mental -attributes. Moreover, the question of income is much bound up with human -matrimonial alliances; a rich man or woman has the same advantage in -selection as is possessed by an animal endowed with more than the average -physical strength of its species. - - - Finn's Experiments - -Finn adopted the plan of experiment suggested by Prof. Moseley. His -apparatus consisted of a cage divided into three compartments by wire -partitions, so that a bird living in one of them could see its neighbour -in the next compartment. In the middle compartment he placed a hen -Amadavat (_Sporæginthus amandava_), and in each of the other compartments -he put a cock bird. Under such circumstances, the hen in the middle -compartment will sit and roost beside the cock she prefers. The male -amadavat, he writes, in _The Country-Side_, vol. i. p. 142, "is in -breeding plumage red with white spots, and the hen brown. The red varies -in intensity even in full-plumaged birds, and I submitted to the hen -first of all two male birds, one of a coppery and the other of a rich -scarlet tint. In no long time she had made her choice of the latter bird; -the other, I am sorry to say, very soon died; and, as he had appeared -perfectly healthy, I fear grief was accountable for his end--a warning to -future experimenters to remove the rejected suitor as early as possible. -In the present case I took away the favoured bird, and put in the side -compartments he and his rival had occupied two other cocks, which -differed in a similar way, though not to the same extent. Again the hen -kept at the side of the rich red specimen, so, deeming I knew her views -about the correct colour for an amadavat, I took her away too, and tried -a second hen with these two males. This was an unusually big bird, and a -very independent one, for she would not make up her mind at all, and -ultimately I released all three without having gained any result. - -"Subsequently I made another experiment with linnets. In this case all -three were allowed to fly in a big aviary-cage together, a method which I -do not recommend. - -"In this case, however, the handsomest cock, which showed much richer red -on the breast, had a crippled foot, and proved, as I had expected, to be -in fear of the other; nevertheless, the hen mated with him. It must be -said, in justice to the duller bird, that he did not press the advantage -his soundness gave him, but with a less gentle bird than the linnet this -would have happened." - -It is obvious that there is a wide field for observation on these lines. -In the case of large birds the experiment could be made still more -conclusive by confining the three birds to be experimented on in a single -enclosure, divided into three compartments by fences. The males should be -placed each in a separate compartment, and have a wing clipped so as to -prevent them leaving their respective compartments, while the hen should -be allowed the power of flight so that she can visit at will any -compartment. - -Finn has also recorded (_loc. cit._) some other observations bearing on -the question of sexual selection. He writes:-- - -"One cannot observe or read about the habits of birds very much without -finding out that, whatever may be the value of beauty, strength counts -for a great deal. Male birds constantly fight for their mates, and the -beaten individual, if not killed, is at any rate kept at a distance by -his successful rival, so that, if he be really more beautiful, his beauty -is not necessarily of much service to him. I was particularly impressed -by this about a couple of years ago, when I frequently watched the -semi-domesticated mallards in Regent's Park in the pairing season. These -birds varied a good deal in colour; in some the rich claret breast was -wanting, and others had even a slate-coloured head instead of the normal -brilliant green. Yet I found these 'off-coloured' birds could succeed in -getting and keeping mates when correctly-dressed drakes pined in lonely -bachelorhood; one grey-breasted bird had even been able to indulge in -bigamy. That strength ruled here was obvious from the way in which the -wedded birds drove away their unmated rivals, a proceeding in which their -wives most thoroughly sympathised. - -"Evidently, beauty does not count for much with the park duck, and the -same seems to be the case with the fowl. As a boy, I often used to visit -a yard wherein was a very varied assortment of fowls. Among these was one -very handsome cock, of the typical black and red colouring of the wild -bird, and very fully 'furnished' in the matter of hackle and sickle -feathers. Yet the hens held him in no great account, while the master of -the yard, a big black bird, with much Spanish blood, provided with a huge -pair of spurs, was so admired that he was always attended by some little -bantam hens, although they might have had diminutive husbands of their -own class. - -"It must be remembered, however, that these ducks and fowls had an -unnaturally wide choice. In nature, varieties are rare, and the competing -suitors are likely to be all very much alike; this makes matters very -difficult for the observer, who may easily pass over small differences -which are plain enough to the eyes of the hen birds." - -[Illustration: COURTSHIP OF SKYLARK] - - - Display of Undecorated Cocks - -Finn observed that a young hen Bird of Paradise (_Paradisea apoda_) in -the London Zoological Gardens, mated with a fully adult cock in the next -compartment although a young cock in female plumage in her own -compartment did his best to show off. - -It would thus seem that the very limited evidence at present available is -not sufficient to sustain the theory that the hens select the most -attractive of their suitors. It is significant that plainly-coloured -species of birds show off with as much care as their gaily-plumaged -brethren; and, if they be nearly allied, assume similar courting -attitudes. Thus the homely-attired males of the Spotted-bill (_Anas -poecilorhyncha_), Gadwall, and Black Duck (_Anas superciliosa_), show off -in precisely the same way as does the handsome mallard. - -Howard describes and figures in his excellent and beautifully illustrated -monograph the elaborate display at the pairing season of some of our -plain-coloured little warblers. The skylark has also a notable display. - -The common partridge assumes a nuptial attitude similar to that of the -pheasant, and, although the cock of the former species has nothing -brilliant to show off, the hen partridge pays far more attention to the -display of her suitor than does the hen pheasant. - -The fact that some cock birds show off _after_ the act of pairing seems -to tell against the theory of sexual selection, or at any rate to -indicate the purely mechanical nature of the performance. Finn has -witnessed this post-nuptial display at the Zoological Gardens (London) in -the pied wagtail, the peacock, the Andaman Teal (_Nettium albigulare_), -the Avocet, the Egyptian Goose (_Chenatopex ægyptiaca_), and the Maned -Goose (_Chenonetta jubata_). - -Another objection to the theory that the bright colours of cock birds are -due to feminine selection is presented by those birds which breed in -immature plumage. Darwin admits that this objection would be a valid one -"if the younger and less ornamental males were as successful in winning -females and propagating their kind as the older and more beautiful males. -But," he continues, "we have no reason to suppose that this is the case." - -Unfortunately for the theory of sexual selection, there is evidence to -show that the cock Paradise Fly-catcher (_Terpsiphone paradisi_) in -immature plumage is quite as successful in obtaining a mate as is the -cock in his final plumage. The cock of this beautiful species has a -chestnut plumage in his second year, and a white one in the third and -subsequent years of his life. Nevertheless, a considerable proportion of -the nests found belong to chestnut cocks. - - - Plumage of Herons - -Darwin was of opinion that any novelty in colouring in the male is -admired by the female; and in this manner he sought to overcome some -difficulties to his theory which certain birds presented. - -Writing of the heron family, he says:-- - -"The young of the _Ardea asha_ are white, the adults being -slate-coloured; and not only the young, but the adults of the allied -_Buphus coromandus_ in their winter plumage are white, their colour -changing into a rich golden buff during the breeding season. It is -incredible that the young of these two species, as well as of some other -members of the same family, should have been specially rendered pure -white, and thus made conspicuous to their enemies; or that the adults of -one of these two species should have been specially rendered white during -the winter in a country which is never covered with snow. On the other -hand, we have reason to believe that whiteness has been gained by many -birds as a sexual ornament. We may therefore conclude that an early -progenitor of the _Ardea asha_ and the _Buphus_ acquired a white plumage -for nuptial purposes, and transmitted this colour to their young; so that -the young and the old became white like certain existing egrets, the -whiteness having afterwards been retained by the young whilst exchanged -by the adults for more strongly pronounced tints. But if we could look -still further backwards in time to the still earlier progenitors of these -two species, we should probably see the adults dark-coloured. I infer -that this would be the case, from the analogy of many other birds, which -are dark whilst young, and when adult are white; and more especially from -the adult of the _Ardea gularis_, the colours of which are the reverse of -those of _A. asha_, for the young are dark-coloured and the adults white, -the young having retained a former state of plumage. It appears, -therefore, that the progenitors in their adult condition of the _A. -asha_, the _Buphus_, and of some allies have undergone, during a long -line of descent, the following changes of colour: firstly a dark shade, -secondly pure white, and thirdly, owing to another change of fashion (if -I may so express myself), their present slaty, reddish or golden-buff -tints. These successive changes are intelligible only on the principle of -novelty having been admired by the birds for the sake of novelty." - -This reasoning may appear far-fetched and unconvincing. It seems, -however, quite likely that the hen may select as her mate the suitor who -is conspicuously different from the others, not because she admires -novelty, but because his conspicuousness attracts her attention and -enables her to make up her mind quickly to take him and thus rid herself -of the other troublesome admirers, who are all very much alike. - - - Sexual Dissimilarity - -It is perhaps worthy of note that, after the most successful of her -suitors has succeeded in securing the hen, it may happen that a -disappointed rival makes love to her in the absence of her lord and -master and thereby nullifies the effect of her previous selection. - -It is to be observed that, even if we take it as proved, as Darwin -believed, that the hens alone exercise a choice of mates, and that they -select the most beautiful of their suitors, we are still far from -arriving at an explanation of the fact that the males alone have acquired -beauty. Admitting that the hens always mate with the most beautiful -cocks, we should expect the offspring of each union to be all more or -less alike in beauty--that is to say, more beautiful than the mother and -less so than the cock. How are we to explain the one-sided inheritance of -this beauty? Why is it confined to the cocks? - -In order to meet this objection Darwin had to call to his aid unknown -laws of inheritance. "The laws of inheritance," he writes (_Descent of -Man_, p. 759), "irrespectively of selection, appear to have determined -whether the characters acquired by males for the sake of ornament, for -producing various sounds, and for fighting together, have been -transmitted to the males alone or to both sexes, either permanently or -periodically, during certain seasons of the year. Why various characters -should have been transmitted sometimes in one way and sometimes in -another is not in most cases known; but the period of variability seems -often to have been the determining cause. When the two sexes have -inherited all characters in common, they necessarily resemble each other; -but, as the successive variations may be differently transmitted, every -possible gradation may be found, even within the same genus, from the -closest similarity to the widest dissimilarity between the sexes." - -This statement, although it does not throw any light upon the problem, is -somewhat damaging to the theory of sexual selection. If it be admitted -that dissimilarity between the sexes is due to the fact that the males -have varied in one way and the females in another way, there seems no -necessity for invoking the aid of feminine preference. - -Even greater is the difficulty presented by those species in which the -males alone are provided with horns or antlers. "When," writes Darwin -(_Descent of Man_, p. 767), "the males are provided with weapons which in -the females are absent, there can hardly be a doubt that these serve for -fighting with other males; and that they were acquired through sexual -selection, and were transmitted to the male sex alone. It is not -probable, at least in most cases, that the females have been prevented -from acquiring such weapons on account of their being useless, -superfluous, or in some way injurious. On the contrary, as they are often -used by the males for various purposes, more especially as a defence -against their enemies, it is a surprising fact that they are so poorly -developed, or quite absent, in the females of so many animals." - -We have, we believe, demonstrated that Darwin's theory of sexual -selection is unable to account satisfactorily for all the phenomena of -sexual dimorphism. But, as we have seen, it is quite possible that sexual -selection is a real factor of evolution. - -We trust that what we have said will stimulate some leisured naturalist -to study the question of male and female preference. - -We now pass on to consider briefly some of the other attempts that have -been made to explain the phenomena of sexual dimorphism. - - - Wallace's Explanation of Sexual Dissimilarity - -Wallace does not accept the theory of sexual selection. He admits that -the form of male rivalry, which Darwin calls "the law of battle," is "a -real power in nature," and believes that "to it we must impute the -development of the exceptional strength, size, and activity of the male, -together with the possession of special offensive and defensive weapons, -and of all other characters which arise from the development of these, or -are correlated with them" (_Darwinism_, p. 283). But the view that the -female selects the most beautiful of her suitors has always seemed to -Wallace "to be unsupported by evidence, while it is also quite inadequate -to account for the facts." For example, the accessory plumes of birds -"usually appear in a few definite parts of the body. We require some -cause to initiate the development in one part rather than in another." - -Wallace considers that natural selection is able to explain all the -phenomena of sexual dimorphism. He points out that, when the sexes are -dissimilar among birds, it is almost invariably the female which is -duller coloured. The reason for this is, he believes, that the hen birds, -while sitting, "are exposed to observation and attack by the numerous -devourers of eggs and birds, and it is of vital importance that they -should be protectively coloured in all those parts of the body which are -exposed during incubation. To secure this, all the bright colours and -showy ornaments which decorate the male have not been acquired by the -female, who often remains clothed in the sober hues which were probably -once common to the whole order to which she belongs. The different -amounts of colour acquired by the females have no doubt depended on -peculiarities of habits and environment, and on the powers of defence and -concealment possessed by the species." - -In support of his contention, Wallace asserts that all species of birds, -of which the hens are as conspicuously coloured as the cocks, nest in -holes or build domed nests. The plumes and other ornaments, which the -cocks of certain species display, Wallace would attribute to a surplus of -strength, vitality, and growth power, which is able to expend itself in -this way without injury. - -"If," he writes, "we have found a _vera causa_ for the origin of -ornamental appendages of birds and other animals in a surplus of vital -energy, leading to abnormal growths in those parts of the integument -where muscular and nervous action are greatest, the continuous -development of these appendages will result from the ordinary action of -natural selection in preserving the most healthy and vigorous -individuals, and the still further selective agency of sexual struggle in -giving to the very strongest and most energetic the parentage of the next -generation." (_Darwinism_, p. 293.) "Why," he says, "in allied species -the development of accessory plumes has taken different forms we are -unable to say, except that it may be due to that individual variability -which has served as the starting point for so much of what seems to us -strange in form, or fantastic in colour, both in the animal and vegetable -world." - - - Wallace's Theory Criticised - -Wallace's view that the dull plumage of the hen bird is due to her -greater need of protection is based on the assumption that the hen bird -alone takes part in incubation. - -Is this assumption a correct one? - -It certainly is not in all cases. As D. Dewar has stated in _Birds of the -Plains_, the showy white cock Paradise Fly-catcher (_Terpsiphone -paradisi_) sits in broad daylight on the open nest quite as much as the -hen does. And this may prove to be true of many other species of birds. -Again, the cocks of the various species of Indian sunbirds are brightly -coloured while the hens are dull brown. In these species the hen alone -sits on the eggs, but, as the nest is well covered-in, the hen might -display all the colours of the rainbow without being visible to passing -birds. Moreover, as D. Dewar pointed out in a paper read before the Royal -Society of Arts (_Journal_, vol. lvii., p. 104), although, in most -species of Indian dove, the sexes show little or no dissimilarity, there -is one species (_Oenopopelia tranquebarica_) which exhibits considerable -sexual dimorphism. But the nesting habits of this peculiar species are in -all respects similar to those of the other species of dove. Why then the -marked dissimilarity of the sexes? - -Another objection to the theory of Wallace is that urged by J. T. -Cunningham (_Archiv für_ _Entwicklungsmechanik der Organismen_, vol. -xxvi., p. 378), namely, that the secondary sexual characters in those -species which possess them show an entire absence of uniformity in nature -and position. "Why," asks Cunningham, "should the male constitution of -the stag show itself in bony excrescences of the skull, in the peacock in -excessive growth of the other end of the body? Why should the larynx be -modified in one mammal, the teeth in another, the nose in another? Why is -the male newt distinguished by a dorsal fin, the male frog by a swelling -on the fore foot?" - -Another objection to the explanation of sexual dimorphism suggested by -Wallace, is that in many species of bird, as, for example, the house -sparrow and the green paroquets of India, the external differences -between the sexes are so slight that it is unreasonable to believe that -they are the result of natural selection. It seems impossible to hold -that the Rose-ringed Paroquet (_Palæornis torquatus_)--a species which -nests in holes--would have become extinct if the hens had developed the -narrow rose-coloured collar that characterises the cocks. - -Darwin pointed out that while Wallace's hypothesis might appear plausible -if applied to colour, it can scarcely be said to explain the origin of -such structures as the musical apparatus of certain male insects, or the -larger size of the larynx in some birds and mammals. We thus see that -suggestions offered by Wallace, although they contain a modicum of truth, -fail to explain the phenomena of sexual dimorphism. - -The fairest possible criticism of these views is that of Darwin:-- - -"It will have been seen that I cannot follow Mr Wallace in the belief -that dull colours, when confined to the females, have been in most cases -specially gained for the sake of protection. There can, however, be no -doubt, as formerly remarked, that both sexes of many birds have had their -colours modified, so as to escape the notice of their enemies; or in some -instances, so as to approach their prey unobserved, just as owls have had -their plumage rendered soft, that their flight may not be overheard" -(_The Descent of Man_, p. 745). - - - The Theory of Thomson and Geddes - -Thomson and Geddes have attempted to explain sexual dimorphism on the -hypothesis that males are essentially dissipators of energy, while -females tend to conserve energy. They point out that the spermatozoon is -a small intensely active body, which dissipates its energy in motion, -while the ovum is a large inert body--the result of the female tendency -to conserve energy and to build up material. The various ornaments and -excrescences which appear in male organisms are the result of this male -tendency to dissipate energy. In the spermatozoon the dissipated energy -appears in the form of active movement; in the adult organism it takes -the shape of plumes and other ornaments, of song and contests for the -females. - -This theory, however, does not explain what we might call the haphazard -nature of sexual dimorphism. If sexual dissimilarity is due to the -tendency of the male to dissipate energy, why do we see very marked -dimorphism in one species, and no dimorphism in a very nearly allied -species? Why are the males larger than the females in some species, and -smaller in other species? Again, how is it that in certain species of -birds--the quails of the genus _Turnix_, the Painted Snipe (_Rhynchæa_), -and the Phalaropes--it is the female who possesses the more showy -plumage? Moreover, this theory, equally with that of Wallace, does not -explain why the excrescences which characterise the male appear in -various parts of the body in different species. - - - Stolzmann's Theory - -Stolzmann has made an ingenious attempt to explain why in birds the cock -is so frequently more conspicuously coloured than the hen. He asserts -that among birds the males are more numerous than the females, and that -this preponderance is not advantageous to the species. Those males which -have not managed to secure a mate are apt to persecute the females while -sitting on the eggs, to the detriment of these latter. Natural selection, -says Stolzmann, is concerned with the well-being of the species rather -than of the individual. Hence anything that would tend to lessen the -number of males would be a good thing for the species, so that a -peculiarity, such as bright plumage, which renders the males conspicuous, -or ornamental plumes, which cause their flight to be slow, and so leads -to their destruction, will be seized upon and perpetuated by natural -selection. He points out that the cock of one species of -hummingbird--_Loddigesia mirabilis_--has not only longer tail feathers, -but a shorter wing than the female, and must, in consequence, find it -comparatively difficult to obtain food, and be more liable to fall a -victim to birds of prey than the hen. Stolzmann further suggests that the -excessive pugnacity of male birds at the breeding season may lead to the -destruction of some individuals, and so prove of advantage to the -species. - -Several objections seem to present themselves to this most ingenious -theory. - -In the first place, there does not appear to be any satisfactory evidence -to show that more cocks than hens are born. - -We may grant that a superfluity of cocks is injurious to any species, -since the unmated ones are likely to persecute the hens; we may also -grant that many cocks are handicapped in the struggle for existence by -the excessive growth of certain of their feathers, but we fail to see how -this excessive development has been caused by natural selection in the -manner suggested by Stolzmann. Although it may be advantageous to the -species for the cocks to be showy, natural selection can perpetuate this -only by weeding out the least conspicuous of the cocks. But it is the -more gaudy ones, those, according to Stolzmann, whose presence is -beneficial to the species, which will be eliminated by natural selection. -So that, in this case, that force will act in a manner contrary to the -interests of the species, if Stolzmann's idea is a correct one. - -The theory in question would therefore seem to be untenable. Nevertheless -there is doubtless some truth in the notion that too many males spoil the -species. Thus, excessive showiness and high mortality among the males may -be beneficial to the species. But we must not forget that the more -beneficial it is, the stronger must be the tendency of natural selection -to eliminate the males that possess the desired peculiarity. - - - Neo-Lamarckian Explanation - - - Cunningham's Theory - -J. T. Cunningham makes an attempt to explain the phenomena of sexual -dimorphism on Neo-Lamarckian principles. His theory is set forth in a -paper entitled _The Heredity of Secondary Sexual Characters in relation -to Hormones_, which was read before the Zoological Society of London, and -published in full in the _Archiv für Entwicklungsmechanik der -Organismen_. "The significant correlation of male sexual characters," he -writes, "is not with any general or essential property of the male sex, -such as katabolism (or the tendency to dissipate energy, as we have -called it), but with certain habits and functions confined to one sex, -but differing in different animals. . . . In those animals which possess -such (_i.e._ secondary sexual) characters, the parts of the soma (_i.e._ -the body) affected differ as much as they can differ; any part of the -soma may show a sexual difference: teeth in one mammal, skull in another; -feathers of the tail in one bird, those of the neck in another, and so -on. But in all cases such unisexual characters correspond to their -functions or use in habits and instincts which are associated, but only -indirectly, with sexual production. These habits are as diverse and as -irregular in their distribution as the characters. The cocks of common -fowls and of the Phasianidæ generally are polygamous, fight with each -other for the possession of the females, and take no part in incubation -or care of the young, and they differ from the hens in their enlarged -brilliant plumage, spurs on the legs, and combs, wattles, or other -excrescences on the head. In the Columbidæ _per contra_ the males are not -polygamous, but pair for life, the males do not fight, and share equally -with the females in parental duties. - -"Corresponding with this contrast of sexual habits is the contrast of -sexual dimorphism, which is virtually absent in the Columbidæ. - -"I think, then, the only scientific explanation is that the difference of -habits is the cause of the sexual dimorphism, and that the special sexual -habits which occur in some species but not in others are the causes of -the sexual characters. . . . The habits in question always involve -certain definite stimulations applied to those parts of the body whose -modification constitutes the somatic sexual characters. The stimulations -are confined, as the characters are confined, to one sex, to one period -of life, to one season of the year, to those animals which have the -characters, to those parts of the body which are modified." Mr Cunningham -believes that these stimulations cause hypertrophy or excessive growth of -the part affected, and that this peculiarity is transmitted to the -offspring. And thus he supposes all the ornaments and excrescences of the -males of various species to have arisen. - -As evidence in favour of his view, he points out that these excrescences -are, in many species, not only functionless but absolutely injurious, as -in the case of the comb and wattles of the jungle cock and his domestic -descendants, which merely serve as a handle for enemies to seize. - -Cunningham asserts that the only objection to his theory is the dogma -that acquired characters cannot be inherited. This assertion is, however, -not correct. It is, indeed, a very serious objection that all the -evidence available seems to show that acquired characters are not -inherited, but this is by no means the only difficulty. - -Before mentioning these further objections, let us say a word on the -subject of the inheritance of acquired characters. Mr Cunningham himself -compares the formation of a splint or spavin in a horse as the result of -special strain, to the acquisition of secondary sexual characters. -Unfortunately for Cunningham's theory, but fortunately for mankind in -general, spavined horses and mares do not beget spavined offspring. If, -then, spavin is not inherited, is it not unreasonable to assert that the -thickening of the bone that develops on the head of a butting animal is -inherited? - -Another objection to Cunningham's theory is that many birds which show -off their plumage most vigorously possess no ornamental plumes. As Howard -has recorded, many of our dull-coloured British warblers show off in the -same manner as bright-coloured birds do. If the exercise has caused the -development and inheritance of plumes in some species, why not in the -others? - -Again, Cunningham is not correct in saying that sexual dimorphism is -"virtually absent" in the Columbidæ. Few birds display so striking a -sexual dimorphism as the Orange Dove (_Chrysoena victor_) of Fiji, in -which the male is bright orange and the hen green. We have already cited -the case of the curious sexually dimorphic red turtle-dove. Now, the -courting attitudes and actions of this species are precisely the same as -those of other allied turtle-doves; why, then, have these exercises -caused only one species to become sexually dimorphic? - - - Existing Theories not Satisfactory - -Our survey of the more important attempts which have been made to explain -the phenomena of sexual dimorphism leads to the conclusion that these -still require elucidation. We have weighed each theory in the balance and -found it wanting. - -The outstanding feature of sexual dissimilarity is the apparently -haphazard manner of its occurrence. - -We have already alluded to the case of the doves in India. In that -country four species are widely distributed--namely, the Spotted Dove -(_Turtur suratensis_), the Ring or Collared Dove (_Turtur risorius_), the -Little Brown Dove (_Turtur cambayensis_), and the Red Turtle-dove -(_Oenopopelia_ _tranqebarica_). The habits of all these four species -appear to be identical, nevertheless in the first three the sexes show -little or no dissimilarity in outward appearance, while in the last the -sexual dimorphism is so great that the cock and hen were formerly thought -to belong to different species. - -Another very curious case is that of the South American geese of the -genus _Chloëphaga_, in which some species, as the familiar Upland or -Magellan Goose of our parks (_C. magellanica_), have the sexes utterly -unlike, while in others, as the Ruddy-headed Goose (_C. rubidiceps_), -they are quite similar to each other. - -The ducks furnish us with another very good example of the apparently -haphazard nature of sexual dimorphism. In the Common Mallard or Wild Duck -(_Anas boscas_) the cock is far more showily coloured than the hen, but -in all the species most nearly allied to it the males are as -inconspicuous as the females, _e.g._ in the Indian Spotted-bill (_Anas -poecilorhyncha_), the Australian Grey Duck (_A. superciliosa_), the -African Yellow Bill (_Anas undulata_), and the American Dusky Duck (_A. -obscura_). As the dusky duck inhabits North America, where the mallard is -also found, the case is particularly striking. - -Among mammals the lion and the tiger and the sable and roan antelopes -(_Hippotragus niger_ and _H. equinus_) furnish familiar examples of -nearly-related species, in one of which the sexes are alike and in the -other dissimilar in appearance. - - - Hormones - -Another important point to be borne in mind is the intimate correlation -that exists between the reproductive organs and the general appearance of -the organism, more especially of the secondary sexual characters. These -last, in most cases, do not show themselves until the maturity of the -sexual organs. The well-known effects of castration illustrate this -connection. Again, females in which the reproductive organs have ceased -to be functional often assume male characters. - -It has lately been proved by experiment that, in many cases at any rate, -the development of the ornaments, etc., characteristic of the sexes is -due to the secretion by the sexual cells of what are known as -hormones--that is to say, secretions which excite development of the -secondary sexual characters. The tendency to produce the external -characteristics of the sex to which an organism belongs is inherited, but -the actual development thereof is in many cases dependent on the -secretion of these hormones. Accordingly, if a male individual be -completely castrated it ceases to develop the external characters of its -sex. The evidence upon which the doctrine of hormones is based is -admirably summarised in the above-quoted paper by Cunningham. Into this -evidence we cannot go. It must suffice that the doctrine is quite in -accordance with all the observed results of castration. - -It is worthy of notice that the various features which characterise the -sexes in sexually dimorphic animals are not associated with any -particular organ or parts of the body, nor do they necessarily affect the -same part in allied species. "We cannot say," writes J. T. Cunningham, -"that any part of the soma (_i.e._ the body tissue) is specially sexual -more than another part, except that such differences between the sexes -are usually external. They usually affect the skin, and especially -epidermic appendages, and the superficial parts of the skeleton, or whole -limbs and appendages; or the difference may be one of size of the whole -soma. In mammals and birds the male is often the larger, sometimes very -much so, but there are cases in which the female is larger. There is no -general rule." - -Another important point is, that females, although they themselves show -no trace of the male character, are capable of transmitting it to their -progeny. This can be proved by crossing a hen pheasant with a cock -barn-door-fowl; the male offspring of the union display the plumes so -characteristic of the cock pheasant. These cannot have been derived from -the barn-door-fowl father; they must have come from the dull-coloured hen -pheasant. - -In this connection we may mention the curious fact recorded by Bonhote, -on page 245 of the _Proceedings of the Fourth International -Ornithological Congress_, that in the case of ducks descended from -crosses between the pintail, the mallard, and the spotbill, the drakes in -full breeding plumage showed a mixture of pintail and mallard -characteristics, while, in their non-breeding plumage, the colouring of -the spotbill is predominant. - - - Eye-colour, Comb, and Spurs - -An important point, and one which does not seem to have been pointed out -by any zoologist, is that eye-colour, comb, and spurs in birds and horns -in mammals do not stand in the same relation to the sexual organs as do -the other external characteristics. For example, the castrated Nilgai -(_Boselaphus tragocamelus_) acquires horns, but not the characteristic -male colour. In the common Indian Francolin Partridge (_Francolinus -pondicerianius_), the cock differs from the hen only in the possession of -spurs. The same applies to the various species of Snow Cock -(_Tetraogallus_). There is a breed of game-cocks which display plumage -like that of the hen, but such birds have the comb and spurs developed as -in normally feathered cocks. - -The white eye of the white-eyed Pochard Drake (_Nyroca africana_), and -the yellow eye of the cock Golden Pheasant (_Chrysolophus pictus_), which -are purely male characters, show themselves earlier than the male -plumage. Occasionally a hen golden pheasant assumes the plumage of the -cock, but she never acquires the yellow eye. - -Many birds when kept in captivity lose some of the beauty of their -plumage, and this is usually attributed to the sexual organs becoming -impaired and reacting on the somatic tissue. But this explanation cannot -in all cases be the correct one, because the linnet, although losing the -male plumage in captivity, lives long and well in a cage and breeds -readily with hen canaries. - -Another curious fact is that the male plumage sometimes appears -pathologically in hen birds, more especially in those which have become -sterile from age or disease. This phenomenon occurs comparatively -frequently in the gold pheasant, and more rarely in the common pheasant, -the fowl, and the duck. - -Phenomena such as these seem to suggest that in some cases the bright -colours of the male may be pathological, that the hormones which the male -sexual cells secrete may exercise an injurious effect on the somatic or -body tissues. Decay is known to be accompanied by the production of -brightly coloured pigment in the case of leaves. Finn suggests that the -white plumage which the cock paradise fly-catcher assumes in the fourth -year of his existence may be a livery of decay, a sign of senility. - - - The Four Kinds of Mutations - -It is our belief that sexual dimorphism arises frequently, if not -invariably, as a mutation. Mutations may be of four different kinds. - -Those which appear only, or especially, in conjunction with the male -organs, for example, whiteness in domesticated geese allowed to breed -indiscriminately. - -Those which appear only, or especially, in conjunction with the female -organs; mutations of this description appear to be very rare, but it may -be noted that in fowls allowed to breed indiscriminately, as in India, -completely black hens are common, but completely black cocks are rarely, -if ever, seen. This indicates an association between blackness and -femininity. - -Those which appear in the same manner in both sexes. The great majority -of mutations appear to be of this kind. - -Lastly, those that appear in both sexes but take a different form in the -case of the two sexes; thus in cats a mutation has given rise to sandy -males and tortoise-shell females. The mutation which has produced the -black-winged peacock shows itself in the form of a black wing in the -cock, while it causes the plumage of the hen to be grizzly white. - -We shall deal with the phenomenon of correlation at some length in the -next chapter. It is a subject to which sufficient attention has not been -paid. Even as certain characters are correlated in certain species, so in -some cases are certain characters correlated with sex. - -Why this should be so we are not in a position to say; this, however, -does not affect the indisputable fact that such correlation does exist. - -Physicians in the course of their practice sometimes come across very -curious cases of correlation in human beings. - - - Unilateral Transmission - -"It is," writes Thomson (_Heredity_, p. 290), "an interesting fact that -an abnormal element in the inheritance may find expression in the males -only or in the females only. If we could understand this we should be -nearer understanding what sex really means. - -"Hæmophilia, or a tendency to bleeding, is a heritable abnormality, -partly associated with weakness in the blood-vessels, which do not -contract as they should and are apt to break, and partly connected with a -lack of coagulating power in the blood. It is usually confined to males. -But as it passes from a father through a daughter to a grandson, and so -on, it must be a latent part of the germinal inheritance of the females, -though for some obscure physiological reason it fails to find expression -in them, or has its expression quite disguised. Colour-blindness or -Daltonism has been recorded (Horner) through the males only of seven -generations. Dejerine cites another case (_fide_ Appenzeller) in which -all the males in a family history had cataract through four generations. -There are other instances of what is sometimes awkwardly called the -unilateral transmission of abnormal qualities. Edward Lambert, born in -1717, is said to have been covered with 'spines.' His children showed the -same peculiarity, which began to be manifest from the sixth to the ninth -month after birth. One of his children grew up and handed on the -peculiarity to another generation. Indeed, it is said to have persisted -for five generations, and in the males only--unilateral transmission." - -In our view, these abnormalities are of such a kind that they are only -possible in connection with the male organ; in other words, they are -mutations of the first of the four kinds cited above--those which appear -only in connection with the male organ. - -It is a curious fact that the general rule in nature seems to be that the -male is ahead of the female in the course of evolution. The sexes may be -alike at a given period in the life-history of the species. Presently a -mutation appears which is confined to the male alone; thus arises the -phenomenon of sexual dimorphism. The next step in the evolution of the -species is frequently a mutation on the part of the female which brings -her once again into line with the male, and so the sexual dimorphism -disappears, for a time at any rate. A good example of this is furnished -by the sparrows; in the common sparrow of a large part of Africa (_Passer -swainsoni_) both sexes are very plain, like the hen of the house-sparrow; -in this species (_P. domesticus_) as every one knows, the cock, though by -no means brilliant, is noticeably handsomer than his mate; while in the -Tree-sparrow (_P. montanus_) both sexes have a plumage of masculine type, -much like that of the cock house-sparrow. - -If we consider in conjunction with one another the various facts we have -cited above, we begin to grasp the nature of the phenomena of sexual -dimorphism. - -Let us consider an imaginary case of a defenceless little bird which -builds an open nest. Let us suppose that it is inconspicuously plumaged. -Now suppose that a mutation of the first kind shows itself, a mutation -which affects the cock only and makes him more conspicuous. Let us -further suppose that the cock does not share in the duties of incubation. -It is quite possible that, in spite of this apparently unfavourable -mutation, the species may survive, for, as we have seen, it does not -affect the hen, and she, since she alone incubates, stands the most in -need of protective colouring. Moreover, as Stolzmann has suggested, the -species can possibly afford to lose a few males. But suppose that both -cock and hen share in the duties of incubation, it is then quite likely -that the mutation will cause the species to become extinct, by the -elimination of all the males. Or, let us suppose that the mutation in the -direction of showy plumage affects both sexes, then in such a case the -species will almost certainly become extinct. If, however, the -hypothetical species nested in holes in trees, it is quite possible that -it might survive notwithstanding its showy plumage. - - - Greater Value of Females - -Whether, as Wallace suggests, the hen does most of the incubating, and is -exposed to special danger when sitting on her eggs in an open nest, or, -as Stolzmann urges, it is of advantage to the species that there should -not be too many males, the result is the same, that the species can -afford to allow the cock to be more gaily attired than the hen. In either -case the colouration of the cock becomes a matter of comparatively little -importance to the species, and this, coupled with the fact that the male -tends to mutate more readily than the female, will explain why, in most -species which exhibit sexual dimorphism, it is the cocks that are the -more conspicuous. In certain species the cocks alone incubate, and these -then become more important than the females to the race, so that they -have not been permitted to become showy, while the hens have been allowed -more freedom in this respect. The extreme variability of the Ruff -(_Pavoncella pugnax_) in breeding plumage points to the fact that his -colour is a matter of comparative indifference to the species; in -consequence plenty of latitude is allowed to his tendency to vary. - -Our view, then, is that evolution proceeds by mutations, which may be -large or small. - -The mutation is the result of a rearrangement in part or parts of the -fertilised egg, and this rearrangement shows itself in the adult organism -as a change in one or more of its characteristics. The mutation may be -correlated with only one of the sexual organs, and when this is the case, -it gives rise to the phenomenon of sexual dimorphism. The appearance in -the adult of certain, if not of all, characteristics is affected by -causes other than the nature of the biological molecules from which they -are derived. The tendency to develop in a certain direction is there, but -something else, such as the secretion of hormones from the sexual cells, -is frequently necessary to enable a given tendency to fully develop -itself. Thus it is that castration often affects the bodily appearance of -those animals operated on. When a mutation appears, natural selection -decides whether or not it shall persist. - - - - - CHAPTER VIII - THE FACTORS OF EVOLUTION - - - 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 in a position to decide--_Modus operandi_ of - Natural Selection--Correlation an important factor--Examples of - correlation--Correlation is a subject that requires close - study--Isolation a factor in evolution--Discriminate - isolation--Indiscriminate 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 compared 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. - -We have so far considered three factors of evolution. The first of these -is the tendency of organisms to vary along definite lines. This is a most -important factor, because, unless variation occurs in any given -direction, there can be no evolution in that direction. Variations are -the materials upon which the other factors, or causes, of evolution work. -The second great factor is natural selection. Natural selection may be -compared to a builder, and variations to his materials. The kind of -building that a builder can construct depends very largely on the -material supplied to him. The Forth Bridge could not have been built had -those who constructed it had no material given them but bricks and -mortar. Wallaceians regard natural selection as a builder who is supplied -with every kind of building material--stone, bricks, wood, iron, -aluminium, in any quantities he may desire. They therefore regard natural -selection as the one and only cause which determines evolution. This, -however, is a wrong idea. Natural selection should rather be likened to a -builder who is supplied with a limited variety of building materials, so -that considerable restrictions are imposed on his building operations. -The doors, windows, fireplaces, etc., are supplied to him ready-made. He -merely selects which of these he will use for each building. - -The third factor of evolution which we have considered is sexual -selection. As we have seen, sufficient attention has not been paid to -this subject, so that we are not yet in a position to say how much, if -any, influence it has exercised on the course of evolution. - - - The Struggle for Existence - -In addition to these three factors, there are, we believe, some others. -Before proceeding to a consideration of these, it is important to study -carefully the _modus operandi_ of natural selection, or, in other words, -the nature of the struggle for existence, as many of the statements -contained in recent books on evolution seem to us to be based upon a -mistaken conception of this important factor. - -As usual, Darwin's disciples have failed to improve upon the account he -gave of the nature of the struggle for existence. This is set forth in -Chapter III. of the _Origin of Species_. - -"The causes," writes Darwin (new edition, p. 83), "which check the -natural tendency of each species to increase in number are most obscure. -Look at the most vigorous species; by as much as it swarms in numbers, by -so much will it tend to increase still further. We know not exactly what -the checks are even in a single instance." This is perfectly true. -Nevertheless elaborate theories of protective and warning colouration and -mimicry have been built up on the tacit assumption that the checks to the -multiplication of all, or nearly all, species are the creatures which -prey upon them. Possibly no Wallaceian asserts this in so many words, but -it is a logical deduction from the excessive prominence each one gives to -the various theories of animal colouration; for, if the chief foes of an -organism are not the creatures which prey upon it, how can the particular -shade and pattern of its coat be of such paramount importance to it? - - - Checks on Increase - -We shall endeavour to show that there are checks on the increase of a -species far more potent than the devastation caused by those creatures -which feed upon it. Let us, however, first briefly set forth some of the -checks on the multiplication of organisms which Darwin mentions in the -_Origin of Species_. - -"Eggs, or very young animals," he says, "seem generally to suffer the -most, but this is not invariably the case." This is, as we have already -insisted, a most important point to be borne in mind, especially when -considering the various current theories of animal colouration. When once -the average animal has become adult its chances of survival are -enormously increased. - -A second check mentioned by Darwin is the limitation of food supply. "The -amount of food for each species," he writes (p. 84), "of course gives the -extreme limit to which each can increase; but very frequently it is not -the obtaining food, but the serving as prey to other animals, which -determines the average numbers of a species. Thus there seems to be -little doubt that the stock of partridges, grouse, and hares on any large -estate depends chiefly on the destruction of vermin. . . . On the other -hand, in some cases, as with the elephant and rhinoceros, none are -destroyed by beasts of prey." - -We are inclined to think that neither the food limit nor the beasts of -prey are a very important check on the multiplication of organisms. The -lion, for example, was never so numerous as to reach the limit of its -food supply. Before the white man obtained a foothold in Africa vast -herds of herbivores were to be seen in those districts where lions were -most plentiful. This is a most important fact, for, if the numbers of a -species are not determined by those of the animals that prey upon it, the -particular colour of an organism is probably not of any direct importance -to it. This cuts away the foundation of some of the generally accepted -theories of animal colouration. - -"Climate," writes Darwin (p. 84), "plays an important part in determining -the average numbers of a species, and periodical seasons of extreme cold -or drought seem to be the most effective of all checks. I estimated -(chiefly from the greatly reduced numbers of nests in the spring) that -the winter of 1854-55 destroyed four-fifths of the birds in my own -grounds, and this is a tremendous destruction when we remember that 10 -per cent. is an extraordinarily severe mortality from epidemics with -man." - -In our opinion, Darwin did not lay nearly enough stress upon the -importance of climate as a check on the increase of species. We have seen -that he stated his belief that it is the most effective of all checks. -But even this is not a sufficiently strong statement of the case. It -seems to us that before this check all other checks pale into -insignificance. - -Darwin failed to notice the potent effects of damp. Damp is more -injurious to most species than even cold or drought, as every one who has -tried to keep birds in England knows. All entomologists are aware how -harmful damp is to insects. Caterpillars seem to take cover under leaves -to avoid damp rather than to hide themselves from birds, since these make -a point, when searching for insects, of invariably looking carefully -under leaves. - -It is a well-known fact that a wet winter in England causes much -mortality among rabbits. The increase of the rabbit in Australia is -usually attributed to the fact that the little rodent has not so many -predatory creatures to contend with there as it has in Europe. This is -not so. In Australia the rabbit has to fight against eagles, other large -birds of prey, carnivorous marsupials, feral cats, monitor lizards and -large snakes, to say nothing of the well-organised and persistent attacks -of man. - -Were predacious creatures the most important foes of the rabbit it would -never have obtained a firm foothold in Australia. Damp appears to be its -chief enemy. In Australia this does not exist. Hence the remarkable -increase of the species. Stronger evidence it would not be possible to -advance of the potency of damp as a check on the increase of a species -and of the comparative powerlessness of the attacks of raptorial -creatures. - -The failure of the sandgrouse to establish a footing in England is, we -believe, due to the fact that it is constitutionally unfitted to -withstand our damp climate. - -The camel is an animal that revels in dry habitats, hence the difficulty -of keeping camels in damp Bengal, although they seem to thrive well -enough in the drier parts of India. - -"When a species," writes Darwin (p. 86), "owing to highly favourable -circumstances, increases inordinately in numbers in a small tract, -epidemics--at least, this seems generally to occur with our game -animals--often ensue; and here we have a limiting check independent of -the struggle for life. But even some of these so-called epidemics appear -to be due to parasitic worms, which have from some cause, possibly in -part through facility of diffusion amongst the crowded animals, been -disproportionately favoured: and here comes in a sort of struggle between -the parasite and its prey." - -Thus inadequately does Darwin deal with that bar to the increase of -organisms, which is only second in importance to the effect of climate. -The check occasioned by disease and parasites is one to which naturalists -have as yet paid but little attention. The result is a very general -misunderstanding of the true nature of the struggle for existence, in -other words, of the _modus operandi_ of natural selection. - -The tsetse-fly in Africa is a far more important check on the increase of -some animals than the lions and other beasts of prey. There are in that -continent large tracts of country, known as tsetse-fly belts, in which -neither horse, nor ox, nor dog can exist. If races of these animals were -to arise which could withstand the bite of the tsetse-fly, these species -might increase more rapidly than the rabbit in Australia has done, nor -would it matter if the creatures in question were bright crimson, or any -other conspicuous colour. - -Take the case of the lion in Africa. The chief bar to the increase in -numbers of this species appears to be the teething troubles to which the -whelps are liable. Now suppose that a mutation were to occur in the lion. -Suppose that several members of a litter were all bright blue, and that -these suffered from no teething troubles. They would probably all grow -up, and although at some disadvantage as hunters on account of their -conspicuous colouring, they would nevertheless probably increase at the -expense of the normally coloured lions, because of the immunity of their -offspring from death from teething troubles. Zoologists would then be at -a loss to explain their bright colouring. We should have all manner of -ingenious suggestions raised, namely, that in the moonlight these -creatures were really not at all conspicuous, indeed that they were -obliteratively coloured. In other words, a totally wrong explanation of -their colouring would be given and accepted. It is our belief that many -of the explanations put forward and accepted of the colouration of -existing species are wide of the mark. - -As all bee-keepers are aware, the disease known as foul-brood works more -havoc among their bees than all the insectivorous creatures put together. - -Similarly throat disease among wood-pigeons does more towards keeping -their numbers down than all the efforts of predacious birds. - -A check on multiplication not mentioned by Darwin is that which is -sometimes imposed by the individuals of the species on one another. Thus, -in some animals, as, for example, the hyæna, the male occasionally -devours his own young ones. - -A check of a similar nature results from the habit which the Indian House -Crow (_Corvus splendens_) has of interrupting the pairing operations of -its neighbours. - - - Attributes of Successful Species - -We are now in a position to sum up briefly the more important requisites -for success in the struggle for existence. - -These are not so much specialised structure as courage, a good -constitution, mental capacity and prolificacy. - -Few animals possess all these characteristics in a pre-eminent degree, -for, to use the words of Mr Thompson Seton, "Every animal has some strong -point or it could not live, and some weak point or the other animals -could not live." Courage may be of two kinds--active courage, like that -of the Englishman, or passive courage, like that of the Jew. - -As D. Dewar has said: In the struggle for existence, "An ounce of good -solid pugnacity is worth many pounds of protective colouration." - -It is of course possible for an animal to possess too much courage. An -excessive amount of courage will often cause a creature to fight -unnecessary battles, which may lead to its premature death. This is -perhaps the reason why the pugnacious black form of the leopard is not -more numerous. - -Under a good constitution we must include the power of resisting the -rigours of climate, more especially damp, the ability to resist disease, -and the enjoyment of a good digestion. When from any cause the normal -food of a species becomes scarce, the members of that species will have -to starve or supplement the normal diet with food of an unusual nature; -and those that are endowed with a good digestion will be able to digest -the new food and thus survive, while those which cannot assimilate food -to which they are unaccustomed will become emaciated and perish. We see -this in every hard winter in England, when the redwing, which, unlike -other thrushes, cannot thrive on berries, is the first to die. Most of -the more successful birds--the crows and gulls, for example--are -omnivorous--that is to say, they are able to digest all manner of food. - -Under mental capacity, we would include cunning and sufficient -intelligence to adapt oneself to changed conditions. It is largely -through man's superior mental capacity that he has become the dominant -species. It is true that he displays also courage and a good -constitution, being able to adapt himself to life under the most diverse -conditions; but this is, of course, in part due to his mental capacity, -which enables him to some extent to adapt his environment to himself. - -The advantages of prolificacy are so apparent that it is unnecessary to -dilate upon them. Nearly as important as excessive fertility is the -ability on the part of the parents to look after their young ones. - -Every successful species possesses in a special degree at least one of -the above attributes. It is interesting to take in turn the various -species which are most widely distributed and consider to what extent -they possess these several qualities. - -Let us now consider a factor in evolution which is nearly as important as -natural selection itself--we allude to the phenomenon of correlation. - - - Correlation - -We may define correlation as the interdependence of two or more -characters. This phenomenon is far more common than the majority of -naturalists seem to think. It very frequently happens that one particular -character never appears in an organism without being accompanied by some -other character which we should not expect to be in any way related to -it. - -Darwin called attention to this phenomenon. "In monstrosities," he -writes, on page 13 of the _Origin of Species_ (new edition), "the -correlations between quite different parts are very curious, and many -interesting instances are given in Isidore Geoffroy St Hilaire's great -work on this subject. Breeders believe that long limbs are almost always -accompanied by an elongated head. Some instances of correlation are quite -whimsical: thus cats which are entirely white and have blue eyes are -generally deaf; but it has been lately stated by Mr Tait that this is -confined to the males. - -"Colour and constitutional peculiarities go together, of which many -remarkable cases could be given among animals and plants. From the facts -collected by Heusinger, it appears that white sheep and pigs are injured -by certain plants, whilst dark-coloured individuals escape. Professor -Wyman has recently communicated to me a good illustration of this fact: -on asking some farmers in Virginia how it was that all their pigs were -black, they informed him that the pigs ate the paint-root -(_Lachnanthes_), which coloured their bones pink, and which caused the -hoofs of all but the black varieties to drop off; and one of the -'crackers' (_i.e._ Virginia squatters) added, "we select the black -members of a litter for raising, as they alone have a good chance of -living.' - -"Hairless dogs have imperfect teeth; long-haired and coarse-haired -animals are apt to have, as is asserted, long or many horns; pigeons with -feathered feet have skin between their outer toes; pigeons with short -beaks have small feet, and those with long beaks large feet. - -"Hence, if man goes on selecting, and thus augmenting, any peculiarity, -he will almost certainly modify unintentionally other parts of the -structure, owing to the mysterious laws of the correlation of growth." - -The great importance of the principle of the correlation of organs is, -that _natural selection may indirectly cause the survival of unfavourable -variations, or of variations which are of no utility to the organism, -because they happen to_ _be correlated with organs or structures that are -useful_. - -Physiologists insist more and more upon the close interdependence of the -various parts of the organism. All recent researches tend to show that -each of the organs has, besides its primary function, a number of -subordinate duties to perform, and that the removal of one organ reacts -on all the others. - -In face of these facts we should have expected those zoologists who have -followed Darwin to have paid very close attention to the subject of -correlation. As a matter of fact, the phenomenon seems to have been -almost completely neglected. This is an example of the manner in which -the superficial theories which to-day command wide acceptance have tended -to bar the way to research. - -There seems to be, in the case of some organisms, at any rate, a distinct -correlation between their colouring and their constitution or mental -characters. For example, the black forms of the cobra, the leopard, and -the jaguar are notoriously bad-tempered. - -"There is," writes Col. Cunningham, on p. 344 of _Some Indian Friends and -Acquaintances_, "much variation in the temper of different varieties of -cobras, and, as is often so noticeable among other sorts of animals, -there would seem to be a distinct correlation between darkness of colour -and badness of temper. It is probably in part owing to a recognition of -this that the cobras ordinarily seen in the hands of the so-called snake -charmers are of a very light colour, although the choice may also be to -some extent of æsthetic origin, seeing that the paler varieties are -specially ornamental, due to the brilliancy of their markings and the -great development of their hoods." It would thus appear that there is -also a correlation between the colour of the cobra and the size of its -hood. - -Hesketh Pritchard informs us, in _Through the Heart of Patagonia_, that -the Gauchos assert that a "picaso" colt--that is to say, a black one with -white points--is the reverse of docile. Similarly, black mice are said to -be very hard to tame. - -We have already called attention to the importance of courage and the -power of resisting the rigours of climate in the struggle for existence. -It is apparently because black is so frequently correlated with courage -that it is seen comparatively often in nature, in spite of the fact that -it is a very bad colour as regards protection from enemies. Those birds -and beasts which are black are usually thriving species. The dominance of -the crow tribe is a case in point. Crows, it is true, are not really -courageous, but they are dangerous owing to their gregarious habits, and -are dreaded by other creatures on account of their power of combination. -In _Birds of the_ _Plains_, D. Dewar records an instance of a number of -crows killing in revenge so powerful a bird as the kite. - -Since very many species seem to throw off melanistic variations, it may -perhaps be asked, How is it that more black species do not exist? - -The reply is twofold. In the first place, it is quite likely that in some -organisms black variations are not correlated with courage or extreme -pugnacity, and when such is the case the melanistic varieties will be -more likely to be exterminated by foes, on account of their -conspicuousness. It must be remembered that, other things being equal, -the inconspicuously coloured organism has a better chance of survival -than the showily coloured one. This is, of course, a very different -attitude from that which insists on the all-importance to animals of -protective colouration. Secondly, it is not difficult to see how too much -courage may be fatal to an animal in leading it to take risks which a -more timid creature would refrain from doing. This, as we have already -suggested, is probably the reason why the black panther is so scarce. The -black colour is readily inherited, so there must be some cause which -tends to kill off the black varieties of the panther. - -Lest it be thought the idea that excessive courage and pugnacity are -harmful is mere fancy, let us quote from the account of the nesting -habits of the White-rumped Swallow (_Tachycineta leucorrhoa_) given by Mr -W. H. Hudson on p. 32 of _Argentine Ornithology_. He says that no matter -how many nesting sites are available, there is always much fighting -amongst these birds for the best places. "Most vindictively," he writes, -"do the little things clutch each other, and fall to the earth twenty -times an hour, where they often remain struggling for a long time, -heedless of the screams of alarm their fellows set up above them; for -often, while they thus lie on the ground punishing each other, they fall -an easy prey to some wily pussy who has made herself acquainted with -their habits." - -We have already emphasised the importance to many species of possessing -the power of resisting the effects of damp. In the case of some organisms -favourable variations in this direction may possess a greater survival -value than those in the shape of greater speed or physical strength. - -Now, if there be any correlation between the power of resisting damp and -the colour an animal bears, it is quite probable that animals of this -colour, whether or no it be conspicuous, are likely to survive in -preference to those who are more protectively coloured. There is some -evidence that in certain cases, at any rate, resistance to climate is -correlated with colour peculiarities. For example, some fanciers assert -that yellow-legged poultry resist cold and damp better than those whose -legs are not yellow. Fowls which have yellow legs have also yellow skins. -In this connection the almost universal assumption of orange feet by -domestic guinea-fowls is significant. Normally the feet of these birds -are black, and their natural African habitat is a dry one. - -A grey or white colour appears to be correlated with resistance to cold. -In birds this may perhaps be explained by the fact that the feathers in -some light-coloured varieties are longer than in those of -normally-coloured ones. Thus mealy-coloured canaries have longer feathers -than brightly-coloured ones. - -The Arctic Skua, having no enemies to fear, stands in no need of -protective colouration. It would therefore seem that the white-breasted -form of this bird becomes more numerous as it nears the north pole, not -because of the closer assimilation of its plumage to the colour of the -snowy surroundings, but because the bird has to resist the greater degree -of cold the farther north it finds itself. Similarly, in the region of -the south pole the albino form of the Giant Petrel (_Ossifraga gigantea_) -becomes common. Both these birds are themselves predatory and not liable -to be preyed upon. - -The curious china-white legs of some desert birds--as, for example, -coursers and larks--would seem to indicate a power of resisting the hot -rays radiating from the sand on which these creatures dwell. - -White quills do not wear well either in domestic birds or in wild -albinos. This may explain why it is that when a white wild species of -bird has any black in its plumage the black is almost invariably on the -tips of the wings. - -White quill-feathers are one of the commonest variations observed in -domesticated birds, nevertheless they are as rare as complete whiteness -among birds in their natural state. - -A chestnut or bay colour in mammals appears to be correlated with a high -rate of speed, as in the thoroughbred horse. This perhaps explains why so -many of the swiftest species of antelope, such as the hartebeests and -sassaby (_Damaliscus lunatus_), are chestnut bay in colour. It is further -a remarkable fact that in the Black-buck (_Antilope cervicapra_) and the -Nilgai (_Boselaphus tragocamelus_) the females, which are faster than the -males, are not black or grey like their respective males, but reddish. - -Wild turkeys are bronze; tame ones are black more often than any other -colour. This may be due to the fact that in them nigritude is correlated -with the power to resist damp. Among human beings those races which live -in very swampy districts are often intensely black. - -It is a significant fact that those domestic animals which are bred for -speed or for fighting purposes do not assume all the varied hues that -characterise those that are allowed to breed indiscriminately. -Racehorses, greyhounds, and homing pigeons furnish examples of this. Even -more remarkable is the case of the Indian Aseel or game-cock. This is -bred purely for fighting purposes, and is required to display -extraordinary powers of endurance, since the spurs are cut off in order -to prolong the fight. Thus it is that this Indian race of game-cocks -shows little variation when compared with the English breed, which fights -in a more natural manner. The hens of the Indian form seem never to show -the colouration of the wild jungle fowl, although the cocks may do so. It -would appear that hens having the colouration of their wild ancestors -cannot breed cocks possessed of the requisite courage. The Aseel is said -to be of the highest courage only when the legs, beak and iris are white. - -There is, we believe, not the least doubt that many other connections -between colour and various characteristics have yet to be discovered. It -is high time that competent naturalists paid attention to this subject. A -study of the question will almost certainly throw much light upon many -phenomena of animal colouration which hitherto have not been -satisfactorily explained. It is quite likely that the sandy hue displayed -by birds and beasts which frequent desert regions may be due to a -correlation with the power of withstanding intense dry heat rather than -to its rendering them inconspicuous to their foes. - -As other examples of correlation we may cite the correlation which seems -to obtain between short canine teeth and the absence of a hairy covering -to the body. This phenomenon is observed both in men and pigs. Hairless -dogs almost invariably have their teeth but poorly developed. - -Darwin called attention to the connection between a short beak and small -feet in pigeons; we see the same phenomenon in the dwarf breed of ducks -known as call-ducks. - -A curious correlation exists between fowls' eggs with brown shells and -the incubating habit. Fanciers have long tried in vain to produce a hen -that lays brown eggs without becoming "broody" at certain seasons. - -Among fowls, long legs are invariably correlated with a short tail, as is -well seen in the Malay breed. This correlation may explain the short -tails of wading birds. Short-legged fowls, like Japanese bantams, have -long tails, and it is significant that the short-legged Weka Rails -(_Ocydromus_) of New Zealand have unusually long tails for the family. In -this connection we may say that the tail-like plumes of the cranes are -not tail-feathers, but the tertiary feathers of the wings. As egrets also -have long trains of plumes growing from the back, it cannot be said that -the short tail of the vast majority of the waders is due to the fact that -these birds would be at a disadvantage were their caudal feathers long. - - - Isolation - -Isolation is a most important factor in the making of species. It is a -factor to which Darwin failed to attach sufficient importance, and one -which has been to a large extent neglected by Wallaceians. - - - Divergence of Character - -We have seen how a species can be improved or changed by natural -selection. All those individuals which have varied in a favourable -direction have been preserved, and allowed to leave behind them offspring -that inherit their peculiarities, while those which have not so varied -have perished without leaving behind any descendants. Thus the nature of -the species has changed. The old type has given place to a new one. -Instead of species A, species B exists. This is what Romanes has called -_monotypic_ evolution--the transformation of one species into another -species. But any theory of the origin of species must be able to answer -the question, Why have species multiplied? How is it that species A has -given rise to species B, C, and D, or, while itself continuing to exist, -has thrown off sister species B and C? How is it that in the course of -evolution, species have not been transmuted in linear series instead of -ramifying into branches? This ramification of a species into branches has -been termed by Romanes _polytypic_ evolution. It is easy to see how -natural selection can bring about monotypic evolution, but how can it -have effected polytypic evolution? To use Darwin's phraseology, how is it -that divergence of character has come about? Darwin's reply to this -question is (_Origin of Species_, p. 136), "from the simple circumstance -that the more diversified the descendants from any one species become in -structure, constitution, and habits, by so much will they be better -enabled to seize on many and widely diversified places in the polity of -nature, and so be enabled to increase in numbers. - -"We can clearly discern this in the case of animals with simple habits. -Take the case of a carnivorous quadruped, of which the number that can be -supported in any country has long ago arrived at its full average. If its -natural power of increase be allowed to act, it can succeed in increasing -(the country not undergoing any change in its conditions) only by its -varying descendants seizing on places at present occupied by other -animals: some of them, for instance, being enabled to feed on new kinds -of prey, either dead or alive; some inhabiting new stations, climbing -trees, frequenting water, and some perhaps becoming less carnivorous. The -more diversified in habits and structure the descendants of our -carnivorous animal become, the more places they will be enabled to -occupy. What applies to one animal will apply throughout all time to all -animals--that is, if they vary--for otherwise natural selection can -effect nothing." Darwin was, therefore, of opinion that natural selection -is able to bring about polytypic evolution. Darwin tacitly assumes, in -the illustration he gives, that the various races of the carnivorous -animal are in some way prevented from intercrossing; for if they -interbreed indiscriminately, these races will tend to be obliterated. - - - Isolation - -"That perfectly free intercrossing," writes Professor Lloyd Morgan (on p. -98 of _Animal Life and Intelligence_), "between any or all of the -individuals of a given group of animals is, so long as the characters of -the parents are blended in the offspring, fatal to divergence of -character, is undeniable. Through the elimination of less favourable -variations, the swiftness, strength, and cunning of a race may be -gradually improved. But no form of elimination can possibly differentiate -the group into swift, strong, and cunning varieties, distinct from each -other, so long as all three varieties freely interbreed, and the -characters of the parents blend with the offspring. Elimination may and -does give rise to progress in any given group, _as a group_; it does not -and cannot give rise to differentiation and divergence, so long as -interbreeding with consequent interblending of characters be freely -permitted. Whence it inevitably follows, as a matter of simple logic, -that where divergence has occurred, intercrossing and interbreeding must -in some way have been lessened or prevented. - -"Thus a new factor is introduced, that of _isolation_ or _segregation_. -And there is no questioning the fact that it is of great importance. Its -importance, indeed, can only be denied by denying the swamping effects of -intercrossing, and such denial implies the tacit assumption that -interbreeding and interblending are held in check by some form of -segregation. The isolation explicitly denied is implicitly assumed." - -This is very sound criticism, and is not very materially affected by the -fact that the intercrossing of varieties does not necessarily imply a -blending of their characters in the offspring; for, as we have seen, some -characters do not blend. No matter what form inheritance takes, in order -that natural selection may cause polytypic evolution it must be assisted -by isolation in some form or other. - -Thus isolation is an important factor in evolution, though probably not -so important as its more extreme advocates would have us believe. Wagner, -Romanes, and Gulick have, in insisting upon the importance of the -principle of isolation, rendered valuable service to biological science, -but, in common with most men having a new theory, they have pushed their -conclusions to absurd lengths. - -As Romanes has pointed out, isolation may be discriminate or -indiscriminate. "If," he writes, on p. 5 of vol. iii. of _Darwin and -after Darwin_, "a shepherd divides a flock of sheep without regard to -their characters, he is isolating one section from the other -indiscriminately; but if he places all the white sheep in one field, and -all the black sheep in another field, he is isolating one section from -the other discriminately. Or, if geological subsidence divides a species -into two parts, the isolation will be indiscriminate; but if the -separation be due to one of the sections developing, for example, a -change of instinct determining migration to another area, or occupation -of a different habitat on the same area, then the isolation will be -discriminate, so far as the resemblance of instinct is concerned." - - - Discriminate Isolation - -Other names for indiscriminate isolation are separate breeding and -apogamy. Discriminate isolation is also called segregate breeding and -homogamy. The human breeder resorts to discriminate isolation in that he -separates all those creatures from which he seeks to breed, from those -from which he does not wish to breed. Natural selection itself is, -therefore, a kind of discriminate isolator, since it isolates the fit by -destroying all the unfit, and, inasmuch as it kills off all those -creatures which it fails to isolate, it differs from other forms of -isolation in preventing the inter-breeding of the unisolated forms and -their giving rise to a different race. Thus it is clear that natural -selection, unless aided by some other form of isolation, can give effect -to only monotypic evolution. This is a point on which Romanes rightly -insists strongly. - -There are several other forms of discriminate isolation. Sexual selection -would be one of these. Suppose, for example, that in any species there -are large and small varieties formed, and like tends to breed with like, -then the small individuals will breed with other small individuals, while -large ones will mate with large ones; thus two races--a large one and a -small one--will be evolved side by side, provided, of course, natural -selection does not step in and destroy one of them. - -Another kind of discriminate isolation may be due to the fact that one -variety is ready to pair before the other; thus two races are likely to -arise which breed