[page] 312

THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION.*

[FIRST NOTICE.]

IT is almost needless to say now that the teaching of Mr. Darwin's Origin of Species has effected an almost complete revolution in biology, and that no book has appeared in this century which has excited so much opposition, or which has in a very few years attracted such a widely spread and numerous band of disciples. Eminent men of science who are still in an attitude of opposition to "Darwinian" views may now be numbered on the fingers of a hand, whilst the rising school of thought is almost unanimous in favour of the doctrine of evolution. Very much of the opposition which the views contained in the Origin of Species had to encounter, leaving out of question, of course, the class opposition which was to be expected, was due to the absence of the details of the facts upon which those views were based, an absence which was rendered necessary by the hastened publication of the look. But when the first edition of the book now under consideration came under the notice of thoughtful and unprejudiced readers, there could no longer remain any doubt in their minds that the whole doctrine of the immutability of species and genera must be abandoned, and that the new theory of the origin of all by a process of evolution must be fairly faced.

It is very rarely the case—indeed, we doubt if a parallel instance exists in the world's history—of a great teacher living to see his views generally adopted, when they have been found to be so revolutionary as have been those of Mr. Darwin. Certainly there is no other instance of a man having founded so great a doctrine as this, and being at the same time the author of the minute investigations which have completed and solidified his achievement.

The second edition of this book has appeared in seven years, and it is already in the fourth thousand, a fact more pregnant than any words can be with comfort for those who are interested in the advance of scientific education. The book itself is far from being attractive to the uninitiated; indeed, we may say that to be a reader of any of Mr. Darwin's books involves the previous possession of a considerable amount of biological knowledge, and from the reverent care with which our author details all his facts before suggesting any conclusion, his writings are far from being such as may be regarded as light reading. But for the student of science they are models of composition, for the utter absence of any straining after effect, for the almost painful elaboration of their facts, for the absence of anything approaching to an unsubstantiated conclusion; but most of all, for the absolute and uniform fairness with which Mr. Darwin treats all who may differ from him, all who have gone before him, and all who have in any way contributed facts for his use.

The new edition of the book now before us is, of course, chiefly a reproduction of the first; but numerous and very important additions have been made, and Mr. Darwin seems to have had very little occasion to withdraw or amend what he had written before. The only noteworthy instance of the latter is in the case of a statement made in the first edition concerning the reproduction of supernumerary digits. The law affecting the production of polydactylism seems to be that the more specialised limb—the anterior or arm—is more variable than the other ; and that males are more prone to it than females, as might be expected as a corollary, for males are more specialised in their employments than females. Only one point seems as yet uninvestigated, and that is, which hand is more frequently affected. We should expect it to be the right, as that is more specialised than the left ; and if it should prove to be so, Mr. Darwin's position would be considerably strengthened. There can be no doubt that polydactylism occurs in a more and more perfect and complete form, the nearer we get to that stage of development where vegetative repetition is the rule. This is shown by the reversion which is seen occasionally in the horse to the condition of tridactylism, which characterised the extinct hipparion, illustrations of which may be seen in the Museum of the College of Surgeons. In races of polydactylous cats, the anterior limbs are always first affected, there being often seven toes there

* The Variation of Animals and Plants under Domestication. By Charles Darwin, F.R.S., &c. London: Murray.

to six in the posterior limbs; and the males are much more frequently affected than the females. In certain districts these polydactylous cats seem likely to evict the cats with only twenty toes, and that, probably, because the extra digits serve an evident and very useful purpose. It is further very remarkable that the moat specialised digit, the thumb, is that whose reduplication is most frequent in all animals. The writer has seen a white male cat which was perfectly deaf, had one eye blue and the other yellow, and had three thumbs on each anterior limb.

