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REVIEWS.

ARTIFICIAL SELECTION AND PANGENESIS.*

THE narrow limits of our space make us dread so serious an undertaking as the review of the two wonderfully comprehensive volumes which Mr. Darwin has just laid before English naturalists. The vast accumulation of facts displayed, the complex and intricate thread of induction pursued, and the numerous aspects in which the whole subject is exposed by the author of the "Origin of Species," cause us to approach even an outlinear sketch of the work before us with no little diffidence. Our readers, therefore, will understand that it is from no want of appreciation of the importance of the problem that we refrain from a more lengthy discussion of Mr. Darwin's masterpiece of scientific essayism. Indeed, so difficult do we consider the effort to give a lucid exposition of the latest argument which Mr. Darwin advances, that we regret, for the sake of the theory, that the author was not induced to publish a popular epitome of the facts of his case, and did not address the treatise now before us to the scientific public exclusively. For, after all, it must be confessed that even enthusiastic general readers may quail before nearly 1,000 pages of scientific matter, most of which are in small type, and all of which are, so to speak, crammed with "condensed fact." Nevertheless, we shall try, as clearly as possible, to lay before our readers an elementary notion of what Mr. Darwin tries to prove in the work under notice.

Those who have paid any attention to the question are aware that Mr. Darwin has hitherto confined his argument to the evidences drawn from animals and plants in a natural condition of existence. In the present instance, he brings under notice all the facts he has been able to collect concerning the domestication of animals and plants, and the formation of new breeds by artificial selection. In addition to this branch of the problem, in his second volume he deals with the subsidiary questions of the laws which govern variations and inheritance; and finally he proposes and supports a new hypothesis which has as much intrinsic interest as that of Natural Selection, and which he has termed Pangenesis. The theory and its testimony we may now consider seriatim. We must, however, premise that as Mr. Darwin examines the history and anatomy of every breed of domesticated organism, and gives, as it were, a complete monograph on each, we shall limit our remarks to one or two of the following animals: dogs, cats, horses, asses, pigs, cattle, sheep, goats, rabbits, pigeons, fowls, ducks, geese, peacocks,

* "The Variation of Animals and Plants under Domestication." By Charles Darwin, M.A., F.R.S. 2 vols. London: John Murray. 1868.

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turkeys, and gold fish. Pigeons and rabbits form, perhaps, the best examples of the immense influence of artificial selection in the production of new organic forms. This is because the selection and breeding of these animals have been made so much of an art and science, and because the history of the several breeds is so well and fully recorded. Taking the group of pigeons, and studying the history of its origin, Mr. Darwin, it seems to us, shows conclusively that the 150 different kinds have all descended from one common progenitor, the Columba livia, or rock pigeon. This is a great point to have demonstrated, for it is nothing less than this, that man, by carefully watching the variations of the several generations of pigeons, and selecting for reproduction those which possessed the features required for perpetuation, has succeeded in establishing a number of families of pigeons as different from each other as from the primal parent, as capable of regeneration as any natural species, and exhibiting anatomical peculiarities which, if seen in feral animals, would at once justify the naturalist in regarding such animals as perfectly distinct species. The osteological results of this artificial selection are not so important in pigeons as in other domestic creatures; still, even on this point they are by no means insignificant For example, we find even the total number of vertebræ—a formidable specific feature—modified; in the rock pigeon, the total number being 39, it is 42 or 43 in the Pouter, whilst in the Dutch Roller it is only 38. The total of observed modifications, as summed up by Mr. Darwin, is as follows :—

"To sum up, we may confidently admit that the length of the sternum and frequently the prominence of its crest, the length of the scapula and furculæ have all been reduced in size, compared with the same parts in the rock pigeon; and I presume that this may be safely attributed to disuse or lessened exercise. The wings, as measured from the ends of the radii, have likewise been generally reduced in length; but, owing to the increased growth of the wing-feathers, the wings from tip to tip are commonly longer than in the rock pigeon. The feet as well as the tarsi, conjointly with the middle toe, have likewise in most cases become reduced; and this, it is probable, has been caused by their lessened use; but the existence of some sort of correlation between the feet and the beak is shown more plainly than the effects of disease."