at different seasons. It is unnecessary for us to -discourse further on the subject of discriminate isolation; those -interested in the subject should read vol. iii. of _Darwin and after -Darwin_, by Romanes. - - - Indiscriminate Isolation - -It is impossible to deny the importance of discriminate isolation as a -factor in evolution. On this there can be no room for disagreement among -biologists. It is when we come to the subject of indiscriminate isolation -that we enter a region of zoological strife. - -Is indiscriminate isolation _per se_ a factor of evolution? Romanes, -Gulick, and Wagner assert that it is, Wallace and his adherents assert -that it is not. - -As the burden of proof is on the former, they are entitled to the first -hearing. - -"We may well be disposed, at first sight," writes Romanes (_Darwin and -after Darwin_, p. 10), "to conclude that this kind of isolation can count -for nothing in the process of evolution. For if the fundamental -importance of isolation in the production of organic forms be due to its -segregation of like with like, does it not follow that any form of -isolation which is indiscriminate must fail to supply the very condition -on which all the forms of discriminate isolation depend for their -efficacy in the causing of organic evolution? Or, to return to one's -concrete example, is it not self-evident that the farmer who separated -his flock into two or more parts indiscriminately, would not effect any -more change in his stock than if he had left them all to breed together? -Well, although at first sight this seems self-evident, it is, in fact, -untrue. For, unless the individuals which are indiscriminately isolated -happen to be a very large number, sooner or later their progeny will come -to differ from that of the parent type, or unisolated portion of the -parent stock. And, of course, as soon as this change of type begins, the -isolation ceases to be indiscriminate; the previous apogamy has been -converted into homogamy, with the usual result of causing a divergence of -type. The reason why progeny of an indiscriminately isolated section of -an originally uniform stock--_e.g._ of a species--will eventually deviate -from the original type is, to quote Mr Gulick, as follows:--'No two -portions of a species possess exactly the same average character, and the -initial differences are for ever reacting on the environment and on each -other, in such a way as to ensure increasing divergence as long as the -individuals of the two groups are kept from intergenerating.'" - -The words of Mr Gulick require close scrutiny. We may admit that "no two -portions of a species possess exactly the same average character," but -why should the two, if prevented from interbreeding yet subjected to -similar climatic and other conditions, present the phenomenon of -"increasing divergence?" The reason assigned by Romanes is the "Law" of -Delboeuf, which runs:--"_A constant cause of variation_, however -insignificant it may be, changes the uniformity of type little by little, -and diversifies it _ad infinitum_." From this "Law" it follows, says -Romanes, on p. 13 of vol. iii. _Darwin and after Darwin_, that "no matter -how infinitesimally small the difference may be between the average -qualities of an isolated section of a species compared with the average -qualities of the rest of that species, if the isolation continues -sufficiently long, differentiation of specific type is necessarily bound -to ensue." - -This deduction involves two important assumptions. The first is, that in -each of the separated portions of the given species there is a constant -cause of variation operating in one direction in the case of one portion -and in another direction in the case of the other. This assumption is, -unfortunately, not founded on fact. If we were to take one hundred -race-horses and shut them up in one park and one hundred cart-horses and -shut them up in another park, and prevent the interbreeding of the two -stocks, we should, if Romanes's tacit assumption be true, see the two -types diverge more and more from one another. We know that as a matter of -fact they will tend, generation after generation, to become more like one -another. Galton's Law of Regression, of which we have already spoken, and -which is supported by ample evidence, clearly negatives this tacit -assumption made by Romanes and Gulick. The second assumption upon which -their reasoning is based is that there is no limit to the amount of -change which can be effected by the accumulation of fluctuating -variations; but, as we have already seen (on p. 70), there is a very -definite limit and this limit is quickly reached. - -Thus the arguments of Romanes and Gulick are fundamentally unsound. - - - Mollusca of Sandwich Isles - -But the fact remains, and has to be accounted for, that, as a general -rule, when two portions of a species are separated, so that they are -prevented from interbreeding, they begin to diverge in character, and the -longer they remain thus separated the greater becomes that divergence. -This is an observed fact which cannot be gainsaid. - -It was the observance of this fact which led Gulick to insist with such -emphasis on the importance of geographical isolation as a factor in -evolution. He discovered that the land mollusca of the Sandwich Islands -fall into a great number of varieties. - -These islands are very hilly, and Gulick found that each of the varieties -is confined not merely to one island, but to one valley. "Moreover," -writes Romanes, on p. 16 of _Darwin and after Darwin_, "on tracing this -fauna from valley to valley, it is apparent that a slight variation in -the occupants of valley 2, as compared with those of the adjacent valley -1, becomes more pronounced in the next, valley 3, still more so in 4, -etc., etc. Thus it was possible, as Mr Gulick says, roughly to estimate -the amount of divergence between the occupants of any two given valleys -by measuring the number of miles between them. . . . The variations which -affect scores of species, and themselves eventually run into fully -specific distinctions, are all more or less finely graduated as they pass -from one isolated region to the next; and they have reference to changes -of form or colour, which in no one case presents any appearance of -utility." - -Hitherto three different attempts have been made to explain this and -allied phenomena:-- - -1. That it is the result of isolation. - -2. That it is the result of natural selection. - -3. That it is the result of the action of the environment on the -organism. - -Let us consider these in inverse order. - - - Local Species - -In the case of some organisms, more especially plants, invertebrates, and -fish, the environment does exert a direct influence on their colouration. -But, as we have seen, the changes in colour, etc., thus induced appear -never to be transmitted to the offspring of the organisms so affected. -They disappear when the offspring are removed to other surroundings. - -On the other hand, local races or species--as, for example, the -white-cheeked variety of sparrow found in India--usually retain their -external appearance when the environment is changed. In the one case the -peculiarity is not inherited; in the other it is inherited. - -The Wallaceian explanation is, of course, that the phenomenon is the -result of natural selection. There must, say Wallace and his followers, -be some differences in the environment, differences which we poor human -beings cannot perceive, that have caused the divergence between the -various isolated sections of the species. In the case of some local -species this explanation is probably the correct one, but we have no -hesitation in saying that natural selection is unable to offer a -satisfactory explanation in a considerable number of instances. Take, for -example, the case of the land mollusca of the Sandwich Islands. Mr Gulick -worked for fifteen years at them, and states that so far as he is able to -ascertain the environment in the fifteen valleys is essentially the same. -"To argue," writes Romanes, on p. 17 of vol. iii. of _Darwin and after -Darwin_, "that every one of some twenty contiguous valleys in the area of -the same small island must necessarily present such differences of -environment that all the shells in each are differently modified thereby, -while in no one out of the hundreds of cases of modification in minute -respects of form and colour can any human being suggest an adaptive -reason therefore--to argue thus is merely to affirm an intrinsically -improbable dogma in the presence of a great and consistent array of -opposing facts." - -Men of science not infrequently charge the clergy with adhering to dogma -in face of opposing facts; it seems to us that many of the apostles of -science are in this respect worse offenders than the most orthodox of -Churchmen. - -The example of the mollusca of the Sandwich Islands is by no means a -solitary one. D. Dewar cited some interesting cases in a paper recently -read before the Royal Society of Arts (p. 103 of vol. lvii. of the -Society's Journal): - -"The Indian robins present even greater difficulties to those who profess -to pin their faith to the all-sufficiency of natural selection. Robins -are found in nearly all parts of India, and fall into two species, the -brown-backed (_Thamnobia cambaiensis_) and the black-backed Indian Robin -(_Thamnobia fulicata_). The former occurs only in Northern India, and the -latter is confined to the southern portion of the peninsula. The hen of -each species is a sandy brown bird with a patch of brick-red feathers -under the tail, so that we cannot tell by merely looking at a hen to -which of the two species she belongs. The cock of the South Indian form -is, in winter, a glossy black bird, with a white bar in the wing, and the -characteristic red patch under the tail. The cock of the northern -species, as his name implies, has a sandy-brown back, which contrasts -strongly with the glossy black of his head, neck, and under parts. In -summer the cocks of the two species grow more like one another owing to -the wearing away of the outer edges of their feathers; but it is always -possible to distinguish between them at a glance. The two species meet at -about the latitude of Bombay. Oates states that in a certain zone, from -Ahmednagar to the mouth of the Godaveri valley, both species occur, and -they do not appear to interbreed. - -"It seems impossible to maintain that natural selection, acting on minute -variations, has brought about the divergence between these two species. -Even if it be asserted that the difference in the colour of the feathers -of the back of the two cocks is in some way correlated with adaptability -to their particular environment, how are we to explain the fact that in a -certain zone both species flourish? - -"A similar phenomenon is furnished by the red-vented bulbul. This genus -falls into several species, each corresponding to a definite locality and -differing only in details from the allied species, as, for example, the -distance down the neck to which the black of the head extends. There is a -Punjab Red-vented Bulbul (_Molpastes intermedius_), a Bengal (_Molpastes -bengalensis_), a Burmese (_Molpastes burmanicus_) and a Madras -(_Molpastes hæmorrhous_) species. - -"It does not seem possible to maintain the contention that these various -species are the products of natural selection, for that would mean if the -black of the head of the Punjab species extended further into the neck -the bird could not live in that country." - -Thus, natural selection clearly is unable to explain some cases of -divergence of character due to geographical isolation. - -There remains the third explanation, that the divergence is the result of -the simple fact of isolation. - -We have already shown how insuperable are the objections to the view held -by Romanes and Gulick. - -It seems to us that explanation must lie in the fact that mutations occur -every now and again in some species. If two portions of a species are -separated and a mutation occurs in one portion and not in the other, and -if the mutating form succeeds in supplanting the parent form in that -isolated portion of the species in which it has appeared, we should have -the phenomenon of two races or species differing in appearance although -subjected to what appear to be identical environment. - -This, of course, is pure conjecture. All that can be said of it at -present is that it is not opposed to observed facts. That mutations do -occur must be admitted. At present we are totally in the dark as to what -causes them. They arise at the most unexpected times. - -In favour of the explanation based on "mutation" there is the interesting -fact that geographical isolation does not by any means always cause -divergence of character. This Romanes, with great fairness, freely -admits. "There are," he writes, on p. 133 of vol. iii. of _Darwin and -after Darwin_, "four species of butterflies, belonging to three genera -(_Lycæna donzelii_, _L. pheretes_, _Argynnis pales_, _Erebia manto_), -which are identical in the polar regions and the Alps, notwithstanding -that the sparse Alpine populations have been presumably separated from -their parent stocks since the glacial period." Again, there are "certain -species of fresh-water crustaceans (_Apus_), the representatives of which -are compelled habitually to form small isolated colonies in widely -separated ponds, and nevertheless exhibit no divergence of character, -although apogamy has probably lasted for centuries." - - - Cormorants - -To these examples we may add that of the cormorants. These birds have an -almost worldwide range. One species--our Cormorant (_Phalacrocorax -carbo_)--occurs in every imaginable kind of environment. Isolation has -not effected any changes in the appearance of this species. Yet in New -Zealand there exist no fewer than fourteen other species of cormorant. -New Zealand is a country where climatic conditions are comparatively -uniform, nevertheless it boasts of no fewer than fifteen out of the -thirty-seven known species of cormorant. A possible explanation of this -phenomenon may be found in the comparatively easy conditions under which -cormorants live in New Zealand.[10] Under such circumstances mutants may -be permitted by natural selection to survive, whereas in other parts of -the world such mutants have not been able to hold their own. - -Prof. Bateson has likened natural selection to a competitive examination -to which every organism must submit. The penalty for failure is immediate -death. The standard of the examination may vary with the locality. - -Isolation, then, is a very important factor in the making of species, for -without it, in some form, the multiplication of species is impossible. - - -Let us, in conclusion, briefly summarise what we now know of the method -in which new species are made. We have studied the various factors of -evolution--variation and correlation, heredity, natural selection, sexual -selection, and the other kinds of isolation. How do these combine to -bring new species into being, and to establish the same? - - - Natural Selection - -Let us first consider the factor known as natural selection, since this -is the one on which Darwin laid such great stress. Natural selection, -although a most important factor in evolution, is not an indispensable -one. Evolution is possible without natural selection. - -Let us suppose that there is no such thing as natural selection; that the -numbers of existing species are kept constant by the elimination of all -individuals born in excess of the number required to maintain the species -at the existing figure, and that the elimination of the surplus is -effected, not by natural selection, but by chance, by the drawing of -lots. Under such circumstances there may be evolution, existing species -may undergo change, but the evolution will be determined solely by the -lines along which variations occur. - -If mutations take place along certain fixed lines, and tend to accumulate -in the given directions, evolution will proceed along these lines quite -independently of the utility to the organism of the mutations that occur. -An unfavourable mutation will have precisely the same chance of survival -as a favourable one. - -If, on the other hand, mutations occur indiscriminately on all sides of -the mean, then those mutations which happen to occur most frequently will -have the best chance of survival, and they will mark the lines of -evolution. But suppose that no mutation occurs more frequently than the -others. Under such circumstances there will be no evolution, unless, by -some cause or other, portions of the species are isolated, because in the -long run the mutations will neutralise one another. - -Let us now suppose that natural selection comes into play. The old method -of determining by lot which forms shall persist is replaced by selection -on the fixed principle that the fittest shall survive. The mutations -appear as before, and as before, of the large number that occur, only a -few are permitted to survive. But now the survivors, instead of being a -motley crowd, are a selected band, composed of individuals having many -characteristics in common--a homogeneous company. Thus one result of -natural selection is to accelerate evolution, by weeding out certain -classes of individuals and preventing them breeding with those it has -selected. On the other hand, natural selection will tend to diminish the -number of species which have arisen through mutation, inasmuch as it -weeds out many mutants which would have perished had their survival been -determined by lot. - - - Origin of the Fittest - -From this the kind of work performed by natural selection should be -obvious. Natural selection does not make new species. These make -themselves, or, rather, originate in accordance with the laws of -variation. - -"You can," runs an old proverb, "bring a horse to the drinking fountain, -but you cannot make him drink." You may be able to bring a child into the -world, but you cannot secure its survival. Variation brings into being -mutants, which are incipient species, but variation cannot determine -their survival. It is at this stage that natural selection steps in. - -But because natural selection allows certain mutations to persist, it is -not correct to say that natural selection has caused these mutations or -made or originated the species to which they give rise. - -The Civil Service Commissioners do not make Indian civil servants: they -merely determine which of a number of ready-made men shall become civil -servants. Similarly, natural selection does not make new species, it -simply decides which of a number of ready-made organisms shall survive -and establish themselves as new species. Nor does natural selection -always do as much as this; for it is not the only determinant of -survival. Its position is sometimes comparable to that of the Medical -Board which inspects and rejects the physically unfit of the candidates -which have already been selected by some other authority. - -The examination conducted by natural selection may be compared to a -competitive one. A separate, independent examination is held for each -particular locality; consequently the severity of the competition will -vary with the locality. - -In each competition some candidates pass with ease: they gain an -unnecessarily high total of marks. So in nature do certain organisms, as, -for example, the Leaf-butterflies (_Kallimas_), appear to be over-adapted -to their environment. Other candidates manage to pass only by a very -narrow margin: these are paralleled in nature by those species which are -barely able to maintain themselves, which become extinct the moment the -competition increases in severity. - -The great bulk of the candidates fail to obtain sufficient marks to gain -a place among the chosen few; these unsuccessful candidates correspond to -the mutating forms which perish in the struggle for existence, to those -individuals which happen to have mutated in unfavourable directions. - -Even as many candidates have acquired knowledge of subjects in which they -are not examined, so do many organisms possess characteristics which are -of no utility to them in the struggle for existence. - -Wallaceians expend much time and energy in misguided attempts to explain -the existence of such characters in terms of natural selection. - -Nature's examination, like that held for entrance to the Indian Civil -Service, is a liberal one, so that the qualifications of the successful -candidates vary considerably. Provided a candidate is able to gain more -marks than the other candidates for a vacancy, it matters not in what -subjects the marks are gained. So is it in nature. Natural selection -takes an organism as a whole. One species may have established itself -because of its fleetness, a second because of its courage, a third -because it has a strong constitution, a fourth because it is protectively -coloured, a fifth because it has good digestive powers, and so on. - -We thus perceive the part played by natural selection and other forms of -isolation in the making of species. It is obvious that these do not make -species any more than the Civil Service Commissioners manufacture Indian -civil servants. - -The real makers of species are the inherent properties of protoplasm and -the laws of variation and heredity. These determine the nature of the -organism; natural selection and the like factors merely decide for each -particular organism whether it shall survive and give rise to a species. - -The way in which natural selection does its work is comparatively easy to -understand. But this is only the fringe of the territory which we call -evolution. - -We seem to be tolerably near a solution of the problem of the causes of -the _survival_ of any particular mutation. This, however, is merely a -side issue. The real problem is the cause of variations and mutations, -or, in other words, how species _originate_. At present our knowledge of -the causes of variation and mutation is practically _nil_. We do not even -know along what particular lines mutations occur. - -We have yet to discover whether one mutation invariably leads to another -along the same lines--in other words, whether mutating organisms behave -as though they had behind them a force acting in a definite direction. -The solution of these problems seems afar off. The hope of solving them -lies, not in the speculations in which biologists of to-day are so fond -of indulging, but in observation and experiment, especially the last. - -The future of biology is largely in the hands of the practical breeder. - - - - - FOOTNOTES - - -[1]The white, pied, and "Japan" individuals are not more different from - the type than some variations occurring in wild birds. - -[2]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. - -[3]"Effected" appears in the earlier editions, but in the later editions - has given place to "affected," probably a printer's error. - -[4]Some egrets, such as the rock-egrets (_Demiegretta_) 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. - -[5]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 importations 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 Linnæus. Darwin - himself, at a later date, bred five young from a pair of such hybrids - (_Nature_, Jan. 1, 1880, p. 207). - -[6]In this chapter we use the word Neo-Darwinism in its usually-accepted - sense, _i.e._ as a name for that which should be called Wallaceism, - for the doctrine of the all-sufficiency of natural selection. - -[7]_Animal Colouration_, p. 125. A book full of valuable facts and ideas - on this most interesting subject. - -[8]Even these eggs, closely though they resemble in colouring the - shingle, etc., on which they are laid, are discovered and eaten by - gulls, as Mr A. J. R. Roberts points out in _The Bird Book_. - -[9]_Journal of the Bombay Natural History Society_, Vol xv. (1903-4), p. - 454. - -[10]Hutton and Drummond record other examples of this in the valuable - work entitled _The Animals of New Zealand_. - - - - - INDEX - - - A - Accentor, 1 - _Accipitcr cooperi_, 243 - Acorn, 49 - Acquired characters, 10, 14, 15, 18-24, 60, 107-10 - _Acræeidæ_, 175, 215, 228 - _Ægilops speltæformis_, 118 - _Ægithina tiphia_, 244 - Æsthetic sense in birds, 306 - "African Nature Notes and Reminiscences," 192, 195, 199 - Aggressive resemblance, 173 - Aguara-guazu, 181 - Aitken, E. H., 64 - "Albany Review, The," 43, 48, 195, 204 - Albinism, 64, 65, 99, 283, 284, 362 - _Alcedo ispida_, 289 - Alcock, Col., 216, 217 - Alcohol, 152, 153 - Alexander, 181 - Allen, Grant, 66 - Allotrophy, 159 - Alternating characters, 143 - Alternative inheritance, 127 - Amadavat, 311 - _Amandina erythrocephala_, 122 - _A. fasciata_, 122 - "Amazement," 93 - Amazon parrot, 103 - Amazonian dolphin, 99 - Ammonites, 67 - Ammonium sulphate, 151 - Amoeba, 35 - _Amphidasys betularia_, 101 - _Anas boscas_, 123, 334 - _A. obscura_, 334 - _A. poecilorhyncha_, 315, 334 - _A. superciliosa_, 315, 334 - _A. undulata_, 334 - _Anastomus oscitans_, 282 - Ancon sheep, 95 - _Anemone magellanica_, 118 - _A. sylvestris_, 118 - Anemophilous flowers, 261 - "Animal Colouration," 194, 205, 211, 213, 218, 222 - "Animal Life and Intelligence," 368 - "Animals of New Zealand," 382 - _Anous_, 278 - _Anser cygnoides_, 114 - _Anseranas melanoleucus_, 281 - Antarctic fauna, 191 - Antelope, 48, 199, 334 - _Anthracoceros_, 220 - _Anthropoides paradisea_, 279 - _A. virgo_, 279 - _Antilope cervicapra_, 363 - Ape, 101 - Apogamy, 370 - Appenzeller, 340 - _Apus_, 381 - "Archiv für Entwicklungsmechanik der Organismen," 325, 330 - Arctic fauna, 173, 174, 190, 191 - Arctic regions, 173, 189 - _Ardea asha_, 317, 318 - _A. gularis_, 318 - _Ardeola grayii_, 250, 254 - Argali, 120, 130, 131 - "Argentine Ornithology," 361 - _Argynnis pales_, 381 - _A. paphia_, 103 - Aristotle, 1 - _Artemia milhausenii_, 156 - _A. salina_, 156 - Aseel, 364 - Asexual reproduction, 135 - Asiatic, 140 - Ass, 117, 127, 128, 140 - _Astur badius_, 235 - Atavism, 136, 293 - _Athene chiaradiæ_, 97 - _A. noctua_, 97 - Atoms, biological, 158 - "Auk, The," 190 - _Aularches militaris_, 216 - Avebury, Lord, 205, 260 - "Avicultural Magazine, The," 98 - Avocet, 80 - - - B - Babbler, 244 - Bactrian camel, 121 - Bailey, 88 - Baillon's crake, 251 - Balanced characters, 143 - _Balearica chrysopelargus_, 105 - _B. regulorum_, 105 - _Bassaris astuta_, 242 - Batesian mimicry, 177 - Bateson, 26, 72, 73, 74, 75, 76, 102, 103, 302 - Bats, 42 - Bear, 101, 119, 190, 216, 282 - Beddard, 180, 188, 194, 205, 211 - Bee, 178, 179, 214, 221, 263, 264, 269 - Beech, purple, 87 - Bee-eater, 220, 278 - Beetroots, 71 - Belt, 216 - Beluga, 190 - Bentham, 260 - Bestiary, 125 - Bicheno's finch, 105 - Bilateral symmetry, 252, 253, 257 - Bingham, Col. C. T., 239 - Biological atoms, 158-69, 280 - Biological molecules, 157-69, 280, 285, 291, 293, 294, 295, 344 - Biological radicles, 158-69 - Biophors, 153 - "Bird Book, the," 207 - "Birds of the Plains," 233, 303, 309, 359 - Bison, 119, 126 - Blackcock, 129, 131, 249, 278 - Blackberry, 118 - Blackbird, 201, 203, 207 - Black-buck, 363 - Blakiston, 181 - Bloodsucker, 220 - Blue-bellied waxbill, 104 - Blyth, 115, 251 - Boisier, 263 - _Bombyx arrindia_, 125 - _B. cynthia_, 124 - Bonhote, 126, 288, 289, 290, 291, 292, 293, 337 - Bontebock, 196 - _Boselaphus tragocamelus_, 357, 363 - _Bos frontalis_, 126 - Boulenger, 88 - Bower-bird, 306 - Brain-fever bird, 235, 236, 248 - Bramble, 261 - _Branchipus_, 156 - Brannam, 92 - Brent, Mr, 307 - British Museum, 129, 130, 187 - _Bubo virginianus_, 221 - _Bubulcus coromandus_, 254 - Budgerigars, 101 - Buffalo, 120, 199 - Buffon, 2 - Buff Orpingtons, 65 - Buff-tip moth, 215 - _Bufo melanostictus_, 219 - Bulbul, 123, 220, 221, 244, 245, 255, 256, 279 - Bull, 119 - _Bungarus coeruleus_, 217, 247 - Bunting, reed, 98, 190, 289 - _Buphus coromandus_, 317, 318 - Burbank, 118 - Burnet moth, 102 - Bush-buck, 196 - Butcher-bird, 241, 253 - Buttercups, 70, 267, 274 - Butterfly, 45, 47, 102, 103, 196, 197, 203, 204, 209, 212, 216, - 238, 239, 240, 250, 264, 280, 306, 381 - Buzzard, 262 - - - C - Cacomistle, 242 - _Cairina moschata_, 127, 245 - Californian currant, 119 - _Caloenas nicobarica_, 65 - _Calotes versicolor_, 220 - Camel, 120, 357 - _Campophaga_, 248 - Canary, 100, 101, 102, 117, 120, 127, 280, 338, 362 - _Canis jubatus_, 181 - Capercailzie, 129, 131 - Capuchin monkey, 216 - Carbon, 153 - _Carduelis caniceps_, 255 - _C. carduelis_, 255 - Carnation, 85, 86 - Carnivores, 67 - Carp, 102 - Carrion crow, 123 - Carrot, 71, 269, 270 - _Casarca cana_, 129 - _C. tadornoides_, 129 - "Cassell's Book of the Horse," 69 - Castle, 149 - Castration, effects of, 335, 344 - Cat, 61, 98, 99, 100, 206, 282, 283, 339, 350, 356, 361 - Cat-rabbit, 125 - Cataloe, 119 - Cataract, 340 - Caterpillars, 155, 175, 205, 211, 215, 221, 350 - Cattle, 94, 95, 115 - _Centropus sinensis_, 220, 244 - _Cephalophus doriæ_, 243 - _Cephalopyrus flammiceps_, 244 - _Cervulus muntjac_, 101 - _C. reevesii_, 114 - _C. vaginalis_, 114 - _Cervus paludosus_, 180 - _C. sika_, 120 - _Ceryle rudis_, 202 - Chaffinch, 289 - Chamba monaul, 104 - "Champion Ladybird," 91, 92, 93 - Change of function, theory of, 36, 37 - _Chen nivalis_, 282 - _C. rossi_, 282 - _Chenatopex ægyptiaca_, 316 - _Chenonetta jubata_, 316 - Chinese goose, 99, 114, 121, 130 - Chinese pheasant, 123 - _Chloëphaga dispar_, 105 - _C. magellanica_, 105, 334 - _C. rubidiceps_, 105, 334 - Chromosomes, 145-7 - _Chrysæna victor_, 333 - _Chrysolophus amherstiæ_, 121 - _C. obscurus_, 97 - _C. pictus_, 97, 121, 337 - _Chrysomitris colombiana_, 244 - _Chrysotis æstiva_, 103 - _Ciconia alba_, 282 - _C. boyciana_, 282 - Cinnabar moth, 227 - _Cissopis leveriana_, 281 - Civil Service Commissioners, 385, 387 - Cleistogamous flowers, 260 - Climate as check on multiplication, 349, 350 - Clouded-yellow butterfly, 103 - Clover, 69, 274 - _Clytus arietis_, 178, 229 - Cobra, 224, 225, 226, 358, 359 - _Colias edusa_, 103 - Colour-blindness, 340 - Colouration of Flowers, Law of Progressive, 66 - ---- of Organisms, 170-296 - Columbidæ, 331, 333 - Concealing colouration, 184-7 - Congenital characters, 18, 19 - Conn, 47 - "Contemporary Review," 26 - Cope, 15, 67 - _Copsychus saularis_, 281 - _Coracias affinis_, 123, 255 - _C. indica_, 123, 220, 255 - Cordon-bleu, 104 - Cormorant, 190, 191, 277, 381, 382 - Corn, Indian, 81 - Correlation, 39, 40, 117, 162, 167, 223, 339, 340, 344, 356-65 - _Corvus corone_, 123, 255 - _C. cornix_, 123, 255 - _C. splendens_, 353 - "Country-Side, The," 261, 265, 266, 273, 304, 311, 313 - Courser, 362 - Court-bec, 72 - Cow, 119, 120, 126 - Crab, 155 - Crane, 105, 247, 248, 279, 282, 292 - _Crateropus bicolor_, 242 - _C. canorus_, 179 - _Crax globicera_, 104, 304 - _C. grayi_, 104 - _C. hecki_, 104, 304 - Crested newt, 124 - Cretaceous reptiles, 67 - Crinoids, 67 - Crocodile, 187 - Cross-fertilisation, 69, 258-60 - _Crotalus_, 223 - Crow, 47, 123, 206, 220, 247, 255, 281, 353, 355, 359, 361 - "Crow-pheasant," 220 - Cryptic colouring, 173 - Cuckoo, 220, 233, 235, 236, 243, 244, 247, 248, 289 - ---- shrike, 248 - _Cuculus canorus_, 289 - Cuénot, 149 - Cunningham, Col., 225, 226, 358 - ---- J. T., 15, 19, 20, 324, 325, 329, 331, 332, 333, 336 - Cupples, Mr, 308 - Curassow, 104, 304 - Currant, 119 - Cut-throat finch, 122 - _Cypselus affinis_, 243 - _Cytisus adami_, 119 - - - D - Dafila acuta, 122 - Dahlia, 86 - Daisy, 266, 274 - Daltonism, 340 - _Damaliscus lunatus_, 363 - Damp as a check to multiplication of species, 350, 351 - _Danaidæ_, 175, 179, 215, 216, 226, 228 - _Danais chrysippus_, 179, 250 - Danger signal, 183, 214, 253, 254 - Darter, 277 - Darwin, 1-12, 14, 25-27, 31, 35, 42, 52, 54-7, 59, 60-3, 68, 83, - 96, 112, 114-7, 119, 123, 127, 130, 151, 171, 175, 182, - 184, 233, 259, 299, 301-8, 316, 319-21, 325, 326, 347 - "Darwin and after Darwin," 370-5, 377, 381 - Darwinian theory, 3, 5-8, 11, 13, 27, 28, 35, 42, 45, 52, 75, 111, - 171 - Darwinism, 1, 7, 8, 11, 14, 26 - "Darwinism," 40, 53, 112, 117, 178, 207, 213, 228, 322, 323 - "Darwinism To-day," 16, 45, 67 - _Dasyurus_, 283 - De Candolle, 86 - Decorative plumage, 40 - Deer, 101, 120, 180, 298 - Deerhound, 304, 308 - Deer-ponies, 125 - Degeneration, 168 - Dejerine, 340 - Delage, 33, 147 - Delboeuf, Law of, 373 - _Delias eucharis_, 216, 220, 221 - _Demiegretta_, 100 - Demoiselle crane, 277 - "Descent of Man," 234, 299, 301, 302, 304, 305, 319, 320, 326 - Determination of sex, 165 - "Development and Heredity," 17 - De Vries, 26, 66, 69-72, 75-8, 82-9, 95, 105, 118, 151 - Dewar, D., 43, 44, 47, 48, 195, 204, 206, 208, 210, 225, 233, 236, - 303, 308, 309, 354, 360, 378 - Dewar, G. A. B., 196, 197 - _Dicrurus ater_, 179, 233 - _Didelphys nurina_, 243 - Dimorphism, sexual, 51, 200, 201 - _Dipsacus_, 58 - Disease as a check to multiplication of species, 351 - _Dissemurus paradiseus_, 179, 220 - Divergence of character, 367 - Dog, 59, 68, 99, 100, 125, 225, 226, 282, 283, 304, 308, 352, 357, - 364, 365 - Dog-rose, 261 - Dolphin, 99 - Dominant characters, 142 - Donald, Mr D., 256 - Dragon-fly, 216, 264 - Driesh, 136 - Drongo cuckoo, 233 - Drongo-shrikes, 179, 220 - Drummond, 382 - Duck, 51, 60, 68, 97, 99, 100, 122, 126-8, 190, 247, 249, 282, 292, - 314, 315, 334, 337, 338, 365 - Duiker-buck, 243 - Dyer, Sir William Thistleton, 26 - - - E - Eagle, 65, 190, 350 - Eagle-owl, 221 - East, M. E., 79 - _Echis carinata_, 224 - "Eclipse," 69 - "Edinburgh Review, The," 38 - Eel, 102 - Eggs, colours of birds', 206-9 - Egret, 100, 206, 254, 365 - Eider-duck, 249 - Eimer, 15, 16, 33 - Eisig, 222 - _Elanoides furcatus_, 282 - _Elaps_, 197, 198 - Elder, 49 - Elementary species, 77, 78, 87, 88, 89 - Elk, Irish, 67 - _Emberiza citrinella_, 289 - _E. pyrrhuloides_, 98 - _E. schoeniclus_, 98 - _Entomophila picata_, 281 - Entomophilous flowers, 261 - _Epenthesis folleata_, 103 - Epilobias, 260 - _Equus_, 41 - _Erebia manto_, 381 - _Erythrura prasina_, 102 - "Essays on Evolution," 11, 173, 177, 181, 184, 213, 223, 226, 227, - 229, 230, 231, 234, 237, 238, 239 - _Estrelda cyanogastra_, 104 - _E. phoenicotis_, 104 - Ether, 152, 153 - _Euchelia jacobacæ_, 227 - Eurasian, 140 - European, 140 - _Euxenura maguari_, 282 - Evening primrose, 84, 85, 88 - "Evolution of Sex, The," 306 - Existence, struggle for, 31, 32 - Eye-colour in human beings, 310 - Eyesight of birds, 211, 237-41 - ---- insects, 264 - Eyton, 15 - - - F - "Faery Year, The," 196 - Falcon, 204, 246, 250 - _Falco peregrinator_, 251 - _F. severus_, 251 - False mimicry, 243 - Faults in poultry, 64 - Ferrets, 100, 119 - Finch, 117, 120 - ---- Bicheno's, 105 - ---- chestnut-breasted, 98 - ---- cut-throat, 122 - ---- Gouldian, 98 - ---- Nonpareil, 102 - ---- red-headed, 142 - ---- ringed, 104 - ---- saffron, 244 - ---- yellow-rumped, 98 - Finn, 99, 102, 115, 131, 179, 216, 219, 220, 235, 241, 255, 304, - 309, 310, 313, 315, 316, 358 - Fittest, survival of the, 32 - Flowers, 65, 66 - Flowers, colours of, 258-75 - Fly-catchers, 44, 45, 47, 285, 338 - Flying squirrel, 243 - "Fortnightly Review, The," 37, 38 - Foul-brood, 353 - Fowl, 56, 58, 61, 64, 65, 99, 101, 125, 127, 128, 282, 301, 302, - 307, 314, 330, 336, 338, 339, 361, 362, 364, 365 - Fowl-ducks, 125 - Foxes, 101, 131, 190, 191 - Fox-terrier, 19 - Franqueiro cattle, 95 - _Francolinus pondicerianus_, 337 - Friar-bird, 249 - _Fringella coelebs_, 209 - Fritillary butterfly, 103 - Frog, 325 - Fruits, colours of, 258, 275 - _Fuligula marila_, 290 - Fulmar petrel, 190 - Function, change of, 36, 37 - Fungi, 263 - - - G - Gadow, Dr, 197, 245 - Gadwall, 126, 315 - Galton, 81, 82, 374 - "Game Birds and Wild Fowl of India," 131 - Gametes, segregation of, 143-5 - Gannet, 282 - Gayal, 126 - Gauchos, 359 - Gecko, 210 - Geddes, 306, 326 - Gemmules, 151 - "Genesis of Species," 7, 61 - Geographical isolation, 375 - Geological record, imperfection of, 40-2, 94 - Geranium, 260 - Germ-plasm, continuity of the, 25 - Germinal variations, 106-10 - _Geum urbanum_, 263 - Gibbon ape, 101 - Giraffe, 17, 18, 192, 196 - _Globicera_, 104 - Glutton, 190 - Goat, 283 - Goethe, 2 - Golden pheasant, 97, 129, 149, 337, 338 - Golden tench, 101 - Goldfinch, 127, 255 - Goldfish, 101, 102 - Goose, 99, 100, 105, 115, 121, 130, 190, 281, 316, 334, 339 - Gordon's currant, 119 - Goshawk, 247 - Gouldian Finch, 99 - Graba, 58 - Gradation of colour, principle of, 185 - _Graculipica melanoptera_, 244 - "Grammar of Science, The," 309 - Grass, 273 - Grasshopper, 185 - Greenfinch, 122 - Greyhound, 364 - Grosbeak, 281, 284 - Groundsel, 260 - Grouse, red, 125 - Growth-force, 15, 16, 68 - _Grus leucogeranus_, 282 - Guillemot, 58, 190, 245 - Guinea-fowl, 100, 127, 128, 279, 362 - Guinea-pig, 95, 101, 129, 283 - Gulick, 369, 372-7, 380 - Gull, 190, 191, 207, 247, 290, 355 - _Gygis_, 278 - Gyrfalcon, 190 - - - H - Haeckel, 15, 24 - Hæmophilia, 340 - _Halcyon smyrnensis_, 202 - _Halioetus albicilla_, 65 - Hare, 131, 185, 200 - Harrier, 101 - Hartebeeste, 363 - Hawk-cuckoo, 235, 236 - Hawk-eagle, 101 - Hawks, 222, 235, 236, 247, 277 - _Hecki_, 104 - Helice, 103 - _Heliconidæ_, 175, 215, 216, 228 - Heloderm, 217 - Henslow, 15, 22, 23, 47, 48, 259 - "Heredity," 103, 145, 166, 340 - "Heredity of Acquired Characters in Plants," 22, 48 - "Heredity of Sexual Characters in relation to Hormones," 19, 330 - Heron, 250, 317 - Herring, 193 - Hertwig, 151 - Heusinger, 357 - Hewitt, Mr, 307 - _Hierococcyx varius_, 235, 248 - Hilversum, 84 - Himalayan argali, 120 - Hinny, 127, 136, 140, 162 - _Hipparchia, semele_, 205 - _Hippotragus equinus_, 334 - _H. niger_, 334 - _Hirundo rustica_, 251 - _H. tytleri_, 251 - "History of Creation," 24 - Hobby, 250, 251 - Homogamy, 370 - Honeyeater, 281 - Hormones, 335, 338 - Hornbill, 65, 220 - Horner, 340 - Horse, 61, 68, 69, 95, 96, 100, 101, 117, 127, 128, 140, 266, 267, - 268, 272, 283, 332, 352, 363, 364, 374 - Horse, genealogy of, 41 - Houghton, 91 - Howard, 315, 332 - Hubrecht, 26 - Hume, 131 - Humming-bird, 328 - Hutton, 3 - Hutton, Captain, 115, 382 - Huxley, 3, 6, 11, 40, 100, 111 - Hyæna, 353 - Hybridism, 111-32, 292, 293 - Hydra, 21 - Hydrogen, 152, 153 - _Hydrophasianus chirurgus_, 250 - _Hyla_, 245 - Hypertely, 237, 240 - _Hypolimnas misippus_, 179, 180 - - - I - "Ibis, The," 255, 256 - _Icterus vulgaris_, 244, 281, 284 - Impeyan pheasant, 104 - Indian Civil Service, 385, 386, 387 - Indian corn, 81 - Inheritance, 133-69 - ---- alternative, 127 - ---- blended, 140, 148 - ---- definition of, 138 - ---- of acquired characters, 10, 14, 15, 18-24, 60, 107-10 - ---- particulate, 140 - ---- unilateral, 139, 140, 162 - Insectivores, 67 - Intercrossing, swamping effects of, 42, 83 - Intimidating attitudes, 224, 225 - Iora, 244 - Iridescence, 186 - Irish elk, 67, 168 - Isolation, 366-82, 387 - Isomerism, biological, 154-8 - ---- chemical, 152-4, 157 - _Ithomiinæ_, 228, 246 - Ivy, 261 - - - J - Jacana, 250 - Jackdaw, 51, 306 - Jaeger, 86 - Jaguar, 45, 358 - Japanese greenfinch, 122 - ---- pheasant, 122, 124, 129 - Jardin des plantes, 88 - Java sparrow, 99, 100 - Jelly-fish, 192 - Jesse, W., 255 - Johnston, 92 - "Journal of the Bombay Natural History Society," 209 - "Journal of the Royal Society of Arts," 236, 324, 378 - Jungle-babbler, 179 - Jungle fowl, 332 - - - K - Kallima, 45, 47, 209, 212, 235, 386 - Kellog, 16, 26, 45, 47, 67 - Kingfisher, 202, 203, 206 - Kite, 282 - "Knowledge," 171, 198, 277 - Korchinsky, 15, 33 - Krait, 216, 247 - Kuppa, 224 - - - L - Labernum, 119 - _Lachnanthes_, 357 - Ladybird, 213, 214 - Lamarck, 2, 14, 17, 52 - Lamarckism, 16, 24, 25 - Lambert, Edward, 341 - Lankester, Sir E. Ray, 13, 25 - Lapwing, 207 - Lark, 185, 362 - _Larus ridibundus_, 290 - Latent characters, 149 - Law of battle, 301, 302, 321 - Leaf-butterfly, 45, 47, 209, 235, 386 - Lemming, 190 - Lemur, 242, 243 - _Lemur catta_, 242 - Leopard, black, 101, 354, 358 - _Leucopternis_, 282 - _Ligurinus sinicus_, 122 - Lily, 146 - _Linaria vulgaris peloria_, 86 - Linden, Gräfin von, 155 - Links, missing, 41, 42 - Linnæus, 65, 115 - Linnet, 212, 338 - "Linus I.," 95, 96 - Lion, 192, 334, 349, 352 - _Liothrix luteus_, 179 - Lizard, 64, 207, 210, 212, 216, 217, 220, 223, 269, 350 - _Loddigesia mirabilis_, 328 - Loeb, 147 - _Lophophorus chambanus_, 104 - _L. impeyanus_, 104 - Lucerne, 118 - Lung, 36, 37 - Lutinism, 102 - _Lycæna donzelli_, 381 - _L. pheretes_, 381 - _Lycodon aulicus_, 247 - Lyell, 3 - - - M - Mackerel, 193 - Madingly, 102 - _Mænia typica_, 221 - Magnus, 86 - Magpie, 281 - Magpie colouring, 66, 67, 280, 281 - Magrath, 256 - Male-fern, 49 - Mallard, 65, 97, 122, 126, 132, 293, 313, 315, 334, 337 - Malthus, 31 - Malva, 260 - Manchester School, 27 - Mannikin, 104 - Marbled newt, 124, 245 - Marshall, 28 - ---- Mr G. A. K., 239 - ---- Milnes, 37, 174 - Marsupials, 67 - Masters, 86 - "Materials for the Study of Variation," 73, 103 - Mauchamp sheep, 95 - Mayer, 228 - "Mechanischphysiologische Theorie der Abstammungslehre," 15 - _Medicago media_, 118 - _Megascops asio_, 44 - Melanism, 64, 101, 360 - _Melopsittacus undulatus_, 101 - Mendel, 42, 74, 136, 141, 142, 144, 145 - Mendel's Law, 145, 149, 150, 161 - Mendelism, 145 - _Mesohippus_, 41 - Micellæ, 151 - _Micropus melanoleucus_, 245 - "Mikado, The," 237 - Mildew, 49 - Mimicry, conditions of, 178 - Mimicry, protective, 45, 50, 51, 173, 177-82, 226-51, 275, 293, 294 - Mink, 243 - _Miohippus_, 41 - Missing links, 41, 42 - Missouri currant, 119 - Mivart, Dr St George, 7, 61 - Mole, 180 - _Molge blasii_, 124 - _M. cristata_, 124 - _M. marmorata_, 124 - _M. vulgaris_, 221 - Mollusca, 49 - ---- of Sandwich Islands, 375, 378 - Molpastes, 123, 255 - _Molpastes bengalensis_, 256, 379 - _M. burmanicus_, 379 - _M. hæmorrhous_, 255, 379 - _M. intermedius_, 256, 379 - _M. leucogenys_, 256 - Monaul, 104 - Monkey, 64, 213 - Monotypic evolution, 366 - Monstrosities, 56, 57, 358 - Morgan, Prof. Ll., 368 - ---- T. H., 26 - Morse, 190 - Moseley, Prof., 311 - _Motacilla lugubris_, 122 - _M. melanope_, 122 - Moth, 101, 102, 124, 209, 215, 227, 238, 240 - Mouse, 64, 105, 139, 141, 146, 149, 150, 180, 185, 282, 359 - Mule, 127, 136, 140, 160, 162 - Müller, Fritz, 81, 180 - Müllerian mimicry, 177, 181, 182 - _Munia atricapilla_, 104 - _M. castaneithorax_, 98 - _M. flaviprymna_, 98 - _M. malacca_, 104 - Muscovy duck, 99, 127, 128, 281 - Musk ox, 190, 192 - _Mustela sarmatica_, 243 - Mutations, 41, 43, 66, 69, 72, 75-105, 124, 127, 134, 159, 160, - 169, 223, 280, 281, 284, 292, 295, 339, 341, 342-4, 380-8 - Mutations, theory of, 26, 38, 75, 76, 95 - Myna, 244 - _Myristicivoræ_, 282 - - - N - Naegeli, 15, 16, 151 - Nahrwal, 190 - Natural selection, theory of, stated, 31, 32 - "Nature," 184 - Nautili, 67 - Nectar of flowers, 262, 264, 265, 268, 270, 271 - Neo-Darwinians, 13, 14, 25, 173, 174, 176, 188, 214, 218, 222, 233, - 238, 242, 263, 264 - Neo-Darwinism, 51, 172, 234, 235, 264, 275, 276, 297 - Neo-Lamarckians, 13, 14, 15 - _Neophron_, 282 - _Nepheronia hippia_, 179 - _Nettium albigulare_, 179 - New organs, beginnings of, 36, 73 - Newman, 126 - Newt, 124, 221, 222 - Niata cattle, 95 - Nicobar pigeon, 65 - Nilgai, 337 - Nitrogen, 153 - Noddy, 62, 279 - Nonpareil finch, 102 - _Nyroca africana_, 337 - - - O - Oates, 255, 379 - Obliterative colouration, 184-7 - _Ocydromus_, 365 - _Oenis_, 205 - _Oenopopelia tranquebarica_, 122, 123, 324, 333 - _Oenothera lamarckiana_, 84, 85, 87, 88 - _Ononis repens_, 23 - _O. spinosa_, 22 - Opossum, 243 - Orchid, 268, 269, 270, 272 - _Orgyia antiqua_, 215 - "Origin of Species, The," 7, 9, 11, 31, 53, 57, 63, 114, 170, 194, - 347, 348, 356, 367 - Oriole, 244, 249, 284, 304 - _Oriolus galbula_, 282 - _O. kundoo_, 282 - _O. melanocephalus_, 244, 284 - "Ornithological and Other Oddities," 255 - _Orohippus_, 41 - Orr, 15-7 - Orthogenesis, 15, 16, 34 - _Ossifraga gigantea_, 99, 362 - _Otidiphaps insularis_, 244 - _Ovis ammon_, 120 - _O. vignei_, 120 - Owen, Sir Richard, 7 - Owl, 247, 277, 289 - ---- little, 97, 98 - ---- scops, 101 - ---- snowy, 190 - Ox, 146, 352 - Oxygen, 152, 153, 263 - - - P - Paddy bird, 254 - Paint-root, 357 - _Palæornis torquatus_, 102, 325 - Pallas, 115 - Pansy, 260 - Panther, 360 - _Papilio_, 228, 246 - _P. aristolochiæ_, 179, 216, 220, 221 - _P. polites_, 179 - Paradise, bird of, 62, 249 - Paradise flycatcher, 47, 202, 298, 303, 316, 324, 338 - _Paradisea apoda_, 249 - Paraguay cattle, 94 - _Parnassius apollo_, 155 - Paroquet, 102, 121, 325 - Parrot, 103 - Parthenogenesis, 135, 138 - Partridge, 185, 315, 337 - _Parus leucopterus_, 245 - _Passer domesticus_, 289, 342 - _P. montanus_, 342 - _P. swainsoni_, 342 - Pasteur, 5 - _Pavo nigripennis_, 96 - _Pavoncella pugnax_, 343 - Pea, sweet, 74, 75, 81, 141 - Pear, 72 - Pearson, Karl, 309, 310 - Peckham, 308 - Pekin robin, 179 - Pelagic animals, 173, 192-4 - Penguin, 191 - Pennant's parakeet, 121 - _Petaurus breviceps_, 243 - Petrel, 44, 190, 191, 277, 337 - Pfeffer, 33 - _Phalacrocorax carbo_, 381 - Phalanger, 243 - Phalarope, 327 - _Phasianidæ_, 125, 330 - _Phasianus colchicus_, 114, 123 - _P. torquatus_, 114, 123 - _P. versicolor_, 114, 123, 124 - Pheasant, 97, 104, 114, 121, 123, 128-30, 141, 315, 336, 338 - Pictet, 155, 156 - _Pieris napi_, 155 - _Piezorhynchus_, 285 - Pig, 57, 283, 357, 365 - Pigeon, 61, 62, 65, 68, 71, 72, 91, 92, 93, 98, 101, 109, 126, 127, - 244, 277, 282, 353, 357, 364, 365 - Pigment, massing of, 256 - Pike, 102, 222 - Pimpernel, 261 - Pintail duck, 130, 132, 293, 337 - Pintailed nonpareil finch, 102 - "Plant Breeding," 87 - Plasomes, 151 - Plastidules, 151 - _Platycercus elegans_, 121 - _P. erythropeplus_, 121 - _P. eximius_, 121 - _Pliohippus_, 41 - Plover, 207 - Plumage, decorative, 40 - Pochard, 126, 337 - Poecilomeres, 288-95 - _Poëephila mirabilis_, 99 - Polar bear, 119, 130 - Polar bodies, 135 - Polecat, 119 - Polytypic evolution, 367 - Poppy, 82, 261 - _Porzana bailloni_, 251 - _P. pusilla_, 251 - Post-nuptial display, 316 - _Potentilla tormentilla_, 263 - Poulton, 11, 25, 26, 171, 173, 177, 181, 184, 210, 213, 217, 221, - 223-5, 229-35, 238-42 - _Precis artexia_, 203, 204, 212 - Preferential mating among human beings, 309, 310 - Prepotency, 136 - Prickly pear, 274 - Primrose, evening, 84, 85, 88 - Pritchard, Hesketh, 359 - "Proceedings of the Fourth International Ornithological Congress," - 288, 337 - "Proceedings of the Linnæan Society," 288 - "Proceedings of the Natural History Society of Brunn," 141 - _Protohippus_, 37 - _Pseudoclytia pentata_, 103 - Pseudo-sematic colours, 173 - _Pseudotantalus cinereus_, 282 - Ptarmigan, 190 - _Pteroclurus exustus_, 204 - Puffin, 191 - Pugnacity of animals, 206, 360 - Puma, 45 - Purple beech, 87 - Pycraft, W. P., 277 - _Pycnorhampus affinis_, 284 - _P. icteroides_, 284 - _Pygæra bucephala_, 215 - - - Q - Quail, 185 - Quatrefages, de, 124 - _Quelea quelea_, 98 - _Q. russi_, 98 - _Querquedula crecca_, 290 - Quetelet's Law, 77 - - - R - Rabbit, 99, 100, 105, 183, 253, 283, 350, 352 - Racehorse, 69 - Radicles, biological, 159 - _Rallus aquaticus_, 251 - _R. indicus_, 251 - _Ranunculus bulbosus_, 70 - _Rappia_, 245 - Raspberry, 118 - Rat, 74, 282 - ---- water, 101 - Raven, 190 - Razorbill, 190 - Recessive characters, 142 - Recognition colours, 251-7, 275 - ---- marks, 124 - Red-mantled parakeet, 121 - Redpole, 207 - Redwing, 354 - Reed bunting, 98 - Reeves' pheasant, 129 - Regression, Law of, 82, 374 - Reid, Archdale, 5 - Reindeer, 190 - Rest-harrow, 22 - Reversion, 64, 65, 129, 293 - _Rhinosciurus tupaioides_, 180 - _Rhodocera rhamni_, 155 - _Rhododendron ferrugineum_, 118 - _R. hirsutum_, 118 - _Rhynchæa_, 327 - Ricardo, 28 - Ringed finch, 104 - Robin, 281, 378 - Robin, Indian, 202 - Robinson, Dr H., 171, 198 - ---- E. K., 261, 264, 265, 266, 268, 270, 272-4 - Rodents, 67 - Rogeron, 126 - Roller, 123, 220, 255 - Romanes, 366-81 - Rook, 51, 187 - Rose, 61, 267 - Rosella parakeet, 121 - Rous, Admiral, 69 - Roux, 136 - Ruff, 343 - - - S - Sable, 190 - Saffron finch, 244 - Sainfoin, 267 - Salamander, 217, 219, 221 - _Salix alba_, 118 - _S. pentandra_, 118 - Sandgrouse, 204, 351 - Sandpipers, 185, 190 - Sassaby, 363 - _Satyridæ_, 205 - Scatliff, H. P., 91-3 - Scatliff strain, 91 - Scaup, 290 - Schmankewitsch, 156 - "Science," 166 - _Sciuropterus volucella_, 243 - _Scops giu_, 101 - Scops owl, American, 44 - ----, Indian, 101 - Scoter, 249 - Seal, 190, 191 - Sea-urchin, 149 - Seaweed, 263 - Sebright, Sir John, 63 - Secondary sexual characters, 298 - Segregation, 369 - ---- of gametes, 143-5 - Selous, Edmund, 308 - ---- F. C., 192, 195, 197, 203 - Sematic colours, 173 - _Sesia fuciformis_, 178 - Sexual dimorphism, 51, 297-344 - Sexual selection, theory of, 299-321 - Shaheen, 251 - Shamrock, 274 - Sheathbill, 191 - Sheep, 95, 266, 267, 283, 357, 372 - Sheldrake, 109, 129 - Shikra, 235, 236 - Shoveler, 290 - Shrew, 180, 216 - Sidgwick, 28 - Sidney, 5, 49 - Sika deer, 120 - Silver-washed fritillary butterfly, 103 - Siskin, 127, 244 - Skua, Arctic, 44, 362 - Skua-gull, 191 - Skunk, 186, 217, 221 - Skylark, 315 - Slug, 49, 185 - Smith, Adam, 28 - Snake, 185, 197, 198, 217, 220, 223-6, 247, 356 - Snap-dragon, 268, 272 - Snipe, 69, 327 - Sodium sulphate, 151 - Somatic variations, 106-10 - "Some Indian Friends and Acquaintances," 225, 358 - Sorrel, 274 - Sparrow, 213, 241, 341, 342 - ---- Java, 99, 100 - Sparrow-hawk, 235, 243 - _Spatula clypeata_, 290 - Spavin, 332 - "Species and Varieties," 69, 77, 84, 87, 118 - Species, definition of, 89 - Species, elementary, 77, 78, 87-9 - Spencer, 3, 15, 16, 28, 38, 151 - Spider, 269, 272 - _Sporæginthus amandava_, 311 - Sports, 41, 43, 66, 75, 85, 135 - Squirrel, 101, 186, 243 - Stag, 325 - ---- Irish, 67 - Standfuss, 155 - Stanley crane, 248, 279 - St Hilaire, T. G., 2, 356 - Stick insect, 209 - _Stictoptera annulosa_, 104 - Stoat, 119, 190, 290 - Stolzmann, 327-9, 342, 343 - Stonechat, 353 - Stork, 247, 282 - "Strand Magazine," 64 - _Strix flammea_, 289 - Struggle for existence, 31, 32, 48 - ---- for nourishment, 167 - Suchetet, A., 126, 130 - _Sula capensis_, 282 - _S. serrator_, 282 - Sunbird, 324 - _Surniculus lugubris_, 235, 243 - Survival of the fittest, 32 - Survival value, 33, 34 - Swallow, 250, 251, 279, 361 - Swallow-shrike, 281 - Swallow-tail butterfly, 179 - Swan, 100 - Swift, 243, 250 - Swimming bladder of fishes, 36, 37 - _Sycalis flaveola_, 244 - _Syrphidæ_, 178 - - - T - _Tachycineta leucorrhoa_, 361 - _Tadorna cornuta_, 129 - _T. tadornoides_, 129 - Tails, 62, 64 - Tait, Mr, 356 - Tanager, 281 - Tapir, 42 - Tasmanian devil, 282 - Teal, 290, 316 - Teasel, fuller's, 58 - Teeth, molar, 105 - Tegetmeier, Mr, 307 - Tern, 62, 278 - _Terpsiphone paradisi_, 202, 298, 304, 316, 324 - _Tetraogallus_, 337 - _Tetraonidæ_, 125 - _Tetrapteryx paradisea_, 249 - _Tetrao tetrix_, 129 - _T. urogallus_, 129 - _Thamnobia cambayensis_, 202, 275 - _T. fulicata_, 202, 378 - Thayer, Mr Abbot, 184-7 - Thompson, Seton, 354 - Thomson, 103, 136, 145, 166, 306, 326, 340 - Throat disease, 353 - "Through Southern Mexico," 197, 245 - "Through the Heart of Patagonia," 359 - Thrush, 203, 207, 355 - Tiger, 334 - Tit, 245 - Toad, 210, 219, 241 - Toad-flax, 56 - Tortoise, 222 - Trefoil, 274 - _Trochilium_, 229 - Trogon, 62 - _Tropidonotus piscator_, 220 - Troupial, 244, 281, 284 - Tsetse-fly, 352 - _Tupaia_, 180, 216 - _T. ellioti_, 216 - Turbit, 72, 91-3 - "Turbit, The Modern," 91 - Turkey, 95, 363 - Turnspit dog, 59 - _Turtur cambayensis_, 333 - _T. suratensis_, 333 - _T. risorius_, 33, 123, 126 - Tylor, Mr Alfred, 287 - - - U - Ungulates, 67 - Unilateral transmission, 341 - Unit characters, 148-52 - _Uria grylle_, 245 - _U. lacrymans_, 58 - Urial, 120, 130, 131 - _Urodynamis tritensis_, 243 - - - V - Valezina, 103 - _Vanessa levana_, 154 - _V. prorsa_, 154 - Vapourer moth, 215 - Variation, 52-110 - ---- cause of, 59-60 - ---- continuous, 56, 69, 76, 105 - ---- definite, 55 - ---- determinate, 55 - ---- discontinuous, 43, 56, 72, 73, 76, 78, 79, 87, 105, 106, 133, - 159, 295 - ---- germinal, 106-10, 133 - ---- indefinite, 55, 59 - ---- somatic, 106-110 - _Viola_, 260 - _V. tricolor_, 260 - Volckamer, 86 - Vulture, 282 - - - W - Waggett, 12 - Wagner, 369, 372 - Wagtail, 122, 203 - Wallace, 3, 10, 13, 14, 25, 26, 35-42, 53, 112, 114, 116, 117, 171, - 175, 177, 183, 184, 207, 213, 228, 230, 251, 253, 256, 287, - 296, 308, 321-7, 343, 372, 377 - Wallaceian school of biologists, 14, 24, 25, 47, 192, 210, 251, - 346, 347, 366, 377 - Wallaceism, 172, 202 - Walrus, 190 - Warblers, British, 315, 332 - Warning colours, 173, 176, 198, 212-26 - Wasp, 174, 178, 179, 214, 227 - Wasp-beetle, 229 - Water-rail, 251 - Waxbill, blue-bellied, 104 - Weasel, 190 - Weaver, red-billed, 98 - Weber, 86 - Weir, Mr Jenner, 299 - Weismann, 25, 106, 107, 151, 154 - Weka rail, 365 - "Westminster Review," 112 - Weston, G. E., 127 - Whale, 42, 185, 190, 193 - Wheatear, 253 - Whinchat, 253 - Wiesner, 151 - Wilson, Prof. E. B., 166 - Winter coat, 188 - Wolf, 48, 130, 185, 192 - Wonder horse, 95, 96 - Woodpecker, 102 - Wright, Mr, 304 - Wyman, Professor, 357 - - - X - X-element, 165 - - - Y - Yak, 120 - Yarrow, 268 - "Year-book of the Smithsonian Institution," 184 - Yerbury, Col., 239 - Youatt, 63 - - - Z - Zebra, 196 - Zebu, 120 - Zocher & Co., 56 - Zoological Gardens, Lahore, 309 - ----, London, 104, 119, 126, 130, 206, 304, 316 - Zoological Society of London, 330 - _Zygæna filipendulæ_, 102 - - - - - _OTHER WORKS BY THE SAME AUTHORS_ - - - By DOUGLAS DEWAR - - BOMBAY DUCKS - BIRDS OF THE PLAINS - ANIMALS OF NO IMPORTANCE - Etc. Etc. - - - By FRANK FINN - - ORNITHOLOGICAL AND OTHER ODDITIES - THE WORLD'S BIRDS - WILD BEASTS OF THE WORLD - GARDEN AND AVIARY BIRDS IN INDIA - Etc. 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Each volume -will be carefully illustrated, and as far as text, printing, and paper -are concerned will be a notable book. Great care has been taken in -selecting the biographers, who in most cases have already accumulated -much appropriate material._ - - - _First Volumes._ - - - ELLEN TERRY. By Christopher St. John. - HERBERT BEERBOHM TREE. By Mrs. George Cran. - W. S. GILBERT. By Edith A. Browne. - CHAS. WYNDHAM. By Florence Teignmouth Shore. - GEORGE BERNARD SHAW. By G. K. Chesterton. - - - _A CATALOGUE OF MEMOIRS, BIOGRAPHIES, ETC._ - - - _WORKS UPON NAPOLEON_ - - -NAPOLEON & THE INVASION OF ENGLAND: The Story of the Great Terror, -1797-1805. By H. F. B. Wheeler and A. M. Broadley. With upwards of 100 -Full-page Illustrations reproduced from Contemporary Portraits, Prints, -etc.; eight in Colour. Two Volumes. 32_s._ net. - - _Outlook._--"The book is not merely one to be ordered from the library; - it should be purchased, kept on an accessible shelf, and constantly - studied by all Englishmen who love England." - - _Westminster Gazette._--"Messrs. Wheeler and Broadley have succeeded in - producing a work on the threatened invasion of England by Napoleon, - which treats of the subject with a fulness of detail and a completeness - of documentary evidence that are unexampled." - - -DUMOURIEZ AND THE DEFENCE OF ENGLAND AGAINST NAPOLEON. By J. Holland -Rose, Litt.D. (Cantab.), Author of "The Life of Napoleon," and A. M. -Broadley, joint-author of "Napoleon and the Invasion of England." -Illustrated with numerous Portraits, Maps, and Facsimiles. Demy 8vo. -21_s._ net. - - -THE FALL OF NAPOLEON. By Oscar Browning, M.A., Author of "The Boyhood and -Youth of Napoleon." With numerous Full-page Illustrations. Demy 8vo (9 x -5-3/4 inches). 12_s._ 6_d._ net. - - _Spectator._--"Without doubt Mr. Oscar Browning has produced a book - which should have its place in any library of Napoleonic literature." - - _Truth._--"Mr. Oscar Browning has made not the least, but the most of - the romantic material at his command for the story of the fall of the - greatest figure in history." - - -THE BOYHOOD & YOUTH OF NAPOLEON, 1769-1793. Some Chapters on the early -life of Bonaparte. By Oscar Browning, M.A. With numerous Illustrations, -Portraits, etc. Crown 8vo. 5_s._ net. - - _Daily News._--"Mr. Browning has with patience, labour, careful study, - and excellent taste given us a very valuable work, which will add - materially to the literature on this most fascinating of human - personalities." - - _Literary World._--". . . Mr. Browning has examined all the available - sources of information and carefully weighed his historical evidence. - His discriminating treatment has resulted in a book that is . . . one - that arrests attention by the conviction its reasoned conclusions - carry." - - -THE DUKE OF REICHSTADT (NAPOLEON II.) By Edward de Wertheimer. Translated -from the German. With numerous Illustrations. Demy 8vo. 21_s._ net. -(Second Edition.) - - _Times._--"A most careful and interesting work which presents the first - complete and authoritative account of the life of this unfortunate - Prince." - - _Westminster Gazette._--"This book, admirably produced, reinforced by - many additional portraits, is a solid contribution to history and a - monument of patient, well-applied research." - - -NAPOLEON'S CONQUEST OF PRUSSIA, 1806. By F. Loraine Petre. With an -Introduction by Field-Marshal Earl Roberts, V.C., K.G., etc. With Maps, -Battle Plans, Portraits, and 16 Full-page Illustrations. Demy 8vo (9 x -5-3/4 inches). 12_s._ 6_d._ net. - - _Scotsman._--"Neither too concise, nor too diffuse, the book is - eminently readable. It is the best work in English on a somewhat - circumscribed subject." - - _Outlook._--"Mr. Petre has visited the battlefields and read - everything, and his monograph is a model of what military history, - handled with enthusiasm and literary ability, can be." - - -NAPOLEON'S CAMPAIGN IN POLAND, 1806-1807. A Military History of -Napoleon's First War with Russia, verified from unpublished official -documents. By F. Loraine Petre. With 16 Full-page Illustrations, Maps, -and Plans. New Edition. Demy 8vo (9 x 5-3/4 inches). 12_s._ 6_d._ net. - - _Army and Navy Chronicle._--"We welcome a second edition of this - valuable work. . . . Mr. Loraine Petre is an authority on the wars of - the great Napoleon, and has brought the greatest care and energy into - his studies of the subject." - - -NAPOLEON AND THE ARCHDUKE CHARLES. A History of the Franco-Austrian -Campaign in the Valley of the Danube in 1809. By F. Loraine Petre. With 8 -Illustrations and 6 sheets of Maps and Plans. Demy 8vo (9 x 5-3/4 -inches). 12_s._ 6_d._ net. - - -RALPH HEATHCOTE. Letters of a Diplomatist During the Time of Napoleon, -Giving an Account of the Dispute between the Emperor and the Elector of -Hesse. By Countess Günther Gröben. With Numerous Illustrations. Demy 8vo -(9 x 5-3/4 inches), 12_s._ 6_d._ net. - - .'. _Ralph Heathcote, the son of an English father and an Alsatian - mother, was for some time in the English diplomatic service as first - secretary to Mr. Brook Taylor, minister at the Court of Hesse, and on - one occasion found himself very near to making history. Napoleon became - persuaded that Taylor was implicated in a plot to procure his - assassination, and insisted on his dismissal from the Hessian Court. As - Taylor refused to be dismissed, the incident at one time seemed likely - to result to the Elector in the loss of his throne. Heathcote came into - contact with a number of notable people, including the Miss Berrys, - with whom he assures his mother he is not in love. On the whole, there - is much interesting material for lovers of old letters and journals._ - - -MEMOIRS OF THE COUNT DE CARTRIE. A record of the extraordinary events in -the life of a French Royalist during the war in La Vendée, and of his -flight to Southampton, where he followed the humble occupation of -gardener. With an introduction by Frédéric Masson, Appendices and Notes -by Pierre Amédée Pichot, and other hands, and numerous Illustrations, -including a Photogravure Portrait of the Author. Demy 8vo. 12_s._ 6_d._ -net. - - _Daily News._--"We have seldom met with a human document which has - interested us so much." - - _Athenæum._--"As a record of personal suffering and indomitable - perseverance against opposing circumstances the narrative of De - Cartrie's escape to the Eastern frontier, in the disguise of a - master-gunner, could not easily be surpassed." - - -WOMEN OF THE SECOND EMPIRE. Chronicles of the Court of Napoleon III. By -Frédéric Loliée. With an introduction by _Richard Whiteing_ and 53 -full-page Illustrations, 3 in Photogravure. Demy 8vo. 21_s._ net. - - _Standard._--"M. Frédéric Loliée has written a remarkable book, vivid - and pitiless in its description of the intrigue and dare-devil spirit - which flourished unchecked at the French Court. . . . Mr. Richard - Whiteing's introduction is written with restraint and dignity." - - _Daily Telegraph._--"It is a really fascinating story, or series of - stories, set forth in this volume. . . . Here are anecdotes innumerable - of the brilliant women of the Second Empire, so that in reading the - book we are not only dazzled by the beauty and gorgeousness of - everything, but we are entertained by the record of things said and - done, and through all we are conscious of the coming 'gloom and doom' - so soon to overtake the Court. Few novels possess the fascination of - this spirited work, and many readers will hope that the author will - carry out his proposal of giving us a further series of memories of the - 'Women of the Second Empire.'" - - -LOUIS NAPOLEON AND THE GENESIS OF THE SECOND EMPIRE. By F. H. Cheetham. -With Numerous Illustrations. Demy 8vo (9 x 5-3/4 inches). 16_s._ net. - - -MEMOIRS OF MADEMOISELLE DES ÉCHEROLLES. Translated from the French by -Marie Clothilde Balfour. With an Introduction by G. K. Fortescue. -Portraits, etc. 5_s._ net. - - _Liverpool Mercury._--". . . this absorbing book. . . . The work has a - very decided historical value. The translation is excellent, and quite - notable in the preservation of idiom." - - -JANE AUSTEN'S SAILOR BROTHERS. Being the life and Adventures of Sir -Francis Austen, G.C.B., Admiral of the Fleet, and Rear-Admiral Charles -Austen. By J. H. and E. C. Hubback. With numerous Illustrations. Demy -8vo. 12_s._ 6_d._ net. - - _Morning Post._--". . . May be welcomed as an important addition to - Austeniana . . .; it is besides valuable for its glimpses of life in - the Navy, its illustrations of the feelings and sentiments of naval - officers during the period that preceded and that which followed the - great battle of just one century ago, the battle which won so much but - which cost us--Nelson." - - -SOME WOMEN LOVING AND LUCKLESS. By Teodor de Wyzewa. Translated from the -French by C. H. Jeffreson, M.A. With Numerous Illustrations. Demy 8vo (9 -x 5-3/4 inches), 7_s._ 6_d._ net. - - -POETRY AND PROGRESS IN RUSSIA. By Rosa Newmarch. With 6 full-page -Portraits. Demy 8vo. 7_s._ 6_d._ net. - - _Standard._--"Distinctly a book that should be read . . . pleasantly - written and well informed." - - -THE LIFE OF PETER ILICH TCHAIKOVSKY (1840-1893). By his Brother, Modeste -Tchaikovsky. Edited and abridged from the Russian and German Editions by -Rosa Newmarch. With Numerous Illustrations and Facsimiles and an -Introduction by the Editor. Demy 8vo. 7_s._ 6_d._ net. Second edition. - - _The Times._--"A most illuminating commentary on Tchaikovsky's music." - - _World._--"One of the most fascinating self-revelations by an artist - which has been given to the world. The translation is excellent, and - worth reading for its own sake." - - _Contemporary Review._--"The book's appeal is, of course, primarily to - the music-lover; but there is so much of human and literary interest in - it, such intimate revelation of a singularly interesting personality, - that many who have never come under the spell of the Pathetic Symphony - will be strongly attracted by what is virtually the spiritual - autobiography of its composer. High praise is due to the translator and - editor for the literary skill with which she has prepared the English - version of this fascinating work . . . There have been few collections - of letters published within recent years that give so vivid a portrait - of the writer as that presented to us in these pages." - - -COKE OF NORFOLK AND HIS FRIENDS: The Life of Thomas William Coke, First -Earl of Leicester of the second creation, containing an account of his -Ancestry, Surroundings, Public Services, and Private Friendships, and -including many Unpublished Letters from Noted Men of his day, English and -American. By A. M. W. Stirling. With 20 Photogravure and upwards of 40 -other Illustrations reproduced from Contemporary Portraits, Prints, etc. -Demy 8vo. 2 vols. 32_s._ net. - - _The Times._--"We thank Mr. Stirling for one of the most interesting - memoirs of recent years." - - _Daily Telegraph._--"A very remarkable literary performance. Mrs. - Stirling has achieved a resurrection. She has fashioned a picture of a - dead and forgotten past and brought before our eyes with the vividness - of breathing existence the life of our English ancestors of the - eighteenth century." - - _Pall Mall Gazette._--"A work of no common interest; in fact, a work - which may almost be called unique." - - _Evening Standard._--"One of the most interesting biographies we have - read for years." - - -THE LIFE OF SIR HALLIDAY MACARTNEY, K.C.M.G., Commander of Li Hung -Chang's trained force in the Taeping Rebellion, founder of the first -Chinese Arsenal, Secretary to the first Chinese Embassy to Europe. -Secretary and Councillor to the Chinese Legation in London for thirty -years. By Demetrius C. Boulger, Author of the "History of China," the -"Life of Gordon," etc. With Illustrations. Demy 8vo. Price 24_s._ net. - - _Daily Graphic._--"It is sate to say that few readers will be able to - put down the book without feeling the better for having read it . . . - not only full of personal interest, but tells us much that we never - knew before on some not unimportant details." - - -DEVONSHIRE CHARACTERS AND STRANGE EVENTS. By S. Baring-Gould, M.A., -Author of "Yorkshire Oddities," etc. With 58 Illustrations. Demy 8vo. -21_s._ net. - - _Daily News._--"A fascinating series . . . the whole book is rich in - human interest. It is by personal touches, drawn from traditions and - memories, that the dead men surrounded by the curious panoply of their - time, are made to live again in Mr. Baring-Gould's pages." - - -CORNISH CHARACTERS AND STRANGE EVENTS. By S. Baring-Gould. Demy 8vo. -21_s._ net. - - -THE HEART OF GAMBETTA. Translated from the French of Francis Laur by -Violette Montagu. With an Introduction by John Macdonald, Portraits and -other Illustrations. Demy 8vo. 7_s._ 6_d._ net. - - _Daily Telegraph._--"It is Gambetta pouring out his soul to Léonie - Leon, the strange, passionate, masterful demagogue, who wielded the - most persuasive oratory of modern times, acknowledging his idol, his - inspiration, his Egeria." - - -THE MEMOIRS OF ANN, LADY FANSHAWE. Written by Lady Fanshawe. With -Extracts from the Correspondence of Sir Richard Fanshawe. Edited by H. C. -Fanshawe. With 38 Full-page Illustrations, including four in Photogravure -and one in Colour. Demy 8vo. 16_s._ net. - - .'. _This Edition has been printed direct from the original manuscript - in the possession of the Fanshawe Family, and Mr. H. C. Fanshawe - contributes numerous notes which form a running commentary on the text. - Many famous pictures are reproduced, including paintings by Velazquez - and Van Dyck._ - - -THE LIFE OF JOAN OF ARC. -By Anatole France. -A Translation by Winifred Stephens. -With 8 Illustrations. -Demy 8vo, 9 x 5-3/4 inches, 2 vols. -Price 25_s._ net. - - .'. _Joan of Arc, by her friends accounted a saint, by her enemies a - witch, stands out the one supreme figure of the French 15th century; - that period of storm and stress, that time of birth-giving from which - proceeded the glories of the Renaissance. Bitter controversy raged - round the Maid in her life-time. Round her story to-day literary - polemic waxes high; and her life by Anatole France is the most eagerly - discussed book of the century. That it presents a life-like picture of - the time critics of all parties agree. Its author has well equipped - himself with the best erudition of the last thirty years. To the fruits - of these researches he has added profound philosophy and true - historical insight, and thus into consummate literary art he has - painted a more vivid picture of the French 15th century than has ever - yet been presented in any literature. The Maid herself Monsieur France - regards not as a skilful general or a wily politician as some writers - have endeavoured to make out, but as above all things a saint. It was - by her purity and innate goodness that she triumphed. "It was not Joan - who drove the English out of France . . . And yet the young saint - played the noblest part in the salvation of her country. Hers was the - part of sacrifice. She set the example of high courage and gave to - heroism a new and attractive form._ - - -THE DAUGHTER OF LOUIS XVI. -Marie-Thérèse-Charlotte of France, Duchesse D'Angoulême. -By G. Lenotre. -With 13 Full-page Illustrations. -Demy 8vo. -Price 10_s._ 6_d._ net. - - .'. _M. G. Lenotre is perhaps the most widely read of a group of modern - French writers who have succeeded in treating history from a point of - view at once scientific, dramatic and popular. He has made the - Revolution his particular field of research, and deals not only with - the most prominent figures of that period, but with many minor - characters whose life-stories are quite as thrilling as anything in - fiction. The localities in which these dramas were enacted are vividly - brought before us in his works, for no one has reconstructed 18th - century Paris with more picturesque and accurate detail. "The Daughter - of Louis XVI." is quite equal in interest and literary merit to any of - the volumes which have preceded it, not excepting the famous Drama of - Varennes. As usual, M. Lenotre draws his material largely from - contemporary documents, and among the most remarkable memoirs - reproduced in this book are "The Story of my Visit to the Temple" by - Harmand de la Meuse, and the artless, but profoundly touching narrative - of the unhappy orphaned Princess: "A manuscript written by Marie - Thérèse Charlotte of France upon the captivity of the Princes and - Princesses, her relatives, imprisoned in the Temple." The illustrations - are a feature of the volume and include the so-called "telescope" - portrait of the Princess, sketched from life by an anonymous artist, - stationed at a window opposite her prison in the tower of the Temple._ - - -HUBERT AND JOHN VAN EYCK: Their Life and Work. By W. H. James Weale. With -41 Photogravure and 95 Black and White Reproductions. Royal 4to. £5 5_s._ -net. - - Sir Martin Conway's Note. - - _Nearly half a century has passed since Mr. W. H. James Weale, then - resident at Bruges, began that long series of patient investigations - into the history of Netherlandish art which was destined to earn so - rich a harvest. When he began work Memlinc was still called Hemling, - and was fabled to have arrived at Bruges as a wounded soldier. The van - Eycks were little more than legendary heroes. Roger Van der Weyden was - little more than a name. Most of the other great Netherlandish artists - were either wholly forgotten or named only in connection with paintings - with which they had nothing to do. Mr. Weale discovered Gerard David, - and disentangled his principal works from Memlinc's, with which they - were then confused. During a series of years he published in the - "Beffroi," a magazine issued by himself, the many important records - from ancient archives which threw a flood of light upon the whole - origin and development of the early Netherlandish school. By universal - admission he is hailed all over Europe as the father of this study. It - is due to him in great measure that the masterpieces of that school, - which by neglect were in danger of perishing fifty years ago, are now - recognised as among the most priceless treasures of the Museums of - Europe and the United States. Fullness and accuracy are the - characteristics of all Mr. Weale's work._ - - -VINCENZO FOPPA OF BRESCIA, Founder of the Lombard School, His Life and -Work. By Constance Jocelyn Ffoulkes and Monsignor Rodolfo Majocchi, D.D., -Rector of the Collegio Borromeo, Pavia. Based on research in the Archives -of Milan, Pavia, Brescia, and Genoa, and on the study of all his known -works. With over 100 Illustrations, many in Photogravure, and 100 -Documents. Royal 4to. £3. 11_s._ 6_d._ net. - - .'. _No complete Life of Vincenzo Foppa has ever been written: an - omission which seems almost inexplicable in these days of - over-production in the matter of biographies of painters, and of - subjects relating to the art of Italy. The object of the authors of - this book has been to present a true picture of the master's life based - upon the testimony of records in Italian archives; all facts hitherto - known relating to him have been brought together; all statements have - been verified; and a great deal of new and unpublished material has - been added. The authors have unearthed a large amount of new material - relating to Foppa, one of the most interesting facts brought to light - being that he lived for twenty-three years longer than was formerly - supposed. The illustrations will include several pictures by Foppa - hitherto unknown in the history of art, and others which have never - before been published, as well as reproductions of every existing work - by the master at present known._ - - -MEMOIRS OF THE DUKES OF URBINO. Illustrating the Arms, Art and Literature -of Italy from 1440 to 1630. By James Dennistoun of Dennistoun. A New -Edition edited by Edward Hutton, with upwards of 100 Illustrations. Demy -8vo. 3 vols. 42_s._ net. - - .'. _For many years this great book has been out of print, although it - still remains the chief authority upon the Duchy of Urbino from the - beginning of the fifteenth century. Mr. Hutton has carefully edited the - whole work, leaving the text substantially the same, but adding a large - number of new notes, comments and references. Wherever possible the - reader is directed to original sources. Every sort of work has been - laid under contribution to illustrate the text, and bibliographies have - been supplied on many subjects. Besides these notes the book acquires a - new value on account of the mass of illustrations which it now - contains, thus adding a pictorial comment to an historical and critical - one._ - - -THE PHILOSOPHY OF LONG LIFE. By Jean Finot. A Translation by Harry -Roberts. Demy 8vo. (9 x 5-3/4 inches). 7_s._ 6_d._ net. - - .'. _This is a translation of a book which has attained to the position - of a classic. It has already been translated into almost every - language, and has, in France, gone into fourteen editions in the course - of a few years. The book is an exhaustive one, and although based on - science and philosophy it is in no sense abstruse or remote from - general interest. It deals with life as embodied not only in man and in - the animal and vegetable worlds, but in all that great world of (as the - author holds) misnamed "inanimate" nature as well. For M. Finot argues - that all things have life and consciousness, and that a solidarity - exists which brings together all beings and so-called things. He sets - himself to work to show that life, in its philosophic conception, is an - elemental force, and durable as nature herself._ - - -THE DIARY OF A LADY-IN-WAITING. By Lady Charlotte Bury. Being the Diary -Illustrative of the Times of George the Fourth. Interspersed with -original Letters from the late Queen Caroline and from various other -distinguished persons. New edition. Edited, with an Introduction, by A. -Francis Steuart. With numerous portraits. Two Vols. Demy 8vo. 21_s._ net. - - .'. _This book, which appeared anonymously in 1838, created an enormous - sensation, and was fiercely criticised by Thackeray and in the Reviews - of the time. There is no doubt that it was founded on the diary of Lady - Charlotte Bury, daughter of the 5th Duke of Argyll, and Lady-in-Waiting - to the unfortunate Caroline of Brunswick, when Princess of Wales. It - deals, therefore, with the curious Court of the latter and with the - scandals that occurred there, as well as with the strange vagaries of - the Princess abroad. In this edition names left blank in the original - have been (where possible) filled up, and many notes are given by the - Editor to render it useful to the ever-increasing number of readers - interested in the later Georgian Period._ - - -JUNIPER HALL: Rendezvous of certain illustrious Personages during the -French Revolution, including Alexander D'Arblay and Fanny Burney. -Compiled by Constance Hill. With numerous Illustrations by Ellen G. Hill, -and reproductions from various Contemporary Portraits. Crown 8vo. 5_s._ -net. - - -JANE AUSTEN: Her Homes and Her Friends. By Constance Hill. Numerous -Illustrations by Ellen G. Hill, together with Reproductions from Old -Portraits, etc. Cr. 8vo. 5_s._ net. - - -THE HOUSE IN ST. MARTIN'S STREET. Being Chronicles of the Burney Family. -By Constance Hill, Author of "Jane Austen, Her Home, and Her Friends," -"Juniper Hall," etc. With numerous Illustrations by Ellen G. Hill, and -reproductions of Contemporary Portraits, etc. Demy 8vo. 21_s._ net. - - -STORY OF THE PRINCESS DES URSINS IN SPAIN (Camarera-Mayor). By Constance -Hill. With 12 Illustrations and a Photogravure Frontispiece. New Edition. -Crown 8vo. 5_s._ net. - - -NEW LETTERS OF THOMAS CARLYLE. Edited and Annotated by Alexander Carlyle, -with Notes and an Introduction and numerous Illustrations. In Two -Volumes. Demy 8vo. 25_s._ net. - - _Pall Mall Gazette._--"To the portrait of the man, Thomas, these - letters do really add value; we can learn to respect and to like him - the more for the genuine goodness of his personality." - - _Morning Leader._--"These volumes open the very heart of Carlyle." - - _Literary World._--"It is then Carlyle, the nobly filial son, we see in - these letters; Carlyle, the generous and affectionate brother, the - loyal and warm-hearted friend, . . . and above all, Carlyle as the - tender and faithful lover of his wife." - - _Daily Telegraph._--"The letters are characteristic enough of the - Carlyle we know: very picturesque and entertaining, full of extravagant - emphasis, written, as a rule, at fever heat, eloquently rabid and - emotional." - - -THE NEMESIS OF FROUDE: a Rejoinder to "My Relations with Carlyle." By Sir -James Crichton Browne and Alexander Carlyle. Demy 8vo. 3_s._ 6_d._ net. - - _Glasgow Herald._--". . . The book practically accomplishes its task of - reinstating Carlyle; as an attack on Froude it is overwhelming." - - _Public Opinion._--"The main object of the book is to prove that Froude - believed a myth and betrayed his trust. That aim has been achieved." - - -NEW LETTERS AND MEMORIALS OF JANE WELSH CARLYLE. A Collection of hitherto -Unpublished Letters. Annotated by Thomas Carlyle, and Edited by Alexander -Carlyle, with an Introduction by Sir James Crichton Browne, M.D., LL.D., -F.R.S., numerous Illustrations drawn in Lithography by T. R. Way, and -Photogravure Portraits from hitherto unreproduced Originals. In Two -Volumes. Demy 8vo. 25_s._ net. - - _Westminster Gazette._--"Few letters in the language have in such - perfection the qualities which good letters should possess. Frank, gay, - brilliant, indiscreet, immensely clever, whimsical, and audacious, they - reveal a character which, with whatever alloy of human infirmity, must - endear itself to any reader of understanding." - - _World._--"Throws a deal of new light on the domestic relations of the - Sage of Chelsea. They also contain the full text of Mrs. Carlyle's - fascinating journal, and her own 'humorous and quaintly candid' - narrative of her first love-affair." - - _Daily News._--"Every page . . . scintillates with keen thoughts, - biting criticisms, flashing phrases, and touches of bright comedy." - - -ÉMILE ZOLA: Novelist and Reformer. An Account of his Life, Work, and -Influence. By E. A. Vizetelly. With numerous Illustrations, Portraits, -etc. Demy 8vo. 21_s._ net. - - _Morning Post._--"Mr. Ernest Vizetelly has given . . . a very true - insight into the aims, character, and life of the novelist." - - _Athenæum._--". . . Exhaustive and interesting." - - _M.A.P._--". . . will stand as the classic biography of Zola." - - _Star._--"This 'Life' of Zola is a very fascinating book." - - _Academy._--"It was inevitable that the authoritative life of Emile - Zola should be from the pen of E. A. Vizetelly. No one probably has the - same qualifications, and this bulky volume of nearly six hundred pages - is a worthy tribute to the genius of the master." - - Mr. T. P. O'Connor in _T.P.'s Weekly_.--"It is a story of fascinating - interest, and is told admirably by Mr. Vizetelly. I can promise any one - who takes it up that he will find it very difficult to lay it down - again." - - -MEMOIRS OF THE MARTYR KING: being a detailed record of the last two years -of the Reign of His Most Sacred Majesty King Charles the First, -1646-1648-9. Compiled by Allan Fea. With upwards of 100 Photogravure -Portraits and other Illustrations, including relics. Royal 4to. 105_s._ -net. - - Mr. M. H. Spielmann in _The Academy_.--"The volume is a triumph for the - printer and publisher, and a solid contribution to Carolinian - literature." - - _Pall Mall Gazette._--"The present sumptuous volume, a storehouse of - eloquent associations . . . comes as near to outward perfection as - anything we could desire." - - -MEMOIRS OF A VANISHED GENERATION 1813-1855. Edited by Mrs. Warrenne -Blake. With numerous Illustrations. Demy 8vo. 16_s._ net. - - .'. _This work is compiled from diaries and letters dating from the - time of the Regency to the middle of the nineteenth century. The value - of the work lies in its natural unembellished picture of the life of a - cultured and well-born family in a foreign environment at a period so - close to our own that it is far less familiar than periods much more - remote. There is an atmosphere of Jane Austen's novels about the lives - of Admiral Knox and his family, and a large number of well-known - contemporaries are introduced into Mrs. Blake's pages._ - - -CÉSAR FRANCK: A Study. Translated from the French of Vincent d'Indy. And -with an Introduction by Rosa Newmarch. Demy 8vo. 7_s._ 6_d._ net. - - .'