In his first edition, Mr. Darwin mentions the case of a double-thumbed infant, where the smaller digit was twice amputated, and twice was re- produced with its nail complete. Doubt having been expressed about this case, and the evidence concerning it being in- complete, Mr. Darwin has withdrawn the conclusions he had Made upon it. This withdrawal is not justified, because the facts of such reproduction are fully substantiated in surgical works. Nay, more than that, the reproduction of many digits after intra-uterine amputation of a limb is a well- established fact, so that Mr. Darwin, in his next edition, may go further than he did in his first, and say that, just as the human animal is nearer to that phase of its existence in which it resembles structures in which vegetative repetition is the rule, so attempts at such repetition are visible. If in early infantile life half of a double digit is removed, that half may be reproduced ; and if in intra-uterine life a limb be amputated by processes which are thoroughly well known, attempts will be made to reproduce the elements of the amputated part. This is clearly a most telling instance of reversion.

Amongst the new matter to be found in this edition some very important facts are placed, though they were scarcely needed to strengthen Mr. Darwin's position. Thus the intimate relation- ship which he had already established between the various breeds of domesticated dogs and wild members of the same family, is greatly supported by the singular process of reversion which occurs in dogs which are imported into Guinea, where they are found to alter strangely, their ears growing long and stiff, like those of foxes, to the colour of which they also incline, so that in three or four years they degenerate into very ugly creatures ; and in three or four broods their barking turns into a howl. Such observations as this are being multiplied on all sides, and the first step in the process of proving a common relationship between all animals may be taken as having been accomplished by Mr. Darwin, in his having shown that our domesticated animals have all been derived from feral stock.

The peculiar movements made in the air by the tumbler-pigeon have been a source of much speculation, and in a note, quoted from Mr. W. J. Moore, Mr. Darwin tells us that the pricking of the base of the brain and giving hydrocyanic acid, together with strychnine, to an ordinary pigeon, brings on convulsive movements exactly like those of a tumbler. This is far from being a satisfactory explanation, nor indeed can any be given that is perfectly sufficient. The breed of tumblers is very widely spread, yet we have no information that any artificial process has been used to produce their peculiarities.

The fact seems to have escaped Mr. Darwin's notice, that epilepsy is a very frequent disease amongst all domesticated animals. Dogs, cats, horses, white mice, and birds are all known to suffer from it. In birds, as the writer has frequently seen in a jackdaw, the epileptic attacks often take the form of rotatory movements, from before backwards, with the wings outspread. The bird first throws its head backwards, and turns over several times in that direction, and then resumes its wonted condition, unless the fit is very severe, when it presents the drowsiness so characteristic of epilepsy. In birds these fits are induced by confinement, and cease at once if the animal is allowed to wander about ; and in white mice they are often to be induced by exposure to strong light. Epilepsy is a disease in which the hereditary tendency is very strongly marked, and it would not be impossible to raise a breed of almost any animal in which it should predominate, and in which some special irritation would readily excite it. The " tumble " of the pigeon is apparently a mild form of epilepsy— petit mal—and it may have been originally induced by confinement, and continued by careful selection, though what the irritation is which excites the fits is, as yet, beyond our powers of explanation. We might quote many instances where diseased conditions were regarded as subjects for selection; indeed, the very disease we are now speaking of, epilepsy, was termed the " sacred disease" by the Greeks, and those affected by it were regarded as especially under the protection of the gods. It is possible that the special reverence in which they were held may have tended towards the transmission of their dreadful affliction. The appli-

[page] 313

cation of the principles of the Darwinian philosophy to the investigation of disease, is a field which will prove enormously productive for any one who has the patience and opportunity to take up the research.

[page] 406

THE VARIATION OF ANIMALS AND PLANTS UNDER DOMESTICATION.*

[SECOND NOTICE.]

Nearly a hundred pages are devoted to a minute examination of the evidence upon which Mr. Darwin's conclusion is based, that all our breeds of domestic pigeons are descended from the columba livia, or blue-rock pigeon. We think that every reader who is capable of weighing the value of evidence must come to the conclusion that here Mr. Darwin completely establishes his case; and if it be so, those who can look at the broader question without trepidation must inevitably admit that if anything so different in details of structure as can be found in the blue-rock and fan-tail or pouter pigeons, the further extension of his conclusions is but a matter of time and perseverance. 'The initial difficulty in the way of considering this in its broader aspects will be removed at once, if the reader will bear in mind, that time is the most essential element of change of every kind, and that the important changes seen in pigeons have been artificially and clumsily induced by man in a comparatively very short time; whilst for the modifications of structure induced by natural selection, following those induced by purely natural circumstances, there is an extension of time which we not only cannot measure, but positively can form no conception of.