We cannot dwell upon the other points of anatomical difference which the author describes. We must, therefore, pass on to his reasons for believing that all these several varieties have descended from a common stock. These reasons are:—First, the improbability that more than one wild species should still exist somewhere unknown to ornithologists, or that they should have been extinguished within the historical period; secondly, the improbability of man having in former times thoroughly domesticated as many different species as there are breeds at the present day; thirdly, the unlikelihood of man's selecting several abnormal species; fourthly, the fact that all produce mongrels; fifthly, the important fact that all these races, whether crossed or not, occasionally revert—throw back, as breeders say—to a form which more or less closely resembles what Mr. Darwin regards as the ancestral type, the C. livia.

Rabbits present us with another remarkable example of the production of divergent forms by the influence of artificial selection. As in the case of

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pigeons, Mr. Darwin urges the extreme probability that all the domestic breeds of rabbits have been derived from one ancestor. He then shows what cautious observation is exercised to determine the minute variations and the necessity for careful pairing in order to avoid reversion. On all these particulars his remarks are of the highest interest But in regard to the alterations in the skeleton, we think the domestic rabbits afford conclusive testimony. The changes in the bones of these animals are of the gravest character. The bones of the limbs have increased in weight in proportion to the weight of the body. With the increased size of the body the third cervical vertebra has assumed characters proper to the fourth cervical; and the eighth and ninth dorsal vertebræ have similarly assumed characters proper to the tenth and posterior vertebræ. The skull in the larger breeds has increased in length. The brain appears to have decreased in size. The supra-orbital processes of the frontal bones and the free end of the malar bones have increased in breadth, and in certain breeds the occipital foramen differs from that of the wild rabbit. In like manner, the scapulæ, the bones of the ear, palate, and jaw, have, by processes of correlation, become highly variable and modified. The facts which we have quoted upon the history of two races will be found multiplied in Mr. Darwin's book for every domestic family of animals and plants; and this part of the subject occupies the greater part of the first volume.

The next points to be inquired into are those of variation, its laws and causes, and inheritance. These are discussed in the author's second volume; and their examination leads him to the remarkable hypothesis—Pangenesis, to which we have already referred. Starting with the proposition that the progeny of all animals displays variation—a proposition which it seems to us impossible to gainsay—the author proceeds to indicate the laws under which this tendency is governed. He thus formulates the following rules with respect to inheritance:—first, a tendency in every character, new and old, to be transmitted by seminal and bud generation, though often counteracted by various known or unknown causes; secondly, reversion or atavism, which depends on transmission and development being distinct powers; it acts in various degrees and manners through both seminal and bud generation; thirdly, prepotency of transmission, which may be confined to one sex or be common to both sexes of the prepotent form; fourthly, transmission limited by sex generally to the same sex in which the inherited character first appeared; fifthly, inheritance at corresponding periods of life, with some tending to the earlier development of the inherited character.

It is rather difficult to determine satisfactorily the opinion of the author on the question of the influences which determine variation in animals, as to whether, for instance, they are the result of what the older metaphysicians would style a "natural tendency," or are the consequence of the influence of external conditions. In one portion of his book he so distinctly opposes the theory of the operation of externals, that we are led to think he is of the metaphysical school. But then, further on, he so fully admits the effects of use and disuse in affecting the inheritance of certain qualities, and he so fairly acknowledges the inheritance of certain mutilations, such as those inflicted on rabbits by Dr. Brown-Séquard, that we are convinced

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he objects rather to the extreme arguments of the external-conditionists, if we may so style them, than assumes the existence of so illogical a principle as a natural tendency. On the whole, we are disposed to believe that Mr. Darwin believes that species vary in every generation from the action of external conditions, but that he would employ the expression "external condition" in its widest sense, and would not limit it, as some folk do, to temperature and atmospheric changes. There can, we think, then, be little doubt that Mr. Darwin has demonstrated the following propositions:— 1st, that in every group of animals the individuals tend constantly to diverge by variation from the parent type; 2nd, that these variations are in heritable under certain definite laws already expressed; 3rd, that by selecting and breeding from animals with any particular physical quality, that quality may be enhanced through successive generations till it becomes a permanent character; and, 4th, that the differences thus produced are quite as formidable as those on which naturalists base their distinction of feral species. Thus far, and no farther. There come, then, for consideration the questions of Mr. Darwin's opponents, who say, " You have undoubtedly produced new animal forms, which seem worthy of being called species, but for this fact, that natural species are sterile inter se. Your. species are perfectly fertile, and if allowed to breed together would produce mongrels, and revert to the parent species. Until you explain this anomaly, we decline to accept your views." This is certainly the most difficult point in the whole controversy, and this is Mr. Darwin's reply to it:—