. _There is no purer influence in modern music than that of César - Franck, for many years ignored in every capacity save that of organist - of Sainte-Clotilde, in Paris, but now recognised as the legitimate - successor of Bach and Beethoven. His inspiration "rooted in love and - faith" has contributed in a remarkable degree to the regeneration of - the musical art in France and elsewhere. The now famous "Schola - Cantorum," founded in Paris in 1896, by A. Guilmant, Charles Bordes and - Vincent d'Indy, is the direct outcome of his influence. Among the - artists who were in some sort his disciples were Paul Dukas, Chabrier, - Gabriel Fauré and the great violinist Ysanye. His pupils include such - gifted composers as Benoît, Augusta Holmès, Chausson, Ropartz, and - d'Indy. This book, written with the devotion of a disciple and the - authority of a master, leaves us with a vivid and touching impression - of the saint-like composer of "The Beatitudes."_ - - -FRENCH NOVELISTS OF TO-DAY: Maurice Barres, Réné Bazin, Paul Bourget, -Pierre de Coulevain, Anatole France, Pierre Loti, Marcel Prévost, and -Edouard Rod. Biographical, Descriptive, and Critical. By Winifred -Stephens. With Portraits and Bibliographies. Crown 8vo. 5_s._ net. - - .'. _The writer, who has lived much in France, is thoroughly acquainted - with French life and with the principal currents of French thought. The - book is intended to be a guide to English readers desirous to keep in - touch with the best present-day French fiction. Special attention is - given to the ecclesiastical, social, and intellectual problems of - contemporary France and their influence upon the works of French - novelists of to-day._ - - -THE KING'S GENERAL IN THE WEST, being the Life of Sir Richard Granville, -Baronet (1600-1659). By Roger Granville, M.A., Sub-Dean of Exeter -Cathedral. With Illustrations. Demy 8vo. 10_s._ 6_d._ net. - - _Westminster Gazette._--"A distinctly interesting work; it will be - highly appreciated by historical students as well as by ordinary - readers." - - -THE LIFE AND LETTERS OF ROBERT Stephen Hawker, sometime Vicar of -Morwenstow in Cornwall. By C. E. Byles. With numerous Illustrations by J. -Ley Pethybridge and others. Demy 8vo. 7_s._ 6_d._ net. - - _Daily Telegraph._--". . . As soon as the volume is opened one finds - oneself in the presence of a real original, a man of ability, genius - and eccentricity, of whom one cannot know too much . . . No one will - read this fascinating and charmingly produced book without thanks to - Mr. Byles and a desire to visit--or revisit--Morwenstow." - - -THE LIFE OF WILLIAM BLAKE. By Alexander Gilchrist. Edited with an -Introduction by W. Graham Robertson. Numerous Reproductions from Blake's -most characteristic and remarkable designs. Demy 8vo. 10_s._ 6_d._ net. -New Edition. - - _Birmingham Post._--"Nothing seems at all likely ever to supplant the - Gilchrist biography. Mr. Swinburne praised it magnificently in his own - eloquent essay on Blake, and there should be no need now to point out - its entire sanity, understanding keenness of critical insight, and - masterly literary style. Dealing with one of the most difficult of - subjects, it ranks among the finest things of its kind that we - possess." - - -MEMOIRS OF A ROYAL CHAPLAIN, 1729-63. The correspondence of Edmund Pyle, -D.D., Domestic Chaplain to George II, with Samuel Kerrich, D.D., Vicar of -Dersingham, and Rector of Wolferton and West Newton. Edited and Annotated -by Albert Hartshorne. With Portrait. Demy 8vo. 16_s._ net. - - _Truth._--"It is undoubtedly the most important book of the kind that - has been published in recent years, and is certain to disturb many - readers whose minds have not travelled with the time." - - -GEORGE MEREDITH: Some Characteristics. By Richard Le Gallienne. With a -Bibliography (much enlarged) by John Lane. Portrait, etc. Crown 8vo. -5_s._ net. Fifth Edition. Revised. - - _Punch._--"All Meredithians must possess 'George Meredith; Some - Characteristics,' by Richard Le Gallienne. This book is a complete and - excellent guide to the novelist and the novels, a sort of Meredithian - Bradshaw, with pictures of the traffic superintendent and the head - office at Boxhill. Even Philistines may be won over by the - blandishments of Mr. Le Gallienne." - - -LIFE OF LORD CHESTERFIELD. An account of the Ancestry, Personal -Character, and Public Services of the Fourth Earl of Chesterfield. By W. -H. Craig, M.A. Numerous Illustrations. Demy 8vo. 12_s._ 6_d._ net. - - _Daily Telegraph._--"Mr. Craig has set out to present him (Lord - Chesterfield) as one of the striking figures of a formative period in - our modern history . . . and has succeeded in giving us a very - attractive biography of a remarkable man." - - _Times._--"It is the chief point of Mr. Craig's book to show the - sterling qualities which Chesterfield was at too much pains in - concealing, to reject the perishable trivialities of his character, and - to exhibit him as a philosophic statesman, not inferior to any of his - contemporaries, except Walpole at one end of his life, and Chatham at - the other." - - -A QUEEN OF INDISCRETIONS. The Tragedy of Caroline of Brunswick, Queen of -England. From the Italian of G. P. Clerici. Translated by Frederic -Chapman. With numerous Illustrations reproduced from contemporary -Portraits and Prints. Demy 8vo. 21_s._ net. - - _The Daily Telegraph._--"It could scarcely be done more thoroughly or, - on the whole, in better taste than is here displayed by Professor - Clerici. Mr. Frederic Chapman himself contributes an uncommonly - interesting and well-informed introduction." - - _Westminster Gazette._--"The volume, scholarly and well-informed . . . - forms one long and absorbingly interesting chapter of the _chronique - scandaleuse_ of Court life . . . reads like a romance, except that no - romancer would care or dare to pack his pages so closely with startling - effects and fantastic scenes." - - -LETTERS AND JOURNALS OF SAMUEL GRIDLEY HOWE. Edited by his Daughter Laura -E. Richards. With Notes and a Preface by F. B. Sanborn, an Introduction -by Mrs. John Lane, and a Portrait. Demy 8vo. (9 x 5-3/4 inches). 16_s._ -net. - - _Outlook._--"This deeply interesting record of experience. The volume - is worthily produced and contains a striking portrait of Howe." - - _Daily News._--"Dr. Howe's book is full of shrewd touches; it seems to - be very much a part of the lively, handsome man of the portrait. His - writing is striking and vivid; it is the writing of a shrewd, keen - observer, intensely interested in the event before him." - - -THE LIFE OF ST. MARY MAGDALEN. Translated from the Italian of an Unknown -Fourteenth-Century Writer by Valentina Hawtrey. With an Introductory Note -by Vernon Lee, and 14 Full-page Reproductions from the Old Masters. Crown -8vo. 5_s._ net. - - _Daily News._--"Miss Valentina Hawtrey has given a most excellent - English version of this pleasant work." - - _Academy._--"The fourteenth-century fancy plays delightfully around the - meagre details of the Gospel narrative, and presents the heroine in - quite an unconventional light. . . . In its directness and artistic - simplicity and its wealth of homely detail the story reads like the - work of some Boccaccio of the cloister; and fourteen illustrations - taken from Italian painters happily illustrate the charming text." - - -MEN AND LETTERS. By Herbert Paul, M.P. Fourth Edition. Crown 8vo. 5_s._ -net. - - _Daily News._--"Mr. Herbert Paul has done scholars and the reading - world in general a high service in publishing this collection of his - essays." - - _Punch._--"His fund of good stories is inexhaustible, and his urbanity - never fails. On the whole, this book is one of the very best examples - of literature on literature and life." - - -ROBERT BROWNING: Essays and Thoughts. By J. T. Nettleship. With Portrait. -Crown 8vo. 5_s._ 6_d._ net. (Third Edition.) - - -A LATER PEPYS. The Correspondence of Sir William Weller Pepys, Bart., -Master in Chancery, 1758-1825, with Mrs. Chapone, Mrs. Hartley, Mrs. -Montague, Hannah More, William Franks, Sir James Macdonald, Major -Rennell, Sir Nathaniel Wraxall, and others. Edited, with an Introduction -and Notes, by Alice C. C. Gaussen. With numerous Illustrations. Demy 8vo. -In Two Volumes. 32_s._ net. - - Douglas Sladen in the _Queen_.--"This is indisputably a most valuable - contribution to the literature of the eighteenth century. It is a - veritable storehouse of society gossip, the art criticism, and the - _mots_ of famous people." - - _Academy and Literature._--"The effect consists in no particular - passages, but in the total impression, the sense of atmosphere, and the - general feeling that we are being introduced into the very society in - which the writer moved." - - _Daily News._--"To Miss Alice Gaussen is due the credit of sorting out - the vast collection of correspondence which is here presented to the - public. . . . Her industry is indefatigable, and her task has been - carried out with completeness. The notes are full of interesting items; - the introduction is exhaustive; and the collection of illustrations - enhances the value of the book." - - _World._--"Sir William Pepys's correspondence is admirable." - - -ROBERT LOUIS STEVENSON, AN ELEGY; AND OTHER POEMS, MAINLY PERSONAL. By -Richard Le Gallienne. Crown 8vo. 4_s._ 6_d._ net. - - _Daily Chronicle._--"Few, indeed, could be more fit to sing the dirge - of that 'Virgil of Prose' than the poet whose _curiosa felicitas_ is so - close akin to Stevenson's own charm." - - _Globe._--"The opening Elegy on R. L. Stevenson includes some tender - and touching passages, and has throughout the merits of sincerity and - clearness." - - -RUDYARD KIPLING: a Criticism. By Richard Le Gallienne. With a -Bibliography by John Lane. Crown 8vo. 3_s._ 6_d._ net. - - _Guardian._--"One of the cleverest pieces of criticism we have come - across for a long time." - - _Scotsman._--"It shows a keen insight into the essential qualities of - literature, and analyses Mr. Kipling's product with the skill of a - craftsman . . . the positive and outstanding merits of Mr. Kipling's - contribution to the literature of his time are marshalled by his critic - with quite uncommon skill." - - -POEMS. By Edward Cracroft Lefroy. With a Memoir by W. A. Gill, and a -Reprint of Mr. J. A. Symonds' Critical Essay on "Echoes from Theocritus." -Photogravure Portrait. Crown 8vo. 5_s._ net. - - _The Times._--". . . the leading features of the sonnets are the - writer's intense sympathy with human life in general and with young - life in particular; his humour, his music, and, in a word, the quality - which 'leaves a melody afloat upon the brain, a savour on the mental - palate.'" - - _Bookman._--"The Memoir, by Mr. W. A. Gill, is a sympathetic sketch of - an earnest and lovable character; and the critical estimate, by J. - Addington Symonds, is a charmingly, written and suggestive essay." - - -APOLOGIA DIFFIDENTIS. By W. Compton Leith. Demy 8vo. 7_s._ 6_d._ net. - - .'. _The book, which is largely autobiographical, describes the effect - of diffidence upon an individual life, and contains, with a - consideration of the nature of shyness, a plea for a kindlier judgment - of the inveterate case._ - - _Daily Mail._--"Mr. Leith has written a very beautiful book, and - perhaps the publisher's claim that this will be a new classic is not - too bold." - - -THE TRUE STORY OF MY LIFE: an Autobiography by Alice M. Diehl, Novelist, -Writer, and Musician. Demy 8vo. 10_s._ 6_d._ net. - - -BOOKS AND PERSONALITIES: Essays. By H. W. Nevinson. Crown 8vo. 5_s._ net. - - _Daily Chronicle._--"It is a remarkable thing and probably unique, that - a writer of such personality as the author of 'Between the Acts' should - not only feel, but boldly put on paper, his homage and complete - subjection to the genius of one after another of these men. He is - entirely free from that one common virtue of critics, which is - superiority to the author criticised." - - -OTIA: Essays. By Armine Thomas Kent. Crown 8vo. 5_s._ net. - - -BOOKS AND PLAYS: A Volume of Essays on Meredith, Borrow, Ibsen, and -others. By Allan Monkhouse. Crown 8vo. 5_s._ net. - - -LIBER AMORIS; or, The New Pygmalion. By William Hazlitt. Edited, with an -introduction, by Richard Le Gallienne. To which is added an exact -transcript of the original MS., Mrs. Hazlitt's Diary in Scotland, and -Letters never before published. Portrait after Bewick, and facsimile -Letters. 400 copies only. 4to. 364 pp. Buckram. 21_s._ net. - - -TERRORS OF THE LAW: being the Portraits of Three Lawyers--the original -Weir of Hermiston, "Bloody Jeffreys," and "Bluidy Advocate Mackenzie." By -Francis Watt. With 3 Photogravure Portraits. Fcap. 8vo. 4_s._ 6_d._ net. - - _The Literary World._--"The book is altogether entertaining; it is - brisk, lively, and effective. Mr. Watt has already, in his two series - of 'The Law's Lumber Room,' established his place as an essayist in - legal lore, and the present book will increase his reputation." - - -CHAMPIONS OF THE FLEET. Captains and Men-of-War in the Days that Helped -to make the Empire. By Edward Fraser. With 16 Full-page Illustrations. -Crown 8vo. 6_s._ - - -THE LONDONS OF THE BRITISH FLEET: The Story of Ships bearing the name of -Old Renown in Naval Annals. By _Edward Fraser_. With 8 Illustrations in -colours, and 20 in black and white. 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You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org - - -Title: The Making of Species - -Author: Douglas Dewar - Frank Finn - -Release Date: October 29, 2013 [EBook #44063] - -Language: English - -Character set encoding: ASCII - -*** START OF THIS PROJECT GUTENBERG EBOOK THE MAKING OF SPECIES *** - - - - -Produced by Stephen Hutcheson, Marcia Brooks and the Online -Distributed Proofreading Canada Team at -http://www.pgdpcanada.net (This file was produced from -images generously made available by The Internet -Archive/American Libraries.) - - - - - - -[Illustration: HEX CURASSOW FEEDING YOUNG BIRD, WITH PLUMAGE OF THE -GLOBOSE CURASSOW] - - - - - THE MAKING - OF SPECIES - - - BY DOUGLAS DEWAR, B.A. (Cantab), I.C.S., F.Z.S. - AND FRANK FINN, B.A. (Oxon), F.Z.S., M.B.O.U. - WITH FIFTEEN ILLUSTRATIONS - - - LONDON: JOHN LANE THE BODLEY HEAD - NEW YORK: JOHN LANE COMPANY MCMIX - - _Turnbull & Spears, Printers, Edinburgh_ - - - - - PREFACE - - -Post-Darwinian books on evolution fall naturally into four classes. I. -Those which preach Wallaceism, as, for example, Wallace's _Darwinism_, -Poulton's _Essays on Evolution_, and the voluminous works of Weismann. -II. Those advocating Lamarckism. Cope's _Factors of Evolution_ and the -writings of Haeckel belong to this class. III. The writings of De Vries, -forming a group by themselves. They advocate the theory that species -spring suddenly into being; that new species arise by mutations from -pre-existing species. IV. The large number of books of a more judicial -nature, books written by men who decline to subscribe to any of the above -three creeds. Excellent examples of such works are Kellog's _Darwinism -To-Day_, Lock's _Recent Progress in the Study of Variation, Heredity, and -Evolution_, and T. H. Morgan's _Evolution and Adaptation_. - -All four classes are characterised by defects. - -Books of the two first classes exhibit the faults of ardent partisanship. -They formulate creeds, and, as Huxley truly remarked, "Science commits -suicide when it adopts a creed." The books which come under the third -category have the defects of extreme youth. De Vries has discovered a new -principle, and it is but natural that he should exaggerate its -importance, and see in it more than it contains. But, as time wears on, -these faults will disappear, and the theory of mutations will assume its -true form and fall into its proper place, which is somewhere between the -dustbin, to which Wallaceians would relegate it, and the exalted pinnacle -on to which De Vries would elevate it. - -In the present state of our knowledge, books of Class IV. are the most -useful to the student, since they are unbiassed, and contain a judicial -summing-up of the evidence for and against the various evolutionary -theories which now occupy the field. Their chief defect is that they are -almost entirely destructive. They shatter the faith of the reader, but -offer nothing in place of that which they have destroyed. T. H. Morgan's -_Evolution and Adaptation_, however, contains much constructive matter, -and so is the most valuable work of this class in existence. - -Zoological science stands in urgent need of constructive books on -evolution--books with leanings towards neither Wallaceism, nor -Lamarckism, nor De Vriesism; books which shall set forth facts of all -kinds, concealing none, not even those which do not admit of explanation -in the present state of our knowledge.--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 speculation. We have followed up the exposure of the weak points of -the theories, which at present occupy the field, with certain -suggestions, which, we believe, throw new light on many biological -problems. - -Our aim in writing this book has been twofold. In the first place we have -attempted to place before the general public in simple language a true -statement of the present position of biological science. In the second -place, we have endeavoured to furnish the scientific men of the day with -food for reflection. - -Even as the British nation seems to be slowly but surely losing, through -its conservatism, the commercial supremacy it had the good fortune to -gain last century, so is it losing, through the unwillingness of many of -our scientific men to keep abreast of the times, that scientific -supremacy which we gained in the middle of last century by the labours of -Charles Darwin and Alfred Russell Wallace. To-day it is not among -Englishmen, but among Americans and Continentals, that we have to look -for advanced scientific ideas. - -Even as the Ultra-Cobdenites believe that Free Trade is a panacea for all -economic ills, so do most English men of science believe that natural -selection offers the key to every zoological problem. Both are living in -a 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 dissecting-room, that nature can best be -studied. Far be it from us to deprecate the study of morphology. We wish -merely to insist upon the fact, that the leaders of biological science -must of necessity be those naturalists who go to the tropics and other -parts of the earth where nature can be studied under the most favourable -conditions, and those who conduct scientific breeding experiments. -Natural 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 knowledge -second-hand to be the pioneers of biological science. - -We fear that this book will come as a rude shock to many scientific men. -By way of consolation we may remind such that they will find themselves -in much the same position as that occupied by theologians immediately -after the appearance of the _Origin of Species_. - -At that time theological thought was cramped by dogma. But the clergy -have since reconsidered their position, they have modified their views, -and thus kept abreast of the times. Meanwhile scientific men have lagged -behind. The blight of dogma has seized hold of them. They have adopted a -creed to which all must subscribe or be condemned as heretics. Huxley -said that the adoption of a creed was tantamount to suicide. We are -endeavouring to save biology in England from committing suicide, to save -it from the hands of those into which it has fallen. - -We would emphasise that it is not Darwinism we are attacking, but that -which is erroneously called Neo-Darwinism. Neo-Darwinism is a -pathological growth on Darwinism, which, we fear, can be removed only by -a surgical operation. - -Darwin, himself, protested in vain against the length to which some of -his followers were pushing his theory. On p. 657 of the new edition of -the _Origin of Species_ he wrote: "As my conclusions have lately been -much misrepresented, and as it has been stated that I attribute the -modification of species exclusively to natural selection, I may be -permitted to remark that in the first edition of this work, and -subsequently, I placed in a most conspicuous position--namely, at the -close of the Introduction--the following words: 'I am convinced that -natural selection has been the main but not the exclusive means of -modification.' This has been of no avail. Great is the power of steady -misrepresentation; but the history of science shows that this power does -not long endure." - -Notwithstanding this protest the Wallaceians continue on their course, -and give to the world a spurious Darwinism. It is our belief that were -Darwin alive to-day his sympathies would be with us, and not with those -who call themselves his followers. It was one of Darwin's strong points -that he never avoided facts. If new facts came to light which were -incompatible with a theory of his, he promptly modified his theory. Since -his death a number of new facts have come to light which, in our opinion, -plainly indicate that the theory of natural selection as enunciated by -Darwin needs considerable modification. - -We have in this book set forth certain of these facts and indicated the -directions in which the Darwinian theory seems to require modification. - -This volume originated as the result of several conversations we, the -joint authors, had last summer. We discovered that we had a great many -ideas in common on the subject of evolution. This seemed strange, seeing -that our education had not been on the same lines. One of us took a -degree in natural science at Cambridge, and subsequently entered His -Majesty's Indian Civil Service, but continued his zoological studies in -India as a hobby. The other, a naturalist from childhood, nevertheless -took a classical degree at Oxford, then received a technical zoological -training, adopted zoology as a profession, and held for some years a -position in the Natural History Museum at Calcutta. - -Our conversations revealed that we were both of opinion that biology is -in an unhealthy condition, especially in England, and that the science -sorely needs some fresh impetus. Neither of us had the time to attempt, -single-handed, to give the required impetus, but as one of us happened to -be home on eighteen months' leave, we thought we might undertake the task -in collaboration. - -We felt that we might collaborate the more successfully because the large -number of facts collected by the one of us form the necessary complement -to the philosophical studies of the other. - -We have endeavoured, so far as possible, to avoid technical terms, and -have made a special point of quoting, wherever practicable, familiar -animals as examples, in order that the work may make its appeal not only -to the zoologist but to the general reader. - -It may, perhaps, be urged against us that we have quoted too freely from -popular writings, including those of which we are the authors. Our reply -to this is that the study of bionomics, the science of living animals, -occupies so small a place in English scientific literature that we have -been compelled to have recourse to popular works for many of our facts; -and we would, moreover, point out that a popular work is not necessarily -inaccurate in its information. - -In conclusion, we would warn the reader against the danger of confounding -Inference with Fact. The failure to distinguish between the two has -vitiated much of the work of the Wallaceian school of biologists. - -Facts are always to be accepted. Inferences should be scrutinised with -the utmost care. - -In making our deductions, we have endeavoured to act without bias. We -shall, therefore, welcome any new facts, be they consistent with, or -opposed to, our inferences. - - D. D. - F. F. - - - - - CONTENTS - - - PAGE - - -CHAPTER I 1 - - Rise of the Theory of Natural Selection and its Subsequent Development - - Pre-Darwinian 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 30 - -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--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. - - -CHAPTER III 52 - - 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 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 "discontinuous - 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 111 - - 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. - - -CHAPTER V 133 - - 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--Dominance sometimes - imperfect--Behaviour of the nucleus of the sexual - cell--Chromosomes--Experiments of Delage and Loeb--Those of Cuenot - on mice and Castle on guinea pigs--Suggested modification of the - generally-accepted Mendelian formulae--Unit characters--Biological - isomerism--Biological molecules--Interpretation of the phenomena of - variation and heredity on the conception of biological - molecules--Correlation--Summary of the conception of biological - molecules. - - -CHAPTER VI 170 - - The Colouration of Organisms - - 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 - Muellerian 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--Illustrative 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--Objections 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 recognition 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 297 - - Sexual Dimorphism - - 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--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. - - -CHAPTER VIII 345 - - The Factors of Evolution - - 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 in a position to decide--_Modus operandi_ - of Natural Selection--Correlation an important factor--Examples of - correlation--Correlation is a subject that requires close - study--Isolation a factor in evolution--Discriminate - isolation--Indiscriminate 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 compared 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. - - -Footnotes 389 - - -Index 389 - - - - - LIST OF ILLUSTRATIONS - - - FACING PAGE - - -Heck'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._ - - -A Turbit belonging to Mr H. P. Scatliff 92 - -_From "The Modern Turbit," published by "The Feathered World," London._ - - -Yellow-Rumped and Chestnut-Breasted Finches, with Specimens in -Transitional State 98 - - On the left, the yellow-rumped finch; on the right, the - chestnut-breasted; birds in state of change in the middle. - _By permission of the Avicultural Society._ - - -Male Amherst Pheasant 122 - - The chief colours of this species (_Chrysolophus amherstiae_) are - white and metallic green, so that it is very different in - appearance from its near ally the gold pheasant. - - -Harlequin Quail (_Coturnix delegorguei_) 124 - - _By permission of the Avicultural Society._ - - -Rain Quail (_Coturnix coromandelica_) 124 - - The markings on the throats of these quails are of the type usually - put down as "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._ - - -Bouru Friar-Bird 222 - - Like most of the group to which it belongs, this honey-eater - (_Tropidorhynchus bouruensis_) is a soberly coloured bird, but is - noisy, active, and aggressive. - _By permission of Messrs Hutchinson & Co._ - - -Bouru Oriole 222 - - This "mimicking" oriole (_Oriolus bouruensis_) is of the same tone - of colour as its supposed model the Friar-bird of the same island. - _By permission of Messrs Hutchinson & Co._ - - -King-Crow or Drongo 232 - - This very conspicuous black bird (_Dicrurus ater_), ranging from - Africa to China, is a striking feature of the landscape wherever it - occurs. - _By permission of Messrs Hutchinson & Co._ - - -Drongo-Cuckoo 232 - - The fork of the tail in this bird is unique among cuckoos, but is - nevertheless much less developed than in the supposed model, and - may be an adaptation for evolutions in flight, as such tails - usually appear to be. - _By permission of Messrs Hutchinson & Co._ - - -Shikra Hawk 236 - - The upper surface of the tail, not shown in this drawing, exactly - corresponds with that of the cuckoo "mimic." - _By permission of Messrs Hutchinson & Co._ - - -Hawk-Cuckoo 236 - - This species (_Hierococcyx varius_) is commonly known in India as - the "Brain-fever bird." - _By permission of Messrs Hutchinson & Co._ - - -Brazilian Troupial 284 - - This species (_Icterus vulgaris_) is that most frequently seen in - captivity; the pattern of colour is found in several other allied - forms. - _By permission of Messrs Hutchinson & Co._ - - -Indian Black-Headed Oriole 284 - - Several other orioles besides this (_O. melanocephalus_) have the - black head. - _By permission of Messrs Hutchinson & Co._ - - -Queen Whydah 298 - - This species (_Tetraenura regia_) is a typical example of seasonal - sexual dimorphism, the male being long-tailed and conspicuously - coloured only during the breeding season, and at other times - resembling the sparrow-like female. - _By permission of the Foreign Bird Club._ - - -Courtship of Skylark 314 - - Illustrating display by a species with no decorative colouring or - sex difference. - - - - - THE MAKING OF SPECIES - - - - - CHAPTER I - RISE OF THE THEORY OF NATURAL SELECTION AND ITS SUBSEQUENT DEVELOPMENT - - - Pre-Darwinian 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. - -Darwinism and evolution are not interchangeable terms. On this fact it is -impossible to lay too much emphasis. Charles Darwin was not the -originator of the theory of evolution, nor even the first to advocate it -in modern times. The idea that all existing things have been produced by -natural causes from some primordial material is as old as Aristotle. It -was lost sight of in the mental stagnation of the Middle Ages. In that -dark period zoological science was completely submerged. It was not until -men shook off the mental lethargy that had held them for many generations -that serious attention was paid to biology. From the moment when men -began to apply scientific methods to that branch of knowledge the idea of -evolution found supporters. - -Buffon suggested that species are not fixed, but may be gradually changed -by natural causes into different species. - -Goethe was a thorough-going evolutionist; he asserted that all animals -were probably descended from a common original type. - -Lamarck was the first evolutionist who sought to show the means whereby -evolution has been effected. He tried to prove that the efforts of -animals are the causes of variation; that these efforts originate changes -in form during the life of the individual which are transmitted to its -offspring. - -St Hilaire was another evolutionist who endeavoured to explain how -evolution had occurred. He believed that the transformations of animals -are effected by changes in their environment. These hypotheses were -considered, and rightly considered, insufficient to explain anything like -general evolution, so that the idea failed for a time to make headway. - - - Strength of 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 which afforded a plausible explanation of what they believed -to have occurred. - -Hence the rapturous welcome accorded to the theory of natural selection -by the more progressive biologists. - -Another point in 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 -something to take the part played among domesticated animals by the human -breeder. This he was able to do. As the numbers of species remain -stationary, it is evident that only a small portion of the animals that -are born can reach maturity. A child can see that the individuals most -likely to survive are those best adapted to the circumstances of their -life. Even as the breeder weeds out of his stock the creatures not suited -to his purpose, so in nature do the unfit perish in the everlasting -struggle for existence. - -In nature there is a selection corresponding to that of the breeder. - -It is useless to deny the existence of this selection in nature, this -natural selection. The only disputable point is whether such selection -can do all that Darwin demanded of it. - -The man in the street, then, was able to comprehend the theory of natural -selection. This was greatly in its favour. Men are usually well disposed -towards doctrines which they can readily understand. - -The nineteenth century was a superficial age. It liked simplicity in all -things. If Darwin could show that natural selection was capable of -producing one species, men were not only ready but eager to believe that -it could explain the whole of organic evolution. - -The simplicity of the Darwinian theory has its evil side. It has -undoubtedly tended to make modern biologists superficial in their -methods. It has, indeed, stimulated the imagination of men of science; -but the stimulation has not in all cases been a healthy one. - -So far from adhering to the sound rule laid down by Pasteur, "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 facts in -support of his hypothesis. He enunciated no crude theory, he indulged in -no wild speculations. He was content to marshal a great array of facts, -and to draw logical conclusions therefrom. He was as cautious in his -deductions as he was careful of his facts. He thus stood head and -shoulders above the biologists of his day. He was a giant among pigmies. -So well equipped was he that those who attempted to oppose him found -themselves in the position of men, armed with bows and arrows, who seek -to storm a fortress defended by maxim guns. - -Nor was this all. The majority of the best biologists of his time did not -attempt to oppose him. They were, as we have seen, ready to receive with -open arms any hypothesis which seemed to explain how evolution had -occurred. Some of them perceived that there were weak points in the -Darwinian theory, but they preferred not to expose these; they were -rather disposed to make the best of the hypothesis. It had so many merits -that it seemed to them but reasonable to suppose that subsequent -investigation would prove that the defects were apparent rather than -real. - - - Opponents of Darwin - -We hear much of the "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 obtained acceptance. We venture to say that statements such as -these are misleading. We think we may safely assert that scarcely ever -has a theory which fundamentally changed the prevailing scientific -beliefs met with less opposition. It would have been a good thing for -zoology had Darwin not obtained so easy a victory. - -Sir Richard Owen, a distinguished anatomist, certainly attacked the -doctrine in no unmeasured terms, but his attack was anonymous and so -cannot be considered very formidable. Far more important was the -opposition of Dr St George Mivart, whose worth as a biologist has never -been properly appreciated. His most important work, entitled the _Genesis -of Species_, might be read with profit even now by many of our modern -Darwinians. - -For some time after the publication of the _Origin of Species_ Mivart -appears to be almost the only man of science fully alive to the weak -points of the Darwinian theory. The great majority seem to have been -dazzled by its brilliancy. - -The main attack on Darwinism was conducted by the theologians and their -allies, who considered it to be subversive of the Mosaic account of the -Creation. Now, when one whose scientific knowledge is, to say the best of -it, not extensive, attacks a man who has studied his subject -dispassionately for years, and invariably expresses himself with extreme -caution, the onslaught can have but one 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 position of warriors who do not -know what it is against which they are fighting; they confounded natural -selection with evolution, and directed the main force of their attack -against the latter, under the impression that they were fighting the -Darwinian theory. - -It was the misfortune of those theologians that it is possible to prove -that evolution, or, at any rate, some evolution has occurred; they thus -kicked against the pricks with disastrous results to themselves. When -this attack had been repulsed men believed that the theory of natural -selection had been demonstrated, that it was as much a law of nature as -that of gravitation. What had really happened was that the fact of -evolution had been proved, and the theory of natural selection obtained -the credit. Men thought that Darwinism was evolution. Had the theologians -admitted evolution but denied the ability of natural selection to explain -it, the Darwinian theory, in all probability, would not have gained the -ascendency which it now enjoys. - - - Evolution and Natural Selection - -To us who are able to look back dispassionately upon the biological -warfare of the last century, Darwin's opponents--or the majority of -them--appear very foolish. We must, however, bear in mind that at the -time of the publication of the _Origin of Species_ both natural selection -and evolution were comparatively unknown ideas. Darwin had to fight for -both. He had to prove evolution as well as natural selection. Many of the -facts adduced by him supported both. It is, therefore, not altogether -surprising that many of his opponents failed to distinguish between them. - -A glance at the _Origin of Species_ will suffice to show how considerable -is the portion of the book that deals with the evidence in favour of -evolution rather than of natural selection. - -Of the fourteen chapters which make up the book no fewer than nine are -devoted to proving that evolution has occurred. It has been truly said, -that for every one fact biologists have found in support of the special -theory of natural selection they have found ten facts supporting the -doctrine of evolution. Darwin, then, was in the position of a skilled -barrister who has a plausible case and who knows the ins and outs of his -brief, while his opponents stood in the shoes of inexperienced counsel -who had but recently received their brief, and who had not had the time -to master the details thereof. In such circumstances it is not difficult -to predict which way the verdict of the jury will go. - -Darwin, moreover, had a charming personality. Never was a man with a -theory less dogmatic. Never was the holder of a theory more careful of -the expressions he used. Never was a scientific man more ready to give -ear to his opponents, to meet them half way, and, where necessary, to -compromise. Darwin was not afraid of facts, and was always ready to alter -his views when they appeared to be opposed to facts. The average -scientific man of to-day makes facts fit his theory; if they refuse to -fit it he ignores or denies them. - -Darwin continually modified his views; when he found himself in a tight -place he did not hesitate to resort to Lamarckian factors, such as the -inheritance of the effects of use and disuse and of the effects of -environment. He conceded that natural selection was insufficient to -account for all the phenomena of organic evolution, and advanced the -theory of sexual selection in order to account for facts which the major -hypothesis seemed to him incapable of explaining. - -Darwin, moreover, having ample private means, was not obliged to work for -a living, and was therefore able to devote the whole of his time to -research. The advantages of such a position cannot be over-estimated, -and, perhaps, have not been sufficiently taken into account in -apportioning the praise between Darwin and Wallace for their great -discovery. - - - Huxley - -To all these factors in Darwin's favour we must add his good fortune in -possessing so able a lieutenant as Huxley. - -Huxley was an ardent evolutionist, an able writer, and a brilliant -debater. A man of his mental calibre was able, like a clever barrister, -to make out a plausible case for any theory which he chose to take up. -While nominally a strong supporter of the Darwinian theory, he was in -reality fighting for the doctrine of descent. Had _any_ plausible theory -of evolution been enunciated, Huxley would undoubtedly have fought for it -equally earnestly. - -A firm believer in evolution, Huxley was, as Professor Poulton says, -confronted by two difficulties,--first, the insufficiency of the evidence -of evolution, and, secondly, the absence of any explanation of how the -phenomenon had occurred. The _Origin of Species_ solved both these -difficulties. It adduced much weighty evidence in favour of evolution, -and suggested a _modus operandi_. Small wonder, then, that Huxley became -a champion of Darwinism. But, as Poulton writes, on page 202 of _Essays -on Evolution_, "while natural selection thus enabled Huxley freely to -accept evolution, he was by no means fully satisfied with it." "He never -committed 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 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 adherents gathered round him, a herd of men to whom he -seemed an absolutely unquestionable authority. Darwinism became a creed -to which all must subscribe. It still retains this position in the -popular mind. - - - Growing Opposition to Darwinism - -The ease with which the theory of natural selection gained supremacy was, -as we have already said, a misfortune to biological science. It produced -for a time a considerable mental stagnation among zoologists. Since -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 -majority of biologists that they see everything through Darwinian -spectacles. The wish has been in many cases the father to the -observation. Zoologists are ever on the lookout for the action of natural -selection, and in consequence frequently imagine they see it where it -does not exist. Many naturalists, consciously or unconsciously, stretch -facts to make them fit the Darwinian theory. Those facts which refuse to -be so distorted are, if not actively ignored or suppressed, overlooked as -throwing no light upon the doctrine. This is no exaggeration. A perusal -of almost any popular book dealing with zoological theory leaves the -impression that there is nothing left to be explained in the living -world, that there is no door leading to the secret chambers of nature to -which natural selection is not an "open sesame." - -But the triumph of natural selection has not been so complete as its more -enthusiastic supporters would have us believe. Some there are who have -never admitted the all-sufficiency of natural selection. In the British -Isles these have never been numerous. In the United States of America and -on the Continent they are more abundant. The tendency seems to be for -them to increase in numbers. Hence the recent lamentations of Dr Wallace -and Sir E. Ray Lankester. Modern biologists are commonly supposed to fall -into two schools of thought--the Neo-Darwinian and the Neo-Lamarckian. - -The former are the larger body, and pin their faith absolutely to natural -selection. They deny the inheritance of acquired characters, and preach -the all-sufficiency of natural selection to explain the varied phenomena -of nature. The Neo-Lamarckians do not admit the omnipotency of natural -selection. Some of them allow it no virtue. Others regard it as a force -which keeps variation within fixed limits, which says to each organism, -"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 developments of Darwinism is -incomplete, for it fails to include those who occupy a middle position. -If it be possible to classify a large number of men of which scarcely any -two hold identical views, it is into three, rather than two, classes that -they must be divided. - -Speaking broadly, evolutionists of to-day may be said to represent three -distinct lines of thought. For the sake of classification we may speak of -them as falling into three schools, which we may term the Neo-Lamarckian, -the Wallaceian, and the Neo-Darwinian, according as their views incline -towards those held by Lamarck, Wallace, or Darwin. - - - The Neo-Lamarckian School - -As adherents of the Neo-Lamarckian school, we cite Cope, Spencer, Orr, -Eimer, Naegeli, Henslow, Cunningham, Haeckel, Korchinsky, and a number of -others. It may almost be said of these Neo-Lamarckians that each holds a -totally distinct theory of evolution. So heterogeneous are their views -that it is difficult to find a single article common to the evolutionary -belief of all. It is commonly asserted that all Neo-Lamarckians are -agreed, firstly, that acquired characters are transmissible; and, -secondly, that such transmission is an important factor in the production -of new species. This assertion is certainly true of the great bulk of -Neo-Lamarckians, but it does not appear to hold in the case of those who -believe that evolution is the result of some unknown inner force. So far -as we can see, a belief in the inheritance of acquired characters is not -necessary to the theories of orthogenesis held by Naegeli and Korchinsky. -For that reason it would possibly be more correct to place those who hold -such views in a fourth school. Since, however, a number of undoubted -Neo-Lamarckians, as, for example, Cope, believe in an inner growth-force, -it is convenient to regard Naegeli as a Neo-Lamarckian. His views need -not detain us long. Those who wish to study them in detail will find them -in his _Mechanisch-physiologische Theorie der Abstammungslehre_. - -Naegeli believes that there is inherent in protoplasm a growth-force, -which makes each organism in itself a force making towards progressive -evolution. He holds that animals and plants would have become much as -they are now even if no struggle for existence had taken place. "To the -believers in this kind of . . . orthogenesis," writes Kellog (_Darwinism -To-day_, p. 278), "organic evolution has been, and is now, ruled by -unknown inner forces inherent in organisms, and has been independent of -the influence of the outer world. The lines of evolution are immanent, -unchangeable, and ever slowly stretch toward some ideal goal." 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. - - - Orr's Views - -Spencer and Orr preach nearly pure Lamarckism. The former, while fully -recognising the importance of natural selection, considered that -sufficient weight has not been given to the effects of use and disuse, or -to the direct action of the environment in determining or modifying -organisms. - -The similarity of the views of Orr and Lamarck is best seen by comparing -their respective explanations of the long neck of the giraffe. Lamarck -thought that this was the direct result of continual stretching. The -animal continually strains its neck in the search for food, hence it -grows longer as the individual grows older, and this elongated neck has -been transmitted to the offspring. Orr writes, on page 164 of his -_Development and Heredity_: "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 animal are widely -different from the forces acting upon an animal which eats the grass at -its feet like an ox, or one which must run and climb like a goat or a -deer, and the resultant modifications of growth in the several cases must -also be different. The principle of increased growth in the direction of -the shock, resulting from superabundant repair of the momentary -compression, explains how the giraffe acquired the phenomenal length of -the bones of its forelegs and neck; and the absence of the shock in the -hind-quarters shows why they remained undeveloped and absurdly -disproportionate to the rest of the body." - - - Inheritance of Acquired Characters - -It seems to us that a fatal objection to all these Neo-Lamarckian -theories of evolution is that they are based on the assumption that -acquired characters are inherited, whereas all the evidence goes to show -that such characters are not inherited. In these days, when scientific -knowledge is so widely diffused, it is scarcely necessary to say that all -the characteristics which an organism displays are either congenital or -inborn, or acquired by the organism during its lifetime. Thus a man may -have naturally a large biceps muscle, and this is a congenital character; -or he may by constant exercise develop or greatly increase the size of -the biceps. The large biceps, in so far as it has been increased by -exercise, is said to be an acquired character, for it was not inherited -by its possessor, but acquired by him in his lifetime. We must bear in -mind that the period in the life history of an organism at which a -character appears, is not necessarily a test as to whether it is -congenital or acquired, for a great many congenital characters, such as a -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, -notwithstanding the fact that its ancestors have for generations had the -greater portion of their caudal appendage removed shortly after birth. - -We do not propose to discuss at any great length the vexed question of -the inheritance of acquired characters, for the simple reason that the -Neo-Lamarckians have not brought forward a single instance which -indubitably proves that such characters are inherited. - -Mr J. T. Cunningham, in a paper of great value and interest, entitled -"The Heredity of Secondary Sexual Characters in relation to Hormones: a -Theory of the Heredity of Somatogenic Characters," which appeared in vol. -xxvi., No. 3, of the _Archiv fuer Entwicklungsmechanik 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 _a -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 -inheritance of acquired characters does not play an important part in the -evolution of, at any rate, the higher animals, is based, not on the -ground of _a priori_ reasoning, but on facts. All the evidence seems to -show that such characteristics are not inherited. If, as Mr Cunningham -thinks, all secondary sexual characters are due to the inheritance of the -effects of use, etc., how is it that no Neo-Lamarckian is able to bring -forward a clear case of the inheritance of a well-defined acquired -character? If such characteristics are habitually inherited, countless -examples should be forthcoming. Fanciers in their endeavours are -constantly "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 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 characters are inherited, not on -evidence thereof, but because if such characters are not inherited it is -very difficult to account for many of the phenomena presented by the -organic world? - -In many of the lower animals, as, for example, the hydra, the germinal -material is diffused through the organism, so that a complete individual -can be developed from a small portion of the creature. In such -circumstances it seems not improbable that the external environment may -act directly on the germinal substance, and induce changes in it which -may perhaps be transmitted to the offspring. If this be so, it would seem -that some acquired characters may be inherited in such organisms. Very -many plants can be propagated from cuttings, buds, etc., so that we might -reasonably expect some acquired characters to be hereditary in them. The -majority of botanists appear to hold Lamarckian views; but on the -evidence at present available, it is doubtful whether such views are the -correct ones. - -Plants are so plastic, so protean, so sensitive to their environment that -their external structure appears to be determined by the external -conditions in which they find themselves quite as much as by their -inherited tendencies. In this respect they differ very considerably from -the higher animals. The peacock, for example, presents the same outward -appearance[1] whether bred and reared in Asia or Europe, in a hot or -cold, a damp or a dry climate. The same plant, on the other hand, differs -greatly in outward appearance according as it is grown in a dry or a damp -soil, a hot or a cold country. In his recent book _The Heredity of -Acquired Characters in Plants_, the Rev. G. Henslow cites several -examples of the celerity with which plants react to their environment. On -page 32 he writes: "The following is an experiment I made with the common -rest-harrow (_Ononis spinosa, L._) growing wild in a very dry situation -by a roadside. I collected some seeds, and also took cuttings. These I -planted in a garden border, keeping this well moist with a hand-light -over it, and a saucer of water, so that the air should be thoroughly -moist as well. Its natural conditions were thus completely reversed. They -all grew vigorously. The new branches of the first 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 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 experiment -affords strong evidence against the Lamarckian doctrine. Here we have a -plant which has, perhaps, for thousands of generations developed spines -owing to its dry environment. If acquired characters are inherited we -should have expected this spiny character to have become fixed and -persisted under changed conditions, for some generations 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 environment -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 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 inheritance 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 inheritance 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 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 Wallaceian School - -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 structures displayed by organisms cannot be explained on -the natural selection hypothesis. Those who 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 Theorie_ on the thriving and very healthy plant of Darwinism, -is a much more staunch Darwinian than either Dr Wallace himself, or the -two great authorities in biological science whom he mentions, Sir William -Thistleton Dyer and Professor Poulton." - - - Complexity of the Problem - -Having classified ourselves, it remains for us (the authors of the -present work) to define our position more precisely. Like Darwin we -welcome 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 recognise -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 necessary in the case of contracts between the weak and -the strong. Similarly the earlier economists considered 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 attributes 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. - - - The Aim of the Biologist - -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 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. - - - - - 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--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. - -"The 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. - - - 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 related 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 _The Origin of Species_ 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 -profitable to itself, under the complex and sometimes varying conditions -of life, will have a better chance of surviving, and thus be naturally -selected. From the strong principle of inheritance, 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 geometrical -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. - - - Various Anti-Darwinian Views - -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 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 evolution, 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 _nil_, 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. 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 unfavourable, 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 environment, 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 conditions, 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 orthogenesis 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 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. - - - Darwinism does not explain Variation - -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 variations. 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 objection is that which points out -that it is a long journey from Amoeba to man. It is difficult to 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 objection 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? - - - Theory of Change of Function - -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, 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 connecting 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 unreasonable 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 explanations, 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: "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 -counterbalanced 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. - - - 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 emphasis 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 may indirectly be responsible for characteristics which in -themselves are injurious to the individual. 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 palaeontology 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. - - - Missing Links - -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 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 -palaeontology 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 -_Orohippus_, through the _Mesohippus_, the _Miohippus_, the -_Protohippus_, and the _Pliohippus_, until we reach the one-toed _Equus_. - -Wallace further points out that in order that the fossil of any organism -may be preserved, the "concurrence of a number of favourable conditions" -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. 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, palaeontology 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 -pure ancestors and breed true _inter se_. Nor is this all. - - - Recurrent Mutations - -Experience shows that where a mutation, or sport, or discontinuous -variation occurs, it frequently 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 -priori_ 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. Therefore 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 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 advantage 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 similar habits, such as that -of the jaguar and puma in South America, and the five very -differently-coloured flycatchers in the Nilgiri Hills. - - - Leaf-butterflies - -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 _Darwinism 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. 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 concealment 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 culmination, 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 precariously 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? Kallima continues its way, specifically and absurdly -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. - - - A Dilemma - -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 existence, 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 value, -they are, as Kellog points out, in trouble over the close and detailed -resemblance which the Kallima butterflies bear to dead leaves. - -10. 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," 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 -conditions 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 therefore 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. - - - The Effects of Chance - -Writing of plants, Professor Henslow says, on page 16 of _The Heredity of -Acquired Characters 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 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. - - - The Origin of Mimicry - -12. Natural selection, as we shall see, fails to account for the origin -of what is known as protective 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." It is easy -to understand the profit that these mimics derive from their mimicry. -When once the disguise has been assumed we can comprehend 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 explanation of the phenomena -of sexual dimorphism. Why, for example, in some species of doves and -ducks, the sexes 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. - - - - - 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 - 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 "discontinuous 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. - - - Nature of Variation - -As 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 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 diversity of inheritable deviations of -structure . . . are endless" (page 14, ed. 1902). "The variations 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 domestication, 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 -_Darwinism_ 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 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 altogether new conceptions. Such being the case, his ideas were of -necessity somewhat hazy; they underwent considerable modification as -fresh facts came to his knowledge. - - - Definite and Indefinite Variability - -Towards the end of his life Darwin recognised that variability is of two -kinds--definite and indefinite. Indefinite variation is indiscriminate -variation in all directions around a mean, variation 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 direction 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 perceived that some variations are much more pronounced than -others. He recognised the distinction between what are now known as -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. - - - Monstrosities - -"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 produced 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 structures 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 depend 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 Species_, 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, if the varying individual did -not actually transmit to its offspring its newly acquired character, 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 individuals 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. - - - Minute Variations - -Again, we read (page 34): "Some variations useful to him (_i.e._ 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 arisen in a -seedling. This is known to be the case with the turnspit dog."[2] 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 complexity of -the coadaptations between all organic beings . . . which may have been -effected[3] 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. - -Although the theory of natural selection does not attempt to explain the -causes of variation, 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 domestication 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. Variability is, he stated, governed by unknown laws which -are infinitely complex. - - - Lines of Variation - -It will be convenient to deal with each of 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 variations do not always occur -equally in all directions. The results of many years of the efforts of -practical 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 _Genesis of Species_, "Not only -does it appear that there are barriers which oppose change in certain -directions, but that there are positive tendencies to development along -certain special lines. In a bird which has been kept and studied like the -pigeon, it is difficult to believe that any remarkable spontaneous -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 artificial -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 considerably 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 significant, -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. - - - Breeders' Boasts - -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 _Origin of -Species_, Darwin quotes, with approval, Youatt's description of selection -as "the magician's wand, by means of which he may summon into life -whatever 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 anything 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 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 -carefully 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 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. - - - Albinistic Variations - -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 (_Haliaetus albicilla_) the Nicobar Pigeon -(_Caloenas nicobarica_), 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 Linnaeus, based on experience, 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 identification 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 -sport. Similarly, white animals appear not to give rise to colour -varieties. - -We are never surprised to find that an ordinary upright plant produces as -a sport or mutation 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 variation is furnished by what -Grant Allen calls the "Law of Progressive Colouration" of flowers. - -On pp. 20, 21 of _The 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." - - - Over-development - -So among animals there are many colour patterns and structures that -appear in widely different genera, as, for example, the magpie 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 inherited 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 palaeontologists 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. "Palaeontology," 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 unwieldiness -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 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 proportions 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. - - - Speed of Racehorses - -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 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 multiplication 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. - - - Experiments of De Vries - -De Vries has made some important experiments 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: their 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 -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 character as far as possible by a -very rigid and careful selection. . . . By this method I brought my -strain within two years up to an average of nearly 90 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 produce 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 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 -ameliorations are obtained, and the selection must be made in the same -manner every year. Moreover, the improvement is very limited, and does -not give any promise of further increase." Notwithstanding 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 circumstances 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 experiments, 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 differences not only can, but have actually been -produced by the selection of such variations. This objection is based -upon the assumption that breeders have in the past dealt only with -fluctuating variations. This assumption does not appear to be justified. -It is exceedingly probable that most, if not all, the varieties of -domesticated animals have originated in mutations. 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." - - - Bateson on Variation - -As long ago as 1894 Bateson published his _Materials for the Study of -Variation_, in which he set forth a large number of cases of -discontinuous 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 -continuous, 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 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 perfection 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." - - - Work of Bateson and De Vries - -But Bateson's views fell upon stony ground, because zoologists are mostly -men of theory and not practical breeders. They laboured under the -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 Abbe 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 perpetuating 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 recognise the immense value of his work. Had his -statements in 1894 received the attention they merited, zoological theory -would to-day be considerably 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 -conclusions are applicable to animals. We are far from accepting his -theory of mutations _in toto_. We are, however, convinced that he, like -Bateson, 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. - - - Varieties and Elementary Species - -That eminent botanist, as we have already seen, insists on the -distinction between fluctuating 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. - -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 average comply with the same laws as the -deviations 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 -composite nature, being made up of a collection of varieties and -elementary species. His conception 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 consider (page 141 _Species and -Varieties_) the following as the principal difference between elementary -species and varieties: that the first arise by the 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 retrogression, while others have diverged from the -parental types in a line of digression or in the way of repetition. . . . -The system (of the vegetable kingdom) is built up of species; varieties -are only local and lateral, never of real importance 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 experiment which plants -are in the mutating state and which are not. The great majority, however, -are not at present in the mutating state. - - - Mutations - -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 fluctuating variation -in an organism. If, however, the block be tilted to such an angle that -when left to 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 sometimes 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 variations occur. - -As it is of considerable importance thoroughly to grasp the true nature -of mutations or discontinuous 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 individuals 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 individual 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 mean whether that departure is due to a -mutation or a fluctuating variation. - - - Law of Regression - -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 variation. -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 Mueller and Galton conducted independently enquiries into the amount -of the regression shown by the progeny of parents which have deviated -from the average by fluctuating variation. - -Mueller 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 average, a length of wing of only about 18-1/4 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 18-1/4 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's Dictum - -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 _inter se_, some of them 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 fluctuating 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 -experimental 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. - - - Mutating Plants - -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 _Species and Varieties_ (p. 525), "was found in a locality -near Hilversum, in the vicinity of Amsterdam, where it grew in some -thousands of individuals. Ordinarily 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 producing 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 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 observed 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, however, are, like their parent form, liable to mutations." 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 sometimes gives rise to -the wheat-ear form. "In this variety," writes De Vries (p. 228), "the -flower is suppressed, and the loss is attended by a corresponding -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 (_Linaria vulgaris 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 purple beech seems -to be a mutation which has originated at least three times over. - - - Mutation Theory Criticised - -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 agriculturist 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 variation 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 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 probability that it was produced by crossing various forms of -the polymorphic _Oenothera biennis_, which had been previously introduced -in Europe." - - - Definition of a Species - -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 Linnaean 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 a distinct race is produced. And, finally, -fresh mutations occur, so that a new species is eventually 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 characters, -which they transmit to their offspring. - -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 discontinuous 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 mutations 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. - - - "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_, "I 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 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 descended." - -[Illustration: A TURBIT BELONGING TO MR. H. P. SCATLIFF] - -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 L20. 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 L20. 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 L15, but he also died before the 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 -offspring 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 -L55 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 considerably over L100 in -purchases, and took eight years fixing the peculiarity in question. Had -"Ladybird" 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. - - - 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 -doubtless exercise much ingenuity in explaining how natural selection had -brought about the gradual disappearance of the horns; and -palaeontologists, 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 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 mutating state" in that part of the world. - -The other classical examples of great and sudden variations are the Ancon -sheep of Massachusetts, 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 grandparents of Linus I. had exceptionally long -hair. - - - Mutations among Birds - -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. - -The Golden Pheasant (_Chrysolophus pictus_) produces, in domestication, -the dark-throated form (_C. obscurus_), 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 produces 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 _A. chiaradiae_ in the wild state. In this the -irides are dark, instead of 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 exterminated by local ornithologists. - -The reed bunting (_Emberiza schoeniclus_) exists in two distinct -forms--one having a much stouter bill than the other (_E. pyrrhuloides_). -This probably is an example of a mutation. - -The rare yellow-rumped Finch (_Munia flaviprymna_), of Australia, has -displayed a tendency to change into the allied and far commoner -chestnut-breasted Finch (_M. castaneithorax_) during the lifetime of the -individual (_Avicultural Magazine_, 1907). 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. -russi_, 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 sometimes 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. - -[Illustration: YELLOW-RUMPED AND CHESTNUT-BREASTED FINCHES, WITH -TRANSITIONAL SPECIMENS] - -A well-marked mutation which appears regularly in nature is the -red-headed variety of the beautiful Gouldian Finch (_Poeephila 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 (_Ossifraga 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 pigment, 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 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.[4] 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 creatures are -less conspicuous than white ones. As examples of black mutations which -occur in nature, 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 sometimes brown, while the other bears, when not brown, are almost -invariably black. - - - Color Mutations - -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 giu_)--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, 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 -(_Palaeornis torquatus_), 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 unfavourable 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 Cambridge, has long been known -to collectors as a habitat of a yellow-marked form of the six-spot Burnet -Moth (_Zygaena filipendulae_). These lutinistic forms are not confined to -one genus of Butterflies. Moreover, in the Pin-tailed Nonpareil Finch -(_Eythrura prasina_) of the Eastern Archipelago the red tail and other -red parts of the plumage are not infrequently replaced by yellow in wild -individuals of either sex and of any age. In the blue-fronted Amazon -parrot (_Chrysotis aestiva_)--a most variable bird--the normally red edge -of the pinion is sometimes yellow. Bateson, in his _Materials for the -Study of Variation_, gives other examples of this kind of variation. - - - Mutations among Invertebrates - -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 (_Argynnis paphia_) and the _helice_ -form of the female Clouded-yellow Butterfly (_Colias 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 _Epenthesis 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." - - - Mutating Species - -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 likelihood that they have -suddenly arisen and managed to establish themselves alongside of the -parent species. - -The Curassows, _Crax grayi_, _C. hecki_, each of which is only known by a -very few specimens, appear to be mutations of the female of the globose -Curassow, _Crax globicera_. The fact that when a female _hecki_ bred in -the London Zoological Gardens with a male _globicera_, 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 (_Lophophorus impeyanus_), -the common species of the Himalayas. - -The Three-coloured Mannikin (_Munia malacca_) of South India is probably -simply a white-bellied form of the widely-ranging Black-headed Mannikin -(_M. atricapilla_), which has the abdomen chestnut like the back. -Intermediate wild-caught forms have been recorded. - -The African Cordon-bleu (_Estrelda phoenicotis_) and Blue-bellied Waxbill -(_E. 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 (_Stictoptera annulosa_) of Java, and Bicheno's Finch -(_S. bichenovii_) 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 -(_Chloephaga magellanica_), 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 -(_Balearica chrysopelargus_) 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 convoluted brain or a mouse with -a peculiar pattern of molar teeth, have been come upon by anatomists. - -The above-cited mutations are all very considerable 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 hypothesis of De Vries that species -pass through alternate periods of comparative stability and periods when -swarms of mutations appear. We think it more probable that all species -throw off at greater or less intervals discontinuous variations, and that -it is upon these that natural selection acts. - -We further hope that we have succeeded in making clear what we believe to -be the very sharp distinction between continuous and discontinuous -variations, even when the latter are inconsiderable, as frequently -happens. - - - Somatic and Germinal Variations - -Before leaving the subject of variation it is necessary to notice the -distinction, which Weismann 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 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. - - - Somatic Variations - -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 organism 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 -is the result of a congenital variation or a somatic one. This will be -rendered clear by a hypothetical 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 -organism 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 -environment. 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 survival, 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 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 conspicuous 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 environment. -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. - -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 -environment. In so far as they are due to this latter they do not appear -to be inherited. - -Thus, although we cannot say of many variations 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 in a 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. - - - - - 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. - -The alleged sterility of the hybrids produced 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 useless 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. - -"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 permanent 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 -skilful physiologist, would very probably obtain the desired production -of mutually more or less infertile breeds from a common stock in a -comparatively few years; but still, as the case stands at present, this -little 'rift within the lute' is not to be disguised or overlooked." - - - Alleged Sterility of Hybrids - -Similarly Wallace writes, at the beginning of chapter vii. of his -_Darwinism_: "One of the greatest, or perhaps we may say the greatest, of -all the difficulties in the way of accepting the theory of natural -selection as a complete explanation 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 perfectly 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 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. - - - Fertile 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 _The 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 vaginalis_ and -_reevesii_, and from _Phasianus 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. -cygnoides_), 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 bred _inter 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 (grandchildren 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.