This part of Mr. Darwin's book seems almost to form a complete handbook for pigeon-fanciers, and some of the facts he has detailed are not only important, but curious. Thus he tells us that the especial characters for which each breed is valued are  eminently variable, as in the Fantail, where the number and direction of the tail-feathers, the carriage of the body, and the degree of trembling are all highly variable. It is, first of all, almost unintelligible why fanciers, who, of course, are wholly unscientific in their object of selection, should select trembling as a point. We are ignorant of the ways of pigeons, but have little doubt that this trembling is a sexual peculiarity ; and as it is variable, there  can be no limit to the power of its extension by artificial selection,  go that a new pigeon-breed of "Shakers" might be produced. It

* Animals and Plants under Domestication, By Charles Darwin, F.R.S, London: Murray.

[page] 407

will, no doubt, be regarded as a very humiliating fact, by a certain  class of modern philosophers of both sexes, that in pigeons a "high degree of merit is rarer in the female than in the male;" and that "if a cock and hen Tumbler were of equal merit, the hen would be worth double the value of the cock."

This is all the more remarkable, and will probably be found still more applicable to man than to pigeons, as "it is found that in domesticated pigeons certain sexual differences are found to be developed and to increase with age," whilst "there is no sensible difference at any age between the two sexes in the aboriginal rock-pigeon."

Mr. Darwin carries his minute observations over fowls, ducks, geese, peacocks, canaries, gold-fish, hive-bees, and silk-moths, and makes all contribute their share of information. Of canaries he records one most curious fact, the exact relation of which is yet far from clear. It is that if two top-knotted birds are matched, the young, instead of having very fine top-knots, are generally bald, or even have a wound on their heads. He suggests that it would appear as if the top-knot were due to some morbid condition which is increased to an injurious degree when two birds in this state are paired. Of course the word "morbid," like many of its kind, is purely relative, and may mean either excess or diminution of a process. We have very little knowledge of the conditions which govern growth, but we are certain that vascular supply is an essential, and that the regulation of the same by the vaso-motor system governs the various modifications of the process. Thus the spur of the cock in its normal position has a definitely regulated blood-supply, which might be, by accident, increased or diminished so as to induce disease of the spur. But if it be placed under circumstances where its blood-supply is independent of vaso-motor control, as in John Hunter's experiments of engrafting it into the comb of the cock, its growth may be unlimited. Dr. Stirling has recently shown that this may be the case in organs which are not dislocated, as when the sympathetic is divided in the neck of a rabbit ; in course of time the ear increases very much in size, and the temperature is permanently exalted. In the case of the chicks of two top-knotted canaries, the baldness and wound may be really the result of an excess of blood-supply, just as the original top-knot must arise, and it would be extremely interesting to see what the interbreeding of birds so produced would lead to.

Mr. Darwin has studied canaries so closely, that he can tell us that they differ much in disposition and character, but that is a conclusion to which we think all who keep a number of animals of any one kind will come to. Even guinea-pigs, whose character is about the most insipid of all pets, vary considerably in disposition and tastes, and the degree of variation may be noticed to increase in proportion to the intelligence of the kind of animal observed.

One of the most curious and at present one of the least explicable facts established by Mr. Darwin is the tendency of reversion to a wild state, or to very altered habits, by a mixture of race. 'Thus, if a hen belonging to a variety which does not incubate be crossed by another variety which has equally lost, by artificial selection, the tendency to brood, the product will be inclined to sit steadily on its eggs. A sow of the domesticated Chinese variety, crossed by an Alpine boar which had become remarkably tame, had young which were remarkably wild in confinement, and would not eat swill like common English pigs. Livingstone is quoted to the effect that "it is unaccountable why half-castes are so much more cruel than the Portuguese, but such undoubtedly is the case."

And it was further remarked to the same missionary by a native that ''God made white men, and God made black men, but the Devil made half-castes." No explanation of this is, in the present state of our knowledge, possible ; but it gives an indisputable explanation of the impossibilities of keeping up mixed races, and it must also be offered as an explanation of the barbarities which we hear of as of frequent occurrence in such borderlands as at present extend across the whole continent of America, even under xanthocroic rule, and which we can only agree with our author in considering as reversion of types to a primitive state of savagery.