"Passing over the fact that the amount of external difference between two species is no sure guide to their degree of mutual sterility, so that similar differences in the case of varieties would be no sure guide, we know that with species the cause lies exclusively in differences in their sexual constitution. Now the conditions to which domesticated animals and cultivated plants have been subjected have had no little tendency towards modifying the reproductive system in a manner leading to mutual sterility. But we have good grounds for admitting the directly opposite doctrine of Pallas— namely, that such conditions generally eliminate this tendency; so that the domesticated descendants of species which, in their natural state, would have been in some degree sterile, when crossed become perfectly fertile together. With plants, so far is cultivation from giving a tendency towards mutual sterility, that in several well-authenticated cases already often alluded to, certain species have been affected in a very different manner, for they have become self-impotent, whilst still retaining the faculty of fertilising and being fertilised by distinct species. If the Pallasian doctrine of the diminution of sterility through long-continued domestication be admitted—and it can hardly be rejected—it becomes in the highest degree improbable that similar circumstances should commonly both induce and eliminate the same tendency; though in certain cases, with species having a peculiar constitution, sterility might occasionally be thus induced."

We have already so for transgressed the limits allotted to us, that we have barely space to call attention to Mr. Darwin's theory of Pangenesis, This, which is a modification of Reaumur's and Bonnet's (see Quatrefage's Metamorphoses of Man and the Lower Animals: Hardwicke) Panspermy, may be shortly expressed as follows:—The tissues of the body in both male and female

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(plant and animal) are constantly throwing off minute atoms, which, under favourable circumstances, are capable of reproducing the particular tissue from which they were derived. These accumulate in the ovum on the one side and zoosperm on the other, and in the union of these two the elements of the tissues and organs of two individuals combine. Accordingly, therefore, as one or other of these elements predominates, the resultant will resemble either the male or female parent. But it sometimes happens that the two antagonise each other; and, when this occurs, a certain number of the molecules of the early ancestors, which have lain dormant like so many "statoblasts," come into play and produce reversion. Such is, in rough and imperfect outline, the last theory which Mr. Darwin propounds. It is not only fully en accord with his theory of natural selection, and with the facts which he advances in support of it, but it requires no extreme elasticity of imagination for its acceptance; and it is so thoroughly in agreement with ordinary physical laws and with the phenomena of development, that we think it is likely to find warm advocates in the biologists of all countries. Ere we conclude, let us offer our hearty thanks to Mr. Darwin for the dignified and truly philosophic manner in which he has conducted his controversy with his opponents. He has done good to those who have despite-fully used him, by showing them that he is uninfluenced by the petty feelings which have led them into an indulgence of invective damaging only to their cause. By proving to them that philosophy is beyond vituperation, he has upheld the honour of science, and cast a silent reproach on those who think that credulity and poetic sentiment are higher gifts than reason and observation.

THE STONE AGE.*

SIR JOHN LUBBOCK has done good service to Ethnology in bringing Professor Nilsson's treatise under the notice of the English public. Professor Nilsson, though well known to German Archæologists, and though himself a keen student of British antiquities, has not up to this received the recognition of English students. In the volume before us he has treated of the relics of the men of the Stone Age in Sweden, and he has dealt with his subject in a manner at once so comprehensive and attractive, that his work will be read with as much pleasure and advantage by the professional as by the amateur Archæologist. In order to render the book as useful as possible even to those unconversant with the recent labours of Ethnologists and Geologists, the editor has added an Introduction, which in clearness and force of argument is unsurpassed by anything he has before written. Sir John Lubbock gives a most instructive sketch of the position of prehistoric Ethnology as it stands at present; and as his views embrace the most modern conclusions, we cannot refrain from giving our readers a brief

* "The Primitive Inhabitants of Scandinavia." By Sven Nilsson. Third edition. Edited, with an Introduction, by Sir John Lubbock, Bart., F.R.S. London, Longmans. 1868.

[title page]

THE

POPULAR SCIENCE

REVIEW.

A QUARTERLY MISCELLANY OF
ENTERTAINING AND INSTRUCTIVE ARTICLES ON
SCIENTIFIC SUBJECTS.

EDITED BY HENRY LAWSON, M.D.

VOLUME VII.

LONDON:
ROBERT HARDWICKE, 192 PICCADILLY;
AND ALL BOOKSELLERS.
1868.