[5] . . . 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, both in first crosses and in hybrids, is an -extremely 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 incidental on -unknown peculiarities of the reproductive 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." - - - A Biological Bogey - -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. - - - 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 perfectly -fertile plant hybrids cited by De Vries are the crosses between _Anemone -magellanica_ and _A. sylvestris_, between _Salix alba_ and _Salix -pentandra_, between _Rhododendron hirsutum_ and _R. ferrugineum_. - -He gives an instance of a hybrid--_AEgilops speltaeformis_, 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 raspberry, which is not only fertile, but quite -popular as producing a novel fruit. - - - Sterile Plant Hybrids - -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 -"Gordon's currant," which is considered to be a hybrid between the -Californian and the Missouri species. He also gives _Cytisus adami_ 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. - - - Fertile Mammalian Hybrids - -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 specimen -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, however, succeed at all, which reminds us of -what happens in the case of finch-hybrids. - -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 constantly side by side in the -plains of India, never interbreed at all. - -Among wild ruminants of this hollow-horned family, the Himalayan Argali -(_Ovis ammon_) ram, a giant sheep of the size of a donkey, has been known -to appropriate a herd of ewes of the Urial (_O. vignei_), 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 sika_), 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 strong and useful, the three-quarter bred beasts are -apparently of little value. - - - Fertile Bird Hybrids - -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 recorded. Even among -birds so seldom bred, comparatively, as the parrot family, a fertile -hybrid has been produced, that between the Australian Rosella Parrakeet -(_Platycercus eximius_) and Pennant's Parrakeet (_P. elegans_). The -hybrid was first described as a distinct species, the Red-mantled -Parrakeet (_P. erythropeplus_). 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 (_Chrysolophus amherstiae_) and the Gold Pheasant -(_C. pictus_) have long been known as producing hybrids which are fertile -either _inter se_ or with the parents. Here the species are still more -distinct; not only 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 descendants (_Anas 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 (_Motacilla lugubris_) and the Grey Wagtail (_M. -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 (_Ligurinus 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. - -[Illustration: MALE AMHERST PHEASANT] - -The Red Dove of India (_Oenopopilia tranquebarica_) has produced hybrids -with the tame Collared Dove (_T. 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 displaying 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 -_Molpastes_ bulbuls, and the Indian Roller (_Coracias indica_) and -Burmese Roller (_C. affinis_). 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 interesting experiment when, more than a century -ago, they introduced largely into their coverts the Chinese Ring-necked -Pheasant (_Phasianus torquatus_) and the Japanese _P. versicolor_. So -freely has the former bred with the common species already present there -(_Phasianus 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 Green Pheasant (_P. versicolor_) 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. - - - Fertile Hybrids among Amphibia - -Our Crested Newt (_Molge cristata_) and the Continental Marbled Newt (_M. -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 blasii_. 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. - -[Illustration: HARLEQUIN QUAIL (Coturnix delegorguei)] - -[Illustration: RAIN QUAIL (Coturnix coromandelica)] - - - Insects - -Among insects, M. de Quatrefages states that the hybrid progeny of the -silk-moths _Bombyx cynthia_ and _B. arrindia_ are fertile for eight -generations when bred _inter 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 -(_Phasianidae_), 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 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 frontalis_) 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 succeeded 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 (_Turtur 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 Darwin's view that domestication tends to -eliminate sterility; but it is doubtful if this can be upheld. The hybrid -between the Muscovy duck (_Cairina 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. - - - Characters of Hybrids - -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 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 a modified form in the hybrid; for instance, in that -between the blackcock (_Tetrao tetrix_) and the capercailzie (_T. -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 sheldrakes (_Tadorna cornuta_ and _Casarca cana_), now -in the British Museum, bear a distinct resemblance to the grey Australian -sheldrake (_C. tadornoides_). 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 -_inter se_, there seems to have been no reversion to the original pure -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." - - - Wild Hybrids - -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 offspring "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 _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 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 crossing 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. - - - - - 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--Dominance sometimes - imperfect--Behaviour of the nucleus of the sexual - cell--Chromosomes--Experiments of Delage and Loeb--Those of Cuenot on - mice and Castle on guinea pigs--Suggested modification of the - generally-accepted Mendelian formulae--Unit characters--Biological - isomerism--Biological molecules--Interpretation of the phenomena of - variation and heredity on the conception of biological - molecules--Correlation--Summary of the conception of biological - molecules. - -We have seen that variations may be, firstly, either acquired or -congenital, and, secondly, fluctuating or discontinuous. We have further -seen that acquired variations--at all events in the higher animals--do -not appear to be inherited, 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 congenital variations, -although they do not appear to give rise directly to new species, may -play a 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 _inter 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 inheritance which differs more -or less greatly from the theory held by any other biologist. - -As regards the phenomena of heredity we may say _Tot homines tot -sententiae_. - - - Phenomena of Inheritance - -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. - -2. Why they differ from their parents. - -3. Why the members of a family display individual 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 parthenogenesis 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. - -17. Why differences in the nature of the food administered to the larvae -of ants determines whether these shall develop into sexual or neuter -forms. - -18. Why the application of heat, cold, etc., to certain larvae 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 -appearance from the mule, etc. - -22. It must explain all the facts which constitute 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. - -26. It must render intelligible the effects of castration on animals. - - - Existing Theories Unsatisfactory - -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 critically 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 carefully 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 knowledge can be made. - -By inheritance we mean that which an organism 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--"all the qualities or characters which have their initial -seat, their physical basis, in the fertilised egg cell"--seems to cover -all cases except those where eggs are parthenogenetically developed. - -The first fact of heredity which we must notice is that inheritance may -take several forms. This is apparent from what was set forth in the -chapter dealing with hybrids. - - - Types of Crosses - -In considering the phenomena of inheritance it is convenient to deal with -crosses in which the parents do not closely resemble one another, because -by so doing we are able readily to follow the various characters -displayed by each parent. It may, perhaps, be urged that such crosses -occur but rarely in nature. This is true. But we should bear in mind that -any theory of inheritance must explain the various facts of -cross-breeding, so that, from the point of view of a theory of -inheritance, crosses are as important as what we may term normal -offspring. As inheritance is so much easier to observe in the former, it -is but natural that we should begin with them. Our deductions must, if -they be valid ones, fit all cases of ordinary inheritance, _i.e._ all -cases where the offspring results from the union of parents which closely -resemble one another. Now, when two unlike forms inter-breed, their -offspring will fall into one of six classes. - -I. They may exactly resemble one parent, or rather the type of one -parent, for, of course, they will never be exactly like either parent; -they must of necessity display fluctuating variations. The cases in which -the offspring exactly resemble one parent type in all respects are -comparatively few. They occur only when the parents differ from one -another in one, two, or at the most three characters. Thus when an -ordinary grey mouse is crossed with a white mouse the offspring are all -grey, that is to say, they resemble the grey parent type. Although they -are mongrels or hybrids, they have all the appearance of pure grey mice. -This is what is known as unilateral inheritance. - -II. The offspring may resemble one parent in some characters and the -other in other characters. They may have, for example, the colour of one -parent, the shape of the other, and so on. Thus if a pure, albino, -long-haired, and rough-coated male guinea-pig be crossed with a coloured, -short-haired and smooth-coated female, all the offspring are coloured, -short-haired, and rough-coated. That is to say, they take after the -father in being rough-coated, but after the mother in being pigmented and -short-haired. This form of inheritance is usually seen only in crosses -between two types which differ in but few of their characters. - -III. The offspring may display a blend of the characters of the two -parents. They may be intermediate in type. They are not of necessity -midway between the two parents; one of the parents may be prepotent. The -crosses between the horse and the ass show this well. Both the mule, -where the ass is the sire, and the hinny, where the horse is the sire, -are more like the ass than like the horse; but the hinny is less ass-like -than the mule. The offspring between a European and a native of India -furnishes a good case of blended inheritance; Eurasians are neither so -dark as the Asiatic nor so fair as the European. - -IV. The offspring may show a peculiarity of one parent in some parts of -the body and the peculiarity of the other parent in other parts of the -body. This is known as particulate inheritance. The piebald foal, which -is the result of a cross between a black sire and a white mare, is a good -example of such inheritance. This does not appear to be a common form of -inheritance. - -V. The usual kind of inheritance is perhaps a combination between the -forms II. and III. In such cases the offspring display some paternal -characters and some maternal ones, and some characters in which the -maternal and paternal peculiarities are blended. An example of -inheritance of this description is furnished by a cross between the -golden and the amherst pheasants. - -VI. The offspring may be quite unlike either parent. For example, Cuenot -found that sometimes a grey mouse when crossed with an albino produces -black offspring. - - - Mendel's Experiments - -The first two kinds of inheritance were carefully investigated by Gregor -Johann Mendel, Abbot of Brunn. The results of his experiments were -published in the Proceedings of the Natural History Society of Brunn, in -1854, but attracted very little notice at the time. - -Mendel experimented with peas, of which many varieties exist. He took a -number of varieties, or sub-species, which differed from one another in -well-defined characters, such as the colour of the seed coat, the length -of the stem, etc. He made crosses between the various varieties, being -careful to investigate one character only at a time. He found that the -offspring of such crosses resembled, in that particular character, one -only of the parents, the other parent apparently exerting no influence on -it. Mendel called the character that appeared in the off-spring dominant, -and the character which was suppressed, recessive. Thus when tall and -short varieties were crossed the offspring were all tall. Hence Mendel -said that tallness is a dominant character, and shortness a recessive -character. Mendel then bred these crosses among themselves, and found -that some of the offspring resembled one grandparent as regards the -character in question while some resembled the other, and he found that -those that showed the dominant character were three times as numerous as -those that displayed the recessive character. He further found that all -those of the second generation of crosses which displayed the recessive -character bred true; that is to say, when they were bred together all -their descendants exhibited this characteristic. The dominant forms, -however, did not all breed true; some of them produced descendants that -showed only this dominant character, others, when crossed, gave rise to -some forms having the dominant character and some having the recessive -character. - -It is thus evident that organisms of totally different ancestry may -resemble one another in external appearance. In other words, part of the -material from which an organism is developed may lie dormant. - - - Mendelism - -From the above results Mendel inferred, in the case of what he called -alternating characters, that only one or other of the pair can appear in -the offspring, that they will not blend. If both parents display one of -the opposing characters, the offspring will of course show it. But if one -parent display one character and the other the opposing character, the -hybrid offspring will display one only, and that which is dominant. The -other character is suppressed for the time being. When, however, these -hybrids are bred _inter se_, their gametes or sexual cells split up into -their component parts, and then the recessives are free to unite with -other recessives and thus produce offspring which show the recessive -character. - -His results can be set forth in symbols. - -Let T stand for the tall form and D for the dwarf form. Since the -offspring are composed of both the paternal and maternal gamete, we may -represent them as TD. But dwarfness is, as we have seen, recessive, so -that the offspring all look as though they were pure T's. When, however, -we come to breed these TD's _inter se_, the gamete or sex-cell of each -individual crossed breaks up into its component parts T and D, which -unite with other free T or D units to form TD's or TT's or DD's. What are -the possible combinations? A D of one parent may meet and unite with a D -of the other parent, so that the resulting cells will be pure D, _i.e._ -DD, and will give rise to pure dwarf offspring. Or the D gamete from one -parent may unite with a T gamete from the other parent, and the result -will be a TD cross, but this, as we have seen, will grow up to look like -a pure T, _i.e._ will become a tall organism. Similarly, a T gamete from -one parent may unite with a T gamete of the other, and produce a pure -tall form, or it may unite with a D and produce a hybrid TD, which gives -rise to a tall form. Thus the possible combinations of offspring are DD, -DT, TD, TT, but all these three last contain the dominant T gamete, and -so develop into tall offspring; therefore, _ex hypothesi_, we shall have -three tall forms produced to one dwarf form, but of these three tall -forms two are not pure, and do not breed true. Mendel's experimental -results accorded with what we should expect to obtain if the above -explanation were correct. Hence the inference that there is such a -splitting of the gametes in the sexual act seems a legitimate one. - -Mendel's experiments are of great importance, for they give us some -insight into the nature of the sexual act. But, as is usual in such -cases, Mendel's disciples have greatly exaggerated the value and -importance of his work. It is necessary to bear in mind that Mendel's -results apply only to a limited number of cases--to what we may call -balanced characters. In the case of characters which do not balance one -another, which are, so to speak, not diametrically opposed to one -another, Mendel's law does not hold. A second important point is, that -the dominance is in many cases not nearly so complete as it should be if -the Mendelian formula correctly represented what actually occurs in -nature. Further, the segregation of the gametes does not appear to be so -complete as the above hypothesis requires it to be. The phenomena of -inheritance seem to be far more complex than the thorough-going Mendelian -would have us believe. - -Let it be noted that it is not to the facts of Mendelism, but to some -portions of what we may call the Mendelian theory, that we take -exception. - - - Maturation of the Germ-cells - -Before passing on to consider some of the later developments of -Mendelism, it is necessary for us to set forth briefly certain of the -more important facts regarding the sexual act which the microscope has -brought to light. We propose to state these only in the merest outline. -Those who are desirous of pursuing the subject farther are referred to -Professor Thomson's _Heredity_. - -The germ cells, like all other cells, consist of a nucleus lying in a -mass of cytoplasm. The nucleus is composed of a number of rod-like -bodies, which are called chromosomes, because they are readily stainable. - -These chromosomes appear, under ordinary circumstances, to be joined -together end to end, and then look like a rope in a tangle. - -When a cell is about to divide into two, these chromosomes become -disjoined and can then be counted, and it is found that each cell of each -species of animal or plant has a fixed number of these chromosomes. Thus -the mouse and the lily have twenty-four chromosomes in each cell, while -the ox is said to have sixteen of them per cell. - -When a cell divides into two, each of these chromosomes splits by a -_longitudinal_ fissure into two halves, which appear to be exactly alike. -One-half of every chromosome passes into each of the daughter cells, so -that each of these is furnished with exactly half of each one of the -rod-like chromosomes. In the cell division, which takes place immediately -before the male gamete or generative cell meets the female gamete, the -chromosomes do not divide into equal halves, as is usually the case. In -this division half of them pass into one daughter cell and half into the -other daughter cell, so that, prior to fertilisation both the male and -the female gametes contain only half the normal number of chromosomes. In -the sexual act the male and the female chromosomes join forces and then -the normal number is again made up, each parent contributing exactly one -half. - - - Experiments of Delage and Loeb - -Biologists, with a few exceptions, seem to be agreed that these -chromosomes are the carriers of all that which one generation inherits -from another. Thus the cardinal facts of the sexual act are, firstly, -prior to fertilisation the male and the female gamete each part with half -their chromosomes; and, secondly, the fertilised cell is composed of the -normal number of chromosomes, of which one-half have been furnished by -each parent. Thus the microscope shows that the nucleus of the fertilised -egg is made up of equal contributions from each parent. This is quite in -accordance with the observed phenomena of inheritance. - -But Delage has shown that a non-nucleated fragment of the ovum in some of -the lower animals, as, for example, the sea-urchin, can give rise to a -daughter organism with the normal number of chromosomes when fertilised -by a spermatozoon. Conversely, Loeb showed that the nucleus of the -spermatozoon can be dispensed with. Thus it seems that either the egg or -the spermatozoon of the sea-urchin contains all the essential elements -for the production of the perfect larva of a daughter organism. We are, -therefore, driven to the conclusion that the fertilised ovum contains two -sets of fully-equipped units. Only one of these seems to contribute to -the developing organism. If this set happens to be composed of material -derived from one only of the parents, we can see how it is that we get -unilateral inheritance in the case of a cross. Where, however, the units -from the two parents intermingle, although only one set is active in -development, the result will be blended inheritance. Thus, we may regard -the fertilised egg as made up of two sets of characters--a dominant set, -which is active in the production of the resulting organism, and a -recessive set, which appears to take little or no part in the production -of the organism. - -This is quite in accordance with Mendelian conceptions. - -Let X be an organism having the unit characters A _B_ C D _E_ F _G_, and -let Y be another organism having the unit characters _a_ b _c_ _d_ e _f_ -g. - -Now suppose that these behave as opposed Mendelian units, and that the -unit characters in italics are dominant ones. Then the resulting -individual will resemble each parent in certain unit characters. It may -be represented by the formula a B c d E f G, but it will contain the -characters A b C D e F g in a recessive form, so that its complete -formula may be written - - a B c d E f G} - A b C D e F g - -When these hybrids are paired together it will be _possible_ to get such -forms as - - A B C D E F G - A B C D E F G - - and - - a b c d e f g - a b c d e f g - -which exactly resemble the -respective grandparents, and these should breed -absolutely true, if the segregation of the -gametes is as pure as the Mendel's law seems -to require. - - - Experiments of Cuenot and Castle - -There are, however, certain facts, which recent experimenters have -brought to light, that seem to show that the segregation is not so -complete as the law requires. For example, the so-called pure extracted -forms may be found, when bred with other varieties, to have some latent -characters. Thus Cuenot observed that extracted pure albino mice, that is -to say, those derived from hybrid forms, did not all behave alike when -paired with other mice. Those which had been bred from grey x white -hybrids behaved, on being crossed, differently to those that had been -bred from black x white hybrids; and further, those derived from yellow x -white hybrids yielded yet other results on being intercrossed. Castle -records similar phenomena in the case of guinea-pigs, and accordingly -draws a distinction between recessive and latent characters. Recessive -characters are those which disappear when they come into contact with a -dominant character, but reappear whenever they are separated from the -opposing dominant character. Latency is defined by Castle as "a condition -of activity in which a normally dominant character may exist in a -recessive individual or gamete." - -The ordinary Mendelian pictures a unit character in a cross that obeys -Mendel's law, as follows:-- - - D - R, - - the dominant character only -showing. It seems to us that each unit character -should be represented as a double entity, thus -D(D), the portion within the bracket being -latent. The cross would appear to be represented -by the formula - - D(R) - R(D), - - since the union -appears to take the form of the transfer of -the dormant latent characters. Now an extracted -pure recessive will, on this hypothesis, -bear the formula - - R(D) - R(D). - - When such recessives -are crossed the two dormant portions will -ordinarily change places, and never appear, so -that these extracted recessives will, under -ordinary circumstances, appear to be as pure -as the true pure recessives, which are represented -by the formula - - R(R) - R(R). - -Now, suppose that, from some cause or other, -it is possible for the latent D to change places -with the visible R, it is obvious that the impure -nature of the extracted and hitherto apparently -pure recessives will become manifest. This -seems to be what happens under certain circumstances -to the extracted albino mice. They -possess latent the character of their dominant -ancestor. - - - Unit Characters - -Mendelian phenomena force upon us the conclusion that organisms display a -number of unit characters, each of which behaves in much the same way as -a radicle does in chemistry, inasmuch as for one or more of these -characters others can be substituted without interfering with the -remaining unit characters. For example, it is possible to replace the -chemical radicle NH_{3} by the radicle Na_{2}; _e.g._ (NH_{3})_{2}SO_{4} -(ammonium sulphate) may be transformed into Na_{2}SO_{4} (sodium -sulphate). - -The conclusion that each organism is composed of a number of unit -characters, which sometimes behave more or less independently of one -another, is one which most biologists who have studied the phenomena of -inheritance appear to have arrived at. Zoologists are mostly of opinion -that these characters, or rather their precursors, exist as units in the -fertilised egg. Very varied have been the conceptions of the nature of -these biological units. Almost every biologist has given a name to his -particular conception of them. Thus we have the gemmules of Darwin, the -unit characters of Spencer, the biophors of Weismann, the micellae of -Naegeli, the plastidules of Haeckel, the plasomes of Wiesner, the -idioblasts of Hertwig, the pangens of De Vries, and so on. It is -unnecessary to extend this list. It must suffice that almost every -investigator of the phenomena of inheritance believes in these units, and -calls them by a different name. Moreover, each clothes them with -characteristics according to his taste or the fertility of his -imagination. - - - Chemical Molecules - -These units behave in such a way as to suggest to us an analogy between -them and the chemical molecules. The sexual act would appear to resemble -a chemical synthesis in some respects. One of the most remarkable -phenomena of chemistry is that of isomerism. It not infrequently happens -that two very dissimilar substances are found, upon analysis, to have the -same chemical composition, that is to say, their molecules are found to -be composed of the same kind of atoms and the same number of these. Thus -chemists are compelled to believe that the properties of a molecule are -dependent, not only on the nature of the atoms which compose it, but also -on the arrangement of these within the molecule. To take a concrete -example: Analysis shows that both alcohol and ether are represented by -the chemical formula C_{2}H_{6}O. In other words, the molecule of each of -these compounds is made up of two atoms of the element Carbon, six of the -element Hydrogen, and one of the element Oxygen. Now, every chemical atom -possesses the property which chemists term valency, in other words, the -number of other atoms with which it can directly unite is strictly -limited. All atoms of the same element have the same valency. Monovalent -atoms are those which can, under no circumstances, unite with more than -one other atom. The Hydrogen atom is an example of such an atom. Divalent -atoms, as, for example, that of Oxygen, can unite with one other atom of -similar valency or with two monovalent atoms. Similarly, a trivalent -atom, such as that of Nitrogen, can unite with three monovalent atoms. A -tetravalent atom, such as that of Carbon, can combine with four -monovalent atoms. There are also pentavalent and hexavalent atoms. Now, -by indicating the valency of any given atom by a stroke for each -monovalent atom with which it is able to combine, chemists have been able -to represent the molecule of every compound, or, at any rate, of every -inorganic compound, by what is known as a graphic or structural formula. -Thus, ethylic alcohol is represented by the formula:-- - - H H - | | - H--C--C--O--H = C_{2}H_{6}O, - | | - H H - -and methylic ether by the structural formula:-- - - H H - | | - H--C--O--C--H = C_{2}H_{6}O. - | | - H H - -The formulae indicate a very different arrangement of the nine atoms which -compose the molecule in each case. And to this different arrangement the -differing properties of the two compounds are supposed to be due. A rough -illustration of the phenomenon of isomerism is furnished by written -language. Thus, three different words can be made from the letters t, a, -and r, _e.g._ tar, art, and rat. They also form tra, which does not -happen to be an English word, although it might have been one. - - - Experiments of Graefin von Linden - -Among organisms we sometimes observe a phenomenon which looks very like -isomerism. The classical example of this is furnished by the butterflies -_Vanessa prorsa_ and _Vanessa levana_. - -At one time these were supposed to belong to different species, since -they differ so greatly in appearance. _Vanessa levana_ is red, with black -and blue spots. _Vanessa prorsa_ is deep black, with a broad -yellowish-white band across both wings. It is now known that the _levana_ -is the spring form and the _prorsa_ the summer and autumn form of the -same species. The pupae of _levana_ produce the _prorsa_ form, but -Weismann found that after being placed in a refrigerator they emerged, -not as _prorsa_, but partly as _levana_ and partly as another form -intermediate in many respects between _levana_ and _prorsa_. Weismann -also succeeded, by exposing the winter pupa to a high temperature, in -making it give rise to the _prorsa_ form, and not to the _levana_ form, -as it would ordinarily do. - -Similar results have been obtained with the seasonally dimorphic _Pieris -napi_. Standfuss, the Graefin von Linden, and others have obtained like -results in the case of other seasonally dimorphic butterflies. In some -instances it has been proved that the change in the pigment is a purely -chemical one; a similar transformation can be effected in the extracted -pigment. But, we must bear in mind that the changes which are induced in -this way are not confined to colour; they occur in the marking and shape -of the wing. - -Even more remarkable is the fact that in some sexually dimorphic species -a change of temperature alters the female, so as to cause her to have the -outward appearance of the male. For example, it has been found that -warmth changes the colours of the female _Rhodocera rhamni_ and -_Parnassius apollo_ into the colours of the male. - -By applying rays of strong light, electric shock, or centrifuge, the -Graefin von Linden was able to change the colours of the butterflies to -which the caterpillars gave rise. Pictet experimented on twenty-one -species of butterflies, or rather on their caterpillars, and found that -in nearly all cases when the caterpillars ate unusual food, they -developed into butterflies with abnormal colouring. Schmankewitsch made -the discovery that, in the case of the crustacean _Artemia_, he could -produce either of two species according to the amount of salt in the -water in which these creatures were placed. He declared that the -anatomical differences between the species _Artemia salina_ and _Artemia -milhausenii_ depended solely on the percentage of the salt in the -surrounding water. He further stated that by adding still more salt he -could change the _Artemia_ into a new genus--_Branchipus_. More recent -observers have cast doubt upon these results of Schmankewitsch. They, -however, admit that the degree of salinity of the water has some effect -on the form of the _Artemia_, although they suggest that factors other -than concentration affect the result. In any case, it is now well-known -that changes in the environment effect changes in the colouring of many -crustacea. Pictet has shown that the alternating wet and dry seasons in -some tropical countries are the cause of, or stimulus that induces, -seasonal dimorphism in some butterflies. He was able to effect changes in -the colouring of certain species by means of humidity. - -The most important cases, from our point of view, are those in which the -application of heat or cold to a pupa has affected the colour, shape, -etc., of the emerging butterfly. Here we have but one factor, that of -temperature. All the material for the formation of the butterfly is -already stored up in the pupa. The unit characters, or their precursors, -are all there, and they take one form or another according to the -stimulus applied. - - - Biological Isomerism - -Phenomena of this kind can, we think, be accounted for only on the -assumption that the unit characters affected are each developed from a -definite portion of the fertilised egg, that each of these portions, -these precursors of the unit characters, is, like a chemical molecule, -made up of a number of particles, and that upon the arrangement of these -particles in its precursor in the egg depends the form that the unit -character derived from it will take. One arrangement of these particles -gives rise to one form of unit character, while another arrangement will -give rise to a totally different form of unit character. - -Thus, some organisms seem to display a biological isomerism akin to -chemical isomerism, save that the particles which in organisms take the -place of chemical atoms are infinitely more complex. - -In other words, the precursors in the fertilised egg of each of these -unit characters behave in some respects like chemical molecules. - -In order to avoid the manufacture of fresh terms we may speak -figuratively of the germ cells as being composed of biological molecules, -which in their turn are built up of biological radicles and atoms. These -behave in some ways like chemical molecules, radicles, and atoms, as the -case may be. - - - Biological Molecules - -It seems legitimate to regard each unit character in the adult as the -result of the development of one or more of the biological molecules -which compose the nucleus of the fertilised egg. These biological -molecules are, of course, a million-fold more complex than chemical -molecules. Each biological atom must contain within itself a number of -the very complex protoplasmic molecules. This view of the structure of -the germ cell seems to force itself upon the observer. Notwithstanding -this, the conception will have no value unless it seems to throw light on -the various phenomena of heredity, variation, etc. - -Let us then try to interpret some of these. - -Each chemical element is made up of atoms which are all of the same kind, -but no two elements are made up of the same kind of atoms, although -chemists are now inclined to conceive of all the various kinds of atoms -as made up of varying amounts of some primordial substance. In any case, -the molecules of chemical compounds are made up of various kinds of -atoms. With biological atoms the case would seem to be different. All -would appear to be made up of the same kind of substance, and the -differences shown by the various unit characters that go to make up an -organism would seem to be due to the different numbers and the varying -arrangement of the biological atoms which compose the molecules from -which unit characters are derived. This would be quite in accordance with -the chemical notion of allotropy. Thus, the graphite and the diamond -molecules are both made up of the same kind of atoms. - -But the biological atoms are living, that is to say, they are continually -undergoing anabolism and katabolism, growth and decay. They exhibit all -the phenomena of life, they must grow and divide, and they must absorb -nourishment; hence it is not surprising that they should differ slightly -among themselves, that they should exhibit the phenomenon of variation. -Although probably all are composed of the same living material, no two -are exactly alike, hence the molecules formed by them will also differ -from one another. Thus we can see why it is that all organisms exhibit -fluctuating variations. - -Very different are the discontinuous variations or mutations. These would -seem to be due to either a rearrangement of the biological atoms in the -biological molecule or the splitting up of the latter into two or more -molecules. This, of course, is pure hypothesis. Let us take an imaginary -example. Suppose that a biological molecule contains eighteen biological -atoms, and that these are arranged in the form of an equilateral -triangle, six of them going to each side. Suppose now, that from some -cause or other they rearrange themselves to form an isosceles triangle, -so that only four form the base and seven go to each of the remaining -sides. Such an arrangement would give rise to a mutation. Suppose now -that, from some cause or other, this triangular biological molecule were -to split up into two triangles, each having three atoms to each side, we -should obtain a still more marked mutation. We are far from saying that -the atoms in the organic molecule ever take such forms. We have merely -attempted to give rough but simple illustrations of the kind of processes -which on this hypothesis might be expected to take place in the germ -cells or the fertilised eggs. - -Let us now consider the sexual act from this aspect. The various -molecules (we speak, of course, of biological molecules) of the male -parent meet those of the female parent, and a synthesis occurs, which -results in the formation of a new organism. When these two sets of -gametes meet one another, one of several events may happen. The gametes -may refuse to combine. This will occur whenever they are of very -different constitution; thus it is that widely differing species will not -interbreed. But it may even happen that gametes of individuals of the -same species may refuse to coalesce on account of some peculiarity in the -composition of one or other of them. Secondly, they may be able to form -some sort of a union, but, owing to their diverse nature, the resulting -molecules may be so complex that they cannot be broken up into equal -halves, and as this seems to be necessary for the sexual act, the -resulting organism will be sterile. Thirdly, the two sets of gametes may -enter into a proper union, that is to say, form new molecules, but these -may be of such different structure to the molecules of the gametes, that -the resulting offspring will be quite unlike their parents in appearance. -Fourthly, some or all the groups of radicles in each gamete may be united -so closely that in the sexual act they do not break up, but enter bodily -into the new resulting organism. In these circumstances the inheritance -of the offspring will follow Mendel's law. Fifthly, there may be some -slight disturbance of the molecule, perhaps one or only a few atoms will -be replaced by those of the other gamete. This would give us impure -dominance. - -Thus this hypothesis appears to be compatible with the various modes of -inheritance. - -The curious phenomenon known as prepotency would seem also to be quite in -accordance with the conception. - -In chemical reactions the tendency is for the most stable combinations to -be formed, so in nature. - -We may probably go farther and say, not only will the most stable -biological molecules be formed, but the most stable radicles will -dominate the molecule. Hence, if any two animals are crossed and the -offspring show alternate inheritance, the resulting organism will, in the -case of each unit character, display the most stable of the pair; in -other words, it will take after the parent which happens to have the -greater stability as regards that particular character. The difference -between the mule and the hinny would seem to be explicable on this -supposition. If the union were like a simple chemical synthesis it should -not make any difference which way the cross were made. But if the species -crossed are of varying stability, and if their respective degrees of -stability vary with the sex, it is easy to see that it will make a -difference how the animals are crossed. - -In the cases of creatures that obey Mendel's law, the most stable form of -a unit character will presumably be the dominant one. - -One of the most curious of the phenomena of inheritance is that of -correlation. We shall deal with this more fully in Chapter VIII. It will -suffice here to say that certain characters appear to be linked together -in organisms. Such seem to be transmitted in pairs. The offspring never -exhibits one of such a correlated couple without exhibiting the other -also. - -It would thus seem that certain combinations of biological atoms, certain -molecules, can only exist in conjunction with certain other combinations. -This is quite in accordance with the teaching of physiologists regarding -the interdependence of the various organs of the body. We have now -reached the stage of the fertilised ovum. According to our conception it -is a series or conglomeration of the precursors of the unit characters of -the adult. These precursors we call biological molecules. Each is of a -very complex nature. Each seems to be composed of several portions, only -one of which will take part in the building up of the body of the -offspring, the other portions remaining latent. We further conceive that -it is possible for the various radicles which compose these molecules to -arrange themselves in various manners, and with each new arrangement a -different form of unit character will be developed. These molecules, -then, are built up from radicles derived from both parents, the most -stable combinations being formed and one portion of the molecule -dominating the whole. Under normal circumstances this dominant portion of -the molecule will give rise to a character of a definite type. But it -seems that other factors may come into play and cause a rearrangement of -the radicles which compose it, and this will result in the formation of a -unit character different from that to which it would ordinarily give -rise. - -But, it may be objected, if the colour of an organism be derived from one -of these so-called biological molecules, how is it that it affects the -whole organism, or, at any rate, several of the other unit characters? -The objection may be met in several ways. In the first place, the -colour-forming molecules may split up into as many portions as there are -units which it affects, and each portion may attach itself to a unit. Or -the property which we call colouration may not be derived from a -molecule, it may be an expression in the relative positions of the -various molecules in the fertilised egg. Or the colour-determining -molecule may secrete a ferment or a hormone, and this may be the cause of -the particular colouring of the resulting organism. We do not pretend to -say which (if any) of these alternative suppositions is the correct one. -But it seems to us that some such conception as that which we have set -forth is forced upon us by observed facts. This conception should be -regarded not as a theory, but rather as an indication of the lines along -which we believe the study of inheritance could best be made. - -The fertilised ovum has nothing of the shape of the creature to which it -will give rise. It is merely a potential organism, a something which -under favourable conditions will develop into an organism. - - - Phenomenon of Sex - -In the higher animals each individual is either of the male or the female -sex. A vast amount of ingenuity has been expended by zoologists in the -attempt to ascertain what it is that determines sex. Many theories have -been advanced, but no one of them has obtained anything like general -acceptance, because its opponents are able to adduce facts which appear -to be incompatible with it. - -It is tempting to try to interpret the phenomenon of sex on the -assumption that the female-producing biological molecule or unit is an -isomeride of the male-producing cell. Certain facts, however, seem to -negative the idea, as, for example, the occasional appearance in an -individual of one sex of characteristics of the other sex. - -Possibly the attempts to explain the phenomena of sex-production on a -Mendelian basis may prove to be more successful. It seems not impossible -that each fertilised egg contains material which is capable of developing -into male generative organs and material which is capable of developing -into female generative organs, but that only one kind of material, that -which dominates, succeeds in developing. The number of what are known as -"X-elements" that happen to be present in the fertilised egg appear to -decide which kind of material is to be dominant. - -But the problem of the determination of sex, fascinating though it be, is -not one that can be discussed adequately in a general work on evolution. -Those interested in the subject are referred to Professor Thomson's -_Heredity_, and to the address given by Professor E. B. Wilson, of -Columbia University, before the American Association for the Advancement -of Science, which was fully reported in the issue of _Science_, dated -January 8, 1909. - -Stated briefly, then, our conception is, that the fertilised egg is -composed of a number of entities, to which we have given the name -"biological molecules," because in certain respects their behaviour is -not unlike that of chemical molecules. - -The units which compose these molecules, being made up of protoplasm, are -endowed with all the properties of life, including the inherent -instability which characterises all living matter. - -We suggest that the continuous or fluctuating variations that appear in -the adult organism may be the result of individual differences in the -biological "atoms" that compose the molecule. - -Discontinuous variations, or mutations, on the other hand, may be the -result of a rearrangement of the atoms within the biological molecule. -Upon what causes this rearrangement it would not be very profitable to -speculate in the present state of our knowledge. To do this would be to -inquire into the cause of a re-grouping of entities of the existence of -which we are not certain! For aught we know there may be an intracellular -struggle for nourishment among the various molecules and among the atoms -which compose the molecules. If one molecule enjoys any special advantage -over the others the result may be an unusual degree of development of the -resulting unit character; in other words, the result will be a variation -in the organism. This variation may prove favourable or unfavourable to -its possessor. - - - Struggle for Nourishment - -Certain phenomena seem to point to a struggle for nourishment between the -germinal and the somatic portions of the egg, between the parts from -which the sexual cells of the resulting organism are produced and those -which give rise to the body of the organism. Each molecule may strive, so -to speak, to increase at the expense of the others. Thus, great size in -an organism is likely to be produced at the expense of the germinal -cell-forming molecules. In other words, great size in an organism would -be incompatible with excessive fecundity. This is what we observe in -nature. On the other hand, poor development of bodily tissue, as in the -case of intestinal parasites, would be correlated with great fecundity. -Some organisms are mere sacs full of eggs. - -Success in the struggle for nourishment of one molecule might be shared -by the other molecules near to it, hence the phenomena of correlation. - -It is thus conceivable that, in a brood consisting of several -individuals, a particular molecule or set of molecules in one of the -individuals may receive more than its share of nourishment, and this will -result in the organs of that individual which spring from the -well-nourished molecules being exceptionally well developed. Thus arises -the phenomenon of differences between the members of a litter or brood. - -Natural selection will tend to eliminate those individuals in which the -resulting variation is an unfavourable one. If the environment is such, -as in the case of an internal parasite, that the production of germ cells -is the most necessary function of the organism, then those individuals in -which the germ-forming molecules increase at the expense of the -body-forming ones will tend to be preserved. This would cause the -phenomenon which biologists term degeneration. The nourishment of the -various biological molecules may possibly depend on their relative -positions in the egg. Those in a favourable position will then tend to -develop at the expense of the others. This will result in variation along -definite lines. Each succeeding generation will tend to an increased -development of that particular organ to which the favourably-situated -molecule gives rise. This process may continue, as in the case of the -horns of the Irish elk, until the development of that particular organ -becomes so excessive as to be positively injurious; then natural -selection will step in and eliminate the species. But before this -happens, something may cause a rearrangement of the biological molecules -in the fertilised egg, and thus a mutation may arise, which, so to speak, -strikes out a new line. - - - Origin of Mutations - -Finally, on this conception there may be some sort of connection between -fluctuating variations and mutations. We can picture the fluctuating -variations being piled up, one upon the other, until there results a -rearrangement of the atoms in one or more of the biological molecules -which, in turn, causes a mutation. - -Occasionally this remodelling, as it were, of one biological molecule may -affect certain of the other molecules, and thus lead to correlated -mutations. - - - - - CHAPTER VI - THE COLOURATION OF ORGANISMS - - - 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 Muellerian - 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--Illustrative 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--Objections 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 - recognition 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. - -Since the publication of _The Origin of Species_, naturalists have paid -much attention to the colouration of animals and plants, with the result -that a large majority of scientific men to-day hold the belief that all, -or nearly all, the colours displayed by animals are of direct utility to -them, and are therefore the direct result of natural selection; a few -would add, "and of sexual selection." - -"Among the numerous applications of the Darwinian theory," writes -Wallace, "in the interpretation of the complex phenomena, none have been -more successful than those which deal with the colours of animals and -plants." - - - Robinson on Protective Colouring - -We readily admit that the Darwinian theory has thrown a great deal of -light on the phenomenon of animal colouration; it has reduced to -something like order what was before Darwin's time chaos. While admitting -this we feel constrained to say that many naturalists, especially Dr -Wallace and Professor Poulton, have pushed the various theories of animal -colouration to absurd lengths. As Dr H. Robinson truly says (_Knowledge_, -January 1909), "It seems to have been taken for granted, and some even of -Dr Wallace's writings may be interpreted in this sense, that protective -colouring is necessary to the continued existence of every species, and -that, sexual colouration apart, it is incumbent on naturalists to offer -ingenious speculations in this sense to account for the appearance even -of the most bizarre and conspicuous beasts. Thence it has been but a -short step to the announcement of those speculations as further evidence -in favour of natural selection, and of various assumptions made in the -speculative process as indisputable facts." - -The result of this is that men have ceased to regard the Neo-Darwinian[6] -theories of protective colouration, mimicry, and recognition markings as -mere hypotheses which seem to throw light on certain phenomena in the -organic world. These theories have assumed the rank of laws of nature. To -dispute them would seem to be as futile as to assert that the earth is -flat. To take exception to them would appear to be as ridiculous as to -object to Mont Blanc. To dare to criticise them is heresy of the worst -type. - -Be this as it may, scientific dogma or no scientific dogma, scientific -opinion or no scientific opinion, we have dared to weigh these theories -in the balance of observation and reason, and have found them wanting. We -have examined these mighty images of gold, and silver, and brass, and -iron, and found that there is much clay in the feet. - -We shall devote this chapter to lifting the hem of the garment of -sanctity that envelopes each of these images, and so expose to view the -clay that lies concealed. - -We propose, first, to set forth in outline what we trust will be -considered a fair statement of the various theories of animal colouration -which are generally accepted to-day, then to show up the various weak -points in these, and lastly, to endeavour to ascertain whether there are -not some alternative explanations in certain cases to which the -generally-accepted theory does not apply. - - - Cryptic Colouring - -Neo-Darwinians divide the various forms of colouration into three great -classes:--(1) Cryptic colouring, or protective and aggressive -resemblances; (2) sematic colours, or warning and recognition colours; -and (3) pseudo-sematic colours, or mimicry. A tabular statement of this -scheme of colouring will be found on pp. 293-7 Professor Poulton's -_Essays on Evolution_. - -As regards class (1), Neo-Darwinians point out that the great majority of -animals are so coloured as to make them very difficult to see in their -natural environment, hence the whiteness of the creatures which inhabit -the snow-bound Arctic regions, the sandy colour of desert animals, the -spotted coats of creatures which live among trees, the striped markings -of animals which spend their lives amid long grass, and the transparent -blueness of pelagic animals. The theory is that all kinds of animals, -whether those that hunt or those that are hunted, derive much advantage -from being coloured like their environment. The hunted creatures are -thereby the better able to elude the vigilance of their foes, while those -that hunt are in a position to take their quarry by surprise; so that -natural selection has caused them all to assimilate to the hues of their -surroundings. Neo-Darwinians point to the fact that some Arctic animals -are brown in the summer to match the ground from which the snow has -melted, and turn white in winter to assimilate with their snowy -background. Naturalists further cite, as evidence in favour of this -theory, the case of those creatures which imitate inanimate objects, such -as leaves and twigs, and thereby escape the observation of their foes. - -Thus, the great majority of animals are supposed to be cryptically -coloured, that is to say, coloured so as to be, if not quite invisible, -at least very inconspicuous in their natural habitat. - - - Warning Colouration - -It is, however, generally admitted that many creatures are not -cryptically coloured. Some, indeed, seem to be coloured in such a way as -to render them as conspicuous as possible. The Neo-Darwinians declare -that there is a reason for this. "If," writes Professor Milnes Marshall -(page 133 of his _Lectures on the Darwinian Theory_), "an animal, -belonging to a group liable to be eaten by others, is possessed of a -nauseous taste, or if an animal, such as a wasp, is specially armed and -venomous, it is to its advantage that it should be recognised quickly, -and so avoided by animals that might be disposed to take it as food. - -"Hence arises warning colouration, the explanation of which is due to -Wallace. Darwin, who was unable to explain the reason for the gaudy -colouration of some caterpillars, stated his difficulty to Wallace, and -asked for suggestions. Wallace thought the matter over, considered all -known cases, and then ventured to predict that birds and other enemies -would be found to refuse such caterpillars if offered to them. This -explanation, first applied to caterpillars, soon extended to adult forms, -not only of insects, but of other groups as well. . . . Insects afford -many admirable examples of warning colours, and many well-known instances -occur among butterflies. The best examples of these are found in three -great families of butterflies--the _Heliconidae_, found in South America, -the _Danaidae_, found in Asia and tropical regions generally, and the -_Acraeidae_ of Africa. These have large but rather weak wings, and fly -slowly. They are always very abundant, all have conspicuous colours or -markings, and often a peculiar form of flight, characters by which they -can be recognised at a glance. The colours are nearly always the same on -both upper and under surfaces of the wings; they never try to conceal -themselves, but rest on the upper surfaces of leaves and flowers. -Moreover, they all have juices which exhale a powerful scent; so that, if -they are killed by pinching the body, a liquid exudes which stains the -fingers yellow, and leaves an odour which can only be removed by repeated -washing. This odour is not very offensive to man, but has been shown by -experiment to be so to birds and other insect-eating animals. - -"Warning colours are advertisements, often highly coloured -advertisements, of unsuitability as food. Insects are of two kinds--those -which are extremely difficult to find, and those which are rendered -prominent through startling colours and conspicuous attitudes. Warning -colours may usually be distinguished by being conspicuously exposed when -the animal is at rest. Crude patterns and startling contrasts in colour -are characteristically warning, and these colours and patterns often -resemble each other; black combined with white, yellow, or red, are the -commonest combinations, and the patterns usually consist of rings, -stripes, or spots." - -We trust that we shall be forgiven for this lengthy quotation. Our object -in reproducing so large an extract is to allow the Neo-Darwinians to -speak for themselves. Were we to state their theory in our own words, we -might perhaps be charged with stating it inaccurately. We should add -that, even as natural selection is supposed to have been the cause of -conspicuous colouring in some organisms, so has it caused others to -assume intimidating attitudes or emit warning sounds, such as a hiss, -when attacked. - - - Batesian Mimicry - -We now come to the third great class of animal colours--mimetic colours. -Mimicry is of two kinds, known respectively as Batesian and Muellerian -mimicry, after their respective discoverers. - -It has been found that some apparently warningly coloured butterflies and -other creatures are palatable to insectivorous animals. The explanation -given of this is that these showy but edible butterflies "mimic," that is -to say, have the appearance of, show a general resemblance to, species -which are unpalatable. This is known as Batesian mimicry. "Protective -mimicry," writes Professor Poulton (_Essays on Evolution_, p. 361), "is -here defined as an advantageous superficial resemblance of a palatable -defenceless form to another that is specially defended so as to be -disliked or feared by the majority of enemies of the groups to which both -mimic and model belong--a resemblance which appeals to the senses of -animal enemies . . . but does not extend to deep-seated characters, -except when the superficial likeness is affected thereby." - -As Wallace has pointed out, five conditions must be satisfied before such -protective mimicry can occur:-- - -"1. That the imitative species occur in the same area and occupy the same -station as the imitated. 2. That the imitators are always the more -defenceless. 3. That the imitators are always less numerous in -individuals. 4. That the imitators differ from the bulk of their allies. -5. That the imitation, however minute, is external and visible only, -never extending to internal characters or to such as does not affect the -external characters." (_Darwinism_, Chap. ix.) - -Thus the mimic is supposed to deceive his enemies by deluding them into -the belief that he is the inedible species which they once tried to eat -and vowed never again to touch, so nasty was it. The mimic, then, may be -compared to the ass in the lion's skin. Needless to say, this mimicry is -quite unconscious. It is supposed to have been developed by natural -selection. Every popular book on Evolution cites many examples of such -mimicry. We may therefore content ourselves with mentioning but a few. - - - Examples of Mimicry - -Our common wasps are copied by a beetle (_Clytus arietis_), active in -movement and banded black and yellow, and by several yellow-barred -hover-flies (_Syrphidae_); and the bumble-bee by a clear-winged moth -(_Sesia fuciformis_). There is, indeed, a whole group of these -clear-winged moths, resembling bees, wasps, and other stinging -hymenoptera. The common Indian Danaid butterfly, _Danais chrysippus_, is -marvellously reproduced by the female of _Hypolimnas misippus_, a form -allied to our Purple Emperor. The male of this is black, with white -blue-bordered patches, the female chestnut, edged with black and with -white spots at the tips of the wings, as in the _Danais_. Finn has shown -experimentally that this species is liked by birds. - -Another common Indian Danaid (_D. limniace_), black, spotted with pale -green, is imitated, though not very closely, by the female of one of the -"white" group, _Nepheronia hippia_. Finn found that this insect was eaten -freely by birds, and that the common jungle-babbler (_Crateropus -canorus_) was deceived by the mimicry of the female. The very nauseous -Indian swallow-tail (_Papilio aristolochiae_) is closely imitated by -another swallow-tail (_P. polites_), both having black wings marked with -red and white; _P. aristolochiae_, however, has a red abdomen. This -difference was not noticed by two species of Drongo-shrikes (_Dicrurus -ater_ and _Dissemurus paradiseus_), to which the butterflies were -offered; but the Pekin robin (_Liothrix luteus_)--a very intelligent -little bird--did not fail to pick out and eat the mimic, though it was -deceived by the marvellously perfect imitation of _Danais chrysippus_, by -the female of the _Hypolimnas_. - -Such resemblances can therefore be effective. - -The cases of mimicry usually quoted include very few among mammals, -probably, as Beddard suggests, because the species of that class are -relatively few. - -The insectivorous genus _Tupaia_ is supposed to mimic the squirrels, -which it much resembles as regards form in all respects save the long -muzzle; the idea being that squirrels are so active that carnivorous -animals find it hopeless to pursue them. - -On the other hand, there is a squirrel (_Rhinosciurus tupaioides_) which -is supposed to mimic the tupaias! It has a similar long muzzle, and the -light shoulder-stripe which is a common marking in tupaias. But why the -squirrel, one of the group imitated, should in turn become an imitator is -not explained. - -The true interpretation of the resemblance is probably that both -squirrels and tupaias are adapted to a life in trees. Like profession -begets like appearance: the ground-living shrews much resemble mice, and -the moles find representatives in mole-like rodents. - -Another case, however, wherein true mimicry may have come into play is -that of the South American deer (_Cervus paludosus_) which singularly -resembles in colouration the long-legged wolf or _Aguara-guazu_ (_Canis -jubatus_). Both these species are chestnut in colour, with the front of -the legs black, and the ears lined with white hair; both inhabit the same -regions in South America. - - - Muellerian Mimicry - -The second kind of mimicry--Muellerian mimicry--is where one unpalatable -creature resembles another. This form of mimicry is named after Fritz -Mueller, who suggested the explanation now usually accepted, namely, that -"Life is saved by a resemblance between the warning colours in any area, -inasmuch as the education of young inexperienced enemies is facilitated, -and insect life saved in the process." "It is obvious," writes Poulton -(p. 328 of _Essays on Evolution_), "that the amount of learning and -remembering, and consequently of injury and loss of life involved in -these processes, are reduced when many species in one place possess the -same aposematic colouring, instead of each exhibiting a different danger -signal. . . . The precise statement of advantage was made by Mr Blakiston -and Mr Alexander, of Tokio. 'Let there be two species of insects equally -distasteful to young birds, and let it be supposed that the birds would -destroy the same number of individuals of each before they were educated -to avoid them. Then if these insects are thoroughly mixed and become -undistinguishable to the birds, a proportionate advantage accrues to each -over its former state of existence. These proportionate advantages are -inversely in the duplicate ratio of the respective percentages that would -have survived without the mimicry.'" - -This is rather a cumbrous method of saying that if there are in a -locality a number of young birds, and each of these has to learn by -experience which insects are edible and which are not, each will, if it -learns by one example, devour one insect of any given pattern. Now, if -two species of inedible insects have this pattern, they will between them -lose only one member in the educating process of each bird, whereas if -each species of insect had a colouration peculiar to itself, each species -would lose a whole individual instead of half a one. There can be no -doubt that such a livery of unpalatability is of some advantage to its -possessors. - -It has been shown experimentally that hand-reared young birds have to -acquire their knowledge of flavours and colours by experiment. - -It is well known that in many species the male and the female are not -coloured alike. Such species are said to exhibit sexual dimorphism. In -these cases it is usually the male that is more conspicuously coloured. -Darwin felt that the theory of natural selection could not satisfactorily -account for this phenomenon, so put forward the supplementary theory of -sexual selection. On this hypothesis the females are supposed to be able -to pick and choose their mates, and to select the most beautiful and -ornamental ones, hence the greater showiness of these in most sexually -dimorphic species. Wallace does not accept this theory. He thinks it -unnecessary. He looks upon the brilliant colouring of the males as due to -their superior vigour; moreover, he says that it is the hen that sits -upon the eggs, and so requires a greater degree of protection than the -male, and therefore natural selection has not permitted her to develop -all the ornaments displayed by the cock. With the phenomenon of sexual -dimorphism we shall deal at length in the next chapter. - - - Danger Signals - -Dr Wallace recognizes yet another exception to the rule that animals are -cryptically coloured. Many creatures possess on the body markings which -tend to render them conspicuous rather than difficult to see. Where such -markings occur on gregarious animals, Wallace believes that they have -been evolved by natural selection, either to enable their possessors to -recognize one another, or to act as a danger signal to their fellows. The -white tail of the rabbit is believed by Wallace to serve as a danger -signal. The first member of the company to espy the approaching foe takes -to his heels, and, as he moves, his white tail catches the eye of his -neighbour, who at once follows him, so that, in less time than it takes -to tell, the whole company of rabbits is scampering towards the burrow, -thanks to the white under-surface of the tail. - -Even as Wallace out-Darwin's Darwin, so does Mr Abbott Thayer, an -American naturalist and artist, out-Wallace Wallace. That gentleman seems -to be of opinion that _all_ animals are cryptically or, as he calls it, -concealingly or obliteratively coloured. Even those schemes of colour -which have hitherto been called conspicuous are, he asserts, "purely and -potently concealing" when looked at properly, that is to say, with the -eye of the artist. - -Lest it be thought unnecessary to criticize a hypothesis which appears to -be based upon the assumption that animals see with the eye of the artist, -we may say that Professor Poulton writes approvingly of Thayer's theory. -He frequently alludes to it in his _Essays on Evolution_, and he -published an account of it in the issue of _Nature_, dated April 24, -1902. Moreover the hypothesis has been enunciated in such scientific -journals as _The Auk_ (1896) and _The Year-Book of the Smithsonian -Institution_ (1897). - -Thayer asserts that all animals, or at any rate the great majority, -including many that are usually supposed to be conspicuously coloured, -are in reality obliteratively coloured--that is to say, coloured in such -a way that the effects of light and shade are completely counteracted, -with the result that they are invisible. - - - Obliterative Colouring - -It is possible, says Mr Thayer, to almost obliterate a statue in a -diffused light, by putting white paint on the surfaces in darkest shadow -and dark paint on the most brightly lighted parts, all in due proportion. -Now this is precisely what nature is supposed by Mr Thayer to have done -for all her creatures. - -It is well known that a great many animals, as for example the Indian -black-buck and the hare, are coloured on the upper side and white below. -This is called by Mr Thayer the principle of the gradation of colour. It -runs, he declares, all through the animal world, and is "the main -essential step toward making animals inconspicuous under the descending -light of the sky." - -Animals, he contends, are not protectively coloured to look like clods or -stumps or like surrounding objects, they are simply obliteratively -coloured--coated, as it were, with invisible paint. - -To quote from _The Century Magazine_ (1908): "Whales, lions, wolves, -deer, hares, mice; partridges, quails, sandpipers, larks, sparrows; -frogs, snakes, fishes, lizards, crabs; grasshoppers, slugs, -caterpillars--all these animals, and many thousands more, crawl, crouch, -and swim about their business, hunting and eluding, under cover of this -strange obliterative mask, the smooth and perfect balance between shades -of colour and degrees of illumination." - -Nature having thus visually unsubstantialized the bodies of animals, so -that, if seen at all, they look flat and ghostly, does not stop there. -From solid-shaded bodies they have been converted, as it were, into flat -cards or canvases, and, to complete the illusion of obliteration, -pictures of the background--veritable pictures of the more or less -distant landscape--have been painted on their canvases! Such in effect -are the elaborate "markings of field and forest birds." - -Again he writes: "Brilliantly changeable or metallic colours are usually -supposed to make the birds that wear them conspicuous, but nothing could -be further from the truth. Iridescence is, indeed, one of the strongest -factors of concealment. The quicksilver-like intershifting of many lights -and colours, which the slightest motion generates on an iridescent -surface, like the back of a bird or the wing of a butterfly, destroys the -visibility of that wing or back as such and causes it to blend -inextricably with the gleaming and scintillating labyrinthine-shadowed -world of wind-swayed leaves and flowers." - -According to Thayer, the skunk, which for years has been an important -item of the stock-in-trade of the advocates of the theory of warning -colouration, is an excellent example of obliterative colouring, since its -enemies are supposed to mistake for the sky-line the line of junction -between the white fur of the back and the dark fur of the sides. -Similarly the crocodiles are supposed to mistake a flamingo for the sky -at sunrise or at sunset! - -There is doubtless something in this theory of obliterative colouration. - -Any one can see, by paying a visit to the South Kensington Museum, that -an animal which is of a lighter colour below than above, is less -conspicuous in a poor light than it would be were it uniformly coloured. -There is then no doubt that this scheme of colour, which is so common in -nature, has some protective value. - -To this extent has Mr Thayer made a valuable contribution to zoological -science. But when he informs us that obliterative colouring is a -"universal attribute of animal life," we feel sorely tempted to poke fun -at him. - -We would ask all those who believe in the universality of obliterative -colouring to observe a flock of rooks wending their way to their -dormitories at sunset. - -Let us now pass on to the examination of the more orthodox theories of -animal colouration. - - - Objections to the Theory of Cryptic Colouring - -Before criticising the theory of cryptic colouring, we desire to state -distinctly that we admit that, where other things are equal, it is of -advantage to all creatures which hunt or which are preyed upon to be -inconspicuous. If difficult to distinguish amid their natural -surroundings, the former are likely to secure their prey readily, and the -latter have a chance of escaping from their enemies. Our quarrel is with -the theory of cryptic colouring as it is enunciated by many -Neo-Darwinians, with the theory that every hue, every marking, every -device displayed by an organism is of utility to the organism and has -been directly developed by natural selection. - -The extreme advocates of the theory of cryptic colouring have greatly -exaggerated the degree in which animals are assimilated to their natural -environment. - - - Fauna of Polar Regions - -We grant that a great many creatures, which when seen in a menagerie -appear very conspicuous, are the reverse of conspicuous when standing -motionless amid their natural surroundings. As Beddard has pointed out, -it is often not easy to find a sixpenny piece which has been dropped on -the carpet, but the reason for this is, not that the coin is protectively -coloured, but that any small object, no matter how coloured, is difficult -to distinguish amid a variegated environment. The assumption of a white -winter coat by many organisms that live in northern latitudes has been -cited, again and again, as showing how important it is for an animal to -be protectively coloured. If, it is urged, those creatures that live in -lands which are covered in snow for half of the year have become white in -winter by the action of natural selection in order to escape their foes, -it is obviously of paramount importance to all creatures that they should -be cryptically coloured. Popular books on natural history convey the -impression that during winter the snow-clad, ice-bound Arctic regions are -peopled by a fauna whose fur or hair rivals in whiteness the snowy mantle -of the earth. The impression thus conveyed is misleading. It is true that -an unusually large percentage of the animals that inhabit the polar -regions are white in winter, but the majority of the creatures which -dwell there do not assume the white garb of winter. - -As the fauna of the polar regions is a small one, we are able to give -lists of all the birds and mammals which dwell in the Arctic and the -Antarctic regions. We have arranged these in in three columns. In the -first are placed those creatures which are white throughout the year, in -the third those that retain their colour through the winter, while the -middle column contains those forms which change their colouring with the -season. - - ARCTIC FAUNA. - Mammals. - White. - Polar Bear. - Arctic Fox (some individuals). - White Whale or Beluga. - Changing with the Seasons. - Arctic Fox (most individuals). - Arctic Lemming. - Stoat. - Weasel. - Blue Hare. - Coloured. - Arctic Fox (sometimes). - Reindeer. - Musk-ox. - Glutton. - Moose. - Sable. - Seals. - Walrus. - Narhwal. - Greenland Whale. - Birds. - White. - Ivory Gull. - Snowy Owl. - Gyrfalcon. - Snow Goose. - Changing with the Seasons. - Black Guillemot. - Ptarmigans. - Snow Bunting (whitest in summer!) - Razorbill. - Little Auk (throat only becomes white). - Coloured. - Sea Eagle. - Greenland Redpoll (very pale). - All Arctic Geese and Ducks other than Snow Goose. - Raven. - Cormorant. - Brunnich's Guillemot. - Puffin. - Fulmar Petrel. - Ross's Gull. - Glaucous Gull (very pale). - Sandpipers. - - ANTARCTIC FAUNA. - Mammals. - White. - Antarctic White Seal (_Lobodon carcinophaga_), in some cases. - Changing with the Seasons. - None. - Coloured. - Other Seals than _Lobodon._ - Whales. - Birds. - White. - Sheathbill. - Snowy Petrel. - Giant Petrel (some individuals). - Chick of Emperor Penguin. - Changing with the Seasons. - None. - Coloured. - Penguins. - Cormorant. - Skua Gull. - Giant Petrel (usually). - Other Petrels. - -It will be observed that the third column contains the largest number of -forms. It is thus evident that the whiteness of the Arctic and Antarctic -faunas in winter has been greatly exaggerated. - -The Arctic fox appears in all three columns, as the creature seems to -fall into three races--a permanently white race, a permanently coloured -race, and a seasonally dimorphic race. - -Of the creatures set forth in the middle column of the above tables all -are whiter in winter than in summer with the exception of the snow -bunting, who sets at naught the theory of cryptic colouring by turning -darker in winter! The same may be said of the Alpine chamois. - -The advocates of the theory of protective colouring assert that the -creatures which do not turn white in winter are strong and active animals -which have no enemies to fear. - -This contention is met by F. C. Selous as follows (_African Nature Notes -and Reminiscences_, p. 9): "According to the experience of Arctic -travellers, large numbers of young musk oxen are annually killed by -wolves. . . . Nothing, I think, is more certain than that a far smaller -percentage of so-called protectively coloured giraffes are killed -annually by lions in Africa than of musk oxen by wolves in Arctic -America." - -Another difficulty which confronts the Neo-Wallaceian school is that, _ex -hypothesi_, the assumption of the white coat was gradual. Hence the -change in the direction of whiteness cannot, in its first beginning, have -been of perceptible utility to an organism. How then can natural -selection have operated on it? - - - Pelagic Organisms - -The transparency of pelagic organisms is frequently cited as exemplifying -cryptic colouring. We all know that the common jelly-fish is as -transparent as glass. Floating on the surface of the ocean are millions -of tiny organisms, so transparent as to be invisible to the human eye. At -first sight this certainly appears to be a remarkable case of protective -colouring. Unfortunately, nearly all the more highly developed forms -display conspicuous pigment (as in most jelly-fish) in some part of the -body. - -"An animal floating about in the sea," writes Beddard, "perfectly -transparent, but decked with dense black patches, of the size of saucers, -would betray its whereabouts even to the least observant; if the observer -were stimulated by hunger or fear, the conspicuousness would not be -lessened. . . . Besides the internecine warfare which is continually -going on amongst the smaller surface organisms, they are devoured -wholesale by the larger pelagic fish, and by whales and other Cetacea. A -whale, rushing through the water with open mouth and gulping down all -before him, is not the least inconvenienced by the invisibility of the -organisms devoured in such enormous quantities; nor do a solid phalanx of -herring or mackerel stop to look carefully for their food: they take what -comes in their way, and get plenty in spite of 'protective absence of -colouration.' - -"If the transparency of the pelagic organisms be due entirely to natural -selection, it is remarkable that there is so little modification in this -direction among the species inhabiting the bottom at such depths as are -accessible to the sun's rays; the advantage gained by this transparency -and consequent invisibility would be equally great. And yet this is not -the case; the bulk of the bottom fauna of the coasts are brilliantly -coloured animals, and those that show any protective colouring at all -appear to be coloured so as to resemble stones or sea-weeds."