Equally incomprehensible, yet equally important and interesting, is the fact that in the case of certain crosses, one variety seems to have the tendency to perpetuate its peculiarities more than the other, and to this tendency Mr. Darwin gives the term of "prepotency in transmission." This has been seen to be remarkably the case in certain breeds of cattle, as the short-horn, and in the special instances of brood-mares and greyhounds. In certain human races this is markedly the case. Thus the children of Frenchmen or Portuguese with East-Indian and Chinese mothers have, with the exception of the pigmentary development, the European characters prepondering strongly over the Asiatic, and are usually beautiful; whilst the half-castes of Englishmen and Germans have a tendency to show the Eastern blood rather than the Western, and are generally hideously ugly. In individual families this is also often to be remarked, and in the case of musical genius it is seen in very striking instances. Thus, of our great musical composers, the majority will be found to have had fathers who were noted musicians, but we have failed to find one instance in which the gift seems to have been transmitted from the female line. The children of Jews and Saxons seldom exhibit the Hebrew features with any prominence, especially in childhood. Peculiarities of one sex are also apt to be continued in one sex, to the complete exclusion of the other, even when these peculiarities may be of a perfectly general character.

This is well seen in the case of certain diseases, as in a case quoted from Dr. Sedgwick, in which four brothers suffered almost every week from severe head-aches, from which also their father, paternal uncles, paternal grandfather, and grand-uncles all suffer, yet all the female members of the family escaped. We also know of a case where all the women of a family suffer from nettle-rash if they eat strawberries, yet the males may eat them with impunity. That marvellous tendency to variation which every animal displays in every character forms the foundation upon which the great factor of selection is brought to bear, either by natural agencies or by the conventional selection of man. Mr. Darwin's writing on this subject may be said to be his best and most important, though it is really difficult in a book like this to speak more highly of any one part than of the whole.

Of artificial selection we need say no more here, but on the process of the evolution of new characters by natural selection, a word or two may be said on a certain want of definition in the use of a term for which we are indebted to Mr. Herbert Spencer, and which has now obtained a very extended use, so much so that Mr. Darwin uses it as an equivalent for ''natural selection." The term in question, ''survival of the fittest," is one which is far from expressing the whole of the steps of the process of natural selection, even as far as they are known to us; and instead of having a universal application, as it has now in the mind of most writers, it seems to us that it should have one of a more restricted kind. When we use the superlative term ' fittest," we obviously mean a limited number out of a multitude; and when we speak of the 'survival of the fittest," we infer the destruction of the majority by reason of their want of fitness. When, on the contrary, we say that certain animals survive '' by reason of their fitness," we refer to the destruction of the few and the survival of the many; and it is self-evident that these two conditions are quite different steps of the one process of evolution. To explain this by example, let us suppose that a breed of sheep is introduced into a district cut up by ditches, and that to get their food it shall be necessary for the sheep to be able to jump over these ditches. Suppose that the majority of these sheep have limbs only fourteen inches long, but that a few have a length of fifteen, sixteen, or even seventeen inches, and that these only can jump the ditches. It is evident that the majority will perish by lack of fitness, and that the minority will survive by reason of their fitness. But if the ditches are all exactly equal, and the sheep with limbs. fifteen inches long are able to cross them, those with a length of limb seventeen inches will have no advantage, so that it is clear that this would not be a case of survival of the fittest, but one of survival by fitness. So again, if the sheep remained under the same condition, every year all who had limbs under the necessary length would perish, and thus the minimum limb-length would be maintained. This part of the process secures permanency of structure which has been evolved, but it in no way introduces anything new. But, on the other hand, suppose that one or two ditches were widened, so that only the seventeen-inch-legged sheep could cross, they would have a manifest advantage over all, and would have an increased chance of survival, by being the fittest. 'This would induce a further change of structure, and is manifestly a wholly different step. "Survival of the fittest" is, therefore, the agency by which modifications are made useful, whilst "survival by fitness" is that by which they are rendered permanent. At first sight, the distinction may seem fine, but it is really of sufficient importance to be regarded as necessary.