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 excitdd 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 af the doctrine of evolution. Very much of the oppo- sition which the views contained in the Origin of Species had to encounter, leaving out of question, of course, the class oppo- sition 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 con- sideration 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 in- stance 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 bean 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 unsub- stantiated conclusion ; but most of all, for the absolute and uni- form 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 ex- pected as a corollary, for males are more specialised in their em- ployments than females. Only one point seems as yet uninvesti- gated, 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 polydactyliam occurs in a more and more perfect and complete form, the nearer we get to that stage of develop- ment 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 hip- parion, 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,
11.A., Sc. London: Murray.
to six in the posterior limbs ; and the males are much more fre- quently 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 yel- low, 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, be- cause 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 move- ments 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 confine- ment, and continued by careful selection, though what the irrita- tion is which excites the fits is, as yet, beyond our powers of ex- planation. We might quote many instances where diseased con- ditions 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- cation of the principles of the Darwinian philosophy to the in- vestigation of disease, is a field which will prove enormously pro- ductive for any one who has the patience and opportunity to take up the research.
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