[7] - -Before leaving the subject of marine animals, we may point out that the -majority of the creatures that live in the everlasting blackness of the -depths of the ocean display exceedingly conspicuous colouring, and this -colouring seems to be constant. In such cases the colouring cannot be -useful as such to its possessors. The same may be said of the colour of -blood, or of the colouring of the internal tissues of all organisms. We -must not lose sight of the fact that every organism, and every component -part thereof, must of necessity be either of some colour or perfectly -transparent. It seems to us that since the appearance of _The Origin of -Species_ zoologists have tended to exaggerate the importance of colouring -to organisms; they frequently speak of it as though it were the one and -only factor in the struggle for existence. It is on this account that -they feel it incumbent upon them to find ingenious explanations for every -piece of colouring displayed by every plant or animal. - - - Unimportance of Colour - -The tendency to exaggerate the importance to an animal of its colouring -is doubtless in large part due to the fact that many zoologists are -content to study nature in museums rather than in the open. Some of those -who observe organisms in their natural surroundings, especially in such -favourable localities as the tropics, seem to be of opinion that natural -selection has but little influence on the colouration of organisms. - -Thus D. Dewar writes (_Albany Review_, 1907): "Eight years of -bird-watching in India have convinced me that, so far as the struggle for -existence is concerned, it matters not to a bird whether it be -conspicuously or inconspicuously coloured, that it is not the necessity -for protection against raptorial foes which determines the colouring of a -species; in short, that the theory of protective colouration has but -little application to the fowls of the air." - -Similarly, F. C. Selous writes, on page 13 of _African Nature Notes and -Reminiscences_: "Having spent many years of my life in the constant -pursuit of African game, I have certainly been afforded opportunities -such as have been enjoyed by but few civilised men of becoming intimately -acquainted with the habits and life-history of many species of animals -living in that continent, and all that I have learned during my long -experience as a hunter compels me to doubt the correctness of the now -very generally accepted theories that all the wonderfully diversified -colours of animals--the stripes of the zebra, the blotched coat of the -giraffe, the spots of the bushbuck, the white face and the rump of the -bontebok, to mention only a few--have been coloured either as means of -protection from enemies or for the purpose of mutual recognition by -animals of the same species in times of sudden alarm." - -So also G. A. B. Dewar--a very close observer of nature in -England--writes, in _The Faery Year_: "Few theories in natural history -have received more attention of late years than protective or aggressive -colour, 'mimicry,' and harmony with environment. . . . To doubt this use -of colour to animals seems like inviting back chaos in place of -cosmos--for abandon the theory, and a world of colour is straightway void -of purpose, a muddle of chance. So we all like the theory. Some, however, -perceive plans to aid the wearer in every colour, tint, shade, and -pattern. We may be sceptical of a good many of the cases they cite in -support of colour aid, though attracted by the main idea." - -Writing of the commoner British butterflies, he says: "After a little -practice, any man furnished with good eyesight can easily distinguish -these butterflies--blues, coppers, small heaths, and meadow browns--from -their perches; and so we may be sure that the small beast, bird, or -insect of prey, with sense of colour or form, could also distinguish -them. . . . Quite often, without even searching for them, I can see -cabbage whites and other butterflies asleep on perches to which they by -no means assimilate." Mr G. A. B. Dewar suggests that the safety of the -resting butterfly lies in "the position, the couch on high, . . . not the -mask of colour or marking." - - - Gadow on Coral Snakes - -Two short visits to Southern Mexico sufficed to show Dr Hans Gadow that -some of the commonly accepted explanations of colour phenomena are not -the correct ones. - -Thus writing of coral snakes, he says, on page 95 of _Through Southern -Mexico_: "They are usually paraded as glaring instances of warning -colouration, but I am not at all sure whether this is justifiable. -Certainly these _Elaps_ are most conspicuous and beautiful objects. Black -and carmine or coral red, in alternate rings, are the favourite pattern; -sometimes with narrow golden-yellow rings between them, as if to enhance -the beautiful combination. But these snakes are inclined to be nocturnal -in their habits, and, except when basking, spend most of their time under -rotten stumps, in mouldy ground, or in ants' nests in search of their -prey, which must be very small, to judge from the size of the mouth." - -Dr Gadow goes on to show that although black and red are very strong -contrasts in the day-time, the combination ceases to be effective in the -dark. He suggests that red and black is a self-effacing rather than a -warning pattern. He further points out that several kinds of harmless -snakes have the same colouring and pattern. "There seems," he says, "to -be no reason why we should not call these cases of mimicry; and yet this -is most likely a wrong interpretation, since such harmless snakes are -also found in districts where the _Elaps_ does not occur, not only in -Mexico, but likewise in far-distant parts of the world, where neither -elapines nor any other similarly coloured poisonous snakes exist. To -interpret this as an instance of 'warning colours' in a perfectly -harmless snake, which has no chance of mimicry, amounts in such cases to -nonsense, and we have to look for a different explanation upon -physiological and other grounds." - -It is, to say the least of it, significant that all the opposition to the -theory of protective colouration comes from those who observe nature -first hand, while the warmest supporters of the theory are cabinet -naturalists and museum zoologists. - -In the case of nocturnal creatures, as Dr H. Robinson very sagely points -out (_Knowledge_, January 1909), the value for protective purposes of any -given colouration must depend very largely on the state of the moon. "It -was," he writes, "a common experience in the South African War that on -overcast or moonless nights the nearly black army great-coat made a -picquet sentry invisible at a distance of a few feet. In strong moonlight -this garb could be seen at a great distance, whereas a khaki pea jacket, -useless on a dark night, answered the requirements of invisibility very -well." It is thus evident that the dark colour of the buffalo and sable -antelope cannot be protective on both dark and moonlight nights. - -The theory of protective colouration is based on the tacit assumption -that beasts of prey rely on eyesight for finding their quarry. Raptorial -birds certainly do use their eyes as the means of discovering their -victims; but the great majority of predaceous mammals trust almost -entirely to their power of smell as a means for tracking down their prey. - - - F. C. Selous Quoted - -"Nothing," writes F. C. Selous, on page 14 of _African Nature Notes and -Reminiscences_, "is more certain than that all carnivorous animals hunt -almost entirely by scent until they have closely approached their quarry, -and usually by night, when all the animals on which they prey must look -very much alike as far as colour is concerned." - -The herbivora--the quarry for the beast of prey--too, have a keen sense -of smell, so that they trust their noses rather than their eyes for -safety. - -No observer of nature can have failed to remark how the least movement on -the part of an animal will betray its whereabouts, even though in -colouring it assimilates very closely to the environment. So long as the -hare squats motionless in the furrow, it may remain unobserved, even -though the sportsman be searching for it; but the least movement on its -part at once attracts his eye. Thus, in order that protective colouration -can be of use to its possessor, the latter must remain perfectly -motionless. But, in tropical countries, where flies, gnats, etc., are a -perfect scourge, no large animal is, when awake, motionless for ten -seconds at a time. The tail is in constant motion, flicking off the flies -that attempt to settle on the quadruped. The ears are used in a similar -manner. Thus the so-called protective colouring of herbivora cannot -afford them much protection. It is further worthy of note that the -brush-like tip to the tail of many mammals is not of the same colour as -the skin or fur. It is very frequently black. Thus we have the spectacle -of a protectively coloured creature continually moving, as if to attract -attention, almost the only part of its body that is not protectively -coloured! - - - Sexual Dimorphism - -Many species of birds display what is known as seasonal dimorphism, still -more display sexual dimorphism. - -Seasonally dimorphic birds very often assume a bright livery at the -breeding season; this nuptial plumage is by no means invariably confined -to the cock, so that we are brought face to face with the fact that some -hen birds, that are normally inconspicuously coloured, become showy and -easy to see at the nesting time, that is to say, precisely at the season -when they would seem to be most in need of protection. - -In the great majority of cases of sexual dimorphism among birds the cock -is the more showily coloured. Now, if it be a matter of life-and-death -importance to a bird to be protectively coloured, we should expect the -showily coloured cock birds to be far less numerous than the -dull-plumaged hens, since the former are, _ex hypothesi_, exposed to far -greater danger than the inconspicuous hens. As a matter of fact, cock -birds in practically all species appear to be at least as numerous as the -hens. Nor can it be said that this is due to their more secretive habits. -As a general rule, cock birds show themselves as readily as the hens; -indeed, in the case of the familiar blackbird, the conspicuous cock is -less retiring in his habits than the more sombre hen. It may, perhaps, be -thought that the greater danger to which the sitting bird is exposed -accounts for the fact that hens, notwithstanding their protective -colouration, are not more numerous than the cocks. Unfortunately for the -supposition, in many sexually dimorphic hens, as, for example, the -paradise fly-catcher (_Terpsiphone paradisi_), the showy cock shares the -burden of incubation equally with the hen. - -It frequently happens that allied species of birds are found in -neighbouring countries. The Indian robins, for example, fall into two -species. The brown-backed robin (_Thamnobia cambayensis_) occurs north of -Bombay, while the black-backed species (_T. fulicata_) is found south of -Bombay. The hens of these two species are almost indistinguishable, but -the cocks differ, in that one has a brown back, while the other's back is -glossy black. The Wallaceian theory of colouration seems quite unable to -explain this phenomenon--the splitting up of a genus into local -species--which is continually met with in nature. Equally inimical to the -theory of protective colouration is the existence, side by side, of -species which obtain their living in much the same manner. On every -Indian lake three different species of kingfisher pursue their profession -cheek by jowl; one of these--_Ceryle rudis_--is speckled black and white, -like a Hamburg fowl; the second is the kingfisher we know in England; and -the third is the magnificent white-breasted species--_Halcyon -smyrnensis_--a bright-blue bird with a reddish head and a white wing bar. -It is obvious that all three of these diversely plumaged species cannot -be protectively coloured. It may perhaps be objected that the piscatorial -methods of these kingfishers differ in detail. We admit that this is the -case, but would maintain, at the same time, that these comparatively -slight differences in habit do not account for the very striking -differences in plumage. We may also cite the yellow and pied wagtails of -our own country, which may be seen feeding in the same meadows. Most -familiar and striking of all is the everyday sight of a blackbird and -thrush plying their respective avocations within a few yards of each -other on the same lawn, differently coloured though they be. - -Another weighty objection to the generally accepted theory of protective -colouration is that some of the creatures which assimilate most closely -to their environment are those which appear to be the least in need of -such protection. - - - Precis Artexia - -The butterfly _Precis artexia_, writes F. C. Selous, "is only found in -shady forests, is seldom seen flying until disturbed, and always sits on -the ground amongst dead leaves. Though handsomely coloured on the upper -side, when its wings are closed it closely resembles a dead leaf. It has -a little tail on the lower wing, which looks exactly like the stalk of a -leaf, and from this tail a dark-brown line runs through both wings (which -on the under side are light brown) to the apex of the upper wing. One -would naturally be inclined to look upon this wonderful resemblance to a -dead leaf in a butterfly sitting with closed wings on the ground amongst -real dead leaves as a remarkable instance of protective form and -colouration. And of course it may be that this is the correct -explanation. But what enemy is this butterfly protected against? Upon -hundreds of different occasions I have ridden and walked through forests -where _Precis artexia_ was numerous, and I have caught and preserved many -specimens of these butterflies, but never once did I see a bird -attempting to catch one of them. Indeed, birds of all kinds were scarce -in the forests where these insects were to be found." - -Similarly D. Dewar writes (_Albany Review_, 1907): "If a naturalist be -asked to cite a perfect example of protective colouring, he will, as -likely as not, name the sand grouse (_Pteroclurus exustus_). This species -dwells in open, dry, sandy country, and its dull brownish-buff plumage, -with its soft dark bars, assimilates so closely to the sandy environment -as to make the bird, when at rest, practically invisible, at any rate to -the human eye. Unfortunately for the theory, this bird stands less in -need of protective colouration than any other, for it has wonderful -powers of flight. Even a trained falcon is unable to catch it, because it -can fly upwards in a straight line as though it were ascending an -inclined plane, with the result that the pursuing hawk is never able to -get above it to strike." - - - Striped Caterpillars - -Lord Avebury, who is a typical Wallaceian, points out the connection that -exists between longitudinal stripes on caterpillars and the habit of -feeding either on grass or low-growing plants among grass. The inference, -of course, is that birds mistake these caterpillars for leaves, or, at -any rate, fail to observe them when feeding, not only because they are -green in colour, but because their longitudinal stripes look like the -parallel veins on the blades of grass. But the butterflies of the family -_Satyridae_, as Beddard points out, _all_ possess striped larvae, and these -feed chiefly by night, when neither their colouring nor marking is -visible, while during the day many of them lie up under stones; other -caterpillars of this family feed inside the stems of plants. "Now," -writes Beddard (_Animal Colouration_, p. 101), "in these cases the colour -obviously does not matter: if, therefore, the longitudinal striping is -kept up by constant selection on account of its utility, and has no other -signification, we might expect that in these two species (_Hipparchia -semele_ and _Oenis_), and in others with similar habits, the cessation of -natural selection would have permitted the high standard required in the -other cases to be lowered--perhaps, even, as has been suggested in the -case of cave animals, the colours being useless to their possessors, -might have disappeared altogether--but they have not." - -Many exceedingly conspicuous birds--as, for example all the crow-tribe, -the egrets, the kingfishers--flourish in spite of their showy plumage. -Such creatures, while scarcely constituting a valid objection to the -theory of protective colouration, serve to show that protective colouring -is not a necessity. An animal otherwise able to take care of itself can -afford to dispense with cryptic colouration. "An ounce of good solid -pugnacity is a more effective weapon in the struggle for existence than -many pounds of protective colouration." - -There used to live in the gardens of the Zoological Society of London a -black cat belonging to the manager of one of the restaurants. This animal -used to catch birds on the lawn. We believe that not even Mr Thayer will -maintain that a black cat is cryptically coloured when stalking on a -well-watered lawn! Nevertheless the nigritude of that cat did not prevent -it securing a meal. - - - Colours of Eggs - -The case of birds' eggs furnish an excellent example of the lengths to -which Wallace and his followers have pushed the theory of protective -colouration. - -D. Dewar maintains that it is possible to divide birds' eggs that are -coloured, as opposed to those that are white, into two classes--those -which are protectively coloured and those which are not. The former class -includes all those which are laid in shingle or on the bare ground, as, -for example, the eggs of the ring-plover and the lap-wing.[8] He -maintains that the variously coloured and speckled eggs that are laid in -cup-shaped nests are not protectively coloured at all; he declares that -they are usually very conspicuous when in the nest, and, moreover, it -would be futile for them to be cryptically coloured, for a bird or lizard -that habitually sucks eggs will examine carefully the interior of each -nest it discovers. - -Needless to say, this view does not appeal to the so-called -Neo-Darwinians. Wallace writes, on page 215 of _Darwinism_: "The -beautiful blue or greenish eggs of the hedge-sparrow, the song-thrush, -the blackbird, and the lesser redpole seem at first sight especially -calculated to attract attention, but it is very doubtful whether they are -really so conspicuous when seen at a little distance among their usual -surroundings. For the nests of these birds are either in evergreen, or -holly, or ivy, or surrounded by the delicate green tints of early spring -vegetation, and may thus harmonise very well with the colours around -them. The great majority of the eggs of our smaller birds are so spotted -or streaked with brown or black on variously tinted grounds that, when -lying in the shadow of the nest and surrounded by the many colours and -tints of bark and moss, of purple buds and tender green or yellow -foliage, with all the complex glittering lights and mottled shades -produced among these by the spring sunshine and sparkling rain-drops, -they must have quite a different aspect from that which they possess when -we observe them torn from their natural surroundings." - -The obvious comment on this is that it is very fine and poetic English, -but it is not science. It is futile to deny what should be obvious to -every field naturalist, namely, that the majority of eggs laid in open -nests are most conspicuous. - -D. Dewar thus summarises the main facts which show that eggs in nests (as -opposed to those laid on the bare ground) are not protectively -coloured:-- - -"1. Allied species of birds, even though their nesting habits are very -different, as a rule lay similarly coloured eggs. - -"2. Eggs laid in domed nests certainly do not need protective colouring, -yet many of these are coloured. - -"3. The same is true of many eggs laid in holes in trees or in buildings. - -"4. The protective resemblances of eggs which are laid in the open are -apparent to everyone, which certainly is not true of those deposited in -nests. - -"5. Many birds lay eggs which exhibit very great variations. - -"6. Some birds lay eggs of different types, and these sometimes differ -from one another so greatly that it is difficult to believe that they -could have been laid by the same species."[9] - -7. It not infrequently happens that one species lays in the disused nest -of another, and the eggs of the latter are often very different in -colouring from those of the former. - -We have up to the present considered the theory of general cryptic -colouration, which declares that the majority of creatures are so -coloured as to be inconspicuous. We have still to deal with the -hypothesis of special cryptic colouring. - -Certain animals look, when resting, very like an inanimate object, such -as a dead leaf or a twig. This resemblance is said to be the result of -natural selection, since it enables its possessors to escape destruction; -they are seen, but mistaken for something else. - -The classical examples of this kind of protective colouring are furnished -by the _Kallimas_ or leaf-butterflies, which display an extraordinary -resemblance to dead leaves. - -Other examples are the stick-insects and the lappet moth, which looks -like a bunch of dry leaves. It is needless to multiply instances. In -every work on animal colouration numbers of such cases are cited. - -We may grant that in some cases, at any rate, the resemblance is of value -to its possessor, in that it deceives predatory creatures. But it does -not follow from this that the likeness has originated through the action -of natural selection. In order that there can be selection there must be -varying degrees of a tolerable resemblance to select from. How did the -initial similarity arise? This is a matter upon which Wallaceians are -silent. As Poulton truly says, in discussing the degree of protection -afforded by such resemblances, we tacitly endow animals with senses -exactly similar to our own. Are we justified in so doing? Most certainly -not in the case of the invertebrate animals, especially as regards the -arthropods, of which the eyes are constructed very differently from those -of human beings. - -D. Dewar has often seen a toad shoot out its tongue and touch a lighted -cigarette end, apparently mistaking it for an insect. Similarly, he has -again and again induced a gecko lizard to chase and try to swallow a -piece of black cotton, one end of which was rolled up into a ball. It is -only necessary to take hold of the unrolled end of the cotton and place -the rolled-up end a few inches from the lizard, and gradually draw it -away in order to induce the lizard to attempt to seize it. - - - Eyesight of Birds - -It would therefore seem that all these elaborate "protective" devices are -unnecessary refinements if regarded as a protection against invertebrate, -reptilian, and amphibian foes. Birds, on the other hand, appear to have -exceedingly sharp eyesight, so that in order to deceive them the -resemblance requires to be very close. Indeed, as regards those birds -which systematically hunt for their prey among leaves and grass, it seems -doubtful whether the alleged "protective" resemblances of caterpillars to -twigs, etc., are sufficient to be of much use to them. Thus Beddard -writes (on page 91 of _Animal Colouration_): "Judging of birds by our own -standard--which is the way in which nearly all the problems relating to -colour have been approached--does it seem likely that we should fail to -see a caterpillar, perhaps as long or longer than the arm, of an -obviously different texture from the branches, and displaying in many -cases through its semi-transparent skin the pulsation of the heart, for -which we were particularly searching?" - -Now, birds certainly feed very largely on caterpillars, while they are -but rarely seen to eat butterflies. If, therefore, the aim and object of -these special resemblances is the protection of the species, we should -expect to see them in a nearly perfect state in caterpillars on which -birds feed very largely, and poorly developed in butterflies, which do -not appear to be greatly preyed upon by birds, but have to fear chiefly -the comparatively dull-eyed lizards and mammals, of which the latter hunt -mainly by scent. As a matter of fact, the most striking cases of -resemblance to inanimate objects are seen among butterflies, which seem -to stand least in need of them. - -We have already cited the case of the butterfly _Precis artexia_. Even -more marked does the unnecessary elaboration of the likeness seem to be -in the Kallima butterflies. - - - The Theory of Warning Colouration - -All biologists admit that there exist some organisms which are not -coloured so as to be inconspicuous. Indeed, the colouring of certain -species is such as to render them particularly conspicuous. Such species -are said to be warningly coloured. They are supposed to be inedible, or -to have powerful stings or other weapons of defence, or to resemble in -appearance organisms which are thus protected. In the first two cases -they are said to be warningly coloured, and in the last they are cited as -examples of protective mimicry. With the theory of mimicry we shall deal -shortly. We must first discuss the hypothesis of warning colouration. - -When animals are unpalatable, or when they possess a sting or -poison-fangs, it is, to use the words of Wallace, "important that they -should not be mistaken for defenceless or eatable species of the same -class or order, since in that case they might suffer injury, or even -death, before their enemies discovered the danger or the uselessness of -the attack. They require some signal or danger-flag which shall serve as -a warning to would-be enemies not to attack them, and they have usually -obtained this in the form of conspicuous or brilliant colouration, very -distinct from the protective tints of the defenceless animals allied to -them" (_Darwinism_, page 232). - - - Examples of Warning Colouration - -For examples of so-called warningly coloured animals, we may refer the -reader to Wallace's _Darwinism_, Poulton's _Essays on Evolution_, or -Beddard's _Animal Colouration_. An instance familiar to all is our -English ladybird. "Ladybirds," says Wallace, "are another uneatable -group, and their conspicuous and singularly spotted bodies serve to -distinguish them at a glance from all other beetles." - -In order to establish the theory of warning colouration, it is necessary -to prove that all, or the great majority of conspicuously-coloured -organisms, are either unpalatable or mimic unpalatable forms. If this be -so, we are able to understand that the possession of gaudy colouring may -be of advantage to the individual. But even if this be satisfactorily -proved, we must bear in mind that it does not necessarily follow that -these warning colours can be accounted for on the theory of natural -selection. For, in order to explain the existence of any organ by the -action of natural selection, we must be able to demonstrate the utility, -not only of the perfected organ, but of the organ at its very beginning, -and at each subsequent stage of development. This, as we shall show, is -precisely what the Neo-Darwinians are unable to do. We shall have no -difficulty in proving that it would be more advantageous even to a highly -nauseous creature to have remained inconspicuously coloured rather than -to have gradually become more and more conspicuous. - -In the first place, let us briefly examine the evidence on which rests -the assertion that all gaudily-coloured insects, etc., are unpalatable, -or possess stings, or mimic forms which are thus armed. - -In England wasps, bees, and ladybirds are familiar examples of -conspicuous insects. - -The banded black and yellow pattern of the common wasp and the humble bee -are regarded as advertisements or danger signals of the powerful sting. - -The red-coat with its black spots is similarly believed to be a warning -that the ladybird is not fit to be eaten. - -Caterpillars are usually coloured grey or brown, so as to be -inconspicuous; but numerous exceptions occur which are brightly coloured, -and of these individuals many have been experimentally proved to be -objectionable as food to most insect-eating animals, being either -protected by an unpleasant taste, or covered with hairs or spines. - -Familiar cases are those of the abundant and conspicuous black and yellow -mottled caterpillars of the European Buff-tip Moth (_Pygaera bucephala_), -which are much disliked by birds; and the gaily--coloured Vapourer Moth -caterpillar (_Orgyia antiqua_), with its conspicuous tufts of hair. -Readers will remember that a few years back these caterpillars were a -perfect plague in London, in spite of the abundance of sparrows, which -feed freely on smooth green and brown caterpillars. - -Oft-cited examples of warning colouration, are the three great groups of -mainly tropical butterflies--the _Heliconidae_ of America, the _Acraeidae_ -of Africa, and the _Danainae_ found all over the world. In all of these -the sexes are alike. They are, every one, strikingly coloured, displaying -patterns of black and red, chestnut, yellow, or white. In most -butterflies the lower surface of the wings is of a quiet hue, in order to -render the organism inconspicuous when at rest, but in these warningly -coloured groups the under surface of the wings is as gaudy as the upper -surface. Their flight is slow. They are tough, and exhale a -characteristic odour. - -Belt showed that, in Nicaragua, birds, dragonflies, and lizards seem to -avoid the Heliconine butterflies, as the wings of these last are not -found lying about in places where insectivorous creatures feed, whereas -wings of the edible forms are to be found. Moreover, a Capuchin monkey, -kept by Belt, always refused to eat Heliconine butterflies. - -Finn investigated the palatability of a number of Indian insects. He -found that most of the birds with which he experimented objected to the -Danaine butterflies; but they disliked still more intensely two -butterflies belonging to groups not universally protected--a swallowtail -(_Papilio aristolochiae_) and a white (_Delias eucharis_). - -Finn further experimented with the tree-shrew or Tupaia (_Tupaia -ellioti_), which feeds largely on insects. He found that this creature -refused most emphatically all these warningly-coloured butterflies. It -would under no circumstances eat the _Danainae_, whereas the birds would -do so if no more palatable insects were offered to them at the time. - -Colonel A. Alcock found that a tame Himalayan bear indignantly refused to -eat a locust (_Aularches militaris_) gaily coloured with black, red, and -yellow, and exhaling an unpleasant-smelling froth; but this bear readily -devoured ordinary brown or green species. - -Among cold-blooded vertebrates the common European salamander, with its -bright black and yellow markings, is a striking example of warning -colouration; its skin exudes, on pressure, a very poisonous secretion. - -Colonel A. Alcock has described a small siluroid sea-fish, brightly -banded with black and yellow, and armed with poison spines. - -A well-known Indian poisonous snake, the banded Krait (_Bungarus -coeruleus_), is conspicuously barred with wide bands of black and yellow; -and in South America there occur numerous species of coral snakes, in -which red is added to these conspicuous colours. - -The only known poisonous lizard--the Heloderm of Mexico--is conspicuously -blotched with black and salmon-colour. - -Among birds, no instances of warning colouration have been recorded, -though Professor Poulton has suggested that possibly the striking and -contrasted tints of many tropical species may be due to this cause. The -suggestion is an ingenious one, but is at present totally unsupported by -evidence. - -The skunks are often cited as an excellent example of warning colouration -among mammals. Skunks are most conspicuously arrayed in black and -white--the latter above, not below, as is usual--and have bushy tails, -which they carry erect. Although less powerful and ferocious than other -members of the weasel family, to which they belong, skunks are -notoriously protected by their abundant secretion of a very fetid liquid. - -For further examples of warning colouration we would refer the reader to -Beddard's illuminating book, entitled _Animal Colouration_. - -It should be noticed that in all the cases which we have cited the -colouration is not only conspicuous, but is found in both sexes, whereas -in many undefended animals the male may be just as strikingly coloured, -but the female is not. - -We may take it as proved that there is a very general relation between -gaudy colouring and inedibility, or rather unpalatability, among insects. -It may safely be said that any species of insect which lives, either as -an adult or as a larva, in the open will perish in the struggle for -existence if, being conspicuously coloured, it is neither inedible nor -armed with a weapon such as sting, nor provided with a thick cuticle, nor -resembles in appearance some creature which is protected. - - - Warning Colouring a Drawback - -But from this it is not legitimate to conclude, as Neo-Darwinians do, -that these brilliant colours have been slowly brought into being by -natural selection. - -Why should any creature, having by the "luck" of variation and heredity -acquired some quality--be it strength, pugnacity, sting, or unpleasant -taste--which renders it comparatively immune from persecution, proceed to -advertise the fact by assuming a gaudy or striking colour? It would -surely be better for such an organism to remain inconspicuous. By -becoming showy it is visible to every young bird who, not having yet -learned that the creature in question is unfit for food, seizes and -perhaps kills it. It is true that the young bird vows that never again -will it touch another such organism. But of what avail to the dying -example of warning colouration is the resolution of the young bird? -Moreover, the organism in question, by being conspicuous, also advertises -itself to those few enemies which will eat it. There are always, as -Professor Poulton justly remarks, animals which are enterprising enough -to take advantage of prey which has at least the advantage of being -easily seen and caught. - - - Conspicuous Animals Attacked - -It is possible to cite cases where animals, notwithstanding the fact that -they possess natural defences, become the prey of others in some -exceptional cases. - -The salamander can be eaten with comparative impunity by the toad, a -creature very likely to meet with it. - -The toad itself may be eaten; Finn saw the Indian toad (_Bufo -melanostictus_) eat another of its own kind. He further observed that the -Indian water-snake (_Tropidonotus piscator_) and the "Crow pheasant" -cuckoo (_Centropus sinensis_), in the free state, and the Indian Roller -(_Coracias indica_) and the Pied Hornbill (_Anthracoceros_), in -captivity, eat the warningly-coloured toad. On the other hand, a captive -Racket-tailed drongo rejected toads when offered to it. The common cuckoo -is well known to feed on hairy and "warningly-coloured" caterpillars. - -Finn has also seen the glossy cuckoo in Zanzibar devouring -black-and-yellow caterpillars. Moreover, in America crows are found to -select deliberately highly polished and strongly flavoured beetles. Yet -again, wasps are preyed upon by bee-eaters, and also eaten by our common -toad. In India, Finn found, by many experiments, that the common garden -lizard, or "bloodsucker" (_Calotes versicolor_), would eat, both in -captivity and in freedom, all "warningly-coloured" butterflies, not only -the _Danainae_, but even _Delias eucharis_ and the pre-eminently nauseous -_Papilio aristolochiae_. That this reptile is a great enemy to butterflies -is rendered probable by the frequent occurrence of specimens of these -insects with its semicircular bites in their wings. - -Further, Finn found that bulbuls, the commonest garden birds in India, -ate the _Danainae_ readily in captivity, even when other butterflies could -be had, which was not the case with most other birds. Bulbuls did, -however, usually refuse the _Delias_ and _Papilio_ mentioned above. - -The Skunk is preyed upon in America by the Eagle-owl (_Bubo virginianus_) -and the Puma. - -Thus, animals provided with natural defences are not immune from attack. - -Hence natural selection cannot have encouraged the survival of -individuals which displayed a conspicuous colour, for the sake of the -"warning." - -We must not forget that many creatures armed with powerful weapons -possess the unobtrusive drab, brown, or green colouration which is -associated with concealment from foes. - -There can be little doubt that, but for the fact that the hive-bee can -inflict a sting more severe than that of the wasp, this useful insect -would have been cited as a case of a protectively coloured creature. -Notwithstanding its sober brown colouring, the hive-bee is recognised and -avoided. - -Professor Poulton records that the dull inconspicuous caterpillar of the -moth (_Maenia typica_) is rejected by reptiles. It must be admitted, -however, that these cases among insects are very rare. - -The smooth newt (_Molge vulgaris_), a relation of the salamander, is -protected by a poisonous skin; nevertheless the creature has a dark brown -back and spends most of its time on land. Its black-spotted, yellow -under-surface may have some protective value in the water. Neither the -pike nor the common European water-tortoise will eat this newt. - -Toads are nearly all very inconspicuous; nevertheless they are well -protected by the acrid secretion from the skin glands; moreover, they are -both recognised and avoided by those predacious creatures to whom they -are distasteful. Hawks, although as a rule plainly coloured, are -certainly recognised by all other birds. It would seem, therefore, that -"warning colours," like the similar striking hues of many domestic -animals, are incidental attributes. It has been possible for their owners -to develop them, because for the most part let alone. - -Eisig, long ago, pointed out that the brightly coloured pigment in the -skin of these warningly coloured insects is in certain cases of an -excretory nature. Therefore the inference which should be drawn is, as -Beddard points out on page 173 of his _Animal Colouration, "that the -brilliant colours_ (i.e. _the abundant secretion of pigment_) _have -caused the inedibility of the species, rather than that the inedibility -has necessitated the production of bright colours as an advertisement_." -In other words, Neo-Darwinians put the cart before the horse! - -[Illustration: BOURU FRIAR-BIRD] - -[Illustration: BOURU ORIOLE] - -In some cases these brilliantly coloured insects may be survivals of an -age in which there were no birds. When these came into being and began to -prey upon insects, the conspicuously coloured species which were not -inedible or very unpalatable would soon become extinct, while those that -were inedible would survive as warningly-coloured insects. In other cases -it is not improbable that these warningly-coloured creatures have arisen -by mutations from more soberly-hued insects. It is conceivable that every -now and again a mutation occurs which renders its possessor conspicuous. -This will result in the early destruction of these aberrant individuals -unless their newly-acquired gaudiness is either correlated with, or the -result of, distastefulness. - - - Aposematic Sounds - -In the case of warning colouration, the Neo-Darwinians have, as usual, -pursued their theory to absurd lengths. Professor Poulton, for example, -extends it to sounds and attitudes. "Sound," he writes, on page 324 of -_Essays on Evolution_, "may be employed as an Aposematic character, as in -the hiss of some snakes and some lizards. Certain poisonous snakes when -disturbed produce by an entirely different method a far-reaching sound -not unlike the hiss. Thus the rattle-snake (_Crotalus_) of America -rapidly vibrates the series of dry, horny, cuticular cells, movably -articulated to each other and to the end of the tail. The stage through -which the character probably arose is witnessed in another genus which -vibrates its tail among dry leaves, and thus produces a warning sound. -The deadly little Indian snake (_Echis carinata_) ('the Kuppa') makes a -penetrating swishing sound by writhing the coils of its body one over the -other. Special rows of the lateral scales are provided with serrated -keels which cause the sound when they are rubbed against each other. -Large birds, when attacked, often adopt a threatening attitude, -accompanied by an intimidating sound which usually suggests more or less -closely the hiss of a serpent, and thus includes an element of mimicry. . -. . The cobra warns an intruder chiefly by attitude and by the broadening -of its flattened neck, the effect being heightened in some species by the -'spectacles.' In such cases we often witness a combination of cryptic and -Aposematic methods, the animal being concealed until disturbed, when it -instantly assumes a warning attitude. - -"The benefit of such intimidating attitudes is clear: a venomous snake -gains far more advantage by terrifying than by killing an animal it -cannot eat. By striking, the serpent temporarily loses its poison, and -with this a reserve of defence. Furthermore, the poison does not cause -immediate death, and the enemy would have time to injure or destroy the -snake." - - - Intimidating Attitudes - -At first sight this reasoning may seem very convincing. But consider for -a moment the process by which the hiss originated and gradually increased -by natural selection. We must suppose that the rattle-snake was formerly -incapable of making any sound. One day a variety appeared in which the -skin was slightly hardened, so that when the creature moved its body -rapidly there issued a slight sound. This must have caused an enemy to -refrain from attack; it thus lived to transmit this peculiarity to its -offspring, and those which made more noise than their ancestors escaped, -while those that made less succumbed to their enemies. For ourselves, we -find it quite impossible to believe that the rattle was thus gradually -evolved by means of natural selection. Indeed, we are inclined to think -that neither the hiss of the cobra nor its "intimidating attitude" has -any terrifying effect on its adversary. In the case of the cobra we are -able to cite positive evidence that dogs and cattle show no alarm at the -attitude. - -"Dogs," writes D. Dewar of this display, "regard it as a huge joke. Of -this I have satisfied myself again and again, for when out coursing at -Muttra we frequently came across cobras, which the dogs used invariably -to chase, and we sometimes had great difficulty in keeping the dogs off, -since they seemed to be unaware that the creature was venomous." - -Colonel Cunningham writes, on page 347 of _Some Indian Friends and -Acquaintances_: "Sporting dogs are very apt to come to grief where cobras -abound, as there is something very alluring to them in the sight of a -large snake when it sits up nodding and snarling; and it is often -difficult to come up in time to prevent the occurrence of irreparable -mischief." - -Colonel Cunningham also states that many ruminants have a great animosity -to snakes, and are prone to attack any that they may come across. - -We may therefore well be sceptical as to the value of intimidating -attitudes to those creatures which are in the habit of striking them. - - - Mimicry - -In a work of this kind it is neither possible nor necessary to consider -in great detail the mass of evidence which has been advanced in favour of -the theory of mimetic resemblance. - -Chapters vii. and viii. of Professor Poulton's _Essays on Evolution_ -contain an up-to-date statement of the facts in favour of the theory. -Professor Poulton believes that in all cases mimetic resemblance is the -result of the action of natural selection. - -He admits that there is no direct evidence in its favour, but asserts -that "the facts of the cosmos, so far as we know them, are consistent -with the theory, and none of them inconsistent with it" (page 271). - - - Theory of Protective Mimicry - -We are not at all sure that no facts are against the theory of protective -mimicry. We shall presently set forth some which to us seem, if not -actually inconsistent with the theory, at least to point to the -conclusion that the phenomenon may be explained otherwise than as a -product of natural selection. - - - Evidence for the Theory - -Let us first briefly state the case for the theory of protective mimicry. - -1. It is asserted that the mimicking species and that which is mimicked -are often not nearly related. For example, the unpalatable larva of the -Cinnabar Moth (_Euchelia jacobaeae_) is said to mimic a wasp, because it -has black and yellow rings round its body. - -"The conclusion which emerges most clearly," writes Poulton (p. 232), "is -the entire independence of zoological affinity exhibited by these -resemblances." This is supposed to be proof that Darwin was wrong when he -asserted that the original likeness was due to affinity. Says Poulton: -"The preservation of an original likeness due to affinity undoubtedly -explains certain cases of mimicry, but we cannot appeal to this principle -in the most remarkable instances." - -2. It is asserted that species which are mimicked are invariably either -armed with a sting, well defended, or unpalatable, so that it is against -the interest of insectivorous creatures to attack them. It is further -asserted that the species imitated are "even more unpalatable than the -generality of their order." - -3. It is pointed out that the most distasteful groups of butterflies--the -_Danaidae_, the _Acraeinae_, the _Ithomiinae_, and the _Heliconinae_--consist -of large numbers of species which closely resemble one another. This is -said to be due to Muellerian mimicry. Mayer states that in South America -there are 450 species of inedible _Ithomiinae_ which display only 15 -distinct colours, while the 200 species of _Papilio_, which are edible, -exhibit 36 distinct colours. Nevertheless, he says, there is no lack of -individual variability among the former hence their conservatism as -regards colour cannot be attributed to their having but little tendency -to vary. - -4. It is asserted that although in many cases the mimetic resemblances -extend to the minutest detail, nevertheless they are not accompanied by -any changes in the mimetic species except such as assist in the -production or strengthening of a superficial likeness. - -Pictures illustrating such cases of mimicry are figured on pp. 241, 247, -and 251 of Wallace's _Darwinism_ (1890 edition). - -5. It is stated that mimetic resemblance is not confined to colour, but -extends to pattern, form, attitude, and movement; that deep-seated organs -are affected when the superficial resemblance is intensified, but not -otherwise. Poulton cites _Clytus arietis_, the "wasp-beetle," as an -example of this. - -6. It is asserted that mimetic resemblances are produced in the most -diverse ways; that the modes whereby the similarity in appearance is -brought about are varied, but the result is uniform. - -"A lepidopterous insect," writes Poulton (p. 251), "requires above all to -gain transparent wings, and this, in the most striking cases that have -been studied, is produced by the loose attachment of the scales, so that -they easily and rapidly fall off and leave the wing bare except for a -marginal line and along the veins (_Hemaris_, _Trochilium_)." - -7. It is alleged that the imitator and imitated are always found in the -same locality. If they did not do so no advantage would be derived from -the resemblance. It is further alleged that where the mimicking species -is edible it is invariably less abundant where it occurs than the species -it imitates. - -8. It is pointed out that it sometimes happens that where in the mimic -the sexes differ in appearance, the male copies one species, the female -quite a different one. This is said to be because the deception would be -liable to be detected if the mimicking species became common relatively -to that which is imitated. "We therefore find that two or more models are -mimicked by the same species" (_Essays on Evolution_, p. 372). - -Occasionally the female mimics two other species, _i.e._ she occurs in -two forms, each like a different species. - -It sometimes happens that the female alone mimics. This is said by -Wallace to be due to her greater need of protection. When she is laden -with eggs her flight is slow, and therefore she requires a special degree -of protection. - -9. It is said that in some species we find a non-mimetic ancestor -preserved on islands where the struggle for existence is less severe, -while on the adjacent continent mimicry has been developed. - -10. It is alleged that in the cases where moths resemble butterflies the -former are either as diurnal as the butterflies or are species which -"readily fly by day when disturbed." - -11. It is asserted that some seasonally dimorphic forms are examples of -mimicry only in one state, in the form that comes into being at the time -when the struggle for existence is most severe; that is to say, in the -dry season, in Africa, when insect life is far less abundant than in the -rainy season. - -In other cases the mimicry of the dry-weather form is said to be far more -perfect. - -Instances of this phenomenon are set forth in Professor Poulton's _Essays -on Evolution_. - - - Alternative Theories - -It will be observed that we have quoted very largely from Professor -Poulton's work. Our reason for so doing is that he appears to be the most -prominent advocate of the theory of protective mimicry, and his work, -which was published in 1908, may be taken as the latest Neo-Darwinian -pronouncement on the subject. - -Hence if we can show, as we believe we can, that his arguments are not -sound, we may take it that we have demonstrated that the theory in its -present form is untenable. - -It is worthy of notice that Professor Poulton sets forth three other -suggestions which have been proposed as substitutes for natural selection -as an explanation of the phenomena of mimicry. - -The first is the theory of External Causes, namely, that the resemblance -is due to some external cause, such as food or climate. - -The second is the theory of Internal Causes, which states that mimetic -resemblance is due to internal developmental causes. - -The third is the suggestion that sexual selection has caused the origin -of these resemblances. - -He then proceeds to demolish these to his own satisfaction, and adds -triumphantly, "The conclusion appears inevitable that under no theory, -except natural selection, do the various resemblances of animals to their -organic and inorganic environments fall together into a natural -arrangement and receive a common explanation" (p. 228). - -To reasoning of this description there is an obvious reply. Even if it be -granted that the alternatives to the theory of natural selection as set -forth by Professor Poulton are untenable, it does not follow that natural -selection affords an adequate explanation. If A, B, C and D are charged -with theft and the prosecutor proves that neither A nor B nor C committed -the theft, this will not suffice to secure the conviction of D. It is -quite possible that a fifth person, E, may be the culprit. - -Much of the popularity of the theory of natural selection is due to the -fact that biologists have not yet been able to discover a substitute for -it. - -It seems to us that the proper method of making progress in science is -not to bolster up natural selection by ingenious speculations, but to -look around for other hitherto undiscovered causes. - -[Illustration: KING-CROW OR DRONGO] - -[Illustration: DRONGO-CUCKOO] - - - Objections to the Theory that the so-called Cases of Mimicry owe their - Origin to Natural Selection - -It is obvious that for one creature to resemble another can be of little -or no benefit to either until the resemblance is tolerably close. It is, -therefore, insufficient to prove the utility of the perfected -resemblance. We may readily grant this and yet maintain that the origin -of the resemblance cannot be due to the action of natural selection. - -The Drongo-cuckoo (_Surniculus lugubris_) displays so great a likeness to -the King Crow (_Dicrurus ater_) that it is frequently held up by -Neo-Darwinians as an excellent example of mimicry among birds. But D. -Dewar writes, on page 204 of _Birds of the Plains_: "I do not pretend to -know the colour of the last common ancestor of all the cuckoos, but I do -not believe that the colour was black. What then caused _Surniculus -lugubris_ to become black and assume a king-crow-like tail? - -"A black feather or two, even if coupled with some lengthening of the -tail, would in no way assist the cuckoo in placing its egg in the -drongo's nest. Suppose an ass were to borrow the caudal appendage of the -king of the forest, pin it on behind him, and then advance among his -fellows with loud brays, would any donkey of average intelligence be -misled by the feeble attempt at disguise? I think not. Much less would a -king-crow be deceived by a few black feathers in the plumage of a cuckoo. -I do not believe that natural selection has any direct connection with -the nigritude of the drongo-cuckoo." - -Darwin was fully alive to this difficulty when he wrote: "As some writers -have felt much difficulty in understanding how the first step in the -process of mimicry could have been effected through natural selection, it -may be well to remark that the process probably commenced long ago -between forms not widely dissimilar in colour" (_Descent of Man_, 10th -Ed., p. 324). Such a statement is of course quite inconsistent with the -Neo-Darwinian position. "The conclusion which emerges most clearly," -writes Poulton (_Essays on Evolution_, p. 232), "is the entire -independence of zoological affinity exhibited by these resemblances; and -one of the rare cases in which Darwin's insight into a biological problem -did not lead him right was when he suggested that a former closer -relationship may help us to a general understanding of the origin of -mimicry. The preservation of an original likeness due to affinity -undoubtedly explains certain cases of mimicry, but we cannot appeal to -this principle in the most remarkable instances." - -It is unnecessary to labour this point. It is surely evident to everyone -with average intelligence that, until the resemblance between two forms -has advanced a considerable way, the likeness cannot be of utility to -either, or at any rate of sufficient utility to give its possessor a -survival advantage in the struggle for existence. Until it reaches this -stage, natural selection cannot operate on it. It is therefore absurd to -look upon natural selection as the direct cause of the origin of the -likeness. When once a certain degree of resemblance has risen, it is -quite likely that in some cases natural selection has strengthened the -likeness. - -The second great objection to the Neo-Darwinian explanation of the -phenomenon known as mimicry is that in many cases the resemblance is -unnecessarily exact. Even as we saw how the Kallimas, or dead-leaf -butterflies, carried their resemblance to dead leaves to such an extent -as to make it appear probable that factors other than natural selection -have had a share in its production, so do we see in certain cases of -mimetic resemblance an unnecessarily faithful likeness. - - - The Brain-fever Bird - -The common Hawk Cuckoo of India (_Hierococcyx varius_) furnishes an -example of this: "The brain-fever bird," writes Finn, on page 58 of -_Ornithological and Other Oddities_, "is the most wonderful feather copy -of the Indian Sparrow-hawk or Shikra (_Astur badius_). All the markings -in the hawk are reproduced in the cuckoo, which is also of about the same -size, and of similar proportions in the matter of tail and wing; and both -hawk and cuckoo having a first plumage quite different from the one they -assume when adult, the resemblance extends to that too. Moreover, their -flight is so much the same that unless one is near enough to see the -beak, or can watch the bird settle and note the difference between the -horizontal pose of the cuckoo and the erect bearing of the hawk, it is -impossible to tell them apart on a casual view." Moreover, the tail of -the cuckoo sometimes hangs down vertically, thus intensifying the -likeness to the hawk. - -It is quite possible that the brain-fever bird derives some benefit from -the resemblance; indeed, it has been seen to alarm small birds, even as -the hawk-like common cuckoo frightens its dupes, but, as D. Dewar pointed -out, on page 105 of vol. 57 of the _Journal of the Society of Arts_, -"this is not sufficient to explain a likeness which is so faithful as to -extend to the marking of each individual feather. When a babbler espies a -hawk-like bird, it does not wait to inspect each feather before fleeing -in terror; hence all that is necessary to the cuckoo is that it should -bear a general resemblance to the shikra. The fact that the likeness -extends to minute details in feather marking, points to the fact that in -each case identical causes have operated to produce this type of -plumage." This conclusion is still further strengthened by the fact that -the likeness extends to the immature plumage, that is to say, exists at a -time when it cannot assist the cuckoo in its parasitical work. - -Poulton meets this objection as follows: - -[Illustration: SHIKRA HAWK] - -[Illustration: HAWK-CUCKOO] - - - Hypertely - -"All such criticism is founded on our imperfect knowledge of the struggle -for existence. The impressions and judgments of man are immensely -influenced by the 'corroborative detail,' giving 'artistic verisimilitude -to a bold and unconvincing narrative.' Indeed, the laughter which is -invariably raised by this passage from _The Mikado_ is, I have always -thought, not only or chiefly due to the humour of the application, but to -the way in which a great and familiar truth breaks in upon the listener -with all the pleasing surprise which belongs to epigram. Birds, the chief -enemies of insects, are known to have powers of sight far superior to -those of man, and, from our experience of them in captivity, it may be -safely asserted that their attention is attracted by excessively minute -detail. Until our knowledge of the struggle for life is far more -extensive than at present, the argument founded on Hypertely may be left -to contend with another argument often employed against the explanation -of cryptic and mimetic resemblance by natural selection. Hypertely -assumes that there are unnecessary details in the resemblance, that the -resemblance is perfect beyond the requirements of the insect; the second -argument maintains that birds are so supremely sharp-sighted that no -resemblance, however perfect, is of any avail against them. In the -meantime the majority of naturalists will probably reject both extremes, -and believe that the enemies are certainly sharp-sighted and successful -in pursuit, but that perfection in detail makes their task a harder one, -and gives to the individuals possessing it in a higher degree than -others, increased chances of escape, and of becoming the parents of -future generations." (_Essays on Evolution_, p. 302.) - -This long quotation requires careful consideration, since to us it -appears to be typical of the kind of reasoning resorted to by -Neo-Darwinians. - -Note the reference to our "imperfect knowledge of the struggle for -existence." This is almost invariably the last refuge of the -Neo-Darwinian when worsted in argument. We fully admit that there is -still much to be learned of the nature of the struggle for existence, but -such a statement sounds very curious when uttered to those who pin their -faith to the theory which sees in the principle of natural selection an -explanation of all the phenomena of the organic world. Natural selection, -be it remembered, is but a name for the struggle for existence. - - - Birds capturing Butterflies - -"Birds," says Professor Poulton, "are the chief enemies of insects." This -may be so. But we greatly doubt whether they are the chief enemies of -butterflies and moths, among which the most perfect examples of mimicry -are supposed to occur. - -We have watched birds closely for some years, but believe that we could -almost count on our fingers the cases in which we have seen a bird chase -a butterfly. - -Professor Poulton, being aware of this objection, sets forth, on pp. -283-292 of _Essays on Evolution_, the evidence he has gathered in favour -of the view that birds are the chief enemies of butterflies and other -lepidoptera. - -As the result of five years' observation in S. Africa, Mr G. A. K. -Marshall was able to record some eight cases of birds capturing -butterflies. In three cases the butterfly seized was warningly coloured, -or, at any rate, conspicuous! In two of these eight cases the bird failed -to capture its quarry! - -Says Mr Marshall, "the fact that birds refrain from pursuing butterflies -may be due rather to the difficulty in catching them than to any -widespread distastefulness on the part of these insects." - -During six years' observation in India and Ceylon, Colonel Yerbury -records some half dozen cases of birds capturing, or attempting to -capture, insects. He writes: "In my opinion an all-sufficient reason for -the rarity of the occurrence exists in the fact that in butterflies the -edible matter is a minimum, while the inedible wings, etc., are a -maximum." - -Colonel C. T. Bingham in Burma states that between 1878 and 1891 he on -two occasions witnessed the systematic hawking of butterflies by birds, -although he observed on other occasions some isolated cases. - -This appears to be the sum total of the evidence adduced by Professor -Poulton as regards the capture of butterflies by birds. This seems to us -an altogether insufficient foundation upon which to build the theory that -the cases of resemblance between unrelated species have been effected by -natural selection. - -It is, however, to be noted that probably among birds the most dangerous -enemies of butterflies are not those that habitually catch insect prey on -the wing. Such are experts in the art of fly-catching, and would despise -the comparatively meatless butterfly. One often comes across butterflies -with an identical notch in each wing, which leaves little room for doubt -that those particular butterflies had been snapped at, _while resting_, -by a bird. Among birds the chief enemies of butterflies and moths are -probably to be found in those that hunt for their food in bushes and -trees. - -Thus, what we do know of the nature of the struggle for existence offers -but poor support to the Neo-Darwinian explanations of the cases of -so-called mimicry in nature. - - - Observing-powers of Birds - -Professor Poulton's idea of pitting the argument of Hypertely against -that of the alleged supreme sharp-sightedness of birds is ingenious, but -is not likely to satisfy very many people save those content to live in a -fools' paradise. If birds are supremely sharp-sighted, and pay attention -to excessively minute detail, the difficulty of accounting for the -_origin_ of protective mimicry on the natural selection hypothesis -becomes all the greater. - -The question whether or not birds are good observers is a most -interesting one. Unfortunately, hitherto, but little attention has been -paid to the subject. The evidence available seems to point to the fact -that birds, like savages, have sharp eyes only for certain objects--that -is to say, for the things they are accustomed to look out for. All -observers of nature must have noticed how quick a butcher-bird is to -catch sight of a tiny insect upon the ground at a distance of some yards -from his perch. - -On the other hand, it is said that when there is snow upon the ground -wood pigeons will approach quite close to a man wearing white clothes and -a white hat, provided he keep perfectly still. Finn once witnessed in -Calcutta a sparrow pick up a very young toad, obviously by mistake, for -it dropped it at once with evident distaste. Birds of prey are supposed -to have remarkably good eyesight; yet they can readily be caught by a net -stretched out before their quarry. They are not trained to be on the -watch for such things as nets, and so do not appear to notice one when -erected. - -It is thus our belief that the very perfection and detail of some -so-called mimetic resemblances are a very serious objection to the theory -of protective mimicry as enunciated by Professor Poulton and other -Neo-Darwinians. - -There is yet a further objection to this theory, one which, in our -opinion, is fatal to the hypothesis in its generally accepted form. - -A number of cases occur where two species, in no way related, show close -resemblance to one another under such circumstances that neither can -possibly derive any benefit from the likeness. The theory of protective -mimicry is quite unable to explain these cases. This fact leads to a -suspicion that, in the instances where the theory does at first sight -appear to offer an explanation, the resemblance may also be due to mere -coincidence. - -We may perhaps call the cases which the theory of mimicry is unable to -account for "false mimicry," but in so doing we must bear in mind the -possibility that some, at any rate, of the examples of so-called mimicry -may, on further investigation, prove to be nothing of the kind. - - - "False" Mimicry among Mammals - -The Cacomistle of Mexico (_Bassaris astuta_), one of the raccoon family, -has a grey body and long black-and-white ringed tail, just like the -ring-tailed Lemur of Madagascar (_Lemur catta_); both are arboreal and -about the same size, and this lemur's colouration is exceptional in its -family. - -The banded Duiker-buck of West Africa (_Cephalophus doriae_), has the -same very unusual colouration as the thylacine or marsupial wolf of -Tasmania, light brown, with bold black bands across the hinder part of -the back, and the animals are about the same size. - -The dormouse of Europe closely resembles a small American Opossum -(_Didelphys murina_), and a larger opossum (_D. crassicaudata_) is very -like the Siberian Mink (_Mustela sibirica_). - -The Flying Squirrel of North America (_Sciuropterus volucella_) is -closely copied by the Flying Phalanger (_Petaurus breviceps_) of -Australia. - -It will be readily seen that in no one of these cases can the likeness be -of utility to either the "model" or the "copy." - - - False Batesian Mimicry among Birds - -There are many instances of this phenomenon among birds. The New Zealand -Cuckoo (_Urodynamis tritensis_) shows a far closer resemblance to the -American Sparrow-hawk (_Accipiter cooperi_) than to any New Zealand hawk, -and in fact closely mimics this quite alien bird. - -The stormy petrel, a purely oceanic bird, closely resembles in size, -colour, and style of flight the Indian Swift (_Cypselus affinis_), a -purely inland creature; both are sooty black, with a conspicuous white -patch on the lower back. - -The Pied Babbling Thrush (_Crateropus bicolor_) of Africa is singularly -like the Pied Myna (_Graeulipica melanoptera_) of Java, both being of -about the same size, with white body and black wings and tail quills. -This, we may add, is a very unusual colouration among small birds. - -The black-headed Oriole (_Oriolus melanocephalus_) of India is very -similar in appearance to the common Troupial (_Icterus vulgaris_) of -Brazil; indeed, the troupials, a purely American group, are so like the -old world orioles in colour that they usurp their name in America. - -The little insectivorous Iora (_AEgithina tiphia_) of India strongly -resembles in size and colour a Siskin (_Chrysomitris colambiana_) from -South America, the males in both being black above and yellow below, -while in the females the black is replaced by olive-green. - -Another Indian babbler (_Cephalopyrus flammiceps_), yellowish-green, with -orange forehead, is closely copied by, or copies, the well-known -Brazilian Saffron-finch (_Sycalis flaveola_). - -In Fergusson Island, near New Guinea, there is a ground pigeon -(_Otidiphaps insularis_) which is black with chestnut wings, like several -of the powerful ground cuckoos of the genus _Centropus_, but no species -of these cuckoos so coloured appears to inhabit the island. - -In Africa there is a tit (_Parus leucopterus_) which has the same very -unusual colouration as an East-Indian bulbul (_Micropus melanoleucus_), -both being black with a white patch on the wing-coverts. These two birds -are about the same size. As showing the purely coincidental character of -such resemblances, we may mention that this same rare pattern occurs -again in our Black Guillemot (_Uria grylle_) and in the Muscovy Duck -(_Cairina moschata_). - - -We have already quoted Gadow (p. 198) on "false mimicry" among snakes. He -also gives, on p. 110 of _Through Southern Mexico_, an example of this -phenomenon among amphibia. It is, he writes, "impossible to distinguish -certain green tree-frogs of the African genus _Rappia_ from a _Hyla_, -unless we cut them open. If they lived side by side, which they do not, -this close resemblance would be extolled as an example of mimicry." - -We should be very greatly surprised if abundant examples of "false -mimicry" are not found among insects. We trust that this remark will -stimulate some entomologist to pay attention to the subject. - -It is the essence of Muellerian mimicry that both model and copy are -immune from attack from enemies. Unfortunately for the theory, similar -resemblances occur among birds of prey, where neither party can benefit -from the association. This gives rise to what we may perhaps call false -Muellerian mimicry. Thus the goshawk and peregrine falcon resemble each -other in being brown above and streaked below in immature plumage, and -having barred underparts and a grey upper plumage when adult. - - - Theory of Mimicry Criticised - -Having stated the more important objections to the theory of protective -mimicry, it now remains for us to deal specifically with each head of -evidence offered in its favour. - -1. With regard to the assertion that the model and its copy are often not -nearly related, we have shown that among mammals and birds instances of -resemblance between widely-separated groups occur under such -circumstances that neither party can derive any benefit therefrom. - -2. As regards the assertion that species which are mimicked are either -well-defended or unpalatable, this certainly does not hold good with -regard to some at any rate of the coincidental resemblances among birds -which we have pointed out; even if these pairs of similar species lived -in the same country it would require considerable ingenuity to say why -one should mimic the other. - -3. As regards the argument that the inedible species of _Ithomiinae_, -etc., display only fifteen colours, while the less numerous edible -_Papilios_ display more than double this number of colours, we may draw -attention to the fact that those birds which are most immune from attack -are precisely those which display the smallest range as regards colour, -e.g., hawks, owls, crows, gulls, storks, and cranes. As we have already -submitted, no question of Muellerian association comes in here. - -On the other hand, the eminently edible families of game-birds and ducks -display great variety of colour, in the males at all events. - -4. As regards the statement that although in many cases the mimetic -resemblances extend to the minutest detail, they are not accompanied by -any structural changes except such as assist in the production of a -superficial likeness, we may refer to the case we have already cited of -the New Zealand cuckoo, which, though it so closely copies an American -hawk, is typically cuculine in structure. Here, of course, there can be -no question of advantage to the "mimicking" cuckoo in the resemblances. - -5. In answer to the argument that mimetic resemblance extends to form, -attitude, and movement, as well as colour, and that deep-seated organs -are affected only when the superficial resemblance is thereby -intensified, we may draw attention to such cases as the following:-- - -(_a_) The harmless Indian Snake (_Lycodon aulicus_) is closely similar to -the well-known Krait (_Bungarus coeruleus_), also Indian; but the -resemblance extends to a structural detail which can hardly have mimetic -value--namely, the harmless snake has long, fang-like front teeth, though -these are unconnected with poison-glands. Animals which come into contact -with the krait and its mimic are hardly likely to inspect their teeth. - -(_b_) A considerable number of birds of the shrike group--known as -Cuckoo-Shrikes (_Campophaga_)--closely resemble cuckoos in plumage; but -even if they derive any benefit from mimicking birds which are credited -with being mimics already, they cannot profit by the fact that the shafts -of the rump-feathers in both groups are stiffened; this being a -peculiarity which would not be perceptible until the bird was in the -grasp of an aggressor. - -(_c_) As a third case of coincidence we may refer to the tubercle in the -nostril of the Brain-fever-bird (_Hierococcyx varius_), as a minute -detail of hawk-like appearance, though not present in the particular -species imitated. - -6. The argument that mimetic resemblances are produced in the most -diverse ways, but the result is uniform, loses much of its force when we -consider the various methods by which short-tailed birds appear to have -long caudal appendages. - -In the peacock it is the upper tail coverts which are elongated; in the -Stanley Crane (_Tetrapteryx paradisea_) it is the innermost or tertiary -quills of wing; in one of the egrets some of the feathers of the upper -back grow to a great length and form a train; in the Bird of Paradise -(_Paradisea apoda_) the long flank plumes are commonly mistaken for the -tail. - -In these cases there can be no question of mimicry. - -7. We have shown that the idea that imitator and imitated are always -found in the same area is absolutely fallacious. In birds, for example, -the most striking resemblances appear to occur between species that dwell -far apart. - -8. We can cite, as parallel to the case of a mimicking species of which -the male copies one model and the female another, the strange similarity -between the barred brown plumage of the female blackcock and that of the -female eider-duck. The males of these species, although both black and -white, differ greatly in appearance; but the male blackcock is admittedly -very like the male of another species of sea-duck--the scoter. - -9. Against the supposed ancestral non-mimetic forms existing on islands -we can pit the "mimetic" orioles in small islands and their non-mimetic -cousins on the mainland. In Australia an oriole of what appears to be an -ancestral style lives beside, but declines to mimic, a friar bird of a -very pronounced type. - -10. The case of certain diurnal moths mimicking butterflies appears to be -explicable without the aid of the theory of protective mimicry. When two -species adopt the same method of obtaining food, it not infrequently -happens that a professional likeness springs up between them. Of this the -swifts and swallows afford a striking illustration. - -11. As a set-off to the cases where the alleged mimicry is confined to -certain seasons of the year, we may cite the case of the pheasant-tailed -Jacana (_Hydrophasianus chirurgus_), which in its winter plumage might -easily be mistaken, when on the wing, for the paddy bird or Pond Heron -(_Ardeola grayii_), both being of like size and having a brown back, long -green legs, and white wings. Moreover, they are to be found in the same -localities in India. At the breeding season, however, they are absolutely -different in plumage. - -Yet another argument commonly adduced in favour of the theory of -protective mimicry is that local variations of the imitated species are -sometimes followed by the imitator; thus the butterfly _Danais -chrysippus_ shows a white patch on the hind wings in Africa, and this is -followed by its mimic. - -But the same thing occurs, quite irrationally, so to speak, among birds. -The peregrine falcon and hobby of Europe are only winter migrants to -India, where they are replaced as residents by the Shaheen (_Falco -peregrinator_) and Indian Hobby (_F. severus_). Both these differ from -the migratory forms by being blacker above and chestnut below, instead of -cream colour. Thus the resemblance occurs in each race. A similar -distinction, as noted by Blyth, exists between the Common Swallow -(_Hirundo rustica_) and the Swallow (_H. tytleri_) of Eastern Asia, the -latter having the whole ventral surface rufous instead of only the -throat. Yet no one will suggest that swallows mimic falcons, or that -there is mimicry between the peregrine and hobby. It is obvious that such -parallel changes occur independently of mimicry. - -The Water-rail (_Rallus aquaticus_) and Baillon's Crake (_Porzana -bailloni_) of Europe are distinguished from their allies of Eastern Asia -by having the sides of the head plain grey, whereas the Eastern Asiatic -forms (_R. indicus_ and _P. pusilla_) have a brown streak along each side -of the face. Here, again, we have an instance of birds of the same family -varying together with geographical distribution. - - - "Recognition" Colours - -One of the prettiest conceits of the Wallaceian school of zoologists is -the theory of recognition markings. - -"If," writes Wallace, on page 217 of _Darwinism_, "we consider the habits -and life-histories of those animals which are more or less gregarious, -comprising a large proportion of the herbivora, some carnivora, and a -considerable number of all orders of birds, we shall see that a means of -ready recognition of its own kind, at a distance or during rapid motion, -in the dusk of twilight or in partial cover, must be of the greatest -advantage and often lead to the preservation of life. Animals of this -kind will not usually receive a stranger in their midst. While they keep -together they are generally safe from attack, but a solitary straggler -becomes an easy prey to the enemy; it is therefore of the highest -importance that, in such a case, the wanderer should have every facility -for discovering its companions with certainty at any distance within the -range of vision. - -"Some means of easy recognition must be of vital importance to the young -and inexperienced of each flock, and it also enables the sexes to -recognise their kind and thus avoid the evils of infertile crosses; and I -am inclined to believe that its necessity has had a more widespread -influence in determining the diversities of animal colouration than any -other cause whatever. To it may probably be imputed the singular fact -that whereas bilateral symmetry of colouration is very frequently lost -among domesticated animals, it almost universally prevails in a state of -nature; for if the two sides of an animal were unlike, and the diversity -of colouration among domestic animals occurred in a wild state, easy -recognition would be impossible among numerous closely allied forms." - -As examples of recognition colouration, Wallace cites, among others, the -white upturned tail of the rabbit--a "signal flag of danger," the -conspicuous white patch displayed by many antelopes, the white marks on -the wing- and tail-feathers of the British species of butcher-birds, the -stone-chat, the whin-chat, and the wheat-ear. - -Wallace therefore asserts, firstly, that recognition marks not only help -herbivorous animals to keep together, but act as a danger signal; the -member of a flock which first catches sight of the enemy takes to its -heels, displaying its white flag, which is the signal of danger to the -other members of the flock. Secondly, that recognition marks prevent the -evils of infertile crosses. Thirdly, that the necessity of being able to -recognise one another has rigidly preserved bilateral symmetry among -animals in a state of nature. - -As regards assertion number one, we would point out that where a flock of -herbivora is being stalked by a beast of prey, the member of the flock -nearest to the enemy--that is to say, the hindmost member--will probably -be the first to observe him. As that creature will be more unfavourably -situated for escape than the rest of the herd, it will not be to their -advantage to follow the line it has taken. Moreover, being at the rear of -the flock, it is not in a good position to take the lead, and its pursuer -is likely to see the danger signal before its friends do. It would thus -seem that "danger signals," while possibly sometimes of service to their -possessors, are on the whole ornaments which might profitably be -dispensed with. Natural selection can scarcely be charged with the -production of a character of such doubtful utility to the organism. - -Moreover, flourishing species of many gregarious animals do not possess -any "signal flag of danger," while, on the other hand, a great many -solitary species display markings that render them very conspicuous when -in motion. Take the case of the famous Indian Paddy Bird (_Ardeola -grayii_). This, when at rest, is coloured so as to be very difficult to -distinguish from its surroundings, but flight transforms it, for it then -displays its milk-white pinions, which would make a perfect danger -signal, if only it were not peculiarly solitary in its habits. Its -gregarious brethren, the Cattle Egrets (_Bubulcus coromandus_), on the -other hand, display no danger signal. - - - Interbreeding of Allied Species - -That these recognition marks prevent the intercrossing of allied species -and the production of infertile hybrids appears to be pure fiction. As we -have already shown, hybrids between allied species are by no means always -infertile. Moreover, species which differ only in colour seem usually to -interbreed in those parts where they meet. - -"This interbreeding," writes Finn, on page 14 of _Ornithological and -Other Oddities_, "occurs where the carrion crow (_Corvus corone_) meets -the hooded crow (_Corvus cornix_), where the European and Himalayan -goldfinches (_Carduelis carduelis_ and _C. caniceps_) encounter each -other, and where the blue rollers of India and Burma (_Coracias indicus_ -and _C. affinis_) come into contact, to say nothing of other cases." - -Of these other cases, the Indian bulbuls of the genus _Molpastes_ form a -very remarkable one. In all places where two of the so-called species -meet they appear to interbreed, and so freely do they interbreed that at -the points where the allied species run into one another it is not -possible to refer the bulbuls to either species. Thus William Jesse -writes of the Madras Red-vented Bulbul (_Molpastes haemorrhous_) (page 487 -of _The Ibis_ for July 1902): "This bird, although I have given it the -above designation, is not the true _M. haemorrhous_. I have examined -numbers of skins and taken nests and eggs time after time, and have come -to the conclusion that our type is very constant, and at the same time -differs from all the red-vented bulbuls hitherto described. The -dimensions tally with those given by Oates for _M. haemorrhous_, while the -black of the crown terminates rather abruptly on the hind neck, and is -not extended along the back, as is the case with _M. intermedius_ and _M. -bengalensis_. On the other hand, as in the two last species, the ear -coverts are chocolate. Furthermore, I may add--although I attach little -importance to this--that the eggs of the Lucknow bird which I have seen -are, without exception, far smaller than my eggs of genuine _M. -intermedius_ from the Punjab. My own opinion is that the Lucknow race is -the result of a hybridisation between the other three species." - -Further, in Bannu, Mr D. Donald saw _M. intermedius_ and _M. leucogenys_ -paired at the same nest. That gentleman could not possibly be mistaken on -the point, as the latter species has white cheeks and yellow under -tail-coverts, while the cheeks of the former species are dark-coloured -and the patch of feathers under the tail is red. Similarly, Whitehead and -Magrath, writing of the birds of the Kurram Valley (_Ibis_, January -1909), record that the former shot no fewer than twelve bulbuls, which -undoubtedly appear to be hybrids between these two species. As these -hybrids differ considerably _inter se_, there seems no room for doubt -that they breed with one another and with the parent species. - - - Symmetry in Nature - -Wallace's third statement, that if the two sides of animals in a state of -nature were alike, easy recognition would be impossible among numerous -closely allied forms, reminds us forcibly of the sad case of the boy -whose tailor was his mother. _Humanum est errare_: she made her son one -pair of trousers that fastened up behind, so that the poor boy when -wearing them never knew whether he was going to or coming home from -school! If animals are able to recognise their mates, their bilateral -symmetry does not seem necessary to enable them to distinguish their -fellows from allied species. - -It is, indeed, true that asymmetrically marked animals are very rarely -seen in the wild state, while they are the rule rather than the exception -among domesticated species. But this appears to be due, not to the -necessity of recognition markings in nature, but to the fact that those -animals that display a tendency to massed pigment perish in the struggle -for existence, since this massing of pigment appears to be correlated -with weakness of constitution. In other words, this massing of pigment is -an unfavourable variation, which under natural conditions dooms its -possessor. In the easier circumstances of domestication, animals which -are irregularly pigmented are able to survive, so that, among them, the -almost universal tendency to the massing of pigment can be followed -without let or hindrance. - -It is unnecessary to say more upon this subject. The few facts we have -set forth suffice to destroy this particular excrescence on the Darwinian -theory. - - - The Colouring of Flowers and Fruits - -Extremely interesting though the subject be, we are unable to consider at -length the generally accepted theory that the colour markings and -perfumes of wild flowers are the result of the unconscious selection -exercised by insects. - -While not denying that many flowers profit by their colouring, that these -colours may sometimes serve to attract the insects, by means of which -cross-fertilisation is effected, we are not prepared to go to the length -of admitting that all the colours, etc., displayed by flowers and floral -structures are due to the unconscious selection exercised by insects. It -is one thing to admit that the colour of its flowers is of direct utility -to a plant; it is quite another to assert that the colour in question -owes its origin and development to natural selection. Our attitude -towards the generally accepted explanation of the colours of flowers is -similar to that which we adopt towards the theory of protective mimicry -among animals. In certain cases we are prepared to admit that the -mimicking organism derives benefit from the likeness; but this, we -assert, is no proof that natural selection has originated the likeness. - - - Cross- versus Self-fertilisation - -The theory that flowers have developed their colours in order to attract -insects to them, and thus secure cross-fertilisation, is based on the -assumption that cross-fertilisation is advantageous to plants. It is -questionable whether this assumption is justified. True it is that -numbers of experiments have been performed, which show that, in many -cases, flowers which are artificially self-fertilised yield comparatively -few seeds. But experiments of this kind do not prove very much. - -To place on the stigma pollen from the anthers of the same flower, in -case of a plant which for many generations has been cross-fertilised, is -to subject the plant in question to a novel experience--an experience -which may be compared to transplanting it to another soil. The immediate -effect may appear to be unfavourable, although, if the experiment be -persisted in, the ultimate results may prove beneficial to the plant. - -That this is the case with some flowers that are artificially fertilised -is asserted by the Rev. G. Henslow. This observer states, that had Darwin -pursued his investigations further, he would probably have modified his -views regarding the benefits of self-fertilisation. Darwin's statement -that "Nature abhors perpetual self-fertilisation" seems to be as far from -the truth as that which declares "Nature abhors a vacuum." - -From the mere fact that cross-fertilised flowers yield a greater quantity -of seed than they do when self-fertilised, it does not necessarily follow -that cross-fertilisation is advantageous. The amount of seed produced is -probably not always a criterion as to the advantages of the crossing to -the plant. Some flowers yield most seed when fertilised by the pollen -from flowers belonging to a different species! - -It is significant that some plants produce cleistogamous flowers, that is -to say, flowers which invariably fertilise themselves. Such flowers never -open; so that the visits of insects are precluded. - -According to Bentham, the Pansy (_Viola tricolor_) is the only British -species of _Viola_ in which the showy flowers produce seeds. The other -species are all propagated by their cleistogamous flowers. The genus -_Viola_ is an advanced species: it would therefore seem that the -production of cleistogamous flowers is an advance on the production of -entomophilous flowers. Cleistogamous blossoms are obviously more -economical. - - - Insects and Flowers - -In the case of the malvas, epilobias and geraniums, where we see, side by -side, races of which the individuals produce insect-fertilised flowers -and those that are characterised by self-fertilised flowers, the latter -are quite as thriving as the former. - -The common groundsel, which, according to Lord Avebury, is "rarely -visited by insects," flourishes like the green bay tree, as many -gardeners know to their cost. The same may be said of the pimpernels. In -this connection it is important to bear in mind that the anemophilous, or -wind-fertilised, angiosperms, as, for example, the grasses, are believed -to be descendants of insect-fertilised or entomophilous forms. - -A weighty objection to the theory that the colours of flowers have been -developed because they attract insects has been urged by Mr E. Kay -Robinson, namely, that among wild flowers the most highly coloured ones -are the least attractive to insects. - -"Show me," writes he, on page 222 of _The Country-Side_ for March 20, -1909, "the insect-collector who will seek for specimens among the -brilliant scarlet poppies. Of what use is the dog rose, with its large -discs of pinky-white, to him? On the other hand, does he not find that by -far the most attractive flowers are the almost invisible spurge laurel -blossoms in February and March, the fuzzy sallow catkins in March and -April, the bramble blossom in midsummer, and the ivy's small green -flowers in autumn? Of these only the bramble has any pretensions to -colour, and if you try, as I have tried, the experiment of picking off -every petal from sprays of bramble blossoms you will find that its -attraction to moths does not appear diminished. - -"The fact that insects do visit many conspicuously coloured flowers does -not show that the colour attracts them, when the fact is borne in mind -that they neglect others which are equally coloured, while the flowers -which they particularly haunt are inconspicuous. Conspicuous flowers -_which have abundance of nectar_ attract insects, of course, but so do -inconspicuous flowers which have nectar. If they have no nectar, neither -the conspicuous nor the inconspicuous flowers attract insects other than -pollen or petal eaters, whose visits are not good for the plant. This -shows that the nectar attracts the insects and that the colour of the -flowers makes no difference." - -In autumn many leaves assume bright and beautiful tints. These are not -believed to be in any way useful to the plant. The autumnal hues and -shades are regarded, and rightly regarded, as the garb of death and -decay. Such colours are the result of the oxidation of the chlorophyll or -green colouring matter of the leaves. Why should not the colours of the -petals of the flowers, which wither and fade long before the green leaves -do, be due to a similar cause? The bright colours of fruits are supposed -to have been effected by natural selection in order to attract -fruit-eating animals. Surely a hungry animal does not require that its -food be brightly coloured in order to find it! We must remember that -during the greater part of the year most animals have no occupation save -that of finding their food. Inconspicuously coloured fruits, like those -of the ivy, are frequently eaten by birds. The bright colours of some -ripening fruits are undoubtedly the colours of decay. Many fungi and -seaweeds have bright colours. It is never hinted that these are of any -direct utility to their possessor. - -Every flower, every plant, every organism must be of some colour. - - - Honey - -Many flowering plants produce honey. This is said by some botanists to -have been directly caused by natural selection, because the honey -attracts insects. Possibly those who take up this attitude are putting -the cart before the horse. It is probable that honey, like oxygen, is an -ordinary product of the metabolism of the plant, and that the visits of -bees and other insects to such plants are the result rather than the -cause of the honey being there. Boisier found that some plants, for -example, _Potentilla tormentilla_ and _Geum urbanum_, gave honey in -Norway, but very little near Paris. - -He further discovered that by supplying certain plants copiously with -water he could induce them to produce more than their normal output of -honey. - -As is their habit, Neo-Darwinians have pushed their pet theory to absurd -lengths in its application to flowers. They assert that the visits of -insects are responsible for not merely the general colour of every -flower, but also the various lines, spots, and other markings of flowers. -The lines that frequently occur on the petals are supposed to guide the -insects to the honey! This particular refinement of Neo-Darwinism, to -quote Kay Robinson, "needs little discussion. Insects have very poor -sight. You can see this when a bee or a butterfly flies bang against a -whitewashed wall; when a wasp pounces upon a black spot on a sunlit -floor, mistaking it for a fly; or when a settled dragon-fly will allow -you to poke it in the face with the end of a walking-stick, although it -will be off like a flash if you raise your arm. There is, therefore, -large reason to doubt whether insects can even see the fine lines in the -throats of flowers which are supposed to guide them to the nectar. It is -rather absurd, too, to suppose that such lines can be needed, since -insects come in swarms to inconspicuous and apparently scentless flowers -or to 'sugared' tree-trunks in the dark. Where there is nectar, insects -which have come to the feast from a distance need no pencilled lines to -guide them over the last quarter of an inch of their journey." - - - Scents of Flowers - -Neo-Darwinians further assert that the scents of flowers have been -developed by natural selection because they serve to attract insect -visitors to the flowers. In support of this contention it is urged that -the most highly scented flowers are not usually the most conspicuous -ones, since it is not necessary for a flower to be both highly coloured -and strongly scented. Again, those flowers which open at night are -usually very highly scented. - -Plausible though this view seems, there are weighty objections to it. -These are so admirably summarised by Kay Robinson in the issue of _The -Country-Side_ for March 27, 1909, that we feel we cannot do better than -reproduce his words:-- - -"It is true that many flowers which are strongly scented are visited by -insects, but these flowers have abundance of nectar, and the insects come -in spite of the scent, and not on account of it. They visit unscented -flowers, provided that they have nectar, equally freely; and they do not -visit flowers which have scent without nectar. - -"Moreover, fruits are more generally scented even than flowers; but what -explanation have those, who attribute the scents of flowers to the tastes -of insects, for the scents of fruits? Insects which visit fruits are only -robbers. Therefore, if we say that plants have scents for the purpose of -attracting insects, we accuse all plants which have scented fruits of -attempted suicide. - -"There are hosts of plants, again, with scented leaves. Here also the -insects are only robbers, and it is quite clear that the scent is not -useful in attracting insects. If, therefore, you adopt the insect theory -to explain the scents of flowers, you must invent entirely new theories -to explain the scents of fruits and leaves." - -It is thus evident that the ordinarily accepted explanation of the -colours, scents, and markings of flowers is far from satisfactory. - - - Kay Robinson's Theory - -Mr E. Kay Robinson has put forth in recent issues of _The Country-Side_ -(March 20, 27, and April 3, 1909) quite a new explanation of the -phenomena, and one which deserves careful consideration. He maintains -that "the real, primary, and original meaning of the colours, markings, -nectar and scents of flowers is not to attract insects, but to deter -grazing and browsing animals." - -"I say," he writes, "that grazing and browsing animals avoid eating -conspicuous flowers. I have watched a flock of five hundred sheep pass -across a yard-wide strip of close-nibbled turf on the Norfolk coast, -grazing as they passed, and the number of open daisy blossoms after they -had passed seemed the same as before they came. Every one of five hundred -sheep had eaten something from that yard of grass, and not one had eaten -any of the hundred and thirty odd daisies. - -"Every summer the farm horses are turned into the same old pasture, and -as the summer wanes the field always presents the same appearance--the -green grass close-grazed, the tall buttercups left standing high. - -"Once, leaning over a gate with friends, I pointed out that a flock of -sheep grazing in a sainfoin field were nibbling the greenstuff close, but -were not eating the flowery stalks, when one sheep near us accidentally -pulled up a whole sainfoin plant by the roots and proceeded to munch it -upwards. Inch by inch the stem passed into its jaws, and I began to be -afraid that it was going to establish an 'exception' to my rule. But, -just when the bright cluster of pink sainfoin blossom was within two -inches of its teeth, it gave an extra nip, and the flower head fell to -the ground, and the sheep resumed its search for greenstuff. - -"I do not say that this would always happen--I should be sorry for any -theory which depended upon the intelligence of a sheep--but it was a very -striking object-lesson to my two companions; and any one who looks around -during this summer with an inquiring mind will find plenty of evidence -that grazing, browsing, and nibbling animals avoid flowers, and stick to -greenstuff when they can get it. - -"I do not say that all animals avoid the same flowers. Horses, for -instance, may dislike large flowers like roses and conspicuous yellow -flowers like buttercups, but they will bite off flat clusters of minute -white or pale yellow flowers, such as yarrow or wild parsnip. These -distinctions made by certain kinds of beasts will probably in the future -be found to afford valuable evidence as to the regions of origin of our -flowers and animals. Such plants as the yarrow and the wild parsnip, for -instance, probably did not originate in the home of the wild horse, -because they are not protected against it. - -"As a general rule, however, there is abundance of evidence that plants -with conspicuous flowers gain a large advantage in the struggle for -existence, because grazing and browsing animals avoid them; while there -is no real evidence at all that conspicuous flowers attract insects." - -Kay Robinson extends this explanation to the shape, the scent, and the -nectar of flowers. He admits that many flowers are adapted to the visits -of insects, but this is, he asserts, but a secondary result. The "real, -primary meaning" of the shapes of flowers of curious configuration is, he -insists, "a deterrent to grazing or browsing animals." - -According to him plants, like the snap-dragon, which have "blossoms in -the semblance of a mouth," are avoided by grazing animals, because they -mistake such flowers for mouths, and have no wish to be bitten! Orchids, -he asserts, "are strongly deterrent to grazing and browsing animals, -which are looking for greenstuff, and regard these gaudy, spidery, winged -blossoms as live creatures." "If this is not the truth," he asks, "will -any adherent of the theory that we owe the shapes of flowers to insects -explain why some of our common British orchids are so like bees, spiders, -etc.? Some which have no particular resemblance to any insect still -exhibit weird shapes, suggestive to the human mind of living things, such -as lizards, etc. The reason why they look like bees, spiders, lizards, -and various unclassed creatures is quite simple. Grazing animals are -looking for greenstuff, and do not wish to eat living creatures which may -bite or sting or taste nasty. Thus the orchids have acquired the power of -looking like creatures. - -"Every one," he continues, "who is familiar with the blossom of the wild -carrot--a flat head of minute, dull-white blossoms--must have noticed how -very often the centre blossom in each head is purplish or reddish-black. -This makes it very conspicuous in the middle of the flat white flower -head. Now what conceivable use can this barren little blackish -blossom--scarcely bigger than a pin's head--be to the wild carrot plant -if we regard the flat head of white flowers as an attraction to the sight -of insects? If, on the other hand, we rightly regard the flat head of -white blossoms as an advertisement to grazing animals that it is not -wholesome greenstuff, but innutritious blossoms liable to be infested -with ants and other stinging insects, we see at once the great use of -this small blackish flower in the middle. It looks like an insect, and -possibly in the home of the wild carrot there is some minute blackish -insect with a peculiarly villainous smell or taste--or perhaps a potent -sting--which grazing animals carefully avoid whenever they can see it. -Thus the wild carrot flourishes; though here in Britain--where the wild -carrot has established itself now--we may fail at first to see the exact -meaning of the trick. I think, however, that, when we understand it, it -fits admirably into the theory that the shapes and colours of flowers are -primarily useful as deterrents to grazing and browsing animals and not as -attractions to insects. - -"Thus we see," he concludes, "that the queer shapes of these orchids, -which are a great stumbling-block in the way of those who preach that we -owe the shapes of flowers to the tastes of insects, become a strong -confirmation of my theory that we owe the shapes of flowers to grazing -and browsing animals." - -Of the nectar of flowers, Kay Robinson writes: "Since this is eagerly -sought for by hosts of insects, whose visits are in most cases useful to -the flowers, it seems only natural to suppose that we see cause and -effect in this connection. - -"Here, however, I will outline my theory of the origin of nectar and of -flowers in general. - -"I think there is no doubt whatever that all the parts of a flower are -modified leaves. The original type of flowering plant--I think we may -safely assume--had a single stem and produced its seed at the summit, as -the crown of its year's endeavour. The flower, before it became what we -would recognise as a flower, was a cluster of protecting leaves round the -seed-making parts of the plant. To the production of the seed the whole -energies of the plant were devoted, and into the cluster of leaves at the -top of the stem all the essences of the plant were concentrated. If -during the coming spring you handle and examine the leaves at the end of -the strong shoots of thorns or fruit bushes, you will find that the -surface of the young leaves is quite sticky. If you observe browsing -animals also, you will discover that--contrary to expectation--they do -not like strong-growing, juicy shoots, evidently preferring mature leaves -lower down the branch. This shows, I think, that plants have the power of -protecting their new shoots by crowding into them the volatile oils and -essences which they produce as a protection against animals. Now nectar -appears always to be distasteful to grazing and browsing animals; and -they also dislike scented flowers. I think, therefore, that it is -reasonable to suppose that the nectar and scents which now distinguish so -many flowers were first produced as an exudation of concentrated sap upon -the surfaces of the protecting leaves round the seed-making parts of the -original flowers. As these leaves became more efficiently protective by -assuming colours, shapes, and markings which warned animals of their -character, so their apparatus for producing scent and honey became -specialised; and at this point the insect appeared upon the scene as a -factor in the life's success of the plant." - -Such, then, is Kay Robinson's bold and original theory. In some respects -it seems far-fetched. The natural inclination is to ask, "Is it possible -that cattle can be so stupid, so blind, as to really believe that a -snap-dragon is the mouth of an animal, or that an orchid is a spider?" - -At present we know so little of animal psychology that we are not yet in -a position to give an answer to this question. Horses, we know, are apt -to be frightened by the most harmless things, such as a piece of brown -paper lying on the road. Mr Robinson's theory should give a stimulus to -the study of the mind of animals--a study which, if properly undertaken, -will probably throw a flood of light upon some of the problems of -evolution. Mr Robinson's theory equally with the ordinarily-accepted -hypothesis, utterly fails to explain the first origins of colours, -scents, etc. When once a flower has acquired a certain amount of colour, -it is easy to understand how that flower may attract insects or repel -grazing animals. But how can the origin of the colour or other -characteristic be explained? - -We asked Mr Kay Robinson how he would account for the great success in -the struggle for existence of some species of grasses on which -herbivorous animals feed so largely. He replied, in the issue of _The -Country-Side_, dated April 3, 1909:-- - -"The grass has a manner of growth which defies the grazing animal. Its -long, thin leaves are constantly pushing upwards from the ground, and, if -they are grazed down one day, they will have pushed up again the next. -Moreover, when the outside blade of grass has exhausted its power of -growing, there is another blade inside it with many inches still to grow, -and another inside that which has scarcely begun to grow, and yet another -further in which has not yet seen daylight; and so on. In a state of -nature grazing animals are nowhere so numerous on any given patch of -ground from day to day as to keep down the grass. If they were, -carnivorous animals would stay there to eat the grazing animals, and grow -fat and multiply. Thus the grazing herds are scattered and wandering, -followed wherever they go by the beasts of prey; and in their absence the -grass pushes ahead, so that when the grazing animals return its clump is -larger and its roots are stronger, and it is better able to survive -attack than before. - -"The method of the clovers and trefoils is quite different. When -circumstances are favourable and enemies few, they will form large-leaved -luxuriant clumps, with fine heads of blossom; but where grazing animals -abound they have the power of adapting themselves to altered -circumstances. They creep so closely along the ground that the teeth of -the grazing animal cannot pick them up between the surrounding grass, and -they produce leaves so small and short-stalked that to eat them would be -like nibbling the pile off velvet. Any clover or trefoil thus growing in -self-defence is accepted as the 'shamrock' of Ireland; and it is -certainly a fine emblem for a race which regards itself as surviving in -spite of incessant oppression. - -"These are the reasons, however, why the grasses and clovers or trefoils -continue to enrich old pastures when most of the other plants disappear, -with the exception of daisies and buttercups, and the acid sorrels." - -We should be glad to hear how Mr Robinson accounts for the conspicuous -flowers in the species of "prickly pear" (_Euphorbia_), which is so -abundant in India, and which is not browsed upon by animals. - -We regret that we are not able to devote more space to this most -interesting theory. We can only add that, even if it fail to become -widely accepted, it is of great value as showing that it is possible to -offer a plausible explanation of a large number of phenomena, which nine -out of ten botanists explain in a very different way. - -So satisfied are the majority of naturalists with the "insect theory," -that they seem of late years to have paid but little attention to the -subject of floral colouration. This affords a striking instance of the -pernicious influence which Neo-Darwinism is exercising on the minds of -men to-day. It tends to stifle research instead of stimulating it. - - - Accepted Theories Unsatisfactory - -We have now dealt with the theory of protective colouration, the theory -of warning colouration, the theory of mimicry, and the theory of -recognition markings. We have shown that although many organisms -undoubtedly derive profit from the fact that they are difficult to see in -their natural surroundings or from their resemblance to other organisms, -the hypothesis that this inconspicuousness or the mimicry of these -animals has been caused by the natural selection of small variations is -untenable. - -Warning colours, we have shown, although a disadvantage to their -possessors, are sometimes seen in nature because they are accompanied by -unpalatability. The theory of recognition markings must, we fear, be laid -to rest in the burial ground of exploded hypotheses. - -The extreme popularity of the existing theories regarding animal -colouration and their very general acceptance are to be attributed, -firstly, to their simplicity; secondly, to the fact that they have thrown -light on many phenomena which previously had seemed inexplicable; -thirdly, that if we assume, as the great majority of biologists do, that -evolution has been effected by the accumulation of numerous variations, -small in degree and indefinite in direction, we seemed forced either to -accept Neo-Darwinism or admit that the whole subject of animal -colouration baffles us, in other words, to reject what appears like -cosmos and substitute for it chaos. - -With a few exceptions, books that deal with the colours of organisms, -while emphasising the evidence in favour of the generally-accepted -theories, seem almost entirely to ignore the host of facts that do not -appear to fit in with them. - -This is largely due to the almost unavoidable bias of the human mind when -obsessed by a pet theory. There are none so blind as those who will not -see. It is also, in part, the consequence of the prevalent neglect of the -scientific method of comparison which leads men to theorise on -insufficient evidence. This, of course, is a natural result of -specialisation in biology. Naturalists are in the habit of confining -their study to the habits of the animals of one particular country and -then making far-reaching generalisations therefrom. - -As an example of the kind of theorising to which this method leads, we -may cite the often-quoted theory which ascribes the green colouring of -some arboreal fruit-eating pigeons to adaptation to an existence among -tropical foliage, and ignores the fact that in America tree-haunting -pigeons are never of this colour, and that it is not by any means -universal even among the old-world pigeons. - - - White Down of Nestlings - -Similarly, a theory has been advanced (W. P. Pycraft, _Knowledge_, 1904, -p. 275) that the white down of some nestling birds, is an adaptation to -resisting the heat of the sun in open nests. This is at once negatived by -the fact that young owls, usually hatched in shaded places, are also -generally white, while young cormorants, living in open nests, are black; -yet the allied darters, with the same breeding haunts in some cases, have -white young. Lest it should be thought that black has some especial value -in a nestling living exposed, we may mention that young petrels, which -are born in holes, have black or dark down. - -As we have already pointed out, naturalists in too readily accepting the -theory that variation is minute in degree and indefinite in direction, -have raised quite unnecessary difficulties, even for the selection -hypothesis. We have cited certain facts, which seem to show that -variations, as a rule, are not indefinite in direction; of these the most -striking is furnished by birds in which the tail feathers are greatly -elongated. Were variations indeterminate, we might reasonably expect to -find that the elongation occurred in one particular feather or pair of -feathers in one species, in another pair in a second species, in a third -pair in a third species, and so on. But this is not the case; no bird has -one _single_ long feather in its tail, and when two are elongated, as is -so commonly the case, these are almost invariably the middle or the -outside pair; _e.g._, in the European bee-eater and pheasant it is the -former, in the swallow and blackcock, the latter. - -Exceptions are so rare that they may almost be said to prove the rule; -_e.g._, although most terns have the outer-tail feathers elongated, in -some of the Noddy Terns (_Anous_, _Gygis_) the third pair, in others the -fourth pair, of tail feathers are the longest. This must mean one of two -things, either that the variation, as regards length in tail feathers, -other than middle or outer, does not ordinarily occur, or that it occurs, -but is, in some way, inimical to the welfare of the species. The latter -hypothesis does not seem probable, as the Noddies are particularly -abundant birds where they occur, that is to say, in the tropical seas; -therefore, we can only conclude that that particular variation has not -occurred in birds as a whole. - -We have adduced abundant evidence to show that mutations or discontinuous -variations occur in nature; and as these afford much more favourable -material on which natural selection can act, it is reasonable to suppose -that they have played a considerable part in evolution. - -When discussing the phenomena of inheritance, we attempted to show that, -not improbably, these discontinuous variations are due to some -re-arrangement in the constituent parts of the unit characters, or -biological molecules, as we have called them. - - - Cranes - -In this connection we may mention the apparently singular phenomenon of -different species in the same natural group, exhibiting either a definite -excess or deficiency of plumage on the head. Among cranes, most species -are more or less bald; but the Demoiselle (_Anthropoides virgo_) has a -fully-feathered head with long side-plumes, while the head of the Stanley -Crane (_A. paradisea_) appears to be swollen, so abundantly is it -feathered. The crowned cranes, although bare-cheeked, have double crests, -the two parts of which have been respectively compared to a pen-wiper and -a bunch of toothpicks! - -Among the guinea-fowls, several species are crested, while others, as, -for example, the domestic one, are bare-headed. Now, on the theory of -evolution, by accumulation of minute variations, phenomena such as these -are difficult of explanation; but, on the assumption that a slight -rearrangement of the biological atoms in the molecule may produce very -diverse results, as we see in the case of chemical molecules, and of -seasonally dimorphic butterflies, there is no particular ground for -surprise at such a phenomenon. - -In this connection we may cite the significant fact, so well known to -canary breeders, that two crested birds when mated tend to produce a -bald-headed one. - -If the colour of any part of an organism be due to the internal -arrangement of the constituent parts of the biological molecule from -which it is derived, we should expect any rearrangement of the component -parts to produce quite a different colour. In other words, we should -expect occasionally to see colour-mutations. These are precisely what we -do see. Similarly, if the scheme of colouring of an organism be due to a -certain grouping of biological molecules, we should expect the same -scheme of colouring to occur in organisms which are not nearly related. -This, too, we observe in nature. - -Many of the phenomena of mimicry, and all the cases which we have cited -as pseudo-mimicry, seem to us to be referable to this. - - - Magpie Colouring - -Take, for example, the magpie colouration in birds--that is to say, a -scheme of colouring in which the body is white, and head, wings, and tail -black. This occurs in the following birds belonging to the most diverse -groups:-- - -The Magpie. - -The Magpie Tanager (_Cissopis leveriana_). - -The Magpie Robin (_Copsychus saularis_), cock only; in the hen the black -is replaced by brownish grey. - -The Pied Honeyeater (_Entomophila picata_). - -The Chaplain Crow (white-bodied form of the hoodie crow). - -The New Ireland Swallow Shrike (_Artamus insignis_). - -The Magpie Goose (_Anseranas melanoleucus_). - -Combinations of this kind, in which the black is replaced by brown or -grey, are excessively rare. - -On the other hand, we see in several birds the combination in which the -white is replaced by yellow:-- - -The Common Troupial (_Icterus vulgaris_). - -The Black-headed Oriole (_Oriolus melano cephalus_). - -The Black-and-yellow Grosbeak, male only. - -What we may call imperfect magpie colouration, _i.e._ where the head -becomes white, occurs in several species of birds. The head of a black -species sometimes becomes white as a mutation; in the domestic Muscovy -duck, for example, an individual is sometimes produced having a white -head, although the black of the remainder of the plumage remains -unchanged. - -As examples of this scheme of colouration we may cite-- - -Black-and-white Fruit Pigeons (_Myristicivorae_). - -Several Gannets (_Sula capensis_, _S. serrator_, etc.) - -Swallow-tailed Kite (_Elanoides furcatus_). - -Several Storks (_Euxenura maguari_, _Anastomus oscitans_, _Pseudotantalus -cinereus_). - -Moreover, a common variety of the barn-door fowl has also a white body -and black primaries and tail, showing that this scheme of colour may -arise as a mutation. - -A further elimination of black in the tail and body leads us to white -birds with more or less black wings:-- - -White Storks (_Ciconia alba_, _C. boyciana_, and _Euxenura maguari_). - -The White Crane (_Grus leucogeranus_). - -The Snow Geese (_Chen nivalis_, _C. rossi_). - -The Common Gannet (_Sula bassana_). - -The White Buzzard (_Leucopternis_). - -The Scavenger Vultures (_Neophron_). - -A recurring combination in mammals is black, with a white marking on the -breast. - -Most of the bears, even young brown bears, show a tendency to this. It is -also found in the Tasmanian devil, and in varieties of our domestic cats, -rats, and dogs; also in the domestic duck. - -The white-spotted pelage, not uncommon in deer, especially fawns, is -curiously repeated in the Australian carnivorous marsupials, known as -Native Cats (_Dasyurus_). - -In domestic animals we frequently find the following localisation of -white--white socks, collar, breast, and muzzle. The arrangement occurs in -cats, dogs, rabbits, guinea-pigs and mice, also in the horse and pig, but -without the collar. The arrangement is not seen in goats, cattle, or -sheep, nor in wild animals of any kind. This would lead to the conclusion -that the combination is correlated with some character unfavourable to -survival under natural conditions. - -Many variations which frequently occur among both wild and domestic -animals do not persist in nature. - - - Albinos - -As instances of such variations we may mention pure albino forms, that is -to say those in which pigment does not occur in the eyes. - -It is easy to see why this variation is not allowed to persist in nature. -Its possessors are handicapped by bad eyesight, and so have no chance of -surviving in the struggle for existence. It is thus that natural -selection acts. On the other hand, white species with pigmented eyes are -fairly numerous. These enjoy normal eyesight, but labour under the -disadvantage of being easily seen by their foes. Hence we find that white -species generally either occur in a snowy habitat, or are powerful and -both able and ready to defend themselves. In this connection it is -interesting to notice that in New Zealand all birds, whether introduced -or indigenous, are particularly liable to albinism. Owing to the fewness -of their enemies these albinistic forms are able to persist. - -A variation, or rather a mutation, that frequently occurs among -domesticated birds, but which is seen in very few wild species, is that -which takes the form of white primary feathers on the wing. This -variation must often occur in nature, but it rarely establishes itself, -apparently because white feathers do not resist wear so well as coloured -ones do. - - - Biological Molecules and Colour - -Black-and-yellow colouration occurs in several widely separated species -of birds. The arrangement of the two colours follows to some extent the -same rules as the black-and-white combination. - -Several birds have a yellow body with black head, wings, and tail, such -as-- - -The Black-headed Oriole (_Oriolus melanocephalus_). - -The Black-and-Yellow Grosbeaks (_Pycnorhamphus icteroides_, _P. affinis_) -(cock). - -The Common Troupial (_Icterus vulgaris_). - -In others the black on the head is nearly or quite suppressed, that on -the tail remaining to a greater or less extent; such are-- - -The Golden Orioles (_Oriolus galbula_, _O. kundoo_, etc.). - -Several species of _Icterus_. - -Several fly-catchers of the genus _Piezorhynchus_ (males only). - -[Illustration: BRAZILIAN TROUPIAL] - -[Illustration: INDIAN BLACK-HEADED ORIOLE] - - -We have said sufficient to show that certain combinations of colours -recur in nature in species which are neither nearly related to one -another nor subjected to similar environment. For such phenomena it is -difficult, if not impossible, to account on the theory that natural -selection, acting on minute variations, is responsible for all the varied -colouring of the animal kingdom. The facts, however, are in accordance -with the supposition that the organism is the result of the growth and -development of a number of units or biological molecules which exist in -the fertilised egg. - -If there be any truth in the supposition, the colouration of every animal -must be due to the development of one or more of these molecules. -Colouration may be expression of the arrangement of all the molecules in -the fertilised egg, or it may be due to the development of a number of -molecules whose function is to determine the colouring of an organism, or -it may be the result of the development of one such molecule, which -perhaps splits up in such a way that a portion attaches itself to each of -the other molecules. - -But it is idle to speculate on this point. As we have already insisted, -the tendency to build up elaborate theories on very slender foundations -is a too frequent failing of zoologists. We desire merely to emphasise -the fact that the phenomena of animal colouration almost force us to the -conclusion that the colouring of each organism is the result of the -development of a number of units. - -It may be objected that, if this be the case, the number of the units -which contribute to the colour of any organism must be exceedingly large, -since we see in nature an almost limitless number of different schemes of -colouring. If the colour of each animal be the result of the development -of a few units, it might be thought, firstly, that the diversity of -schemes of colouration which we observe in nature could not possibly -occur; and secondly, that, under such circumstances, the colour pattern -of a bird or beast should be of the nature of a mosaic, each colour being -sharply defined and separated from every other colour, instead of the -colours shading one into the other, as is so frequently the case. - -Such objections would be based on a misconception as to the nature of the -units which combine to produce the colouration of an organism. _These -units show themselves as centres of development of colour_, as points -from which the colour or colouring they represent spreads, until it meets -and mingles with other patches of colour which are being developed from -other centres. The colour produced at one centre may spread more rapidly -than that which forms at another; this, of course, will result in a -preponderance in the organism of the colour which is produced at the -former centre. - -Further, we must bear in mind that the development of each -colour-producing unit is largely affected by conditions external to it, -as we shall see when dealing with Sexual Dimorphism. - -More than one naturalist, who has paid careful attention to the subject -of animal colouration, has perceived that through the apparently endless -diversity of the colouring of organisms something like order runs. - - - Mr Tylor Quoted - -Over thirty years ago Mr Alfred Tylor called attention to this important -fact. That observer, whose views met with the approval of Wallace, was of -opinion that colour follows structure, and that in a many-hued animal it -changes at points where the function changes. - -"If," writes Mr Tylor, "we take highly decorated species--that is, -animals marked by alternate dark or light bands or spots, such as the -zebra, some deer, or the carnivora, we find, first, that the region of -the spinal column is marked by a dark stripe; secondly, that the regions -of the appendages, or limbs, are differently marked; thirdly, that the -flanks are striped or spotted, along or between the regions of the lines -of the ribs; fourthly, that the shoulder and hip regions are marked by -curved lines; fifthly, that the pattern changes, and the direction of the -lines, or spots, at the head, neck, and every joint of the limbs; and, -lastly, that the tips of the ears, nose, tail, and feet, and the eyes are -emphasised in colour." - -More recently Mr J. Lewis Bonhote has devoted much attention to this -important subject. The results of his researches are summarised on page -185 of vol. xxix. of the _Proceedings of the Linnaean Society_, and on -page 258 of the _Proceedings of the Fourth International Ornithological -Congress_, 1905. Mr Bonhote states that the presence or absence of colour -tends almost invariably to make its appearance, first of all, on certain -definite tracts, common to mammals and birds alike, which he calls -_poecilomeres_. - - - Poecilomeres - -"Poecilomeres," he writes, "are situated on the following parts, viz., -chin, malar stripe, maxillary stripe, a spot above and slightly in front -of the eye, a spot below or slightly behind the eye, the ear, crown of -the head, occiput, fore-end of sternum, vent, rump, thighs, wrist, -shoulders (above and below). - -"Now, there is hardly any species of bird on which one or more of these -poecilomeres is not 'picked out' (to use a painter's expression) in some -colour different from that of the surrounding parts, and, in fact, most -of the so-called recognition or protective markings will be found on -these patches. - -"On the other hand, among many species the differentiation of colour on -the poecilomeres is not so conspicuous as to attract the eye or to serve -in any way for protection or mimicry, _yet we still find them marked by -differences of colour so slight that, unless especially looked for, they -would never be noticed_. - -"Or, again, some species occasionally, but not invariably, show a few -white feathers on certain parts of their body, and, when such is the -case, it will be found that these white feathers appear on the -poecilomeres. . . . There is hardly a species in which examples of these -poecilomeres may not be found. . . . The Kingfisher (_Alcedo ispida_) -shows the various head poecilomeres very clearly, and as examples of -inconspicuous differences on these tracts, the rump of the hen sparrow -(_Passer domesticus_) and hen chaffinch (_Fringilla coelebs_), the malar -stripe and dark ear-patch of the hen Yellow Bunting (_Emberiza -citrinella_), and the dark ante-orbital patch of the Barn Owl (_Strix -flammea_) are familiar examples. And, lastly, as an instance of the class -where a few white feathers frequently, but not invariably, appear, the -young of the cuckoo (_Cuculus canorus_) forms a good example. - -"These spots may, however, appear in a transitory manner, as, for -instance, where a change of plumage (not necessarily moult) is -occurring." - -As an instance of this, Bonhote cites the case of a young male Shoveler -(_Spatula clypeata_), "in which the metallic colour on the head first -showed itself on the post-orbital and auricular poecilomeres, gradually -meeting and joining up across the head with the crown and occipital -poecilomeres, and then finally spreading forwards. And it may be well to -note that the joining up of the auricular and post-orbital poecilomeres -formed a metallic patch similar in size and position to that found in the -male Teal (_Querquedula crecca_), and, further, in the last stage, when -the whole head, except the portion round the beak, was metallic, the -markings are similar to those found permanently in the hen Scaup -(_Fuligula marila_). - -"Now, these resemblances taking place in the normal pure-bred wild -shoveler, the question of reversion does not come in, and no one would -suppose these resemblances due to anything more than transitional -variation, and it is the object of this portion of the paper to show that -variation in colour follows along definite lines." - - - Biological Molecules - -Mr Bonhote continues: "As a further illustration of how widely spread -these lines are throughout the mammalian and avian kingdoms, we may note -the assumption of the brown head in the case of the Black-headed Gull -(_Larus ridibundus_), which invariably follows each year on lines similar -to those related in the case of the shoveler, and . . . the method by -which, on the approach of winter, the stoat assumes his white dress, is -(although the change is from brown to white) again conducted along -precisely similar lines." Mr Bonhote argues with great force that, as the -process occurs in two animals so widely separated, the fundamental cause -must be a deep-seated one. There can be no doubt that these poecilomeres -of Bonhote are connected with our biological molecules. Each of these -poecilomeres is the result of the development of one of these unit -characters; each is to be regarded as the centre of activity, the sphere -of influence of a biological molecule, or the portion of one, which -controls the colouring of a definite region of the organism. In the case -of creatures which display the same colour throughout, these molecules -all give rise to the same kind of colouring; in the case of animals which -display a variety of colours and markings the various molecules give -origin to various colours. But we must bear in mind that the final colour -to which each colour-producing molecule gives rise depends to some extent -on circumstances other than the constitution of the molecule. Thus it is -that the young in most organisms differ in colour and marking from the -adults. On this also depends the phenomena of seasonal and sexual -dimorphism. The same colour-producing molecule may give rise to one -colour under one set of conditions and to a totally different colour -under another set of conditions. - -It is a significant fact that under abnormal conditions the feathers of -birds tend to disappear precisely on those spots where the poecilomeres -of Bonhote occur. - -Thus in a sickly cage bird the feathers frequently show a tendency to -fall off on the following spots: crown of head, lores, jaws, head -generally, rump, vent and thighs. - -Many wild birds--as, for example, the cranes--display patches of naked -skin on the head, and these are usually situated on poecilomeres. -Similarly, natural excessive developments of plumage tend to occur on the -poecilomeres, or, rather, the spots characterised by poecilomeres--for -example, the train of the peacock. Loral plumage, it is true, is seldom -long, but is often of a peculiar nature. - -Colour mutations tend to occur on the poecilomeres. Thus it is that these -poecilomeres often form the distinctive characters and markings of allied -species. This is precisely what we should expect if the poecilomeres -correspond to biological molecules and mutations are the result of the -rearrangement of the constituent parts of these molecules. - -Still more significant is the fact that the colour-markings in hybrids -tend to follow poecilomeres. - -Bonhote has performed a large number of experiments in hybridising ducks. -Some of his hybrids were produced from three pure ancestors, as, for -example, the pintail, the spotbill, and the mallard; others from two -ancestors. Some of these hybrids were crossed with other hybrids, and -others with the parent forms, hence Bonhote secured a number of hybrids, -each of which had a distinctive appearance; but _all_ the variations -appearing among the hybrids were found to start on one or more of the -poecilomeres. - -Certain of the hybrids showed a resemblance to one or other of the parent -species, others were unlike either parent, and resembled either no known -species or species other than their parents. - -When a hybrid shows a resemblance to a species other than that to which -either parent belongs, it is said to exhibit the phenomenon of atavism or -reversion,--the individual is supposed to have been "thrown back" to an -ancestral form. - -The true explanation of the phenomenon would seem to be that, as the -result of the crossing, biological molecules in the fertilised egg have -been formed which, on development, give rise to combinations of colour -like those seen in other species. - -Thus the phenomena of "mimicry" and "reversion" are, we believe, due to -the fact that in the fertilised egg of both the pattern and its copy a -similar arrangement of biological molecules obtains. If we regard the -sexual act as resembling in many respects a chemical synthesis, the -phenomenon need not surprise us. - -To sum up, the observed facts of animal colouration seem to indicate that -there are in each organism some twelve or thirteen centres of colouring, -which we suggest may correspond with portions of the fertilised egg. From -each of these centres the colour develops and spreads, so that every part -of the organism is eventually coloured. These centres of colouring are -not altogether independent of one another. Sometimes they all give rise -to the same hue, in which case we have a uniformly-coloured organism, -such as the raven. More often from some one colour develops, and from -others another colour; if these two colours happen to be black and white, -the result is a pied organism, which displays a definite pattern due to -the correlation of the various colour-producing biological molecules. - -Thus it occasionally happens that two widely different organisms exhibit -very similar markings, and therefore resemble one another. When this -resemblance is believed to be of advantage to one or other of the -similarly-coloured species, naturalists call it mimicry, and assert that -the likeness is due to the action of natural selection; but where neither -organism can profit by the resemblance, zoologists make no attempt to -explain it. What we suggest is that the colouration of an animal depends -upon the structure, or, at any rate, the nature, of the parts of the egg -which produce these centres of colour. But this is not by any means the -only cause that determines the colouration of the organism. If it were, -young creatures in their first plumage would invariably resemble the -parents, the two sexes would always be alike, and there would be no such -phenomenon as seasonal dimorphism. - -As a matter of fact, the portions of the egg (we call them, for the sake -of clearness, colour-producing biological molecules) which give rise to -the poecilomeres exhibit themselves merely in the shape of tendencies; -the ultimate form the colouring will take depends to a large extent upon -other and extraneous circumstances, such as the secretion of hormones. - -Thus it is that organisms seem to display an almost endless diversity of -colouration. But beneath all this diversity we see something like order. -It occasionally happens (_why_, we do not know) that one, or more, of the -biological molecules which make up the nucleus of the fertilised ovum -becomes altered in the sexual act, with the result that a discontinuous -variation or mutation appears in the resulting organism. The mutation may -be a favourable one, or one which does not affect in any way the chances -of an organism in the struggle for existence, or an unfavourable one. In -the last of the three cases the organism will perish early and not leave -behind any offspring exhibiting its peculiarity. - -It is thus that natural selection acts. Natural selection weeds out -relentlessly all organisms which display unfavourable variations. It is -thus obvious that many species may, and we believe do, exist which -possess characters of no direct utility to them, or even slightly harmful -ones. For this reason Wallace and his followers fail in their attempts to -prove that every patch of colour in every organism is of direct utility. -Natural selection has to take an animal as it finds it--the good with the -bad. If an organism as a whole is not wanting--that is to say, if it is -able to hold its own against other organisms, and is fitted to fill any -place in nature--that organism will probably survive, although it may be -defective in many respects. As its name implies, natural selection is a -mere selecting agency. It has to choose from what is presented to it. It -is not, as many seem to think, a manufacturer or inducer of variations. -Natural selection can no more _make_ an animal vary in any given -direction than the human breeder can. Its power is limited to the -destroying of all variations which do not pass the test prescribed by it. - - - - - CHAPTER VII - SEXUAL DIMORPHISM - - - 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--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. - -In some species the sexes are so similar in appearance that it is not -possible to tell by mere outward inspection to which sex a given -individual belongs. - -In other species the sexes differ so widely in external appearance that -it is difficult to believe that the male and the female belong to the -same species. Between these two extremes are a great number of species in -which the sexes are more or less dissimilar. Those species in which the -sexes differ in appearance are said to be sexually dimorphic. The -phenomena of sexual dimorphism are fatal to that form of Neo-Darwinism -which sees in natural selection an explanation of all the peculiarities -of animal structure and colouration. - -It is not easy to understand how natural selection can have caused marked -sexual dimorphism in a species where the habits of the sexes are the -same, in the Paradise Flycatcher (_Terpsiphone paradisi_), for example, -where the cock and the hen obtain their food in the same way, and share -equally the duties of nest-building, incubation, and feeding the young. - -Of course, in all species where each individual carries only one of the -two kinds of sexual organs, there must of necessity be some slight -difference between the individuals that carry the male organ, which -performs one function, and those that carry the female organ, which -performs another function. - -But in many species the sexes display differences which have no direct -connection with the generative organs--for example, the deer, where the -stag alone has horns. - -Those characters which differ with the sex, but are not directly -connected with the organs of reproduction, are known as secondary sexual -characters. - -[Illustration: QUEEN WHYDAH] - - - Theory of Sexual Selection - -In nearly all species where the male and female differ in beauty, it is -the male who surpasses the female. Natural selection is, in many cases, -not able to explain the origin of these differences, or why, when they -occur, the male should be more beautiful than the female. This Darwin -saw. In order to account for the phenomena of sexual dimorphism, he -formulated the theory of sexual selection. This hypothesis is based on -the assumption that there is, in all species of animals, a competition -among the males to secure females as mates. It is not difficult to -understand how this competition arises in polygamous species. Assuming -that approximately equal numbers of males and females are born (an -assumption which appears to be justified as regards the majority of -species), it is clear that for every male who secures more than one wife, -at least one male will be obliged to live in a state of single -blessedness. - -But how can there be competition in the case of monogamous species? The -sexes being approximately equal in number, there are sufficient females -to allow of a mate for every male. - - - The Law of Battle - -Such is the nature of things, said Darwin, that, even under these -circumstances, there is competition among the males for females. - -"Let us take any species," he writes, on page 329 of _The Descent of Man_ -(Ed. 1901), "a bird for instance, and divide the females inhabiting a -district into two equal bodies, the one consisting of the more vigorous -and better-nourished individuals, and the other of the less vigorous and -healthy. The former, there can be little doubt, would be ready to breed -in the spring before the others; and this is the opinion of Mr Jenner -Weir, who has carefully attended to the habits of birds during many -years. There can also be no doubt that the most vigorous, best nourished, -and earliest breeders would on an average succeed in rearing the largest -number of fine offspring. The males, as we have seen, are generally ready -to breed before the females; the strongest, and with some species the -best armed of the males, drive away the weaker; and the former would then -unite with the more vigorous and better-nourished females, because they -are the first to breed. Such vigorous pairs would surely rear a larger -number of offspring than the retarded females, which would be compelled -to unite with the conquered and less powerful males, supposing the sexes -to be numerically equal; and this is all that is wanted to add, in the -course of successive generations, to the size, strength, and courage of -the males, or to improve their weapons." - -From this competition among the males there arise, firstly, contests -between the males for mates; secondly, the preference of the females for -favoured males. - -It is a matter of common knowledge that at the breeding season the males -of nearly all, if not all, species are very pugnacious. Two males often -engage in desperate fights for one or more females; the victor drives -away his foe and secures the harem. In such contests the stronger male -wins, and thus emerges that particular form of sexual selection which -Darwin termed "the law of battle." - -"There are," writes Darwin, on page 324 of _The Descent of Man_, "many -other structures and instincts which must have developed through sexual -selection--such as the weapons of offence and the means of defence of the -males for fighting with and driving away their rivals--their courage and -pugnacity--their various ornaments--their contrivances for producing -vocal or instrumental music--and their glands for emitting odours." The -former characters have, according to Darwin, been developed by the law of -battle, and the latter, since they serve only to allure or excite the -female, by the preference of the female. - -"It is clear," continues Darwin, "that these characters are the result of -sexual and not of ordinary selection, since unarmed, unornamented, or -unattractive males would succeed equally well in the battle for life and -in leaving a numerous progeny, but for the presence of better-endowed -males. We may infer that this would be the case, because the females, -which are unarmed and unornamented, are able to survive and procreate -their kind. . . . Just as man can improve the breed of his game-cocks by -the selection of those birds which are victorious in the cockpit, so it -appears that the strongest and most vigorous males, or those provided -with the best weapons, have prevailed under nature, and have led to the -improvement of the natural breed or species." - - - Selection by Females - -"With mammals," says Darwin (_loc. cit._, p. 763), "the male appears to -win the female much more through the law of battle than through the -display of his charms." - -In the case of birds, however, feminine preference comes more into play. -It is well known that cocks display their charms to the hens at the -breeding season, and Darwin believed that the hen selected the most -beautiful of her rival suitors. - -"Just as man," he writes (p. 326 of _The Descent of Man_, new edition, -1901), "can give beauty, according to his standard of taste, to his male -poultry, or, more strictly, can modify the beauty originally acquired by -the parent species, can give to the Sebright bantam a new and elegant -plumage, an erect and peculiar carriage, so it appears that female birds -in a state of nature have, by a long selection of the more attractive -males, added to their beauty or other attractive qualities." - -Thus the theory of sexual selection is based on three assumptions. -Firstly, that there is in all species competition among the males for -females with which to mate. Secondly, that this results in either "the -law of battle" among the males, or selection by the female of one among -several admirers. Thirdly, that the female selects, as a rule, the most -attractive of her suitors. - -The evidence upon which Darwin founds this theory may be thus -summarised:-- - -1. In cases where the sexes differ in appearance, or power of song, it is -almost invariably the cock who is the more beautiful or the better -singer, as the case may be. - -2. All male birds that possess accessory plumes or other attractions, -make a most elaborate display of these before the females at the mating -season, hence "it is obviously probable that these appreciate the beauty -of their suitors." - -3. Darwin was able to cite specific instances in which the hens showed -preference. - -In the case of polygamous species there can be no doubt that there is -considerable competition among males for their wives. It cannot be said -that the contention is so well established in the case of monogamous -species. D. Dewar suggests that circumstances may occur in which the hens -have to fight for the cock, or in which the male is in the happy position -of being able to select his mate. He states his belief that in many cases -the selection is mutual, as in the case of human beings. - -"I have seen," he writes, on page 13 of _Birds of the Plains_, "one hen -Paradise Flycatcher (_Terpsiphone paradisi_) drive away another and then -go and make up to a cock bird. Similarly, I have seen two hen orioles -behave in a very unladylike manner to one another all because they both -had designs on the same cock. He sat and looked on from a distance at the -contest." - -Darwin quotes, on page 500 of _The Descent of Man_, a case of a male -exercising selection: "It appears to be rare when the male refuses any -particular female, but Mr Wright of Geldersley House, a great breeder of -dogs, informs me that he has known some instances: he cites the case of -one of his own deerhounds who would not take any notice of a particular -female mastiff, so that another deerhound had to be employed." - -Similarly, Finn records, in _The Country-Side_ for August 29th, 1908, -that the male Globose Curassow (_Crax globicera_) in the London -Zoological Gardens, which bred with the female Heck's Curassow (_C. -hecki_), as related on p. 104, selected the hen of this very distinctly -coloured form or species in preference to any of the typical hens of his -own kind. - - - Male Attractiveness - -The cases on record of cocks being in a position to select their mates -are comparatively rare, while instances of selection on the part of the -hens are far more numerous. - -Hence it would seem that the sex, which is in a minority, and so has the -opportunity of selecting a mate, does exert a choice and prefer one -particular individual; and that, for the reasons pointed out by Darwin, -it is in most cases the female who is in the position of being able to -pick and choose her mate. It is, as Darwin truly said, far more difficult -to decide what qualities determine the choice of the female. He believed -that it is "to a large extent the external attractions of the male, -though no doubt his vigour, courage, and other mental qualities come into -play." - -Darwin argued that it is the love of hen birds for "external attractions" -in cock birds that has brought into being all the wonderful plumes that -characterise such birds as the peacock. "Many female progenitors of the -peacock," he writes, on page 661 of _The Descent of Man_ (ed. 1901), -"during a long line of descent, have appreciated this superiority, for -they have unconsciously, by the continued preference of the most -beautiful males, rendered the peacock the most splendid of living birds." - -This conclusion has been vigorously attacked. It is argued, with some -show of reason, that it is absurd to credit birds with aesthetic tastes -equal, if not superior, to those of the most refined and civilised of -human beings. - -Is it likely, it is asked, that a bird, which will nest in an old shoe -cast off by a tramp, can appreciate beauty of plumage? - -As Geddes and Thomson say (page 29 of _The Evolution of Sex_), "When we -consider the complexity of the markings of the male bird or insect, and -the slow gradations from one step of perfection to another, it seems -difficult to credit birds or butterflies with a degree of aesthetic -development exhibited by no human being without special aesthetic -acuteness and special training. Moreover, the butterfly, which is -supposed to possess this extraordinary development of psychological -subtlety, will fly naively to a piece of white paper on the ground, and -is attracted by the primary aesthetic stimulus of an old-fashioned -wall-paper, not to speak of the gaudy and monotonous brightness of some -of our garden flowers. Thus we have the further difficulty, that we must -suppose the female butterfly to have a double standard of taste, one for -the flowers which she and her mate both visit, the other for the far more -complex colourings and markings of the males. And even among birds, if we -take those unmistakable hints of real awakening of the aesthetic sense -which are exhibited by the Australian bower-bird or by the common jackdaw -in its fondness for bright objects, how very rude is his taste compared -with the critical examination of infinitesimal variations of plumage on -which Darwin relies. Is not, therefore, his essential supposition too -glaringly anthropomorphic? - -"Again, the most beautiful males are often extremely combative; and on -the conventional view this is a mere coincidence, yet a most unfortunate -one for Mr Darwin's view. Battle thus constantly decides the question of -pairing, and in cases where, by hypothesis, the female should have most -choice, she has simply to yield to the victor." - -Darwin, with characteristic fairness, quotes some instances which appear -to be opposed to the theory that the hen selects the most beautiful of -her suitors. He informs us that Messrs Hewitt, Tegetmeier, and Brent, who -have all had a long experience of domesticated birds, "do not believe -that the females prefer certain males on account of the beauty of their -plumage. . . . Mr Tegetmeier is convinced that a game-cock, though -disfigured by being dubbed and with his hackles trimmed, would be -accepted as readily as a male retaining all his natural ornaments. Mr -Brent, however, admits that the beauty of the male probably aids in -exciting the female; and her acquiescence is necessary. Mr Hewitt is -convinced that the union is by no means left to mere chance, for the -female almost invariably prefers the most vigorous, defiant, and -mettlesome male"; and, in consequence, when there is a game-cock in the -farmyard, the hens will all resort to him in preference to the cock of -their own breed. Darwin thinks that "some allowance must be made for the -artificial state in which these birds have long been kept," and cites in -his favour the case of Mr Cupples' female deerhound that thrice produced -puppies, and on each occasion showed a marked preference for one of the -largest and handsomest, but not the most eager, of four deerhounds living -with her, all in the prime of life. - -The question what is it that determines the choice of the female is -obviously one of considerable importance, and it was to be expected that -many zoologists would have conducted experiments with a view to deciding -it. This legitimate expectation has not been realised. - -The matter of sexual selection remains to-day practically where Darwin -left it. Wallace rejects the whole theory, and believes that natural -selection alone can explain all the phenomena of sexual dimorphism. To -such an extent does the enticing idea of the all-puissance of natural -selection dominate the minds of scientific men that but few of them have -paid any attention to the question of sexual selection. This neglect of -the subject affords an example of the baneful results of the too-ready -acceptance of an enticing theory, "Natural selection explains everything, -why then investigate further?" seems to be the general attitude of our -present-day naturalists. - -Edmund Selous and D. Dewar have made some observations on birds, and the -Peckhams on spiders, in a state of nature. Such observations demonstrate -that selective mating occurs in nature, but, for the most part, fail to -show what it is that determines the choice. - -D. Dewar, however, states (_Birds of the Plains_, p. 42) that the -coloured peahens in the Zoological Gardens at Lahore show a decided -preference for the white cocks, which are kept in the aviary along with -normally coloured cocks. He gives it as his opinion that "the hens select -the white cocks, not because they are white, but because of the strength -of the sexual instincts of these latter. The white cocks continually show -off before the hens; the sexual desire is developed more highly in them -than in the ordinary cocks, and it is this that attracts the hens." - - - Pearson's Investigations - -The only zoologists who have investigated experimentally the question of -sexual selection appear to be Karl Pearson and Frank Finn. The former -tried to determine, by actual measurements, whether there is any -preferential mating among human beings as regards physical -characteristics. "Our statistics," he writes, on page 427 of _The Grammar -of Science_, "run to only a few hundreds, and were not collected _ad -hoc_. Still, as far as they go, they show no evidence of preferential -mating in mankind on the basis of stature, or of any character _very_ -closely correlated with stature. Men do not appear, for example, to -select tall women for their wives, nor do they refuse to mate with very -tall or very short women." As regards eye-colour, Pearson seems to have -arrived at somewhat more definite results. "We conclude," he writes (p. -428), "that in mankind there certainly exists a preferential mating in -the matter of eye-colour, or of some closely allied character in the -male; in the case of the female there also appears to be some change of -type due to preferential mating. . . . The general tendency is for -lighter-eyed to mate, the darker-eyed being relatively less frequently -mated." - -But Pearson's experiments seem to show that as regards stature and -eye-colour there is "a quite sensible tendency of like to mate with -like." "In fact," writes Pearson, "husband and wife for one of these -characters are more alike than uncle and niece, and for the other more -alike than first cousins." He adds, "Such a degree of resemblance in two -mates, which we reasonably assume to be not peculiar to man, could not -fail to be of weight if all the stages between like and unlike were -destroyed by differential selection." - -Two obvious criticisms of the results obtained by Prof. Pearson occur to -us. The first is that his conclusions do not seem to be in accordance -with the popular notion that fair-haired men prefer dark hair in a woman, -while dark-haired men prefer fair-haired women, and _vice versa_. The -second is that the human animal is not a typical one. Husbands and wives -are selected for mental and moral qualities rather than physical ones. -The same may, of course, be to some extent true of animals, but in these -there must of necessity be far less variation as regards mental -attributes. Moreover, the question of income is much bound up with human -matrimonial alliances; a rich man or woman has the same advantage in -selection as is possessed by an animal endowed with more than the average -physical strength of its species. - - - Finn's Experiments - -Finn adopted the plan of experiment suggested by Prof. Moseley. His -apparatus consisted of a cage divided into three compartments by wire -partitions, so that a bird living in one of them could see its neighbour -in the next compartment. In the middle compartment he placed a hen -Amadavat (_Sporaeginthus amandava_), and in each of the other compartments -he put a cock bird. Under such circumstances, the hen in the middle -compartment will sit and roost beside the cock she prefers. The male -amadavat, he writes, in _The Country-Side_, vol. i. p. 142, "is in -breeding plumage red with white spots, and the hen brown. The red varies -in intensity even in full-plumaged birds, and I submitted to the hen -first of all two male birds, one of a coppery and the other of a rich -scarlet tint. In no long time she had made her choice of the latter bird; -the other, I am sorry to say, very soon died; and, as he had appeared -perfectly healthy, I fear grief was accountable for his end--a warning to -future experimenters to remove the rejected suitor as early as possible. -In the present case I took away the favoured bird, and put in the side -compartments he and his rival had occupied two other cocks, which -differed in a similar way, though not to the same extent. Again the hen -kept at the side of the rich red specimen, so, deeming I knew her views -about the correct colour for an amadavat, I took her away too, and tried -a second hen with these two males. This was an unusually big bird, and a -very independent one, for she would not make up her mind at all, and -ultimately I released all three without having gained any result. - -"Subsequently I made another experiment with linnets. In this case all -three were allowed to fly in a big aviary-cage together, a method which I -do not recommend. - -"In this case, however, the handsomest cock, which showed much richer red -on the breast, had a crippled foot, and proved, as I had expected, to be -in fear of the other; nevertheless, the hen mated with him. It must be -said, in justice to the duller bird, that he did not press the advantage -his soundness gave him, but with a less gentle bird than the linnet this -would have happened." - -It is obvious that there is a wide field for observation on these lines. -In the case of large birds the experiment could be made still more -conclusive by confining the three birds to be experimented on in a single -enclosure, divided into three compartments by fences. The males should be -placed each in a separate compartment, and have a wing clipped so as to -prevent them leaving their respective compartments, while the hen should -be allowed the power of flight so that she can visit at will any -compartment. - -Finn has also recorded (_loc. cit._) some other observations bearing on -the question of sexual selection. He writes:-- - -"One cannot observe or read about the habits of birds very much without -finding out that, whatever may be the value of beauty, strength counts -for a great deal. Male birds constantly fight for their mates, and the -beaten individual, if not killed, is at any rate kept at a distance by -his successful rival, so that, if he be really more beautiful, his beauty -is not necessarily of much service to him. I was particularly impressed -by this about a couple of years ago, when I frequently watched the -semi-domesticated mallards in Regent's Park in the pairing season. These -birds varied a good deal in colour; in some the rich claret breast was -wanting, and others had even a slate-coloured head instead of the normal -brilliant green. Yet I found these 'off-coloured' birds could succeed in -getting and keeping mates when correctly-dressed drakes pined in lonely -bachelorhood; one grey-breasted bird had even been able to indulge in -bigamy. That strength ruled here was obvious from the way in which the -wedded birds drove away their unmated rivals, a proceeding in which their -wives most thoroughly sympathised. - -"Evidently, beauty does not count for much with the park duck, and the -same seems to be the case with the fowl. As a boy, I often used to visit -a yard wherein was a very varied assortment of fowls. Among these was one -very handsome cock, of the typical black and red colouring of the wild -bird, and very fully 'furnished' in the matter of hackle and sickle -feathers. Yet the hens held him in no great account, while the master of -the yard, a big black bird, with much Spanish blood, provided with a huge -pair of spurs, was so admired that he was always attended by some little -bantam hens, although they might have had diminutive husbands of their -own class. - -"It must be remembered, however, that these ducks and fowls had an -unnaturally wide choice. In nature, varieties are rare, and the competing -suitors are likely to be all very much alike; this makes matters very -difficult for the observer, who may easily pass over small differences -which are plain enough to the eyes of the hen birds." - -[Illustration: COURTSHIP OF SKYLARK] - - - Display of Undecorated Cocks - -Finn observed that a young hen Bird of Paradise (_Paradisea apoda_) in -the London Zoological Gardens, mated with a fully adult cock in the next -compartment although a young cock in female plumage in her own -compartment did his best to show off. - -It would thus seem that the very limited evidence at present available is -not sufficient to sustain the theory that the hens select the most -attractive of their suitors. It is significant that plainly-coloured -species of birds show off with as much care as their gaily-plumaged -brethren; and, if they be nearly allied, assume similar courting -attitudes. Thus the homely-attired males of the Spotted-bill (_Anas -poecilorhyncha_), Gadwall, and Black Duck (_Anas superciliosa_), show off -in precisely the same way as does the handsome mallard. - -Howard describes and figures in his excellent and beautifully illustrated -monograph the elaborate display at the pairing season of some of our -plain-coloured little warblers. The skylark has also a notable display. - -The common partridge assumes a nuptial attitude similar to that of the -pheasant, and, although the cock of the former species has nothing -brilliant to show off, the hen partridge pays far more attention to the -display of her suitor than does the hen pheasant. - -The fact that some cock birds show off _after_ the act of pairing seems -to tell against the theory of sexual selection, or at any rate to -indicate the purely mechanical nature of the performance. Finn has -witnessed this post-nuptial display at the Zoological Gardens (London) in -the pied wagtail, the peacock, the Andaman Teal (_Nettium albigulare_), -the Avocet, the Egyptian Goose (_Chenatopex aegyptiaca_), and the Maned -Goose (_Chenonetta jubata_). - -Another objection to the theory that the bright colours of cock birds are -due to feminine selection is presented by those birds which breed in -immature plumage. Darwin admits that this objection would be a valid one -"if the younger and less ornamental males were as successful in winning -females and propagating their kind as the older and more beautiful males. -But," he continues, "we have no reason to suppose that this is the case." - -Unfortunately for the theory of sexual selection, there is evidence to -show that the cock Paradise Fly-catcher (_Terpsiphone paradisi_) in -immature plumage is quite as successful in obtaining a mate as is the -cock in his final plumage. The cock of this beautiful species has a -chestnut plumage in his second year, and a white one in the third and -subsequent years of his life. Nevertheless, a considerable proportion of -the nests found belong to chestnut cocks. - - - Plumage of Herons - -Darwin was of opinion that any novelty in colouring in the male is -admired by the female; and in this manner he sought to overcome some -difficulties to his theory which certain birds presented. - -Writing of the heron family, he says:-- - -"The young of the _Ardea asha_ are white, the adults being -slate-coloured; and not only the young, but the adults of the allied -_Buphus coromandus_ in their winter plumage are white, their colour -changing into a rich golden buff during the breeding season. It is -incredible that the young of these two species, as well as of some other -members of the same family, should have been specially rendered pure -white, and thus made conspicuous to their enemies; or that the adults of -one of these two species should have been specially rendered white during -the winter in a country which is never covered with snow. On the other -hand, we have reason to believe that whiteness has been gained by many -birds as a sexual ornament. We may therefore conclude that an early -progenitor of the _Ardea asha_ and the _Buphus_ acquired a white plumage -for nuptial purposes, and transmitted this colour to their young; so that -the young and the old became white like certain existing egrets, the -whiteness having afterwards been retained by the young whilst exchanged -by the adults for more strongly pronounced tints. But if we could look -still further backwards in time to the still earlier progenitors of these -two species, we should probably see the adults dark-coloured. I infer -that this would be the case, from the analogy of many other birds, which -are dark whilst young, and when adult are white; and more especially from -the adult of the _Ardea gularis_, the colours of which are the reverse of -those of _A. asha_, for the young are dark-coloured and the adults white, -the young having retained a former state of plumage. It appears, -therefore, that the progenitors in their adult condition of the _A. -asha_, the _Buphus_, and of some allies have undergone, during a long -line of descent, the following changes of colour: firstly a dark shade, -secondly pure white, and thirdly, owing to another change of fashion (if -I may so express myself), their present slaty, reddish or golden-buff -tints. These successive changes are intelligible only on the principle of -novelty having been admired by the birds for the sake of novelty." - -This reasoning may appear far-fetched and unconvincing. It seems, -however, quite likely that the hen may select as her mate the suitor who -is conspicuously different from the others, not because she admires -novelty, but because his conspicuousness attracts her attention and -enables her to make up her mind quickly to take him and thus rid herself -of the other troublesome admirers, who are all very much alike. - - - Sexual Dissimilarity - -It is perhaps worthy of note that, after the most successful of her -suitors has succeeded in securing the hen, it may happen that a -disappointed rival makes love to her in the absence of her lord and -master and thereby nullifies the effect of her previous selection. - -It is to be observed that, even if we take it as proved, as Darwin -believed, that the hens alone exercise a choice of mates, and that they -select the most beautiful of their suitors, we are still far from -arriving at an explanation of the fact that the males alone have acquired -beauty. Admitting that the hens always mate with the most beautiful -cocks, we should expect the offspring of each union to be all more or -less alike in beauty--that is to say, more beautiful than the mother and -less so than the cock. How are we to explain the one-sided inheritance of -this beauty? Why is it confined to the cocks? - -In order to meet this objection Darwin had to call to his aid unknown -laws of inheritance. "The laws of inheritance," he writes (_Descent of -Man_, p. 759), "irrespectively of selection, appear to have determined -whether the characters acquired by males for the sake of ornament, for -producing various sounds, and for fighting together, have been -transmitted to the males alone or to both sexes, either permanently or -periodically, during certain seasons of the year. Why various characters -should have been transmitted sometimes in one way and sometimes in -another is not in most cases known; but the period of variability seems -often to have been the determining cause. When the two sexes have -inherited all characters in common, they necessarily resemble each other; -but, as the successive variations may be differently transmitted, every -possible gradation may be found, even within the same genus, from the -closest similarity to the widest dissimilarity between the sexes." - -This statement, although it does not throw any light upon the problem, is -somewhat damaging to the theory of sexual selection. If it be admitted -that dissimilarity between the sexes is due to the fact that the males -have varied in one way and the females in another way, there seems no -necessity for invoking the aid of feminine preference. - -Even greater is the difficulty presented by those species in which the -males alone are provided with horns or antlers. "When," writes Darwin -(_Descent of Man_, p. 767), "the males are provided with weapons which in -the females are absent, there can hardly be a doubt that these serve for -fighting with other males; and that they were acquired through sexual -selection, and were transmitted to the male sex alone. It is not -probable, at least in most cases, that the females have been prevented -from acquiring such weapons on account of their being useless, -superfluous, or in some way injurious. On the contrary, as they are often -used by the males for various purposes, more especially as a defence -against their enemies, it is a surprising fact that they are so poorly -developed, or quite absent, in the females of so many animals." - -We have, we believe, demonstrated that Darwin's theory of sexual -selection is unable to account satisfactorily for all the phenomena of -sexual dimorphism. But, as we have seen, it is quite possible that sexual -selection is a real factor of evolution. - -We trust that what we have said will stimulate some leisured naturalist -to study the question of male and female preference. - -We now pass on to consider briefly some of the other attempts that have -been made to explain the phenomena of sexual dimorphism. - - - Wallace's Explanation of Sexual Dissimilarity - -Wallace does not accept the theory of sexual selection. He admits that -the form of male rivalry, which Darwin calls "the law of battle," is "a -real power in nature," and believes that "to it we must impute the -development of the exceptional strength, size, and activity of the male, -together with the possession of special offensive and defensive weapons, -and of all other characters which arise from the development of these, or -are correlated with them" (_Darwinism_, p. 283). But the view that the -female selects the most beautiful of her suitors has always seemed to -Wallace "to be unsupported by evidence, while it is also quite inadequate -to account for the facts." For example, the accessory plumes of birds -"usually appear in a few definite parts of the body. We require some -cause to initiate the development in one part rather than in another." - -Wallace considers that natural selection is able to explain all the -phenomena of sexual dimorphism. He points out that, when the sexes are -dissimilar among birds, it is almost invariably the female which is -duller coloured. The reason for this is, he believes, that the hen birds, -while sitting, "are exposed to observation and attack by the numerous -devourers of eggs and birds, and it is of vital importance that they -should be protectively coloured in all those parts of the body which are -exposed during incubation. To secure this, all the bright colours and -showy ornaments which decorate the male have not been acquired by the -female, who often remains clothed in the sober hues which were probably -once common to the whole order to which she belongs. The different -amounts of colour acquired by the females have no doubt depended on -peculiarities of habits and environment, and on the powers of defence and -concealment possessed by the species." - -In support of his contention, Wallace asserts that all species of birds, -of which the hens are as conspicuously coloured as the cocks, nest in -holes or build domed nests. The plumes and other ornaments, which the -cocks of certain species display, Wallace would attribute to a surplus of -strength, vitality, and growth power, which is able to expend itself in -this way without injury. - -"If," he writes, "we have found a _vera causa_ for the origin of -ornamental appendages of birds and other animals in a surplus of vital -energy, leading to abnormal growths in those parts of the integument -where muscular and nervous action are greatest, the continuous -development of these appendages will result from the ordinary action of -natural selection in preserving the most healthy and vigorous -individuals, and the still further selective agency of sexual struggle in -giving to the very strongest and most energetic the parentage of the next -generation." (_Darwinism_, p. 293.) "Why," he says, "in allied species -the development of accessory plumes has taken different forms we are -unable to say, except that it may be due to that individual variability -which has served as the starting point for so much of what seems to us -strange in form, or fantastic in colour, both in the animal and vegetable -world." - - - Wallace's Theory Criticised - -Wallace's view that the dull plumage of the hen bird is due to her -greater need of protection is based on the assumption that the hen bird -alone takes part in incubation. - -Is this assumption a correct one? - -It certainly is not in all cases. As D. Dewar has stated in _Birds of the -Plains_, the showy white cock Paradise Fly-catcher (_Terpsiphone -paradisi_) sits in broad daylight on the open nest quite as much as the -hen does. And this may prove to be true of many other species of birds. -Again, the cocks of the various species of Indian sunbirds are brightly -coloured while the hens are dull brown. In these species the hen alone -sits on the eggs, but, as the nest is well covered-in, the hen might -display all the colours of the rainbow without being visible to passing -birds. Moreover, as D. Dewar pointed out in a paper read before the Royal -Society of Arts (_Journal_, vol. lvii., p. 104), although, in most -species of Indian dove, the sexes show little or no dissimilarity, there -is one species (_Oenopopelia tranquebarica_) which exhibits considerable -sexual dimorphism. But the nesting habits of this peculiar species are in -all respects similar to those of the other species of dove. Why then the -marked dissimilarity of the sexes? - -Another objection to the theory of Wallace is that urged by J. T. -Cunningham (_Archiv fuer_ _Entwicklungsmechanik der Organismen_, vol. -xxvi., p. 378), namely, that the secondary sexual characters in those -species which possess them show an entire absence of uniformity in nature -and position. "Why," asks Cunningham, "should the male constitution of -the stag show itself in bony excrescences of the skull, in the peacock in -excessive growth of the other end of the body? Why should the larynx be -modified in one mammal, the teeth in another, the nose in another? Why is -the male newt distinguished by a dorsal fin, the male frog by a swelling -on the fore foot?" - -Another objection to the explanation of sexual dimorphism suggested by -Wallace, is that in many species of bird, as, for example, the house -sparrow and the green paroquets of India, the external differences -between the sexes are so slight that it is unreasonable to believe that -they are the result of natural selection. It seems impossible to hold -that the Rose-ringed Paroquet (_Palaeornis torquatus_)--a species which -nests in holes--would have become extinct if the hens had developed the -narrow rose-coloured collar that characterises the cocks. - -Darwin pointed out that while Wallace's hypothesis might appear plausible -if applied to colour, it can scarcely be said to explain the origin of -such structures as the musical apparatus of certain male insects, or the -larger size of the larynx in some birds and mammals. We thus see that -suggestions offered by Wallace, although they contain a modicum of truth, -fail to explain the phenomena of sexual dimorphism. - -The fairest possible criticism of these views is that of Darwin:-- - -"It will have been seen that I cannot follow Mr Wallace in the belief -that dull colours, when confined to the females, have been in most cases -specially gained for the sake of protection. There can, however, be no -doubt, as formerly remarked, that both sexes of many birds have had their -colours modified, so as to escape the notice of their enemies; or in some -instances, so as to approach their prey unobserved, just as owls have had -their plumage rendered soft, that their flight may not be overheard" -(_The Descent of Man_, p. 745). - - - The Theory of Thomson and Geddes - -Thomson and Geddes have attempted to explain sexual dimorphism on the -hypothesis that males are essentially dissipators of energy, while -females tend to conserve energy. They point out that the spermatozoon is -a small intensely active body, which dissipates its energy in motion, -while the ovum is a large inert body--the result of the female tendency -to conserve energy and to build up material. The various ornaments and -excrescences which appear in male organisms are the result of this male -tendency to dissipate energy. In the spermatozoon the dissipated energy -appears in the form of active movement; in the adult organism it takes -the shape of plumes and other ornaments, of song and contests for the -females. - -This theory, however, does not explain what we might call the haphazard -nature of sexual dimorphism. If sexual dissimilarity is due to the -tendency of the male to dissipate energy, why do we see very marked -dimorphism in one species, and no dimorphism in a very nearly allied -species? Why are the males larger than the females in some species, and -smaller in other species? Again, how is it that in certain species of -birds--the quails of the genus _Turnix_, the Painted Snipe (_Rhynchaea_), -and the Phalaropes--it is the female who possesses the more showy -plumage? Moreover, this theory, equally with that of Wallace, does not -explain why the excrescences which characterise the male appear in -various parts of the body in different species. - - - Stolzmann's Theory - -Stolzmann has made an ingenious attempt to explain why in birds the cock -is so frequently more conspicuously coloured than the hen. He asserts -that among birds the males are more numerous than the females, and that -this preponderance is not advantageous to the species. Those males which -have not managed to secure a mate are apt to persecute the females while -sitting on the eggs, to the detriment of these latter. Natural selection, -says Stolzmann, is concerned with the well-being of the species rather -than of the individual. Hence anything that would tend to lessen the -number of males would be a good thing for the species, so that a -peculiarity, such as bright plumage, which renders the males conspicuous, -or ornamental plumes, which cause their flight to be slow, and so leads -to their destruction, will be seized upon and perpetuated by natural -selection. He points out that the cock of one species of -hummingbird--_Loddigesia mirabilis_--has not only longer tail feathers, -but a shorter wing than the female, and must, in consequence, find it -comparatively difficult to obtain food, and be more liable to fall a -victim to birds of prey than the hen. Stolzmann further suggests that the -excessive pugnacity of male birds at the breeding season may lead to the -destruction of some individuals, and so prove of advantage to the -species. - -Several objections seem to present themselves to this most ingenious -theory. - -In the first place, there does not appear to be any satisfactory evidence -to show that more cocks than hens are born. - -We may grant that a superfluity of cocks is injurious to any species, -since the unmated ones are likely to persecute the hens; we may also -grant that many cocks are handicapped in the struggle for existence by -the excessive growth of certain of their feathers, but we fail to see how -this excessive development has been caused by natural selection in the -manner suggested by Stolzmann. Although it may be advantageous to the -species for the cocks to be showy, natural selection can perpetuate this -only by weeding out the least conspicuous of the cocks. But it is the -more gaudy ones, those, according to Stolzmann, whose presence is -beneficial to the species, which will be eliminated by natural selection. -So that, in this case, that force will act in a manner contrary to the -interests of the species, if Stolzmann's idea is a correct one. - -The theory in question would therefore seem to be untenable. Nevertheless -there is doubtless some truth in the notion that too many males spoil the -species. Thus, excessive showiness and high mortality among the males may -be beneficial to the species. But we must not forget that the more -beneficial it is, the stronger must be the tendency of natural selection -to eliminate the males that possess the desired peculiarity. - - - Neo-Lamarckian Explanation - - - Cunningham's Theory - -J. T. Cunningham makes an attempt to explain the phenomena of sexual -dimorphism on Neo-Lamarckian principles. His theory is set forth in a -paper entitled _The Heredity of Secondary Sexual Characters in relation -to Hormones_, which was read before the Zoological Society of London, and -published in full in the _Archiv fuer Entwicklungsmechanik der -Organismen_. "The significant correlation of male sexual characters," he -writes, "is not with any general or essential property of the male sex, -such as katabolism (or the tendency to dissipate energy, as we have -called it), but with certain habits and functions confined to one sex, -but differing in different animals. . . . In those animals which possess -such (_i.e._ secondary sexual) characters, the parts of the soma (_i.e._ -the body) affected differ as much as they can differ; any part of the -soma may show a sexual difference: teeth in one mammal, skull in another; -feathers of the tail in one bird, those of the neck in another, and so -on. But in all cases such unisexual characters correspond to their -functions or use in habits and instincts which are associated, but only -indirectly, with sexual production. These habits are as diverse and as -irregular in their distribution as the characters. The cocks of common -fowls and of the Phasianidae generally are polygamous, fight with each -other for the possession of the females, and take no part in incubation -or care of the young, and they differ from the hens in their enlarged -brilliant plumage, spurs on the legs, and combs, wattles, or other -excrescences on the head. In the Columbidae _per contra_ the males are not -polygamous, but pair for life, the males do not fight, and share equally -with the females in parental duties. - -"Corresponding with this contrast of sexual habits is the contrast of -sexual dimorphism, which is virtually absent in the Columbidae. - -"I think, then, the only scientific explanation is that the difference of -habits is the cause of the sexual dimorphism, and that the special sexual -habits which occur in some species but not in others are the causes of -the sexual characters. . . . The habits in question always involve -certain definite stimulations applied to those parts of the body whose -modification constitutes the somatic sexual characters. The stimulations -are confined, as the characters are confined, to one sex, to one period -of life, to one season of the year, to those animals which have the -characters, to those parts of the body which are modified." Mr Cunningham -believes that these stimulations cause hypertrophy or excessive growth of -the part affected, and that this peculiarity is transmitted to the -offspring. And thus he supposes all the ornaments and excrescences of the -males of various species to have arisen. - -As evidence in favour of his view, he points out that these excrescences -are, in many species, not only functionless but absolutely injurious, as -in the case of the comb and wattles of the jungle cock and his domestic -descendants, which merely serve as a handle for enemies to seize. - -Cunningham asserts that the only objection to his theory is the dogma -that acquired characters cannot be inherited. This assertion is, however, -not correct. It is, indeed, a very serious objection that all the -evidence available seems to show that acquired characters are not -inherited, but this is by no means the only difficulty. - -Before mentioning these further objections, let us say a word on the -subject of the inheritance of acquired characters. Mr Cunningham himself -compares the formation of a splint or spavin in a horse as the result of -special strain, to the acquisition of secondary sexual characters. -Unfortunately for Cunningham's theory, but fortunately for mankind in -general, spavined horses and mares do not beget spavined offspring. If, -then, spavin is not inherited, is it not unreasonable to assert that the -thickening of the bone that develops on the head of a butting animal is -inherited? - -Another objection to Cunningham's theory is that many birds which show -off their plumage most vigorously possess no ornamental plumes. As Howard -has recorded, many of our dull-coloured British warblers show off in the -same manner as bright-coloured birds do. If the exercise has caused the -development and inheritance of plumes in some species, why not in the -others? - -Again, Cunningham is not correct in saying that sexual dimorphism is -"virtually absent" in the Columbidae. Few birds display so striking a -sexual dimorphism as the Orange Dove (_Chrysoena victor_) of Fiji, in -which the male is bright orange and the hen green. We have already cited -the case of the curious sexually dimorphic red turtle-dove. Now, the -courting attitudes and actions of this species are precisely the same as -those of other allied turtle-doves; why, then, have these exercises -caused only one species to become sexually dimorphic? - - - Existing Theories not Satisfactory - -Our survey of the more important attempts which have been made to explain -the phenomena of sexual dimorphism leads to the conclusion that these -still require elucidation. We have weighed each theory in the balance and -found it wanting. - -The outstanding feature of sexual dissimilarity is the apparently -haphazard manner of its occurrence. - -We have already alluded to the case of the doves in India. In that -country four species are widely distributed--namely, the Spotted Dove -(_Turtur suratensis_), the Ring or Collared Dove (_Turtur risorius_), the -Little Brown Dove (_Turtur cambayensis_), and the Red Turtle-dove -(_Oenopopelia_ _tranqebarica_). The habits of all these four species -appear to be identical, nevertheless in the first three the sexes show -little or no dissimilarity in outward appearance, while in the last the -sexual dimorphism is so great that the cock and hen were formerly thought -to belong to different species. - -Another very curious case is that of the South American geese of the -genus _Chloephaga_, in which some species, as the familiar Upland or -Magellan Goose of our parks (_C. magellanica_), have the sexes utterly -unlike, while in others, as the Ruddy-headed Goose (_C. rubidiceps_), -they are quite similar to each other. - -The ducks furnish us with another very good example of the apparently -haphazard nature of sexual dimorphism. In the Common Mallard or Wild Duck -(_Anas boscas_) the cock is far more showily coloured than the hen, but -in all the species most nearly allied to it the males are as -inconspicuous as the females, _e.g._ in the Indian Spotted-bill (_Anas -poecilorhyncha_), the Australian Grey Duck (_A. superciliosa_), the -African Yellow Bill (_Anas undulata_), and the American Dusky Duck (_A. -obscura_). As the dusky duck inhabits North America, where the mallard is -also found, the case is particularly striking. - -Among mammals the lion and the tiger and the sable and roan antelopes -(_Hippotragus niger_ and _H. equinus_) furnish familiar examples of -nearly-related species, in one of which the sexes are alike and in the -other dissimilar in appearance. - - - Hormones - -Another important point to be borne in mind is the intimate correlation -that exists between the reproductive organs and the general appearance of -the organism, more especially of the secondary sexual characters. These -last, in most cases, do not show themselves until the maturity of the -sexual organs. The well-known effects of castration illustrate this -connection. Again, females in which the reproductive organs have ceased -to be functional often assume male characters. - -It has lately been proved by experiment that, in many cases at any rate, -the development of the ornaments, etc., characteristic of the sexes is -due to the secretion by the sexual cells of what are known as -hormones--that is to say, secretions which excite development of the -secondary sexual characters. The tendency to produce the external -characteristics of the sex to which an organism belongs is inherited, but -the actual development thereof is in many cases dependent on the -secretion of these hormones. Accordingly, if a male individual be -completely castrated it ceases to develop the external characters of its -sex. The evidence upon which the doctrine of hormones is based is -admirably summarised in the above-quoted paper by Cunningham. Into this -evidence we cannot go. It must suffice that the doctrine is quite in -accordance with all the observed results of castration. - -It is worthy of notice that the various features which characterise the -sexes in sexually dimorphic animals are not associated with any -particular organ or parts of the body, nor do they necessarily affect the -same part in allied species. "We cannot say," writes J. T. Cunningham, -"that any part of the soma (_i.e._ the body tissue) is specially sexual -more than another part, except that such differences between the sexes -are usually external. They usually affect the skin, and especially -epidermic appendages, and the superficial parts of the skeleton, or whole -limbs and appendages; or the difference may be one of size of the whole -soma. In mammals and birds the male is often the larger, sometimes very -much so, but there are cases in which the female is larger. There is no -general rule." - -Another important point is, that females, although they themselves show -no trace of the male character, are capable of transmitting it to their -progeny. This can be proved by crossing a hen pheasant with a cock -barn-door-fowl; the male offspring of the union display the plumes so -characteristic of the cock pheasant. These cannot have been derived from -the barn-door-fowl father; they must have come from the dull-coloured hen -pheasant. - -In this connection we may mention the curious fact recorded by Bonhote, -on page 245 of the _Proceedings of the Fourth International -Ornithological Congress_, that in the case of ducks descended from -crosses between the pintail, the mallard, and the spotbill, the drakes in -full breeding plumage showed a mixture of pintail and mallard -characteristics, while, in their non-breeding plumage, the colouring of -the spotbill is predominant. - - - Eye-colour, Comb, and Spurs - -An important point, and one which does not seem to have been pointed out -by any zoologist, is that eye-colour, comb, and spurs in birds and horns -in mammals do not stand in the same relation to the sexual organs as do -the other external characteristics. For example, the castrated Nilgai -(_Boselaphus tragocamelus_) acquires horns, but not the characteristic -male colour. In the common Indian Francolin Partridge (_Francolinus -pondicerianius_), the cock differs from the hen only in the possession of -spurs. The same applies to the various species of Snow Cock -(_Tetraogallus_). There is a breed of game-cocks which display plumage -like that of the hen, but such birds have the comb and spurs developed as -in normally feathered cocks. - -The white eye of the white-eyed Pochard Drake (_Nyroca africana_), and -the yellow eye of the cock Golden Pheasant (_Chrysolophus pictus_), which -are purely male characters, show themselves earlier than the male -plumage. Occasionally a hen golden pheasant assumes the plumage of the -cock, but she never acquires the yellow eye. - -Many birds when kept in captivity lose some of the beauty of their -plumage, and this is usually attributed to the sexual organs becoming -impaired and reacting on the somatic tissue. But this explanation cannot -in all cases be the correct one, because the linnet, although losing the -male plumage in captivity, lives long and well in a cage and breeds -readily with hen canaries. - -Another curious fact is that the male plumage sometimes appears -pathologically in hen birds, more especially in those which have become -sterile from age or disease. This phenomenon occurs comparatively -frequently in the gold pheasant, and more rarely in the common pheasant, -the fowl, and the duck. - -Phenomena such as these seem to suggest that in some cases the bright -colours of the male may be pathological, that the hormones which the male -sexual cells secrete may exercise an injurious effect on the somatic or -body tissues. Decay is known to be accompanied by the production of -brightly coloured pigment in the case of leaves. Finn suggests that the -white plumage which the cock paradise fly-catcher assumes in the fourth -year of his existence may be a livery of decay, a sign of senility. - - - The Four Kinds of Mutations - -It is our belief that sexual dimorphism arises frequently, if not -invariably, as a mutation. Mutations may be of four different kinds. - -Those which appear only, or especially, in conjunction with the male -organs, for example, whiteness in domesticated geese allowed to breed -indiscriminately. - -Those which appear only, or especially, in conjunction with the female -organs; mutations of this description appear to be very rare, but it may -be noted that in fowls allowed to breed indiscriminately, as in India, -completely black hens are common, but completely black cocks are rarely, -if ever, seen. This indicates an association between blackness and -femininity. - -Those which appear in the same manner in both sexes. The great majority -of mutations appear to be of this kind. - -Lastly, those that appear in both sexes but take a different form in the -case of the two sexes; thus in cats a mutation has given rise to sandy -males and tortoise-shell females. The mutation which has produced the -black-winged peacock shows itself in the form of a black wing in the -cock, while it causes the plumage of the hen to be grizzly white. - -We shall deal with the phenomenon of correlation at some length in the -next chapter. It is a subject to which sufficient attention has not been -paid. Even as certain characters are correlated in certain species, so in -some cases are certain characters correlated with sex. - -Why this should be so we are not in a position to say; this, however, -does not affect the indisputable fact that such correlation does exist. - -Physicians in the course of their practice sometimes come across very -curious cases of correlation in human beings. - - - Unilateral Transmission - -"It is," writes Thomson (_Heredity_, p. 290), "an interesting fact that -an abnormal element in the inheritance may find expression in the males -only or in the females only. If we could understand this we should be -nearer understanding what sex really means. - -"Haemophilia, or a tendency to bleeding, is a heritable abnormality, -partly associated with weakness in the blood-vessels, which do not -contract as they should and are apt to break, and partly connected with a -lack of coagulating power in the blood. It is usually confined to males. -But as it passes from a father through a daughter to a grandson, and so -on, it must be a latent part of the germinal inheritance of the females, -though for some obscure physiological reason it fails to find expression -in them, or has its expression quite disguised. Colour-blindness or -Daltonism has been recorded (Horner) through the males only of seven -generations. Dejerine cites another case (_fide_ Appenzeller) in which -all the males in a family history had cataract through four generations. -There are other instances of what is sometimes awkwardly called the -unilateral transmission of abnormal qualities. Edward Lambert, born in -1717, is said to have been covered with 'spines.' His children showed the -same peculiarity, which began to be manifest from the sixth to the ninth -month after birth. One of his children grew up and handed on the -peculiarity to another generation. Indeed, it is said to have persisted -for five generations, and in the males only--unilateral transmission." - -In our view, these abnormalities are of such a kind that they are only -possible in connection with the male organ; in other words, they are -mutations of the first of the four kinds cited above--those which appear -only in connection with the male organ. - -It is a curious fact that the general rule in nature seems to be that the -male is ahead of the female in the course of evolution. The sexes may be -alike at a given period in the life-history of the species. Presently a -mutation appears which is confined to the male alone; thus arises the -phenomenon of sexual dimorphism. The next step in the evolution of the -species is frequently a mutation on the part of the female which brings -her once again into line with the male, and so the sexual dimorphism -disappears, for a time at any rate. A good example of this is furnished -by the sparrows; in the common sparrow of a large part of Africa (_Passer -swainsoni_) both sexes are very plain, like the hen of the house-sparrow; -in this species (_P. domesticus_) as every one knows, the cock, though by -no means brilliant, is noticeably handsomer than his mate; while in the -Tree-sparrow (_P. montanus_) both sexes have a plumage of masculine type, -much like that of the cock house-sparrow. - -If we consider in conjunction with one another the various facts we have -cited above, we begin to grasp the nature of the phenomena of sexual -dimorphism. - -Let us consider an imaginary case of a defenceless little bird which -builds an open nest. Let us suppose that it is inconspicuously plumaged. -Now suppose that a mutation of the first kind shows itself, a mutation -which affects the cock only and makes him more conspicuous. Let us -further suppose that the cock does not share in the duties of incubation. -It is quite possible that, in spite of this apparently unfavourable -mutation, the species may survive, for, as we have seen, it does not -affect the hen, and she, since she alone incubates, stands the most in -need of protective colouring. Moreover, as Stolzmann has suggested, the -species can possibly afford to lose a few males. But suppose that both -cock and hen share in the duties of incubation, it is then quite likely -that the mutation will cause the species to become extinct, by the -elimination of all the males. Or, let us suppose that the mutation in the -direction of showy plumage affects both sexes, then in such a case the -species will almost certainly become extinct. If, however, the -hypothetical species nested in holes in trees, it is quite possible that -it might survive notwithstanding its showy plumage. - - - Greater Value of Females - -Whether, as Wallace suggests, the hen does most of the incubating, and is -exposed to special danger when sitting on her eggs in an open nest, or, -as Stolzmann urges, it is of advantage to the species that there should -not be too many males, the result is the same, that the species can -afford to allow the cock to be more gaily attired than the hen. In either -case the colouration of the cock becomes a matter of comparatively little -importance to the species, and this, coupled with the fact that the male -tends to mutate more readily than the female, will explain why, in most -species which exhibit sexual dimorphism, it is the cocks that are the -more conspicuous. In certain species the cocks alone incubate, and these -then become more important than the females to the race, so that they -have not been permitted to become showy, while the hens have been allowed -more freedom in this respect. The extreme variability of the Ruff -(_Pavoncella pugnax_) in breeding plumage points to the fact that his -colour is a matter of comparative indifference to the species; in -consequence plenty of latitude is allowed to his tendency to vary. - -Our view, then, is that evolution proceeds by mutations, which may be -large or small. - -The mutation is the result of a rearrangement in part or parts of the -fertilised egg, and this rearrangement shows itself in the adult organism -as a change in one or more of its characteristics. The mutation may be -correlated with only one of the sexual organs, and when this is the case, -it gives rise to the phenomenon of sexual dimorphism. The appearance in -the adult of certain, if not of all, characteristics is affected by -causes other than the nature of the biological molecules from which they -are derived. The tendency to develop in a certain direction is there, but -something else, such as the secretion of hormones from the sexual cells, -is frequently necessary to enable a given tendency to fully develop -itself. Thus it is that castration often affects the bodily appearance of -those animals operated on. When a mutation appears, natural selection -decides whether or not it shall persist. - - - - - CHAPTER VIII - THE FACTORS OF EVOLUTION - - - 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 in a position to decide--_Modus operandi_ of - Natural Selection--Correlation an important factor--Examples of - correlation--Correlation is a subject that requires close - study--Isolation a factor in evolution--Discriminate - isolation--Indiscriminate 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 compared 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. - -We have so far considered three factors of evolution. The first of these -is the tendency of organisms to vary along definite lines. This is a most -important factor, because, unless variation occurs in any given -direction, there can be no evolution in that direction. Variations are -the materials upon which the other factors, or causes, of evolution work. -The second great factor is natural selection. Natural selection may be -compared to a builder, and variations to his materials. The kind of -building that a builder can construct depends very largely on the -material supplied to him. The Forth Bridge could not have been built had -those who constructed it had no material given them but bricks and -mortar. Wallaceians regard natural selection as a builder who is supplied -with every kind of building material--stone, bricks, wood, iron, -aluminium, in any quantities he may desire. They therefore regard natural -selection as the one and only cause which determines evolution. This, -however, is a wrong idea. Natural selection should rather be likened to a -builder who is supplied with a limited variety of building materials, so -that considerable restrictions are imposed on his building operations. -The doors, windows, fireplaces, etc., are supplied to him ready-made. He -merely selects which of these he will use for each building. - -The third factor of evolution which we have considered is sexual -selection. As we have seen, sufficient attention has not been paid to -this subject, so that we are not yet in a position to say how much, if -any, influence it has exercised on the course of evolution. - - - The Struggle for Existence - -In addition to these three factors, there are, we believe, some others. -Before proceeding to a consideration of these, it is important to study -carefully the _modus operandi_ of natural selection, or, in other words, -the nature of the struggle for existence, as many of the statements -contained in recent books on evolution seem to us to be based upon a -mistaken conception of this important factor. - -As usual, Darwin's disciples have failed to improve upon the account he -gave of the nature of the struggle for existence. This is set forth in -Chapter III. of the _Origin of Species_. - -"The causes," writes Darwin (new edition, p. 83), "which check the -natural tendency of each species to increase in number are most obscure. -Look at the most vigorous species; by as much as it swarms in numbers, by -so much will it tend to increase still further. We know not exactly what -the checks are even in a single instance." This is perfectly true. -Nevertheless elaborate theories of protective and warning colouration and -mimicry have been built up on the tacit assumption that the checks to the -multiplication of all, or nearly all, species are the creatures which -prey upon them. Possibly no Wallaceian asserts this in so many words, but -it is a logical deduction from the excessive prominence each one gives to -the various theories of animal colouration; for, if the chief foes of an -organism are not the creatures which prey upon it, how can the particular -shade and pattern of its coat be of such paramount importance to it? - - - Checks on Increase - -We shall endeavour to show that there are checks on the increase of a -species far more potent than the devastation caused by those creatures -which feed upon it. Let us, however, first briefly set forth some of the -checks on the multiplication of organisms which Darwin mentions in the -_Origin of Species_. - -"Eggs, or very young animals," he says, "seem generally to suffer the -most, but this is not invariably the case." This is, as we have already -insisted, a most important point to be borne in mind, especially when -considering the various current theories of animal colouration. When once -the average animal has become adult its chances of survival are -enormously increased. - -A second check mentioned by Darwin is the limitation of food supply. "The -amount of food for each species," he writes (p. 84), "of course gives the -extreme limit to which each can increase; but very frequently it is not -the obtaining food, but the serving as prey to other animals, which -determines the average numbers of a species. Thus there seems to be -little doubt that the stock of partridges, grouse, and hares on any large -estate depends chiefly on the destruction of vermin. . . . On the other -hand, in some cases, as with the elephant and rhinoceros, none are -destroyed by beasts of prey." - -We are inclined to think that neither the food limit nor the beasts of -prey are a very important check on the multiplication of organisms. The -lion, for example, was never so numerous as to reach the limit of its -food supply. Before the white man obtained a foothold in Africa vast -herds of herbivores were to be seen in those districts where lions were -most plentiful. This is a most important fact, for, if the numbers of a -species are not determined by those of the animals that prey upon it, the -particular colour of an organism is probably not of any direct importance -to it. This cuts away the foundation of some of the generally accepted -theories of animal colouration. - -"Climate," writes Darwin (p. 84), "plays an important part in determining -the average numbers of a species, and periodical seasons of extreme cold -or drought seem to be the most effective of all checks. I estimated -(chiefly from the greatly reduced numbers of nests in the spring) that -the winter of 1854-55 destroyed four-fifths of the birds in my own -grounds, and this is a tremendous destruction when we remember that 10 -per cent. is an extraordinarily severe mortality from epidemics with -man." - -In our opinion, Darwin did not lay nearly enough stress upon the -importance of climate as a check on the increase of species. We have seen -that he stated his belief that it is the most effective of all checks. -But even this is not a sufficiently strong statement of the case. It -seems to us that before this check all other checks pale into -insignificance. - -Darwin failed to notice the potent effects of damp. Damp is more -injurious to most species than even cold or drought, as every one who has -tried to keep birds in England knows. All entomologists are aware how -harmful damp is to insects. Caterpillars seem to take cover under leaves -to avoid damp rather than to hide themselves from birds, since these make -a point, when searching for insects, of invariably looking carefully -under leaves. - -It is a well-known fact that a wet winter in England causes much -mortality among rabbits. The increase of the rabbit in Australia is -usually attributed to the fact that the little rodent has not so many -predatory creatures to contend with there as it has in Europe. This is -not so. In Australia the rabbit has to fight against eagles, other large -birds of prey, carnivorous marsupials, feral cats, monitor lizards and -large snakes, to say nothing of the well-organised and persistent attacks -of man. - -Were predacious creatures the most important foes of the rabbit it would -never have obtained a firm foothold in Australia. Damp appears to be its -chief enemy. In Australia this does not exist. Hence the remarkable -increase of the species. Stronger evidence it would not be possible to -advance of the potency of damp as a check on the increase of a species -and of the comparative powerlessness of the attacks of raptorial -creatures. - -The failure of the sandgrouse to establish a footing in England is, we -believe, due to the fact that it is constitutionally unfitted to -withstand our damp climate. - -The camel is an animal that revels in dry habitats, hence the difficulty -of keeping camels in damp Bengal, although they seem to thrive well -enough in the drier parts of India. - -"When a species," writes Darwin (p. 86), "owing to highly favourable -circumstances, increases inordinately in numbers in a small tract, -epidemics--at least, this seems generally to occur with our game -animals--often ensue; and here we have a limiting check independent of -the struggle for life. But even some of these so-called epidemics appear -to be due to parasitic worms, which have from some cause, possibly in -part through facility of diffusion amongst the crowded animals, been -disproportionately favoured: and here comes in a sort of struggle between -the parasite and its prey." - -Thus inadequately does Darwin deal with that bar to the increase of -organisms, which is only second in importance to the effect of climate. -The check occasioned by disease and parasites is one to which naturalists -have as yet paid but little attention. The result is a very general -misunderstanding of the true nature of the struggle for existence, in -other words, of the _modus operandi_ of natural selection. - -The tsetse-fly in Africa is a far more important check on the increase of -some animals than the lions and other beasts of prey. There are in that -continent large tracts of country, known as tsetse-fly belts, in which -neither horse, nor ox, nor dog can exist. If races of these animals were -to arise which could withstand the bite of the tsetse-fly, these species -might increase more rapidly than the rabbit in Australia has done, nor -would it matter if the creatures in question were bright crimson, or any -other conspicuous colour. - -Take the case of the lion in Africa. The chief bar to the increase in -numbers of this species appears to be the teething troubles to which the -whelps are liable. Now suppose that a mutation were to occur in the lion. -Suppose that several members of a litter were all bright blue, and that -these suffered from no teething troubles. They would probably all grow -up, and although at some disadvantage as hunters on account of their -conspicuous colouring, they would nevertheless probably increase at the -expense of the normally coloured lions, because of the immunity of their -offspring from death from teething troubles. Zoologists would then be at -a loss to explain their bright colouring. We should have all manner of -ingenious suggestions raised, namely, that in the moonlight these -creatures were really not at all conspicuous, indeed that they were -obliteratively coloured. In other words, a totally wrong explanation of -their colouring would be given and accepted. It is our belief that many -of the explanations put forward and accepted of the colouration of -existing species are wide of the mark. - -As all bee-keepers are aware, the disease known as foul-brood works more -havoc among their bees than all the insectivorous creatures put together. - -Similarly throat disease among wood-pigeons does more towards keeping -their numbers down than all the efforts of predacious birds. - -A check on multiplication not mentioned by Darwin is that which is -sometimes imposed by the individuals of the species on one another. Thus, -in some animals, as, for example, the hyaena, the male occasionally -devours his own young ones. - -A check of a similar nature results from the habit which the Indian House -Crow (_Corvus splendens_) has of interrupting the pairing operations of -its neighbours. - - - Attributes of Successful Species - -We are now in a position to sum up briefly the more important requisites -for success in the struggle for existence. - -These are not so much specialised structure as courage, a good -constitution, mental capacity and prolificacy. - -Few animals possess all these characteristics in a pre-eminent degree, -for, to use the words of Mr Thompson Seton, "Every animal has some strong -point or it could not live, and some weak point or the other animals -could not live." Courage may be of two kinds--active courage, like that -of the Englishman, or passive courage, like that of the Jew. - -As D. Dewar has said: In the struggle for existence, "An ounce of good -solid pugnacity is worth many pounds of protective colouration." - -It is of course possible for an animal to possess too much courage. An -excessive amount of courage will often cause a creature to fight -unnecessary battles, which may lead to its premature death. This is -perhaps the reason why the pugnacious black form of the leopard is not -more numerous. - -Under a good constitution we must include the power of resisting the -rigours of climate, more especially damp, the ability to resist disease, -and the enjoyment of a good digestion. When from any cause the normal -food of a species becomes scarce, the members of that species will have -to starve or supplement the normal diet with food of an unusual nature; -and those that are endowed with a good digestion will be able to digest -the new food and thus survive, while those which cannot assimilate food -to which they are unaccustomed will become emaciated and perish. We see -this in every hard winter in England, when the redwing, which, unlike -other thrushes, cannot thrive on berries, is the first to die. Most of -the more successful birds--the crows and gulls, for example--are -omnivorous--that is to say, they are able to digest all manner of food. - -Under mental capacity, we would include cunning and sufficient -intelligence to adapt oneself to changed conditions. It is largely -through man's superior mental capacity that he has become the dominant -species. It is true that he displays also courage and a good -constitution, being able to adapt himself to life under the most diverse -conditions; but this is, of course, in part due to his mental capacity, -which enables him to some extent to adapt his environment to himself. - -The advantages of prolificacy are so apparent that it is unnecessary to -dilate upon them. Nearly as important as excessive fertility is the -ability on the part of the parents to look after their young ones. - -Every successful species possesses in a special degree at least one of -the above attributes. It is interesting to take in turn the various -species which are most widely distributed and consider to what extent -they possess these several qualities. - -Let us now consider a factor in evolution which is nearly as important as -natural selection itself--we allude to the phenomenon of correlation. - - - Correlation - -We may define correlation as the interdependence of two or more -characters. This phenomenon is far more common than the majority of -naturalists seem to think. It very frequently happens that one particular -character never appears in an organism without being accompanied by some -other character which we should not expect to be in any way related to -it. - -Darwin called attention to this phenomenon. "In monstrosities," he -writes, on page 13 of the _Origin of Species_ (new edition), "the -correlations between quite different parts are very curious, and many -interesting instances are given in Isidore Geoffroy St Hilaire's great -work on this subject. Breeders believe that long limbs are almost always -accompanied by an elongated head. Some instances of correlation are quite -whimsical: thus cats which are entirely white and have blue eyes are -generally deaf; but it has been lately stated by Mr Tait that this is -confined to the males. - -"Colour and constitutional peculiarities go together, of which many -remarkable cases could be given among animals and plants. From the facts -collected by Heusinger, it appears that white sheep and pigs are injured -by certain plants, whilst dark-coloured individuals escape. Professor -Wyman has recently communicated to me a good illustration of this fact: -on asking some farmers in Virginia how it was that all their pigs were -black, they informed him that the pigs ate the paint-root -(_Lachnanthes_), which coloured their bones pink, and which caused the -hoofs of all but the black varieties to drop off; and one of the -'crackers' (_i.e._ Virginia squatters) added, "we select the black -members of a litter for raising, as they alone have a good chance of -living.' - -"Hairless dogs have imperfect teeth; long-haired and coarse-haired -animals are apt to have, as is asserted, long or many horns; pigeons with -feathered feet have skin between their outer toes; pigeons with short -beaks have small feet, and those with long beaks large feet. - -"Hence, if man goes on selecting, and thus augmenting, any peculiarity, -he will almost certainly modify unintentionally other parts of the -structure, owing to the mysterious laws of the correlation of growth." - -The great importance of the principle of the correlation of organs is, -that _natural selection may indirectly cause the survival of unfavourable -variations, or of variations which are of no utility to the organism, -because they happen to_ _be correlated with organs or structures that are -useful_. - -Physiologists insist more and more upon the close interdependence of the -various parts of the organism. All recent researches tend to show that -each of the organs has, besides its primary function, a number of -subordinate duties to perform, and that the removal of one organ reacts -on all the others. - -In face of these facts we should have expected those zoologists who have -followed Darwin to have paid very close attention to the subject of -correlation. As a matter of fact, the phenomenon seems to have been -almost completely neglected. This is an example of the manner in which -the superficial theories which to-day command wide acceptance have tended -to bar the way to research. - -There seems to be, in the case of some organisms, at any rate, a distinct -correlation between their colouring and their constitution or mental -characters. For example, the black forms of the cobra, the leopard, and -the jaguar are notoriously bad-tempered. - -"There is," writes Col. Cunningham, on p. 344 of _Some Indian Friends and -Acquaintances_, "much variation in the temper of different varieties of -cobras, and, as is often so noticeable among other sorts of animals, -there would seem to be a distinct correlation between darkness of colour -and badness of temper. It is probably in part owing to a recognition of -this that the cobras ordinarily seen in the hands of the so-called snake -charmers are of a very light colour, although the choice may also be to -some extent of aesthetic origin, seeing that the paler varieties are -specially ornamental, due to the brilliancy of their markings and the -great development of their hoods." It would thus appear that there is -also a correlation between the colour of the cobra and the size of its -hood. - -Hesketh Pritchard informs us, in _Through the Heart of Patagonia_, that -the Gauchos assert that a "picaso" colt--that is to say, a black one with -white points--is the reverse of docile. Similarly, black mice are said to -be very hard to tame. - -We have already called attention to the importance of courage and the -power of resisting the rigours of climate in the struggle for existence. -It is apparently because black is so frequently correlated with courage -that it is seen comparatively often in nature, in spite of the fact that -it is a very bad colour as regards protection from enemies. Those birds -and beasts which are black are usually thriving species. The dominance of -the crow tribe is a case in point. Crows, it is true, are not really -courageous, but they are dangerous owing to their gregarious habits, and -are dreaded by other creatures on account of their power of combination. -In _Birds of the_ _Plains_, D. Dewar records an instance of a number of -crows killing in revenge so powerful a bird as the kite. - -Since very many species seem to throw off melanistic variations, it may -perhaps be asked, How is it that more black species do not exist? - -The reply is twofold. In the first place, it is quite likely that in some -organisms black variations are not correlated with courage or extreme -pugnacity, and when such is the case the melanistic varieties will be -more likely to be exterminated by foes, on account of their -conspicuousness. It must be remembered that, other things being equal, -the inconspicuously coloured organism has a better chance of survival -than the showily coloured one. This is, of course, a very different -attitude from that which insists on the all-importance to animals of -protective colouration. Secondly, it is not difficult to see how too much -courage may be fatal to an animal in leading it to take risks which a -more timid creature would refrain from doing. This, as we have already -suggested, is probably the reason why the black panther is so scarce. The -black colour is readily inherited, so there must be some cause which -tends to kill off the black varieties of the panther. - -Lest it be thought the idea that excessive courage and pugnacity are -harmful is mere fancy, let us quote from the account of the nesting -habits of the White-rumped Swallow (_Tachycineta leucorrhoa_) given by Mr -W. H. Hudson on p. 32 of _Argentine Ornithology_. He says that no matter -how many nesting sites are available, there is always much fighting -amongst these birds for the best places. "Most vindictively," he writes, -"do the little things clutch each other, and fall to the earth twenty -times an hour, where they often remain struggling for a long time, -heedless of the screams of alarm their fellows set up above them; for -often, while they thus lie on the ground punishing each other, they fall -an easy prey to some wily pussy who has made herself acquainted with -their habits." - -We have already emphasised the importance to many species of possessing -the power of resisting the effects of damp. In the case of some organisms -favourable variations in this direction may possess a greater survival -value than those in the shape of greater speed or physical strength. - -Now, if there be any correlation between the power of resisting damp and -the colour an animal bears, it is quite probable that animals of this -colour, whether or no it be conspicuous, are likely to survive in -preference to those who are more protectively coloured. There is some -evidence that in certain cases, at any rate, resistance to climate is -correlated with colour peculiarities. For example, some fanciers assert -that yellow-legged poultry resist cold and damp better than those whose -legs are not yellow. Fowls which have yellow legs have also yellow skins. -In this connection the almost universal assumption of orange feet by -domestic guinea-fowls is significant. Normally the feet of these birds -are black, and their natural African habitat is a dry one. - -A grey or white colour appears to be correlated with resistance to cold. -In birds this may perhaps be explained by the fact that the feathers in -some light-coloured varieties are longer than in those of -normally-coloured ones. Thus mealy-coloured canaries have longer feathers -than brightly-coloured ones. - -The Arctic Skua, having no enemies to fear, stands in no need of -protective colouration. It would therefore seem that the white-breasted -form of this bird becomes more numerous as it nears the north pole, not -because of the closer assimilation of its plumage to the colour of the -snowy surroundings, but because the bird has to resist the greater degree -of cold the farther north it finds itself. Similarly, in the region of -the south pole the albino form of the Giant Petrel (_Ossifraga gigantea_) -becomes common. Both these birds are themselves predatory and not liable -to be preyed upon. - -The curious china-white legs of some desert birds--as, for example, -coursers and larks--would seem to indicate a power of resisting the hot -rays radiating from the sand on which these creatures dwell. - -White quills do not wear well either in domestic birds or in wild -albinos. This may explain why it is that when a white wild species of -bird has any black in its plumage the black is almost invariably on the -tips of the wings. - -White quill-feathers are one of the commonest variations observed in -domesticated birds, nevertheless they are as rare as complete whiteness -among birds in their natural state. - -A chestnut or bay colour in mammals appears to be correlated with a high -rate of speed, as in the thoroughbred horse. This perhaps explains why so -many of the swiftest species of antelope, such as the hartebeests and -sassaby (_Damaliscus lunatus_), are chestnut bay in colour. It is further -a remarkable fact that in the Black-buck (_Antilope cervicapra_) and the -Nilgai (_Boselaphus tragocamelus_) the females, which are faster than the -males, are not black or grey like their respective males, but reddish. - -Wild turkeys are bronze; tame ones are black more often than any other -colour. This may be due to the fact that in them nigritude is correlated -with the power to resist damp. Among human beings those races which live -in very swampy districts are often intensely black. - -It is a significant fact that those domestic animals which are bred for -speed or for fighting purposes do not assume all the varied hues that -characterise those that are allowed to breed indiscriminately. -Racehorses, greyhounds, and homing pigeons furnish examples of this. Even -more remarkable is the case of the Indian Aseel or game-cock. This is -bred purely for fighting purposes, and is required to display -extraordinary powers of endurance, since the spurs are cut off in order -to prolong the fight. Thus it is that this Indian race of game-cocks -shows little variation when compared with the English breed, which fights -in a more natural manner. The hens of the Indian form seem never to show -the colouration of the wild jungle fowl, although the cocks may do so. It -would appear that hens having the colouration of their wild ancestors -cannot breed cocks possessed of the requisite courage. The Aseel is said -to be of the highest courage only when the legs, beak and iris are white. - -There is, we believe, not the least doubt that many other connections -between colour and various characteristics have yet to be discovered. It -is high time that competent naturalists paid attention to this subject. A -study of the question will almost certainly throw much light upon many -phenomena of animal colouration which hitherto have not been -satisfactorily explained. It is quite likely that the sandy hue displayed -by birds and beasts which frequent desert regions may be due to a -correlation with the power of withstanding intense dry heat rather than -to its rendering them inconspicuous to their foes. - -As other examples of correlation we may cite the correlation which seems -to obtain between short canine teeth and the absence of a hairy covering -to the body. This phenomenon is observed both in men and pigs. Hairless -dogs almost invariably have their teeth but poorly developed. - -Darwin called attention to the connection between a short beak and small -feet in pigeons; we see the same phenomenon in the dwarf breed of ducks -known as call-ducks. - -A curious correlation exists between fowls' eggs with brown shells and -the incubating habit. Fanciers have long tried in vain to produce a hen -that lays brown eggs without becoming "broody" at certain seasons. - -Among fowls, long legs are invariably correlated with a short tail, as is -well seen in the Malay breed. This correlation may explain the short -tails of wading birds. Short-legged fowls, like Japanese bantams, have -long tails, and it is significant that the short-legged Weka Rails -(_Ocydromus_) of New Zealand have unusually long tails for the family. In -this connection we may say that the tail-like plumes of the cranes are -not tail-feathers, but the tertiary feathers of the wings. As egrets also -have long trains of plumes growing from the back, it cannot be said that -the short tail of the vast majority of the waders is due to the fact that -these birds would be at a disadvantage were their caudal feathers long. - - - Isolation - -Isolation is a most important factor in the making of species. It is a -factor to which Darwin failed to attach sufficient importance, and one -which has been to a large extent neglected by Wallaceians. - - - Divergence of Character - -We have seen how a species can be improved or changed by natural -selection. All those individuals which have varied in a favourable -direction have been preserved, and allowed to leave behind them offspring -that inherit their peculiarities, while those which have not so varied -have perished without leaving behind any descendants. Thus the nature of -the species has changed. The old type has given place to a new one. -Instead of species A, species B exists. This is what Romanes has called -_monotypic_ evolution--the transformation of one species into another -species. But any theory of the origin of species must be able to answer -the question, Why have species multiplied? How is it that species A has -given rise to species B, C, and D, or, while itself continuing to exist, -has thrown off sister species B and C? How is it that in the course of -evolution, species have not been transmuted in linear series instead of -ramifying into branches? This ramification of a species into branches has -been termed by Romanes _polytypic_ evolution. It is easy to see how -natural selection can bring about monotypic evolution, but how can it -have effected polytypic evolution? To use Darwin's phraseology, how is it -that divergence of character has come about? Darwin's reply to this -question is (_Origin of Species_, p. 136), "from the simple circumstance -that the more diversified the descendants from any one species become in -structure, constitution, and habits, by so much will they be better -enabled to seize on many and widely diversified places in the polity of -nature, and so be enabled to increase in numbers. - -"We can clearly discern this in the case of animals with simple habits. -Take the case of a carnivorous quadruped, of which the number that can be -supported in any country has long ago arrived at its full average. If its -natural power of increase be allowed to act, it can succeed in increasing -(the country not undergoing any change in its conditions) only by its -varying descendants seizing on places at present occupied by other -animals: some of them, for instance, being enabled to feed on new kinds -of prey, either dead or alive; some inhabiting new stations, climbing -trees, frequenting water, and some perhaps becoming less carnivorous. The -more diversified in habits and structure the descendants of our -carnivorous animal become, the more places they will be enabled to -occupy. What applies to one animal will apply throughout all time to all -animals--that is, if they vary--for otherwise natural selection can -effect nothing." Darwin was, therefore, of opinion that natural selection -is able to bring about polytypic evolution. Darwin tacitly assumes, in -the illustration he gives, that the various races of the carnivorous -animal are in some way prevented from intercrossing; for if they -interbreed indiscriminately, these races will tend to be obliterated. - - - Isolation - -"That perfectly free intercrossing," writes Professor Lloyd Morgan (on p. -98 of _Animal Life and Intelligence_), "between any or all of the -individuals of a given group of animals is, so long as the characters of -the parents are blended in the offspring, fatal to divergence of -character, is undeniable. Through the elimination of less favourable -variations, the swiftness, strength, and cunning of a race may be -gradually improved. But no form of elimination can possibly differentiate -the group into swift, strong, and cunning varieties, distinct from each -other, so long as all three varieties freely interbreed, and the -characters of the parents blend with the offspring. Elimination may and -does give rise to progress in any given group, _as a group_; it does not -and cannot give rise to differentiation and divergence, so long as -interbreeding with consequent interblending of characters be freely -permitted. Whence it inevitably follows, as a matter of simple logic, -that where divergence has occurred, intercrossing and interbreeding must -in some way have been lessened or prevented. - -"Thus a new factor is introduced, that of _isolation_ or _segregation_. -And there is no questioning the fact that it is of great importance. Its -importance, indeed, can only be denied by denying the swamping effects of -intercrossing, and such denial implies the tacit assumption that -interbreeding and interblending are held in check by some form of -segregation. The isolation explicitly denied is implicitly assumed." - -This is very sound criticism, and is not very materially affected by the -fact that the intercrossing of varieties does not necessarily imply a -blending of their characters in the offspring; for, as we have seen, some -characters do not blend. No matter what form inheritance takes, in order -that natural selection may cause polytypic evolution it must be assisted -by isolation in some form or other. - -Thus isolation is an important factor in evolution, though probably not -so important as its more extreme advocates would have us believe. Wagner, -Romanes, and Gulick have, in insisting upon the importance of the -principle of isolation, rendered valuable service to biological science, -but, in common with most men having a new theory, they have pushed their -conclusions to absurd lengths. - -As Romanes has pointed out, isolation may be discriminate or -indiscriminate. "If," he writes, on p. 5 of vol. iii. of _Darwin and -after Darwin_, "a shepherd divides a flock of sheep without regard to -their characters, he is isolating one section from the other -indiscriminately; but if he places all the white sheep in one field, and -all the black sheep in another field, he is isolating one section from -the other discriminately. Or, if geological subsidence divides a species -into two parts, the isolation will be indiscriminate; but if the -separation be due to one of the sections developing, for example, a -change of instinct determining migration to another area, or occupation -of a different habitat on the same area, then the isolation will be -discriminate, so far as the resemblance of instinct is concerned." - - - Discriminate Isolation - -Other names for indiscriminate isolation are separate breeding and -apogamy. Discriminate isolation is also called segregate breeding and -homogamy. The human breeder resorts to discriminate isolation in that he -separates all those creatures from which he seeks to breed, from those -from which he does not wish to breed. Natural selection itself is, -therefore, a kind of discriminate isolator, since it isolates the fit by -destroying all the unfit, and, inasmuch as it kills off all those -creatures which it fails to isolate, it differs from other forms of -isolation in preventing the inter-breeding of the unisolated forms and -their giving rise to a different race. Thus it is clear that natural -selection, unless aided by some other form of isolation, can give effect -to only monotypic evolution. This is a point on which Romanes rightly -insists strongly. - -There are several other forms of discriminate isolation. Sexual selection -would be one of these. Suppose, for example, that in any species there -are large and small varieties formed, and like tends to breed with like, -then the small individuals will breed with other small individuals, while -large ones will mate with large ones; thus two races--a large one and a -small one--will be evolved side by side, provided, of course, natural -selection does not step in and destroy one of them. - -Another kind of discriminate isolation may be due to the fact that one -variety is ready to pair before the other; thus two races are likely to -arise which breed at different seasons. It is unnecessary for us to -discourse further on the subject of discriminate isolation; those -interested in the subject should read vol. iii. of _Darwin and after -Darwin_, by Romanes. - - - Indiscriminate Isolation - -It is impossible to deny the importance of discriminate isolation as a -factor in evolution. On this there can be no room for disagreement among -biologists. It is when we come to the subject of indiscriminate isolation -that we enter a region of zoological strife. - -Is indiscriminate isolation _per se_ a factor of evolution? Romanes, -Gulick, and Wagner assert that it is, Wallace and his adherents assert -that it is not. - -As the burden of proof is on the former, they are entitled to the first -hearing. - -"We may well be disposed, at first sight," writes Romanes (_Darwin and -after Darwin_, p. 10), "to conclude that this kind of isolation can count -for nothing in the process of evolution. For if the fundamental -importance of isolation in the production of organic forms be due to its -segregation of like with like, does it not follow that any form of -isolation which is indiscriminate must fail to supply the very condition -on which all the forms of discriminate isolation depend for their -efficacy in the causing of organic evolution? Or, to return to one's -concrete example, is it not self-evident that the farmer who separated -his flock into two or more parts indiscriminately, would not effect any -more change in his stock than if he had left them all to breed together? -Well, although at first sight this seems self-evident, it is, in fact, -untrue. For, unless the individuals which are indiscriminately isolated -happen to be a very large number, sooner or later their progeny will come -to differ from that of the parent type, or unisolated portion of the -parent stock. And, of course, as soon as this change of type begins, the -isolation ceases to be indiscriminate; the previous apogamy has been -converted into homogamy, with the usual result of causing a divergence of -type. The reason why progeny of an indiscriminately isolated section of -an originally uniform stock--_e.g._ of a species--will eventually deviate -from the original type is, to quote Mr Gulick, as follows:--'No two -portions of a species possess exactly the same average character, and the -initial differences are for ever reacting on the environment and on each -other, in such a way as to ensure increasing divergence as long as the -individuals of the two groups are kept from intergenerating.'" - -The words of Mr Gulick require close scrutiny. We may admit that "no two -portions of a species possess exactly the same average character," but -why should the two, if prevented from interbreeding yet subjected to -similar climatic and other conditions, present the phenomenon of -"increasing divergence?" The reason assigned by Romanes is the "Law" of -Delboeuf, which runs:--"_A constant cause of variation_, however -insignificant it may be, changes the uniformity of type little by little, -and diversifies it _ad infinitum_." From this "Law" it follows, says -Romanes, on p. 13 of vol. iii. _Darwin and after Darwin_, that "no matter -how infinitesimally small the difference may be between the average -qualities of an isolated section of a species compared with the average -qualities of the rest of that species, if the isolation continues -sufficiently long, differentiation of specific type is necessarily bound -to ensue." - -This deduction involves two important assumptions. The first is, that in -each of the separated portions of the given species there is a constant -cause of variation operating in one direction in the case of one portion -and in another direction in the case of the other. This assumption is, -unfortunately, not founded on fact. If we were to take one hundred -race-horses and shut them up in one park and one hundred cart-horses and -shut them up in another park, and prevent the interbreeding of the two -stocks, we should, if Romanes's tacit assumption be true, see the two -types diverge more and more from one another. We know that as a matter of -fact they will tend, generation after generation, to become more like one -another. Galton's Law of Regression, of which we have already spoken, and -which is supported by ample evidence, clearly negatives this tacit -assumption made by Romanes and Gulick. The second assumption upon which -their reasoning is based is that there is no limit to the amount of -change which can be effected by the accumulation of fluctuating -variations; but, as we have already seen (on p. 70), there is a very -definite limit and this limit is quickly reached. - -Thus the arguments of Romanes and Gulick are fundamentally unsound. - - - Mollusca of Sandwich Isles - -But the fact remains, and has to be accounted for, that, as a general -rule, when two portions of a species are separated, so that they are -prevented from interbreeding, they begin to diverge in character, and the -longer they remain thus separated the greater becomes that divergence. -This is an observed fact which cannot be gainsaid. - -It was the observance of this fact which led Gulick to insist with such -emphasis on the importance of geographical isolation as a factor in -evolution. He discovered that the land mollusca of the Sandwich Islands -fall into a great number of varieties. - -These islands are very hilly, and Gulick found that each of the varieties -is confined not merely to one island, but to one valley. "Moreover," -writes Romanes, on p. 16 of _Darwin and after Darwin_, "on tracing this -fauna from valley to valley, it is apparent that a slight variation in -the occupants of valley 2, as compared with those of the adjacent valley -1, becomes more pronounced in the next, valley 3, still more so in 4, -etc., etc. Thus it was possible, as Mr Gulick says, roughly to estimate -the amount of divergence between the occupants of any two given valleys -by measuring the number of miles between them. . . . The variations which -affect scores of species, and themselves eventually run into fully -specific distinctions, are all more or less finely graduated as they pass -from one isolated region to the next; and they have reference to changes -of form or colour, which in no one case presents any appearance of -utility." - -Hitherto three different attempts have been made to explain this and -allied phenomena:-- - -1. That it is the result of isolation. - -2. That it is the result of natural selection. - -3. That it is the result of the action of the environment on the -organism. - -Let us consider these in inverse order. - - - Local Species - -In the case of some organisms, more especially plants, invertebrates, and -fish, the environment does exert a direct influence on their colouration. -But, as we have seen, the changes in colour, etc., thus induced appear -never to be transmitted to the offspring of the organisms so affected. -They disappear when the offspring are removed to other surroundings. - -On the other hand, local races or species--as, for example, the -white-cheeked variety of sparrow found in India--usually retain their -external appearance when the environment is changed. In the one case the -peculiarity is not inherited; in the other it is inherited. - -The Wallaceian explanation is, of course, that the phenomenon is the -result of natural selection. There must, say Wallace and his followers, -be some differences in the environment, differences which we poor human -beings cannot perceive, that have caused the divergence between the -various isolated sections of the species. In the case of some local -species this explanation is probably the correct one, but we have no -hesitation in saying that natural selection is unable to offer a -satisfactory explanation in a considerable number of instances. Take, for -example, the case of the land mollusca of the Sandwich Islands. Mr Gulick -worked for fifteen years at them, and states that so far as he is able to -ascertain the environment in the fifteen valleys is essentially the same. -"To argue," writes Romanes, on p. 17 of vol. iii. of _Darwin and after -Darwin_, "that every one of some twenty contiguous valleys in the area of -the same small island must necessarily present such differences of -environment that all the shells in each are differently modified thereby, -while in no one out of the hundreds of cases of modification in minute -respects of form and colour can any human being suggest an adaptive -reason therefore--to argue thus is merely to affirm an intrinsically -improbable dogma in the presence of a great and consistent array of -opposing facts." - -Men of science not infrequently charge the clergy with adhering to dogma -in face of opposing facts; it seems to us that many of the apostles of -science are in this respect worse offenders than the most orthodox of -Churchmen. - -The example of the mollusca of the Sandwich Islands is by no means a -solitary one. D. Dewar cited some interesting cases in a paper recently -read before the Royal Society of Arts (p. 103 of vol. lvii. of the -Society's Journal): - -"The Indian robins present even greater difficulties to those who profess -to pin their faith to the all-sufficiency of natural selection. Robins -are found in nearly all parts of India, and fall into two species, the -brown-backed (_Thamnobia cambaiensis_) and the black-backed Indian Robin -(_Thamnobia fulicata_). The former occurs only in Northern India, and the -latter is confined to the southern portion of the peninsula. The hen of -each species is a sandy brown bird with a patch of brick-red feathers -under the tail, so that we cannot tell by merely looking at a hen to -which of the two species she belongs. The cock of the South Indian form -is, in winter, a glossy black bird, with a white bar in the wing, and the -characteristic red patch under the tail. The cock of the northern -species, as his name implies, has a sandy-brown back, which contrasts -strongly with the glossy black of his head, neck, and under parts. In -summer the cocks of the two species grow more like one another owing to -the wearing away of the outer edges of their feathers; but it is always -possible to distinguish between them at a glance. The two species meet at -about the latitude of Bombay. Oates states that in a certain zone, from -Ahmednagar to the mouth of the Godaveri valley, both species occur, and -they do not appear to interbreed. - -"It seems impossible to maintain that natural selection, acting on minute -variations, has brought about the divergence between these two species. -Even if it be asserted that the difference in the colour of the feathers -of the back of the two cocks is in some way correlated with adaptability -to their particular environment, how are we to explain the fact that in a -certain zone both species flourish? - -"A similar phenomenon is furnished by the red-vented bulbul. This genus -falls into several species, each corresponding to a definite locality and -differing only in details from the allied species, as, for example, the -distance down the neck to which the black of the head extends. There is a -Punjab Red-vented Bulbul (_Molpastes intermedius_), a Bengal (_Molpastes -bengalensis_), a Burmese (_Molpastes burmanicus_) and a Madras -(_Molpastes haemorrhous_) species. - -"It does not seem possible to maintain the contention that these various -species are the products of natural selection, for that would mean if the -black of the head of the Punjab species extended further into the neck -the bird could not live in that country." - -Thus, natural selection clearly is unable to explain some cases of -divergence of character due to geographical isolation. - -There remains the third explanation, that the divergence is the result of -the simple fact of isolation. - -We have already shown how insuperable are the objections to the view held -by Romanes and Gulick. - -It seems to us that explanation must lie in the fact that mutations occur -every now and again in some species. If two portions of a species are -separated and a mutation occurs in one portion and not in the other, and -if the mutating form succeeds in supplanting the parent form in that -isolated portion of the species in which it has appeared, we should have -the phenomenon of two races or species differing in appearance although -subjected to what appear to be identical environment. - -This, of course, is pure conjecture. All that can be said of it at -present is that it is not opposed to observed facts. That mutations do -occur must be admitted. At present we are totally in the dark as to what -causes them. They arise at the most unexpected times. - -In favour of the explanation based on "mutation" there is the interesting -fact that geographical isolation does not by any means always cause -divergence of character. This Romanes, with great fairness, freely -admits. "There are," he writes, on p. 133 of vol. iii. of _Darwin and -after Darwin_, "four species of butterflies, belonging to three genera -(_Lycaena donzelii_, _L. pheretes_, _Argynnis pales_, _Erebia manto_), -which are identical in the polar regions and the Alps, notwithstanding -that the sparse Alpine populations have been presumably separated from -their parent stocks since the glacial period." Again, there are "certain -species of fresh-water crustaceans (_Apus_), the representatives of which -are compelled habitually to form small isolated colonies in widely -separated ponds, and nevertheless exhibit no divergence of character, -although apogamy has probably lasted for centuries." - - - Cormorants - -To these examples we may add that of the cormorants. These birds have an -almost worldwide range. One species--our Cormorant (_Phalacrocorax -carbo_)--occurs in every imaginable kind of environment. Isolation has -not effected any changes in the appearance of this species. Yet in New -Zealand there exist no fewer than fourteen other species of cormorant. -New Zealand is a country where climatic conditions are comparatively -uniform, nevertheless it boasts of no fewer than fifteen out of the -thirty-seven known species of cormorant. A possible explanation of this -phenomenon may be found in the comparatively easy conditions under which -cormorants live in New Zealand.[10] Under such circumstances mutants may -be permitted by natural selection to survive, whereas in other parts of -the world such mutants have not been able to hold their own. - -Prof. Bateson has likened natural selection to a competitive examination -to which every organism must submit. The penalty for failure is immediate -death. The standard of the examination may vary with the locality. - -Isolation, then, is a very important factor in the making of species, for -without it, in some form, the multiplication of species is impossible. - - -Let us, in conclusion, briefly summarise what we now know of the method -in which new species are made. We have studied the various factors of -evolution--variation and correlation, heredity, natural selection, sexual -selection, and the other kinds of isolation. How do these combine to -bring new species into being, and to establish the same? - - - Natural Selection - -Let us first consider the factor known as natural selection, since this -is the one on which Darwin laid such great stress. Natural selection, -although a most important factor in evolution, is not an indispensable -one. Evolution is possible without natural selection. - -Let us suppose that there is no such thing as natural selection; that the -numbers of existing species are kept constant by the elimination of all -individuals born in excess of the number required to maintain the species -at the existing figure, and that the elimination of the surplus is -effected, not by natural selection, but by chance, by the drawing of -lots. Under such circumstances there may be evolution, existing species -may undergo change, but the evolution will be determined solely by the -lines along which variations occur. - -If mutations take place along certain fixed lines, and tend to accumulate -in the given directions, evolution will proceed along these lines quite -independently of the utility to the organism of the mutations that occur. -An unfavourable mutation will have precisely the same chance of survival -as a favourable one. - -If, on the other hand, mutations occur indiscriminately on all sides of -the mean, then those mutations which happen to occur most frequently will -have the best chance of survival, and they will mark the lines of -evolution. But suppose that no mutation occurs more frequently than the -others. Under such circumstances there will be no evolution, unless, by -some cause or other, portions of the species are isolated, because in the -long run the mutations will neutralise one another. - -Let us now suppose that natural selection comes into play. The old method -of determining by lot which forms shall persist is replaced by selection -on the fixed principle that the fittest shall survive. The mutations -appear as before, and as before, of the large number that occur, only a -few are permitted to survive. But now the survivors, instead of being a -motley crowd, are a selected band, composed of individuals having many -characteristics in common--a homogeneous company. Thus one result of -natural selection is to accelerate evolution, by weeding out certain -classes of individuals and preventing them breeding with those it has -selected. On the other hand, natural selection will tend to diminish the -number of species which have arisen through mutation, inasmuch as it -weeds out many mutants which would have perished had their survival been -determined by lot. - - - Origin of the Fittest - -From this the kind of work performed by natural selection should be -obvious. Natural selection does not make new species. These make -themselves, or, rather, originate in accordance with the laws of -variation. - -"You can," runs an old proverb, "bring a horse to the drinking fountain, -but you cannot make him drink." You may be able to bring a child into the -world, but you cannot secure its survival. Variation brings into being -mutants, which are incipient species, but variation cannot determine -their survival. It is at this stage that natural selection steps in. - -But because natural selection allows certain mutations to persist, it is -not correct to say that natural selection has caused these mutations or -made or originated the species to which they give rise. - -The Civil Service Commissioners do not make Indian civil servants: they -merely determine which of a number of ready-made men shall become civil -servants. Similarly, natural selection does not make new species, it -simply decides which of a number of ready-made organisms shall survive -and establish themselves as new species. Nor does natural selection -always do as much as this; for it is not the only determinant of -survival. Its position is sometimes comparable to that of the Medical -Board which inspects and rejects the physically unfit of the candidates -which have already been selected by some other authority. - -The examination conducted by natural selection may be compared to a -competitive one. A separate, independent examination is held for each -particular locality; consequently the severity of the competition will -vary with the locality. - -In each competition some candidates pass with ease: they gain an -unnecessarily high total of marks. So in nature do certain organisms, as, -for example, the Leaf-butterflies (_Kallimas_), appear to be over-adapted -to their environment. Other candidates manage to pass only by a very -narrow margin: these are paralleled in nature by those species which are -barely able to maintain themselves, which become extinct the moment the -competition increases in severity. - -The great bulk of the candidates fail to obtain sufficient marks to gain -a place among the chosen few; these unsuccessful candidates correspond to -the mutating forms which perish in the struggle for existence, to those -individuals which happen to have mutated in unfavourable directions. - -Even as many candidates have acquired knowledge of subjects in which they -are not examined, so do many organisms possess characteristics which are -of no utility to them in the struggle for existence. - -Wallaceians expend much time and energy in misguided attempts to explain -the existence of such characters in terms of natural selection. - -Nature's examination, like that held for entrance to the Indian Civil -Service, is a liberal one, so that the qualifications of the successful -candidates vary considerably. Provided a candidate is able to gain more -marks than the other candidates for a vacancy, it matters not in what -subjects the marks are gained. So is it in nature. Natural selection -takes an organism as a whole. One species may have established itself -because of its fleetness, a second because of its courage, a third -because it has a strong constitution, a fourth because it is protectively -coloured, a fifth because it has good digestive powers, and so on. - -We thus perceive the part played by natural selection and other forms of -isolation in the making of species. It is obvious that these do not make -species any more than the Civil Service Commissioners manufacture Indian -civil servants. - -The real makers of species are the inherent properties of protoplasm and -the laws of variation and heredity. These determine the nature of the -organism; natural selection and the like factors merely decide for each -particular organism whether it shall survive and give rise to a species. - -The way in which natural selection does its work is comparatively easy to -understand. But this is only the fringe of the territory which we call -evolution. - -We seem to be tolerably near a solution of the problem of the causes of -the _survival_ of any particular mutation. This, however, is merely a -side issue. The real problem is the cause of variations and mutations, -or, in other words, how species _originate_. At present our knowledge of -the causes of variation and mutation is practically _nil_. We do not even -know along what particular lines mutations occur. - -We have yet to discover whether one mutation invariably leads to another -along the same lines--in other words, whether mutating organisms behave -as though they had behind them a force acting in a definite direction. -The solution of these problems seems afar off. The hope of solving them -lies, not in the speculations in which biologists of to-day are so fond -of indulging, but in observation and experiment, especially the last. - -The future of biology is largely in the hands of the practical breeder. - - - - - FOOTNOTES - - -[1]The white, pied, and "Japan" individuals are not more different from - the type than some variations occurring in wild birds. - -[2]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. - -[3]"Effected" appears in the earlier editions, but in the later editions - has given place to "affected," probably a printer's error. - -[4]Some egrets, such as the rock-egrets (_Demiegretta_) 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. - -[5]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 importations 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 Linnaeus. Darwin - himself, at a later date, bred five young from a pair of such hybrids - (_Nature_, Jan. 1, 1880, p. 207). - -[6]In this chapter we use the word Neo-Darwinism in its usually-accepted - sense, _i.e._ as a name for that which should be called Wallaceism, - for the doctrine of the all-sufficiency of natural selection. - -[7]_Animal Colouration_, p. 125. A book full of valuable facts and ideas - on this most interesting subject. - -[8]Even these eggs, closely though they resemble in colouring the - shingle, etc., on which they are laid, are discovered and eaten by - gulls, as Mr A. J. R. Roberts points out in _The Bird Book_. - -[9]_Journal of the Bombay Natural History Society_, Vol xv. (1903-4), p. - 454. - -[10]Hutton and Drummond record other examples of this in the valuable - work entitled _The Animals of New Zealand_. - - - - - INDEX - - - A - Accentor, 1 - _Accipitcr cooperi_, 243 - Acorn, 49 - Acquired characters, 10, 14, 15, 18-24, 60, 107-10 - _Acraeeidae_, 175, 215, 228 - _AEgilops speltaeformis_, 118 - _AEgithina tiphia_, 244 - AEsthetic sense in birds, 306 - "African Nature Notes and Reminiscences," 192, 195, 199 - Aggressive resemblance, 173 - Aguara-guazu, 181 - Aitken, E. H., 64 - "Albany Review, The," 43, 48, 195, 204 - Albinism, 64, 65, 99, 283, 284, 362 - _Alcedo ispida_, 289 - Alcock, Col., 216, 217 - Alcohol, 152, 153 - Alexander, 181 - Allen, Grant, 66 - Allotrophy, 159 - Alternating characters, 143 - Alternative inheritance, 127 - Amadavat, 311 - _Amandina erythrocephala_, 122 - _A. fasciata_, 122 - "Amazement," 93 - Amazon parrot, 103 - Amazonian dolphin, 99 - Ammonites, 67 - Ammonium sulphate, 151 - Amoeba, 35 - _Amphidasys betularia_, 101 - _Anas boscas_, 123, 334 - _A. obscura_, 334 - _A. poecilorhyncha_, 315, 334 - _A. superciliosa_, 315, 334 - _A. undulata_, 334 - _Anastomus oscitans_, 282 - Ancon sheep, 95 - _Anemone magellanica_, 118 - _A. sylvestris_, 118 - Anemophilous flowers, 261 - "Animal Colouration," 194, 205, 211, 213, 218, 222 - "Animal Life and Intelligence," 368 - "Animals of New Zealand," 382 - _Anous_, 278 - _Anser cygnoides_, 114 - _Anseranas melanoleucus_, 281 - Antarctic fauna, 191 - Antelope, 48, 199, 334 - _Anthracoceros_, 220 - _Anthropoides paradisea_, 279 - _A. virgo_, 279 - _Antilope cervicapra_, 363 - Ape, 101 - Apogamy, 370 - Appenzeller, 340 - _Apus_, 381 - "Archiv fuer Entwicklungsmechanik der Organismen," 325, 330 - Arctic fauna, 173, 174, 190, 191 - Arctic regions, 173, 189 - _Ardea asha_, 317, 318 - _A. gularis_, 318 - _Ardeola grayii_, 250, 254 - Argali, 120, 130, 131 - "Argentine Ornithology," 361 - _Argynnis pales_, 381 - _A. paphia_, 103 - Aristotle, 1 - _Artemia milhausenii_, 156 - _A. salina_, 156 - Aseel, 364 - Asexual reproduction, 135 - Asiatic, 140 - Ass, 117, 127, 128, 140 - _Astur badius_, 235 - Atavism, 136, 293 - _Athene chiaradiae_, 97 - _A. noctua_, 97 - Atoms, biological, 158 - "Auk, The," 190 - _Aularches militaris_, 216 - Avebury, Lord, 205, 260 - "Avicultural Magazine, The," 98 - Avocet, 80 - - - B - Babbler, 244 - Bactrian camel, 121 - Bailey, 88 - Baillon's crake, 251 - Balanced characters, 143 - _Balearica chrysopelargus_, 105 - _B. regulorum_, 105 - _Bassaris astuta_, 242 - Batesian mimicry, 177 - Bateson, 26, 72, 73, 74, 75, 76, 102, 103, 302 - Bats, 42 - Bear, 101, 119, 190, 216, 282 - Beddard, 180, 188, 194, 205, 211 - Bee, 178, 179, 214, 221, 263, 264, 269 - Beech, purple, 87 - Bee-eater, 220, 278 - Beetroots, 71 - Belt, 216 - Beluga, 190 - Bentham, 260 - Bestiary, 125 - Bicheno's finch, 105 - Bilateral symmetry, 252, 253, 257 - Bingham, Col. C. T., 239 - Biological atoms, 158-69, 280 - Biological molecules, 157-69, 280, 285, 291, 293, 294, 295, 344 - Biological radicles, 158-69 - Biophors, 153 - "Bird Book, the," 207 - "Birds of the Plains," 233, 303, 309, 359 - Bison, 119, 126 - Blackcock, 129, 131, 249, 278 - Blackberry, 118 - Blackbird, 201, 203, 207 - Black-buck, 363 - Blakiston, 181 - Bloodsucker, 220 - Blue-bellied waxbill, 104 - Blyth, 115, 251 - Boisier, 263 - _Bombyx arrindia_, 125 - _B. cynthia_, 124 - Bonhote, 126, 288, 289, 290, 291, 292, 293, 337 - Bontebock, 196 - _Boselaphus tragocamelus_, 357, 363 - _Bos frontalis_, 126 - Boulenger, 88 - Bower-bird, 306 - Brain-fever bird, 235, 236, 248 - Bramble, 261 - _Branchipus_, 156 - Brannam, 92 - Brent, Mr, 307 - British Museum, 129, 130, 187 - _Bubo virginianus_, 221 - _Bubulcus coromandus_, 254 - Budgerigars, 101 - Buffalo, 120, 199 - Buffon, 2 - Buff Orpingtons, 65 - Buff-tip moth, 215 - _Bufo melanostictus_, 219 - Bulbul, 123, 220, 221, 244, 245, 255, 256, 279 - Bull, 119 - _Bungarus coeruleus_, 217, 247 - Bunting, reed, 98, 190, 289 - _Buphus coromandus_, 317, 318 - Burbank, 118 - Burnet moth, 102 - Bush-buck, 196 - Butcher-bird, 241, 253 - Buttercups, 70, 267, 274 - Butterfly, 45, 47, 102, 103, 196, 197, 203, 204, 209, 212, 216, - 238, 239, 240, 250, 264, 280, 306, 381 - Buzzard, 262 - - - C - Cacomistle, 242 - _Cairina moschata_, 127, 245 - Californian currant, 119 - _Caloenas nicobarica_, 65 - _Calotes versicolor_, 220 - Camel, 120, 357 - _Campophaga_, 248 - Canary, 100, 101, 102, 117, 120, 127, 280, 338, 362 - _Canis jubatus_, 181 - Capercailzie, 129, 131 - Capuchin monkey, 216 - Carbon, 153 - _Carduelis caniceps_, 255 - _C. carduelis_, 255 - Carnation, 85, 86 - Carnivores, 67 - Carp, 102 - Carrion crow, 123 - Carrot, 71, 269, 270 - _Casarca cana_, 129 - _C. tadornoides_, 129 - "Cassell's Book of the Horse," 69 - Castle, 149 - Castration, effects of, 335, 344 - Cat, 61, 98, 99, 100, 206, 282, 283, 339, 350, 356, 361 - Cat-rabbit, 125 - Cataloe, 119 - Cataract, 340 - Caterpillars, 155, 175, 205, 211, 215, 221, 350 - Cattle, 94, 95, 115 - _Centropus sinensis_, 220, 244 - _Cephalophus doriae_, 243 - _Cephalopyrus flammiceps_, 244 - _Cervulus muntjac_, 101 - _C. reevesii_, 114 - _C. vaginalis_, 114 - _Cervus paludosus_, 180 - _C. sika_, 120 - _Ceryle rudis_, 202 - Chaffinch, 289 - Chamba monaul, 104 - "Champion Ladybird," 91, 92, 93 - Change of function, theory of, 36, 37 - _Chen nivalis_, 282 - _C. rossi_, 282 - _Chenatopex aegyptiaca_, 316 - _Chenonetta jubata_, 316 - Chinese goose, 99, 114, 121, 130 - Chinese pheasant, 123 - _Chloephaga dispar_, 105 - _C. magellanica_, 105, 334 - _C. rubidiceps_, 105, 334 - Chromosomes, 145-7 - _Chrysaena victor_, 333 - _Chrysolophus amherstiae_, 121 - _C. obscurus_, 97 - _C. pictus_, 97, 121, 337 - _Chrysomitris colombiana_, 244 - _Chrysotis aestiva_, 103 - _Ciconia alba_, 282 - _C. boyciana_, 282 - Cinnabar moth, 227 - _Cissopis leveriana_, 281 - Civil Service Commissioners, 385, 387 - Cleistogamous flowers, 260 - Climate as check on multiplication, 349, 350 - Clouded-yellow butterfly, 103 - Clover, 69, 274 - _Clytus arietis_, 178, 229 - Cobra, 224, 225, 226, 358, 359 - _Colias edusa_, 103 - Colour-blindness, 340 - Colouration of Flowers, Law of Progressive, 66 - ---- of Organisms, 170-296 - Columbidae, 331, 333 - Concealing colouration, 184-7 - Congenital characters, 18, 19 - Conn, 47 - "Contemporary Review," 26 - Cope, 15, 67 - _Copsychus saularis_, 281 - _Coracias affinis_, 123, 255 - _C. indica_, 123, 220, 255 - Cordon-bleu, 104 - Cormorant, 190, 191, 277, 381, 382 - Corn, Indian, 81 - Correlation, 39, 40, 117, 162, 167, 223, 339, 340, 344, 356-65 - _Corvus corone_, 123, 255 - _C. cornix_, 123, 255 - _C. splendens_, 353 - "Country-Side, The," 261, 265, 266, 273, 304, 311, 313 - Courser, 362 - Court-bec, 72 - Cow, 119, 120, 126 - Crab, 155 - Crane, 105, 247, 248, 279, 282, 292 - _Crateropus bicolor_, 242 - _C. canorus_, 179 - _Crax globicera_, 104, 304 - _C. grayi_, 104 - _C. hecki_, 104, 304 - Crested newt, 124 - Cretaceous reptiles, 67 - Crinoids, 67 - Crocodile, 187 - Cross-fertilisation, 69, 258-60 - _Crotalus_, 223 - Crow, 47, 123, 206, 220, 247, 255, 281, 353, 355, 359, 361 - "Crow-pheasant," 220 - Cryptic colouring, 173 - Cuckoo, 220, 233, 235, 236, 243, 244, 247, 248, 289 - ---- shrike, 248 - _Cuculus canorus_, 289 - Cuenot, 149 - Cunningham, Col., 225, 226, 358 - ---- J. T., 15, 19, 20, 324, 325, 329, 331, 332, 333, 336 - Cupples, Mr, 308 - Curassow, 104, 304 - Currant, 119 - Cut-throat finch, 122 - _Cypselus affinis_, 243 - _Cytisus adami_, 119 - - - D - Dafila acuta, 122 - Dahlia, 86 - Daisy, 266, 274 - Daltonism, 340 - _Damaliscus lunatus_, 363 - Damp as a check to multiplication of species, 350, 351 - _Danaidae_, 175, 179, 215, 216, 226, 228 - _Danais chrysippus_, 179, 250 - Danger signal, 183, 214, 253, 254 - Darter, 277 - Darwin, 1-12, 14, 25-27, 31, 35, 42, 52, 54-7, 59, 60-3, 68, 83, - 96, 112, 114-7, 119, 123, 127, 130, 151, 171, 175, 182, - 184, 233, 259, 299, 301-8, 316, 319-21, 325, 326, 347 - "Darwin and after Darwin," 370-5, 377, 381 - Darwinian theory, 3, 5-8, 11, 13, 27, 28, 35, 42, 45, 52, 75, 111, - 171 - Darwinism, 1, 7, 8, 11, 14, 26 - "Darwinism," 40, 53, 112, 117, 178, 207, 213, 228, 322, 323 - "Darwinism To-day," 16, 45, 67 - _Dasyurus_, 283 - De Candolle, 86 - Decorative plumage, 40 - Deer, 101, 120, 180, 298 - Deerhound, 304, 308 - Deer-ponies, 125 - Degeneration, 168 - Dejerine, 340 - Delage, 33, 147 - Delboeuf, Law of, 373 - _Delias eucharis_, 216, 220, 221 - _Demiegretta_, 100 - Demoiselle crane, 277 - "Descent of Man," 234, 299, 301, 302, 304, 305, 319, 320, 326 - Determination of sex, 165 - "Development and Heredity," 17 - De Vries, 26, 66, 69-72, 75-8, 82-9, 95, 105, 118, 151 - Dewar, D., 43, 44, 47, 48, 195, 204, 206, 208, 210, 225, 233, 236, - 303, 308, 309, 354, 360, 378 - Dewar, G. A. B., 196, 197 - _Dicrurus ater_, 179, 233 - _Didelphys nurina_, 243 - Dimorphism, sexual, 51, 200, 201 - _Dipsacus_, 58 - Disease as a check to multiplication of species, 351 - _Dissemurus paradiseus_, 179, 220 - Divergence of character, 367 - Dog, 59, 68, 99, 100, 125, 225, 226, 282, 283, 304, 308, 352, 357, - 364, 365 - Dog-rose, 261 - Dolphin, 99 - Dominant characters, 142 - Donald, Mr D., 256 - Dragon-fly, 216, 264 - Driesh, 136 - Drongo cuckoo, 233 - Drongo-shrikes, 179, 220 - Drummond, 382 - Duck, 51, 60, 68, 97, 99, 100, 122, 126-8, 190, 247, 249, 282, 292, - 314, 315, 334, 337, 338, 365 - Duiker-buck, 243 - Dyer, Sir William Thistleton, 26 - - - E - Eagle, 65, 190, 350 - Eagle-owl, 221 - East, M. E., 79 - _Echis carinata_, 224 - "Eclipse," 69 - "Edinburgh Review, The," 38 - Eel, 102 - Eggs, colours of birds', 206-9 - Egret, 100, 206, 254, 365 - Eider-duck, 249 - Eimer, 15, 16, 33 - Eisig, 222 - _Elanoides furcatus_, 282 - _Elaps_, 197, 198 - Elder, 49 - Elementary species, 77, 78, 87, 88, 89 - Elk, Irish, 67 - _Emberiza citrinella_, 289 - _E. pyrrhuloides_, 98 - _E. schoeniclus_, 98 - _Entomophila picata_, 281 - Entomophilous flowers, 261 - _Epenthesis folleata_, 103 - Epilobias, 260 - _Equus_, 41 - _Erebia manto_, 381 - _Erythrura prasina_, 102 - "Essays on Evolution," 11, 173, 177, 181, 184, 213, 223, 226, 227, - 229, 230, 231, 234, 237, 238, 239 - _Estrelda cyanogastra_, 104 - _E. phoenicotis_, 104 - Ether, 152, 153 - _Euchelia jacobacae_, 227 - Eurasian, 140 - European, 140 - _Euxenura maguari_, 282 - Evening primrose, 84, 85, 88 - "Evolution of Sex, The," 306 - Existence, struggle for, 31, 32 - Eye-colour in human beings, 310 - Eyesight of birds, 211, 237-41 - ---- insects, 264 - Eyton, 15 - - - F - "Faery Year, The," 196 - Falcon, 204, 246, 250 - _Falco peregrinator_, 251 - _F. severus_, 251 - False mimicry, 243 - Faults in poultry, 64 - Ferrets, 100, 119 - Finch, 117, 120 - ---- Bicheno's, 105 - ---- chestnut-breasted, 98 - ---- cut-throat, 122 - ---- Gouldian, 98 - ---- Nonpareil, 102 - ---- red-headed, 142 - ---- ringed, 104 - ---- saffron, 244 - ---- yellow-rumped, 98 - Finn, 99, 102, 115, 131, 179, 216, 219, 220, 235, 241, 255, 304, - 309, 310, 313, 315, 316, 358 - Fittest, survival of the, 32 - Flowers, 65, 66 - Flowers, colours of, 258-75 - Fly-catchers, 44, 45, 47, 285, 338 - Flying squirrel, 243 - "Fortnightly Review, The," 37, 38 - Foul-brood, 353 - Fowl, 56, 58, 61, 64, 65, 99, 101, 125, 127, 128, 282, 301, 302, - 307, 314, 330, 336, 338, 339, 361, 362, 364, 365 - Fowl-ducks, 125 - Foxes, 101, 131, 190, 191 - Fox-terrier, 19 - Franqueiro cattle, 95 - _Francolinus pondicerianus_, 337 - Friar-bird, 249 - _Fringella coelebs_, 209 - Fritillary butterfly, 103 - Frog, 325 - Fruits, colours of, 258, 275 - _Fuligula marila_, 290 - Fulmar petrel, 190 - Function, change of, 36, 37 - Fungi, 263 - - - G - Gadow, Dr, 197, 245 - Gadwall, 126, 315 - Galton, 81, 82, 374 - "Game Birds and Wild Fowl of India," 131 - Gametes, segregation of, 143-5 - Gannet, 282 - Gayal, 126 - Gauchos, 359 - Gecko, 210 - Geddes, 306, 326 - Gemmules, 151 - "Genesis of Species," 7, 61 - Geographical isolation, 375 - Geological record, imperfection of, 40-2, 94 - Geranium, 260 - Germ-plasm, continuity of the, 25 - Germinal variations, 106-10 - _Geum urbanum_, 263 - Gibbon ape, 101 - Giraffe, 17, 18, 192, 196 - _Globicera_, 104 - Glutton, 190 - Goat, 283 - Goethe, 2 - Golden pheasant, 97, 129, 149, 337, 338 - Golden tench, 101 - Goldfinch, 127, 255 - Goldfish, 101, 102 - Goose, 99, 100, 105, 115, 121, 130, 190, 281, 316, 334, 339 - Gordon's currant, 119 - Goshawk, 247 - Gouldian Finch, 99 - Graba, 58 - Gradation of colour, principle of, 185 - _Graculipica melanoptera_, 244 - "Grammar of Science, The," 309 - Grass, 273 - Grasshopper, 185 - Greenfinch, 122 - Greyhound, 364 - Grosbeak, 281, 284 - Groundsel, 260 - Grouse, red, 125 - Growth-force, 15, 16, 68 - _Grus leucogeranus_, 282 - Guillemot, 58, 190, 245 - Guinea-fowl, 100, 127, 128, 279, 362 - Guinea-pig, 95, 101, 129, 283 - Gulick, 369, 372-7, 380 - Gull, 190, 191, 207, 247, 290, 355 - _Gygis_, 278 - Gyrfalcon, 190 - - - H - Haeckel, 15, 24 - Haemophilia, 340 - _Halcyon smyrnensis_, 202 - _Halioetus albicilla_, 65 - Hare, 131, 185, 200 - Harrier, 101 - Hartebeeste, 363 - Hawk-cuckoo, 235, 236 - Hawk-eagle, 101 - Hawks, 222, 235, 236, 247, 277 - _Hecki_, 104 - Helice, 103 - _Heliconidae_, 175, 215, 216, 228 - Heloderm, 217 - Henslow, 15, 22, 23, 47, 48, 259 - "Heredity," 103, 145, 166, 340 - "Heredity of Acquired Characters in Plants," 22, 48 - "Heredity of Sexual Characters in relation to Hormones," 19, 330 - Heron, 250, 317 - Herring, 193 - Hertwig, 151 - Heusinger, 357 - Hewitt, Mr, 307 - _Hierococcyx varius_, 235, 248 - Hilversum, 84 - Himalayan argali, 120 - Hinny, 127, 136, 140, 162 - _Hipparchia, semele_, 205 - _Hippotragus equinus_, 334 - _H. niger_, 334 - _Hirundo rustica_, 251 - _H. tytleri_, 251 - "History of Creation," 24 - Hobby, 250, 251 - Homogamy, 370 - Honeyeater, 281 - Hormones, 335, 338 - Hornbill, 65, 220 - Horner, 340 - Horse, 61, 68, 69, 95, 96, 100, 101, 117, 127, 128, 140, 266, 267, - 268, 272, 283, 332, 352, 363, 364, 374 - Horse, genealogy of, 41 - Houghton, 91 - Howard, 315, 332 - Hubrecht, 26 - Hume, 131 - Humming-bird, 328 - Hutton, 3 - Hutton, Captain, 115, 382 - Huxley, 3, 6, 11, 40, 100, 111 - Hyaena, 353 - Hybridism, 111-32, 292, 293 - Hydra, 21 - Hydrogen, 152, 153 - _Hydrophasianus chirurgus_, 250 - _Hyla_, 245 - Hypertely, 237, 240 - _Hypolimnas misippus_, 179, 180 - - - I - "Ibis, The," 255, 256 - _Icterus vulgaris_, 244, 281, 284 - Impeyan pheasant, 104 - Indian Civil Service, 385, 386, 387 - Indian corn, 81 - Inheritance, 133-69 - ---- alternative, 127 - ---- blended, 140, 148 - ---- definition of, 138 - ---- of acquired characters, 10, 14, 15, 18-24, 60, 107-10 - ---- particulate, 140 - ---- unilateral, 139, 140, 162 - Insectivores, 67 - Intercrossing, swamping effects of, 42, 83 - Intimidating attitudes, 224, 225 - Iora, 244 - Iridescence, 186 - Irish elk, 67, 168 - Isolation, 366-82, 387 - Isomerism, biological, 154-8 - ---- chemical, 152-4, 157 - _Ithomiinae_, 228, 246 - Ivy, 261 - - - J - Jacana, 250 - Jackdaw, 51, 306 - Jaeger, 86 - Jaguar, 45, 358 - Japanese greenfinch, 122 - ---- pheasant, 122, 124, 129 - Jardin des plantes, 88 - Java sparrow, 99, 100 - Jelly-fish, 192 - Jesse, W., 255 - Johnston, 92 - "Journal of the Bombay Natural History Society," 209 - "Journal of the Royal Society of Arts," 236, 324, 378 - Jungle-babbler, 179 - Jungle fowl, 332 - - - K - Kallima, 45, 47, 209, 212, 235, 386 - Kellog, 16, 26, 45, 47, 67 - Kingfisher, 202, 203, 206 - Kite, 282 - "Knowledge," 171, 198, 277 - Korchinsky, 15, 33 - Krait, 216, 247 - Kuppa, 224 - - - L - Labernum, 119 - _Lachnanthes_, 357 - Ladybird, 213, 214 - Lamarck, 2, 14, 17, 52 - Lamarckism, 16, 24, 25 - Lambert, Edward, 341 - Lankester, Sir E. Ray, 13, 25 - Lapwing, 207 - Lark, 185, 362 - _Larus ridibundus_, 290 - Latent characters, 149 - Law of battle, 301, 302, 321 - Leaf-butterfly, 45, 47, 209, 235, 386 - Lemming, 190 - Lemur, 242, 243 - _Lemur catta_, 242 - Leopard, black, 101, 354, 358 - _Leucopternis_, 282 - _Ligurinus sinicus_, 122 - Lily, 146 - _Linaria vulgaris peloria_, 86 - Linden, Graefin von, 155 - Links, missing, 41, 42 - Linnaeus, 65, 115 - Linnet, 212, 338 - "Linus I.," 95, 96 - Lion, 192, 334, 349, 352 - _Liothrix luteus_, 179 - Lizard, 64, 207, 210, 212, 216, 217, 220, 223, 269, 350 - _Loddigesia mirabilis_, 328 - Loeb, 147 - _Lophophorus chambanus_, 104 - _L. impeyanus_, 104 - Lucerne, 118 - Lung, 36, 37 - Lutinism, 102 - _Lycaena donzelli_, 381 - _L. pheretes_, 381 - _Lycodon aulicus_, 247 - Lyell, 3 - - - M - Mackerel, 193 - Madingly, 102 - _Maenia typica_, 221 - Magnus, 86 - Magpie, 281 - Magpie colouring, 66, 67, 280, 281 - Magrath, 256 - Male-fern, 49 - Mallard, 65, 97, 122, 126, 132, 293, 313, 315, 334, 337 - Malthus, 31 - Malva, 260 - Manchester School, 27 - Mannikin, 104 - Marbled newt, 124, 245 - Marshall, 28 - ---- Mr G. A. K., 239 - ---- Milnes, 37, 174 - Marsupials, 67 - Masters, 86 - "Materials for the Study of Variation," 73, 103 - Mauchamp sheep, 95 - Mayer, 228 - "Mechanischphysiologische Theorie der Abstammungslehre," 15 - _Medicago media_, 118 - _Megascops asio_, 44 - Melanism, 64, 101, 360 - _Melopsittacus undulatus_, 101 - Mendel, 42, 74, 136, 141, 142, 144, 145 - Mendel's Law, 145, 149, 150, 161 - Mendelism, 145 - _Mesohippus_, 41 - Micellae, 151 - _Micropus melanoleucus_, 245 - "Mikado, The," 237 - Mildew, 49 - Mimicry, conditions of, 178 - Mimicry, protective, 45, 50, 51, 173, 177-82, 226-51, 275, 293, 294 - Mink, 243 - _Miohippus_, 41 - Missing links, 41, 42 - Missouri currant, 119 - Mivart, Dr St George, 7, 61 - Mole, 180 - _Molge blasii_, 124 - _M. cristata_, 124 - _M. marmorata_, 124 - _M. vulgaris_, 221 - Mollusca, 49 - ---- of Sandwich Islands, 375, 378 - Molpastes, 123, 255 - _Molpastes bengalensis_, 256, 379 - _M. burmanicus_, 379 - _M. haemorrhous_, 255, 379 - _M. intermedius_, 256, 379 - _M. leucogenys_, 256 - Monaul, 104 - Monkey, 64, 213 - Monotypic evolution, 366 - Monstrosities, 56, 57, 358 - Morgan, Prof. Ll., 368 - ---- T. H., 26 - Morse, 190 - Moseley, Prof., 311 - _Motacilla lugubris_, 122 - _M. melanope_, 122 - Moth, 101, 102, 124, 209, 215, 227, 238, 240 - Mouse, 64, 105, 139, 141, 146, 149, 150, 180, 185, 282, 359 - Mule, 127, 136, 140, 160, 162 - Mueller, Fritz, 81, 180 - Muellerian mimicry, 177, 181, 182 - _Munia atricapilla_, 104 - _M. castaneithorax_, 98 - _M. flaviprymna_, 98 - _M. malacca_, 104 - Muscovy duck, 99, 127, 128, 281 - Musk ox, 190, 192 - _Mustela sarmatica_, 243 - Mutations, 41, 43, 66, 69, 72, 75-105, 124, 127, 134, 159, 160, - 169, 223, 280, 281, 284, 292, 295, 339, 341, 342-4, 380-8 - Mutations, theory of, 26, 38, 75, 76, 95 - Myna, 244 - _Myristicivorae_, 282 - - - N - Naegeli, 15, 16, 151 - Nahrwal, 190 - Natural selection, theory of, stated, 31, 32 - "Nature," 184 - Nautili, 67 - Nectar of flowers, 262, 264, 265, 268, 270, 271 - Neo-Darwinians, 13, 14, 25, 173, 174, 176, 188, 214, 218, 222, 233, - 238, 242, 263, 264 - Neo-Darwinism, 51, 172, 234, 235, 264, 275, 276, 297 - Neo-Lamarckians, 13, 14, 15 - _Neophron_, 282 - _Nepheronia hippia_, 179 - _Nettium albigulare_, 179 - New organs, beginnings of, 36, 73 - Newman, 126 - Newt, 124, 221, 222 - Niata cattle, 95 - Nicobar pigeon, 65 - Nilgai, 337 - Nitrogen, 153 - Noddy, 62, 279 - Nonpareil finch, 102 - _Nyroca africana_, 337 - - - O - Oates, 255, 379 - Obliterative colouration, 184-7 - _Ocydromus_, 365 - _Oenis_, 205 - _Oenopopelia tranquebarica_, 122, 123, 324, 333 - _Oenothera lamarckiana_, 84, 85, 87, 88 - _Ononis repens_, 23 - _O. spinosa_, 22 - Opossum, 243 - Orchid, 268, 269, 270, 272 - _Orgyia antiqua_, 215 - "Origin of Species, The," 7, 9, 11, 31, 53, 57, 63, 114, 170, 194, - 347, 348, 356, 367 - Oriole, 244, 249, 284, 304 - _Oriolus galbula_, 282 - _O. kundoo_, 282 - _O. melanocephalus_, 244, 284 - "Ornithological and Other Oddities," 255 - _Orohippus_, 41 - Orr, 15-7 - Orthogenesis, 15, 16, 34 - _Ossifraga gigantea_, 99, 362 - _Otidiphaps insularis_, 244 - _Ovis ammon_, 120 - _O. vignei_, 120 - Owen, Sir Richard, 7 - Owl, 247, 277, 289 - ---- little, 97, 98 - ---- scops, 101 - ---- snowy, 190 - Ox, 146, 352 - Oxygen, 152, 153, 263 - - - P - Paddy bird, 254 - Paint-root, 357 - _Palaeornis torquatus_, 102, 325 - Pallas, 115 - Pansy, 260 - Panther, 360 - _Papilio_, 228, 246 - _P. aristolochiae_, 179, 216, 220, 221 - _P. polites_, 179 - Paradise, bird of, 62, 249 - Paradise flycatcher, 47, 202, 298, 303, 316, 324, 338 - _Paradisea apoda_, 249 - Paraguay cattle, 94 - _Parnassius apollo_, 155 - Paroquet, 102, 121, 325 - Parrot, 103 - Parthenogenesis, 135, 138 - Partridge, 185, 315, 337 - _Parus leucopterus_, 245 - _Passer domesticus_, 289, 342 - _P. montanus_, 342 - _P. swainsoni_, 342 - Pasteur, 5 - _Pavo nigripennis_, 96 - _Pavoncella pugnax_, 343 - Pea, sweet, 74, 75, 81, 141 - Pear, 72 - Pearson, Karl, 309, 310 - Peckham, 308 - Pekin robin, 179 - Pelagic animals, 173, 192-4 - Penguin, 191 - Pennant's parakeet, 121 - _Petaurus breviceps_, 243 - Petrel, 44, 190, 191, 277, 337 - Pfeffer, 33 - _Phalacrocorax carbo_, 381 - Phalanger, 243 - Phalarope, 327 - _Phasianidae_, 125, 330 - _Phasianus colchicus_, 114, 123 - _P. torquatus_, 114, 123 - _P. versicolor_, 114, 123, 124 - Pheasant, 97, 104, 114, 121, 123, 128-30, 141, 315, 336, 338 - Pictet, 155, 156 - _Pieris napi_, 155 - _Piezorhynchus_, 285 - Pig, 57, 283, 357, 365 - Pigeon, 61, 62, 65, 68, 71, 72, 91, 92, 93, 98, 101, 109, 126, 127, - 244, 277, 282, 353, 357, 364, 365 - Pigment, massing of, 256 - Pike, 102, 222 - Pimpernel, 261 - Pintail duck, 130, 132, 293, 337 - Pintailed nonpareil finch, 102 - "Plant Breeding," 87 - Plasomes, 151 - Plastidules, 151 - _Platycercus elegans_, 121 - _P. erythropeplus_, 121 - _P. eximius_, 121 - _Pliohippus_, 41 - Plover, 207 - Plumage, decorative, 40 - Pochard, 126, 337 - Poecilomeres, 288-95 - _Poeephila mirabilis_, 99 - Polar bear, 119, 130 - Polar bodies, 135 - Polecat, 119 - Polytypic evolution, 367 - Poppy, 82, 261 - _Porzana bailloni_, 251 - _P. pusilla_, 251 - Post-nuptial display, 316 - _Potentilla tormentilla_, 263 - Poulton, 11, 25, 26, 171, 173, 177, 181, 184, 210, 213, 217, 221, - 223-5, 229-35, 238-42 - _Precis artexia_, 203, 204, 212 - Preferential mating among human beings, 309, 310 - Prepotency, 136 - Prickly pear, 274 - Primrose, evening, 84, 85, 88 - Pritchard, Hesketh, 359 - "Proceedings of the Fourth International Ornithological Congress," - 288, 337 - "Proceedings of the Linnaean Society," 288 - "Proceedings of the Natural History Society of Brunn," 141 - _Protohippus_, 37 - _Pseudoclytia pentata_, 103 - Pseudo-sematic colours, 173 - _Pseudotantalus cinereus_, 282 - Ptarmigan, 190 - _Pteroclurus exustus_, 204 - Puffin, 191 - Pugnacity of animals, 206, 360 - Puma, 45 - Purple beech, 87 - Pycraft, W. P., 277 - _Pycnorhampus affinis_, 284 - _P. icteroides_, 284 - _Pygaera bucephala_, 215 - - - Q - Quail, 185 - Quatrefages, de, 124 - _Quelea quelea_, 98 - _Q. russi_, 98 - _Querquedula crecca_, 290 - Quetelet's Law, 77 - - - R - Rabbit, 99, 100, 105, 183, 253, 283, 350, 352 - Racehorse, 69 - Radicles, biological, 159 - _Rallus aquaticus_, 251 - _R. indicus_, 251 - _Ranunculus bulbosus_, 70 - _Rappia_, 245 - Raspberry, 118 - Rat, 74, 282 - ---- water, 101 - Raven, 190 - Razorbill, 190 - Recessive characters, 142 - Recognition colours, 251-7, 275 - ---- marks, 124 - Red-mantled parakeet, 121 - Redpole, 207 - Redwing, 354 - Reed bunting, 98 - Reeves' pheasant, 129 - Regression, Law of, 82, 374 - Reid, Archdale, 5 - Reindeer, 190 - Rest-harrow, 22 - Reversion, 64, 65, 129, 293 - _Rhinosciurus tupaioides_, 180 - _Rhodocera rhamni_, 155 - _Rhododendron ferrugineum_, 118 - _R. hirsutum_, 118 - _Rhynchaea_, 327 - Ricardo, 28 - Ringed finch, 104 - Robin, 281, 378 - Robin, Indian, 202 - Robinson, Dr H., 171, 198 - ---- E. K., 261, 264, 265, 266, 268, 270, 272-4 - Rodents, 67 - Rogeron, 126 - Roller, 123, 220, 255 - Romanes, 366-81 - Rook, 51, 187 - Rose, 61, 267 - Rosella parakeet, 121 - Rous, Admiral, 69 - Roux, 136 - Ruff, 343 - - - S - Sable, 190 - Saffron finch, 244 - Sainfoin, 267 - Salamander, 217, 219, 221 - _Salix alba_, 118 - _S. pentandra_, 118 - Sandgrouse, 204, 351 - Sandpipers, 185, 190 - Sassaby, 363 - _Satyridae_, 205 - Scatliff, H. P., 91-3 - Scatliff strain, 91 - Scaup, 290 - Schmankewitsch, 156 - "Science," 166 - _Sciuropterus volucella_, 243 - _Scops giu_, 101 - Scops owl, American, 44 - ----, Indian, 101 - Scoter, 249 - Seal, 190, 191 - Sea-urchin, 149 - Seaweed, 263 - Sebright, Sir John, 63 - Secondary sexual characters, 298 - Segregation, 369 - ---- of gametes, 143-5 - Selous, Edmund, 308 - ---- F. C., 192, 195, 197, 203 - Sematic colours, 173 - _Sesia fuciformis_, 178 - Sexual dimorphism, 51, 297-344 - Sexual selection, theory of, 299-321 - Shaheen, 251 - Shamrock, 274 - Sheathbill, 191 - Sheep, 95, 266, 267, 283, 357, 372 - Sheldrake, 109, 129 - Shikra, 235, 236 - Shoveler, 290 - Shrew, 180, 216 - Sidgwick, 28 - Sidney, 5, 49 - Sika deer, 120 - Silver-washed fritillary butterfly, 103 - Siskin, 127, 244 - Skua, Arctic, 44, 362 - Skua-gull, 191 - Skunk, 186, 217, 221 - Skylark, 315 - Slug, 49, 185 - Smith, Adam, 28 - Snake, 185, 197, 198, 217, 220, 223-6, 247, 356 - Snap-dragon, 268, 272 - Snipe, 69, 327 - Sodium sulphate, 151 - Somatic variations, 106-10 - "Some Indian Friends and Acquaintances," 225, 358 - Sorrel, 274 - Sparrow, 213, 241, 341, 342 - ---- Java, 99, 100 - Sparrow-hawk, 235, 243 - _Spatula clypeata_, 290 - Spavin, 332 - "Species and Varieties," 69, 77, 84, 87, 118 - Species, definition of, 89 - Species, elementary, 77, 78, 87-9 - Spencer, 3, 15, 16, 28, 38, 151 - Spider, 269, 272 - _Sporaeginthus amandava_, 311 - Sports, 41, 43, 66, 75, 85, 135 - Squirrel, 101, 186, 243 - Stag, 325 - ---- Irish, 67 - Standfuss, 155 - Stanley crane, 248, 279 - St Hilaire, T. G., 2, 356 - Stick insect, 209 - _Stictoptera annulosa_, 104 - Stoat, 119, 190, 290 - Stolzmann, 327-9, 342, 343 - Stonechat, 353 - Stork, 247, 282 - "Strand Magazine," 64 - _Strix flammea_, 289 - Struggle for existence, 31, 32, 48 - ---- for nourishment, 167 - Suchetet, A., 126, 130 - _Sula capensis_, 282 - _S. serrator_, 282 - Sunbird, 324 - _Surniculus lugubris_, 235, 243 - Survival of the fittest, 32 - Survival value, 33, 34 - Swallow, 250, 251, 279, 361 - Swallow-shrike, 281 - Swallow-tail butterfly, 179 - Swan, 100 - Swift, 243, 250 - Swimming bladder of fishes, 36, 37 - _Sycalis flaveola_, 244 - _Syrphidae_, 178 - - - T - _Tachycineta leucorrhoa_, 361 - _Tadorna cornuta_, 129 - _T. tadornoides_, 129 - Tails, 62, 64 - Tait, Mr, 356 - Tanager, 281 - Tapir, 42 - Tasmanian devil, 282 - Teal, 290, 316 - Teasel, fuller's, 58 - Teeth, molar, 105 - Tegetmeier, Mr, 307 - Tern, 62, 278 - _Terpsiphone paradisi_, 202, 298, 304, 316, 324 - _Tetraogallus_, 337 - _Tetraonidae_, 125 - _Tetrapteryx paradisea_, 249 - _Tetrao tetrix_, 129 - _T. urogallus_, 129 - _Thamnobia cambayensis_, 202, 275 - _T. fulicata_, 202, 378 - Thayer, Mr Abbot, 184-7 - Thompson, Seton, 354 - Thomson, 103, 136, 145, 166, 306, 326, 340 - Throat disease, 353 - "Through Southern Mexico," 197, 245 - "Through the Heart of Patagonia," 359 - Thrush, 203, 207, 355 - Tiger, 334 - Tit, 245 - Toad, 210, 219, 241 - Toad-flax, 56 - Tortoise, 222 - Trefoil, 274 - _Trochilium_, 229 - Trogon, 62 - _Tropidonotus piscator_, 220 - Troupial, 244, 281, 284 - Tsetse-fly, 352 - _Tupaia_, 180, 216 - _T. ellioti_, 216 - Turbit, 72, 91-3 - "Turbit, The Modern," 91 - Turkey, 95, 363 - Turnspit dog, 59 - _Turtur cambayensis_, 333 - _T. suratensis_, 333 - _T. risorius_, 33, 123, 126 - Tylor, Mr Alfred, 287 - - - U - Ungulates, 67 - Unilateral transmission, 341 - Unit characters, 148-52 - _Uria grylle_, 245 - _U. lacrymans_, 58 - Urial, 120, 130, 131 - _Urodynamis tritensis_, 243 - - - V - Valezina, 103 - _Vanessa levana_, 154 - _V. prorsa_, 154 - Vapourer moth, 215 - Variation, 52-110 - ---- cause of, 59-60 - ---- continuous, 56, 69, 76, 105 - ---- definite, 55 - ---- determinate, 55 - ---- discontinuous, 43, 56, 72, 73, 76, 78, 79, 87, 105, 106, 133, - 159, 295 - ---- germinal, 106-10, 133 - ---- indefinite, 55, 59 - ---- somatic, 106-110 - _Viola_, 260 - _V. tricolor_, 260 - Volckamer, 86 - Vulture, 282 - - - W - Waggett, 12 - Wagner, 369, 372 - Wagtail, 122, 203 - Wallace, 3, 10, 13, 14, 25, 26, 35-42, 53, 112, 114, 116, 117, 171, - 175, 177, 183, 184, 207, 213, 228, 230, 251, 253, 256, 287, - 296, 308, 321-7, 343, 372, 377 - Wallaceian school of biologists, 14, 24, 25, 47, 192, 210, 251, - 346, 347, 366, 377 - Wallaceism, 172, 202 - Walrus, 190 - Warblers, British, 315, 332 - Warning colours, 173, 176, 198, 212-26 - Wasp, 174, 178, 179, 214, 227 - Wasp-beetle, 229 - Water-rail, 251 - Waxbill, blue-bellied, 104 - Weasel, 190 - Weaver, red-billed, 98 - Weber, 86 - Weir, Mr Jenner, 299 - Weismann, 25, 106, 107, 151, 154 - Weka rail, 365 - "Westminster Review," 112 - Weston, G. E., 127 - Whale, 42, 185, 190, 193 - Wheatear, 253 - Whinchat, 253 - Wiesner, 151 - Wilson, Prof. E. B., 166 - Winter coat, 188 - Wolf, 48, 130, 185, 192 - Wonder horse, 95, 96 - Woodpecker, 102 - Wright, Mr, 304 - Wyman, Professor, 357 - - - X - X-element, 165 - - - Y - Yak, 120 - Yarrow, 268 - "Year-book of the Smithsonian Institution," 184 - Yerbury, Col., 239 - Youatt, 63 - - - Z - Zebra, 196 - Zebu, 120 - Zocher & Co., 56 - Zoological Gardens, Lahore, 309 - ----, London, 104, 119, 126, 130, 206, 304, 316 - Zoological Society of London, 330 - _Zygaena filipendulae_, 102 - - - - - _OTHER WORKS BY THE SAME AUTHORS_ - - - By DOUGLAS DEWAR - - BOMBAY DUCKS - BIRDS OF THE PLAINS - ANIMALS OF NO IMPORTANCE - Etc. 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. - - - ORNITHOLOGICAL AND OTHER ODDITIES - - BY - FRANK FINN, B.A. (Oxon), F.Z.S. - LATE DEPUTY-SUPERINTENDENT OF THE INDIAN MUSEUM, CALCUTTA - - WITH NUMEROUS ILLUSTRATIONS FROM PHOTOGRAPHS - - _Demy_ 8_vo._ 10_s._ 6_d. net_ - - - PRESS OPINIONS - - _Standard._--"This book, dealing with the courting of birds, how they - fight and mimic, and moult and blush, is one of the most fascinating we - have read for some time. His book will prove as interesting to the - general reader as to the enthusiastic naturalist." - - _Morning Post._--"The book consists of a number of papers--all are - delightfully readable. A very interesting and delightful book. The - style is always clear and free from technicalities; this volume will - certainly prove as entertaining to the general reader as it is - interesting to the naturalist." - - _Globe._--"The pleasantest of reading--produced most charmingly. The - book is illustrated with numbers of beautiful photographs showing bird - and beast life with wonderful truth and charm. We must congratulate Mr - Finn and his publisher on one of the most alluring nature books we have - seen for a long time." - - _Shooting Times._--"The volume is well illustrated, and is certainly a - very amusing and highly instructive publication." - - _Country Side._--"Mr Finn always has something to tell us, and often - something new. He is at home in writing of birds. An eminently readable - book." - - _Bookman._--"Very good. Always worth reading, and is well illustrated." - - _Academy._--"A most readable volume; there is not a dull line in the - whole volume, while the illustrations are remarkably good." - - _Indian Field._--"It is always with the greatest of pleasure that we - pick up a book written by this ever-interesting author. We must - congratulate him on his latest work--a delightful work." - - - BOMBAY DUCKS - - AN ACCOUNT OF SOME OF THE EVERYDAY BIRDS - & BEASTS FOUND IN A NATURALIST'S EL DORADO - - By DOUGLAS DEWAR, F.Z.S., I.C.S. - - With Numerous Illustrations From Photographs of - Living Birds by Captain F. D. S. Fayrer, I.M.S. - - _Demy_ 8_vo._ 16_s. net._ - - - PRESS OPINIONS - - _Spectator._--"Mr Douglas Dewar's book is excellent. . . . A feature of - the book is the photographs of birds by Captain Fayrer. They are most - remarkable, and quite unlike the usual wretched snapshot and blurred - reproductions with which too many naturalists' books are nowadays - illustrated." - - _Standard._--"The East has ever been a place of wonderment, but the - writer of 'Bombay Ducks' brings before Western eyes a new set of - pictures. . . . The book is entertaining, even to the reader who is not - a naturalist first and a reader afterwards. . . . 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There have been few collections - of letters published within recent years that give so vivid a portrait - of the writer as that presented to us in these pages." - - -COKE OF NORFOLK AND HIS FRIENDS: The Life of Thomas William Coke, First -Earl of Leicester of the second creation, containing an account of his -Ancestry, Surroundings, Public Services, and Private Friendships, and -including many Unpublished Letters from Noted Men of his day, English and -American. By A. M. W. Stirling. With 20 Photogravure and upwards of 40 -other Illustrations reproduced from Contemporary Portraits, Prints, etc. -Demy 8vo. 2 vols. 32_s._ net. - - _The Times._--"We thank Mr. Stirling for one of the most interesting - memoirs of recent years." - - _Daily Telegraph._--"A very remarkable literary performance. Mrs. - Stirling has achieved a resurrection. She has fashioned a picture of a - dead and forgotten past and brought before our eyes with the vividness - of breathing existence the life of our English ancestors of the - eighteenth century." - - _Pall Mall Gazette._--"A work of no common interest; in fact, a work - which may almost be called unique." - - _Evening Standard._--"One of the most interesting biographies we have - read for years." - - -THE LIFE OF SIR HALLIDAY MACARTNEY, K.C.M.G., Commander of Li Hung -Chang's trained force in the Taeping Rebellion, founder of the first -Chinese Arsenal, Secretary to the first Chinese Embassy to Europe. -Secretary and Councillor to the Chinese Legation in London for thirty -years. By Demetrius C. Boulger, Author of the "History of China," the -"Life of Gordon," etc. With Illustrations. Demy 8vo. 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Fanshawe - contributes numerous notes which form a running commentary on the text. - Many famous pictures are reproduced, including paintings by Velazquez - and Van Dyck._ - - -THE LIFE OF JOAN OF ARC. -By Anatole France. -A Translation by Winifred Stephens. -With 8 Illustrations. -Demy 8vo, 9 x 5-3/4 inches, 2 vols. -Price 25_s._ net. - - .'. _Joan of Arc, by her friends accounted a saint, by her enemies a - witch, stands out the one supreme figure of the French 15th century; - that period of storm and stress, that time of birth-giving from which - proceeded the glories of the Renaissance. Bitter controversy raged - round the Maid in her life-time. Round her story to-day literary - polemic waxes high; and her life by Anatole France is the most eagerly - discussed book of the century. That it presents a life-like picture of - the time critics of all parties agree. Its author has well equipped - himself with the best erudition of the last thirty years. To the fruits - of these researches he has added profound philosophy and true - historical insight, and thus into consummate literary art he has - painted a more vivid picture of the French 15th century than has ever - yet been presented in any literature. The Maid herself Monsieur France - regards not as a skilful general or a wily politician as some writers - have endeavoured to make out, but as above all things a saint. It was - by her purity and innate goodness that she triumphed. "It was not Joan - who drove the English out of France . . . And yet the young saint - played the noblest part in the salvation of her country. Hers was the - part of sacrifice. She set the example of high courage and gave to - heroism a new and attractive form._ - - -THE DAUGHTER OF LOUIS XVI. -Marie-Therese-Charlotte of France, Duchesse D'Angouleme. -By G. Lenotre. -With 13 Full-page Illustrations. -Demy 8vo. -Price 10_s._ 6_d._ net. - - .'. _M. G. Lenotre is perhaps the most widely read of a group of modern - French writers who have succeeded in treating history from a point of - view at once scientific, dramatic and popular. He has made the - Revolution his particular field of research, and deals not only with - the most prominent figures of that period, but with many minor - characters whose life-stories are quite as thrilling as anything in - fiction. The localities in which these dramas were enacted are vividly - brought before us in his works, for no one has reconstructed 18th - century Paris with more picturesque and accurate detail. "The Daughter - of Louis XVI." is quite equal in interest and literary merit to any of - the volumes which have preceded it, not excepting the famous Drama of - Varennes. As usual, M. Lenotre draws his material largely from - contemporary documents, and among the most remarkable memoirs - reproduced in this book are "The Story of my Visit to the Temple" by - Harmand de la Meuse, and the artless, but profoundly touching narrative - of the unhappy orphaned Princess: "A manuscript written by Marie - Therese Charlotte of France upon the captivity of the Princes and - Princesses, her relatives, imprisoned in the Temple." The illustrations - are a feature of the volume and include the so-called "telescope" - portrait of the Princess, sketched from life by an anonymous artist, - stationed at a window opposite her prison in the tower of the Temple._ - - -HUBERT AND JOHN VAN EYCK: Their Life and Work. By W. H. James Weale. With -41 Photogravure and 95 Black and White Reproductions. Royal 4to. L5 5_s._ -net. - - Sir Martin Conway's Note. - - _Nearly half a century has passed since Mr. W. H. James Weale, then - resident at Bruges, began that long series of patient investigations - into the history of Netherlandish art which was destined to earn so - rich a harvest. When he began work Memlinc was still called Hemling, - and was fabled to have arrived at Bruges as a wounded soldier. The van - Eycks were little more than legendary heroes. Roger Van der Weyden was - little more than a name. Most of the other great Netherlandish artists - were either wholly forgotten or named only in connection with paintings - with which they had nothing to do. Mr. Weale discovered Gerard David, - and disentangled his principal works from Memlinc's, with which they - were then confused. During a series of years he published in the - "Beffroi," a magazine issued by himself, the many important records - from ancient archives which threw a flood of light upon the whole - origin and development of the early Netherlandish school. By universal - admission he is hailed all over Europe as the father of this study. It - is due to him in great measure that the masterpieces of that school, - which by neglect were in danger of perishing fifty years ago, are now - recognised as among the most priceless treasures of the Museums of - Europe and the United States. Fullness and accuracy are the - characteristics of all Mr. Weale's work._ - - -VINCENZO FOPPA OF BRESCIA, Founder of the Lombard School, His Life and -Work. By Constance Jocelyn Ffoulkes and Monsignor Rodolfo Majocchi, D.D., -Rector of the Collegio Borromeo, Pavia. Based on research in the Archives -of Milan, Pavia, Brescia, and Genoa, and on the study of all his known -works. With over 100 Illustrations, many in Photogravure, and 100 -Documents. Royal 4to. L3. 11_s._ 6_d._ net. - - .'. _No complete Life of Vincenzo Foppa has ever been written: an - omission which seems almost inexplicable in these days of - over-production in the matter of biographies of painters, and of - subjects relating to the art of Italy. The object of the authors of - this book has been to present a true picture of the master's life based - upon the testimony of records in Italian archives; all facts hitherto - known relating to him have been brought together; all statements have - been verified; and a great deal of new and unpublished material has - been added. The authors have unearthed a large amount of new material - relating to Foppa, one of the most interesting facts brought to light - being that he lived for twenty-three years longer than was formerly - supposed. The illustrations will include several pictures by Foppa - hitherto unknown in the history of art, and others which have never - before been published, as well as reproductions of every existing work - by the master at present known._ - - -MEMOIRS OF THE DUKES OF URBINO. Illustrating the Arms, Art and Literature -of Italy from 1440 to 1630. By James Dennistoun of Dennistoun. A New -Edition edited by Edward Hutton, with upwards of 100 Illustrations. Demy -8vo. 3 vols. 42_s._ net. - - .'. _For many years this great book has been out of print, although it - still remains the chief authority upon the Duchy of Urbino from the - beginning of the fifteenth century. Mr. Hutton has carefully edited the - whole work, leaving the text substantially the same, but adding a large - number of new notes, comments and references. Wherever possible the - reader is directed to original sources. Every sort of work has been - laid under contribution to illustrate the text, and bibliographies have - been supplied on many subjects. Besides these notes the book acquires a - new value on account of the mass of illustrations which it now - contains, thus adding a pictorial comment to an historical and critical - one._ - - -THE PHILOSOPHY OF LONG LIFE. By Jean Finot. A Translation by Harry -Roberts. Demy 8vo. (9 x 5-3/4 inches). 7_s._ 6_d._ net. - - .'. _This is a translation of a book which has attained to the position - of a classic. It has already been translated into almost every - language, and has, in France, gone into fourteen editions in the course - of a few years. The book is an exhaustive one, and although based on - science and philosophy it is in no sense abstruse or remote from - general interest. It deals with life as embodied not only in man and in - the animal and vegetable worlds, but in all that great world of (as the - author holds) misnamed "inanimate" nature as well. For M. Finot argues - that all things have life and consciousness, and that a solidarity - exists which brings together all beings and so-called things. He sets - himself to work to show that life, in its philosophic conception, is an - elemental force, and durable as nature herself._ - - -THE DIARY OF A LADY-IN-WAITING. By Lady Charlotte Bury. Being the Diary -Illustrative of the Times of George the Fourth. Interspersed with -original Letters from the late Queen Caroline and from various other -distinguished persons. New edition. Edited, with an Introduction, by A. -Francis Steuart. With numerous portraits. Two Vols. Demy 8vo. 21_s._ net. - - .'. _This book, which appeared anonymously in 1838, created an enormous - sensation, and was fiercely criticised by Thackeray and in the Reviews - of the time. There is no doubt that it was founded on the diary of Lady - Charlotte Bury, daughter of the 5th Duke of Argyll, and Lady-in-Waiting - to the unfortunate Caroline of Brunswick, when Princess of Wales. It - deals, therefore, with the curious Court of the latter and with the - scandals that occurred there, as well as with the strange vagaries of - the Princess abroad. In this edition names left blank in the original - have been (where possible) filled up, and many notes are given by the - Editor to render it useful to the ever-increasing number of readers - interested in the later Georgian Period._ - - -JUNIPER HALL: Rendezvous of certain illustrious Personages during the -French Revolution, including Alexander D'Arblay and Fanny Burney. -Compiled by Constance Hill. With numerous Illustrations by Ellen G. Hill, -and reproductions from various Contemporary Portraits. Crown 8vo. 5_s._ -net. - - -JANE AUSTEN: Her Homes and Her Friends. By Constance Hill. Numerous -Illustrations by Ellen G. Hill, together with Reproductions from Old -Portraits, etc. Cr. 8vo. 5_s._ net. - - -THE HOUSE IN ST. MARTIN'S STREET. Being Chronicles of the Burney Family. -By Constance Hill, Author of "Jane Austen, Her Home, and Her Friends," -"Juniper Hall," etc. With numerous Illustrations by Ellen G. Hill, and -reproductions of Contemporary Portraits, etc. Demy 8vo. 21_s._ net. - - -STORY OF THE PRINCESS DES URSINS IN SPAIN (Camarera-Mayor). By Constance -Hill. With 12 Illustrations and a Photogravure Frontispiece. New Edition. -Crown 8vo. 5_s._ net. - - -NEW LETTERS OF THOMAS CARLYLE. Edited and Annotated by Alexander Carlyle, -with Notes and an Introduction and numerous Illustrations. In Two -Volumes. Demy 8vo. 25_s._ net. - - _Pall Mall Gazette._--"To the portrait of the man, Thomas, these - letters do really add value; we can learn to respect and to like him - the more for the genuine goodness of his personality." - - _Morning Leader._--"These volumes open the very heart of Carlyle." - - _Literary World._--"It is then Carlyle, the nobly filial son, we see in - these letters; Carlyle, the generous and affectionate brother, the - loyal and warm-hearted friend, . . . and above all, Carlyle as the - tender and faithful lover of his wife." - - _Daily Telegraph._--"The letters are characteristic enough of the - Carlyle we know: very picturesque and entertaining, full of extravagant - emphasis, written, as a rule, at fever heat, eloquently rabid and - emotional." - - -THE NEMESIS OF FROUDE: a Rejoinder to "My Relations with Carlyle." By Sir -James Crichton Browne and Alexander Carlyle. Demy 8vo. 3_s._ 6_d._ net. - - _Glasgow Herald._--". . . The book practically accomplishes its task of - reinstating Carlyle; as an attack on Froude it is overwhelming." - - _Public Opinion._--"The main object of the book is to prove that Froude - believed a myth and betrayed his trust. That aim has been achieved." - - -NEW LETTERS AND MEMORIALS OF JANE WELSH CARLYLE. A Collection of hitherto -Unpublished Letters. Annotated by Thomas Carlyle, and Edited by Alexander -Carlyle, with an Introduction by Sir James Crichton Browne, M.D., LL.D., -F.R.S., numerous Illustrations drawn in Lithography by T. R. Way, and -Photogravure Portraits from hitherto unreproduced Originals. In Two -Volumes. Demy 8vo. 25_s._ net. - - _Westminster Gazette._--"Few letters in the language have in such - perfection the qualities which good letters should possess. Frank, gay, - brilliant, indiscreet, immensely clever, whimsical, and audacious, they - reveal a character which, with whatever alloy of human infirmity, must - endear itself to any reader of understanding." - - _World._--"Throws a deal of new light on the domestic relations of the - Sage of Chelsea. They also contain the full text of Mrs. Carlyle's - fascinating journal, and her own 'humorous and quaintly candid' - narrative of her first love-affair." - - _Daily News._--"Every page . . . scintillates with keen thoughts, - biting criticisms, flashing phrases, and touches of bright comedy." - - -EMILE ZOLA: Novelist and Reformer. An Account of his Life, Work, and -Influence. By E. A. Vizetelly. With numerous Illustrations, Portraits, -etc. Demy 8vo. 21_s._ net. - - _Morning Post._--"Mr. Ernest Vizetelly has given . . . a very true - insight into the aims, character, and life of the novelist." - - _Athenaeum._--". . . Exhaustive and interesting." - - _M.A.P._--". . . will stand as the classic biography of Zola." - - _Star._--"This 'Life' of Zola is a very fascinating book." - - _Academy._--"It was inevitable that the authoritative life of Emile - Zola should be from the pen of E. A. Vizetelly. No one probably has the - same qualifications, and this bulky volume of nearly six hundred pages - is a worthy tribute to the genius of the master." - - Mr. T. P. O'Connor in _T.P.'s Weekly_.--"It is a story of fascinating - interest, and is told admirably by Mr. Vizetelly. I can promise any one - who takes it up that he will find it very difficult to lay it down - again." - - -MEMOIRS OF THE MARTYR KING: being a detailed record of the last two years -of the Reign of His Most Sacred Majesty King Charles the First, -1646-1648-9. Compiled by Allan Fea. With upwards of 100 Photogravure -Portraits and other Illustrations, including relics. Royal 4to. 105_s._ -net. - - Mr. M. H. Spielmann in _The Academy_.--"The volume is a triumph for the - printer and publisher, and a solid contribution to Carolinian - literature." - - _Pall Mall Gazette._--"The present sumptuous volume, a storehouse of - eloquent associations . . . comes as near to outward perfection as - anything we could desire." - - -MEMOIRS OF A VANISHED GENERATION 1813-1855. Edited by Mrs. Warrenne -Blake. With numerous Illustrations. Demy 8vo. 16_s._ net. - - .'. _This work is compiled from diaries and letters dating from the - time of the Regency to the middle of the nineteenth century. The value - of the work lies in its natural unembellished picture of the life of a - cultured and well-born family in a foreign environment at a period so - close to our own that it is far less familiar than periods much more - remote. There is an atmosphere of Jane Austen's novels about the lives - of Admiral Knox and his family, and a large number of well-known - contemporaries are introduced into Mrs. Blake's pages._ - - -CESAR FRANCK: A Study. Translated from the French of Vincent d'Indy. And -with an Introduction by Rosa Newmarch. Demy 8vo. 7_s._ 6_d._ net. - - .'. _There is no purer influence in modern music than that of Cesar - Franck, for many years ignored in every capacity save that of organist - of Sainte-Clotilde, in Paris, but now recognised as the legitimate - successor of Bach and Beethoven. His inspiration "rooted in love and - faith" has contributed in a remarkable degree to the regeneration of - the musical art in France and elsewhere. The now famous "Schola - Cantorum," founded in Paris in 1896, by A. Guilmant, Charles Bordes and - Vincent d'Indy, is the direct outcome of his influence. Among the - artists who were in some sort his disciples were Paul Dukas, Chabrier, - Gabriel Faure and the great violinist Ysanye. His pupils include such - gifted composers as Benoit, Augusta Holmes, Chausson, Ropartz, and - d'Indy. This book, written with the devotion of a disciple and the - authority of a master, leaves us with a vivid and touching impression - of the saint-like composer of "The Beatitudes."_ - - -FRENCH NOVELISTS OF TO-DAY: Maurice Barres, Rene Bazin, Paul Bourget, -Pierre de Coulevain, Anatole France, Pierre Loti, Marcel Prevost, and -Edouard Rod. Biographical, Descriptive, and Critical. By Winifred -Stephens. With Portraits and Bibliographies. Crown 8vo. 5_s._ net. - - .'. _The writer, who has lived much in France, is thoroughly acquainted - with French life and with the principal currents of French thought. The - book is intended to be a guide to English readers desirous to keep in - touch with the best present-day French fiction. Special attention is - given to the ecclesiastical, social, and intellectual problems of - contemporary France and their influence upon the works of French - novelists of to-day._ - - -THE KING'S GENERAL IN THE WEST, being the Life of Sir Richard Granville, -Baronet (1600-1659). By Roger Granville, M.A., Sub-Dean of Exeter -Cathedral. With Illustrations. Demy 8vo. 10_s._ 6_d._ net. - - _Westminster Gazette._--"A distinctly interesting work; it will be - highly appreciated by historical students as well as by ordinary - readers." - - -THE LIFE AND LETTERS OF ROBERT Stephen Hawker, sometime Vicar of -Morwenstow in Cornwall. By C. E. Byles. With numerous Illustrations by J. -Ley Pethybridge and others. Demy 8vo. 7_s._ 6_d._ net. - - _Daily Telegraph._--". . . As soon as the volume is opened one finds - oneself in the presence of a real original, a man of ability, genius - and eccentricity, of whom one cannot know too much . . . No one will - read this fascinating and charmingly produced book without thanks to - Mr. Byles and a desire to visit--or revisit--Morwenstow." - - -THE LIFE OF WILLIAM BLAKE. By Alexander Gilchrist. Edited with an -Introduction by W. Graham Robertson. Numerous Reproductions from Blake's -most characteristic and remarkable designs. Demy 8vo. 10_s._ 6_d._ net. -New Edition. - - _Birmingham Post._--"Nothing seems at all likely ever to supplant the - Gilchrist biography. Mr. Swinburne praised it magnificently in his own - eloquent essay on Blake, and there should be no need now to point out - its entire sanity, understanding keenness of critical insight, and - masterly literary style. Dealing with one of the most difficult of - subjects, it ranks among the finest things of its kind that we - possess." - - -MEMOIRS OF A ROYAL CHAPLAIN, 1729-63. The correspondence of Edmund Pyle, -D.D., Domestic Chaplain to George II, with Samuel Kerrich, D.D., Vicar of -Dersingham, and Rector of Wolferton and West Newton. Edited and Annotated -by Albert Hartshorne. With Portrait. Demy 8vo. 16_s._ net. - - _Truth._--"It is undoubtedly the most important book of the kind that - has been published in recent years, and is certain to disturb many - readers whose minds have not travelled with the time." - - -GEORGE MEREDITH: Some Characteristics. By Richard Le Gallienne. With a -Bibliography (much enlarged) by John Lane. Portrait, etc. Crown 8vo. -5_s._ net. Fifth Edition. Revised. - - _Punch._--"All Meredithians must possess 'George Meredith; Some - Characteristics,' by Richard Le Gallienne. This book is a complete and - excellent guide to the novelist and the novels, a sort of Meredithian - Bradshaw, with pictures of the traffic superintendent and the head - office at Boxhill. Even Philistines may be won over by the - blandishments of Mr. Le Gallienne." - - -LIFE OF LORD CHESTERFIELD. An account of the Ancestry, Personal -Character, and Public Services of the Fourth Earl of Chesterfield. By W. -H. Craig, M.A. Numerous Illustrations. Demy 8vo. 12_s._ 6_d._ net. - - _Daily Telegraph._--"Mr. Craig has set out to present him (Lord - Chesterfield) as one of the striking figures of a formative period in - our modern history . . . and has succeeded in giving us a very - attractive biography of a remarkable man." - - _Times._--"It is the chief point of Mr. Craig's book to show the - sterling qualities which Chesterfield was at too much pains in - concealing, to reject the perishable trivialities of his character, and - to exhibit him as a philosophic statesman, not inferior to any of his - contemporaries, except Walpole at one end of his life, and Chatham at - the other." - - -A QUEEN OF INDISCRETIONS. The Tragedy of Caroline of Brunswick, Queen of -England. From the Italian of G. P. Clerici. Translated by Frederic -Chapman. With numerous Illustrations reproduced from contemporary -Portraits and Prints. Demy 8vo. 21_s._ net. - - _The Daily Telegraph._--"It could scarcely be done more thoroughly or, - on the whole, in better taste than is here displayed by Professor - Clerici. Mr. Frederic Chapman himself contributes an uncommonly - interesting and well-informed introduction." - - _Westminster Gazette._--"The volume, scholarly and well-informed . . . - forms one long and absorbingly interesting chapter of the _chronique - scandaleuse_ of Court life . . . reads like a romance, except that no - romancer would care or dare to pack his pages so closely with startling - effects and fantastic scenes." - - -LETTERS AND JOURNALS OF SAMUEL GRIDLEY HOWE. Edited by his Daughter Laura -E. Richards. With Notes and a Preface by F. B. Sanborn, an Introduction -by Mrs. John Lane, and a Portrait. Demy 8vo. (9 x 5-3/4 inches). 16_s._ -net. - - _Outlook._--"This deeply interesting record of experience. The volume - is worthily produced and contains a striking portrait of Howe." - - _Daily News._--"Dr. Howe's book is full of shrewd touches; it seems to - be very much a part of the lively, handsome man of the portrait. His - writing is striking and vivid; it is the writing of a shrewd, keen - observer, intensely interested in the event before him." - - -THE LIFE OF ST. MARY MAGDALEN. Translated from the Italian of an Unknown -Fourteenth-Century Writer by Valentina Hawtrey. With an Introductory Note -by Vernon Lee, and 14 Full-page Reproductions from the Old Masters. Crown -8vo. 5_s._ net. - - _Daily News._--"Miss Valentina Hawtrey has given a most excellent - English version of this pleasant work." - - _Academy._--"The fourteenth-century fancy plays delightfully around the - meagre details of the Gospel narrative, and presents the heroine in - quite an unconventional light. . . . In its directness and artistic - simplicity and its wealth of homely detail the story reads like the - work of some Boccaccio of the cloister; and fourteen illustrations - taken from Italian painters happily illustrate the charming text." - - -MEN AND LETTERS. By Herbert Paul, M.P. Fourth Edition. Crown 8vo. 5_s._ -net. - - _Daily News._--"Mr. Herbert Paul has done scholars and the reading - world in general a high service in publishing this collection of his - essays." - - _Punch._--"His fund of good stories is inexhaustible, and his urbanity - never fails. On the whole, this book is one of the very best examples - of literature on literature and life." - - -ROBERT BROWNING: Essays and Thoughts. By J. T. Nettleship. With Portrait. -Crown 8vo. 5_s._ 6_d._ net. (Third Edition.) - - -A LATER PEPYS. The Correspondence of Sir William Weller Pepys, Bart., -Master in Chancery, 1758-1825, with Mrs. Chapone, Mrs. Hartley, Mrs. -Montague, Hannah More, William Franks, Sir James Macdonald, Major -Rennell, Sir Nathaniel Wraxall, and others. Edited, with an Introduction -and Notes, by Alice C. C. Gaussen. With numerous Illustrations. Demy 8vo. -In Two Volumes. 32_s._ net. - - Douglas Sladen in the _Queen_.--"This is indisputably a most valuable - contribution to the literature of the eighteenth century. It is a - veritable storehouse of society gossip, the art criticism, and the - _mots_ of famous people." - - _Academy and Literature._--"The effect consists in no particular - passages, but in the total impression, the sense of atmosphere, and the - general feeling that we are being introduced into the very society in - which the writer moved." - - _Daily News._--"To Miss Alice Gaussen is due the credit of sorting out - the vast collection of correspondence which is here presented to the - public. . . . Her industry is indefatigable, and her task has been - carried out with completeness. The notes are full of interesting items; - the introduction is exhaustive; and the collection of illustrations - enhances the value of the book." - - _World._--"Sir William Pepys's correspondence is admirable." - - -ROBERT LOUIS STEVENSON, AN ELEGY; AND OTHER POEMS, MAINLY PERSONAL. By -Richard Le Gallienne. Crown 8vo. 4_s._ 6_d._ net. - - _Daily Chronicle._--"Few, indeed, could be more fit to sing the dirge - of that 'Virgil of Prose' than the poet whose _curiosa felicitas_ is so - close akin to Stevenson's own charm." - - _Globe._--"The opening Elegy on R. L. Stevenson includes some tender - and touching passages, and has throughout the merits of sincerity and - clearness." - - -RUDYARD KIPLING: a Criticism. By Richard Le Gallienne. With a -Bibliography by John Lane. Crown 8vo. 3_s._ 6_d._ net. - - _Guardian._--"One of the cleverest pieces of criticism we have come - across for a long time." - - _Scotsman._--"It shows a keen insight into the essential qualities of - literature, and analyses Mr. Kipling's product with the skill of a - craftsman . . . the positive and outstanding merits of Mr. Kipling's - contribution to the literature of his time are marshalled by his critic - with quite uncommon skill." - - -POEMS. By Edward Cracroft Lefroy. With a Memoir by W. A. Gill, and a -Reprint of Mr. J. A. Symonds' Critical Essay on "Echoes from Theocritus." -Photogravure Portrait. Crown 8vo. 5_s._ net. - - _The Times._--". . . the leading features of the sonnets are the - writer's intense sympathy with human life in general and with young - life in particular; his humour, his music, and, in a word, the quality - which 'leaves a melody afloat upon the brain, a savour on the mental - palate.'" - - _Bookman._--"The Memoir, by Mr. W. A. Gill, is a sympathetic sketch of - an earnest and lovable character; and the critical estimate, by J. - Addington Symonds, is a charmingly, written and suggestive essay." - - -APOLOGIA DIFFIDENTIS. By W. Compton Leith. Demy 8vo. 7_s._ 6_d._ net. - - .'. _The book, which is largely autobiographical, describes the effect - of diffidence upon an individual life, and contains, with a - consideration of the nature of shyness, a plea for a kindlier judgment - of the inveterate case._ - - _Daily Mail._--"Mr. Leith has written a very beautiful book, and - perhaps the publisher's claim that this will be a new classic is not - too bold." - - -THE TRUE STORY OF MY LIFE: an Autobiography by Alice M. Diehl, Novelist, -Writer, and Musician. Demy 8vo. 10_s._ 6_d._ net. - - -BOOKS AND PERSONALITIES: Essays. By H. W. Nevinson. Crown 8vo. 5_s._ net. - - _Daily Chronicle._--"It is a remarkable thing and probably unique, that - a writer of such personality as the author of 'Between the Acts' should - not only feel, but boldly put on paper, his homage and complete - subjection to the genius of one after another of these men. He is - entirely free from that one common virtue of critics, which is - superiority to the author criticised." - - -OTIA: Essays. By Armine Thomas Kent. Crown 8vo. 5_s._ net. - - -BOOKS AND PLAYS: A Volume of Essays on Meredith, Borrow, Ibsen, and -others. By Allan Monkhouse. Crown 8vo. 5_s._ net. - - -LIBER AMORIS; or, The New Pygmalion. By William Hazlitt. Edited, with an -introduction, by Richard Le Gallienne. To which is added an exact -transcript of the original MS., Mrs. Hazlitt's Diary in Scotland, and -Letters never before published. Portrait after Bewick, and facsimile -Letters. 400 copies only. 4to. 364 pp. Buckram. 21_s._ net. - - -TERRORS OF THE LAW: being the Portraits of Three Lawyers--the original -Weir of Hermiston, "Bloody Jeffreys," and "Bluidy Advocate Mackenzie." By -Francis Watt. With 3 Photogravure Portraits. Fcap. 8vo. 4_s._ 6_d._ net. - - _The Literary World._--"The book is altogether entertaining; it is - brisk, lively, and effective. Mr. Watt has already, in his two series - of 'The Law's Lumber Room,' established his place as an essayist in - legal lore, and the present book will increase his reputation." - - -CHAMPIONS OF THE FLEET. Captains and Men-of-War in the Days that Helped -to make the Empire. By Edward Fraser. With 16 Full-page Illustrations. -Crown 8vo. 6_s._ - - -THE LONDONS OF THE BRITISH FLEET: The Story of Ships bearing the name of -Old Renown in Naval Annals. By _Edward Fraser_. With 8 Illustrations in -colours, and 20 in black and white. Crown 8vo. 6_s._ - - - JOHN LANE, THE BODLEY HEAD, VIGO STREET, LONDON. - - - - - Transcriber's Notes - - ---Retained publisher information from the printed copy (the electronic - edition is in the public domain in the country of publication). - ---Corrected some palpable typos. - ---Converted page headings into section titles (shifted to an appropriate - paragraph break.) - ---Moved all promotional material to the end of the book. - ---In the HTML version, split some illustrations, and rotated others to - portrait mode for better display on e-readers. - ---In the text versions only, represented text font and size variations - (the HTML version preserves the presentation of the original): - ---Text in italics is delimited by _underscores_. - ---Subscripted numbers are preceded by an underscore, as in the formula - for water "H_2O". - ---Split genetic tables within paragraphs into separate lines. - - - - - - - -End of the Project Gutenberg EBook of The Making of Species, by -Douglas Dewar and Frank Finn - -*** END OF THIS PROJECT GUTENBERG EBOOK THE MAKING OF SPECIES *** - -***** This file should be named 44063.txt or 44063.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/4/4/0/6/44063/ - -Produced by Stephen Hutcheson, Marcia Brooks and the Online -Distributed Proofreading Canada Team at -http://www.pgdpcanada.net (This file was produced from -images generously made available by The Internet -Archive/American Libraries.) - - -Updated editions will replace the previous one--the old editions -will be renamed. - -Creating the works from public domain print editions means that no -one owns a United States copyright in these works, so the Foundation -(and you!) can copy and distribute it in the United States without -permission and without paying copyright royalties. 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