THE GENESIS OF SPECIES.

A review in Nature,' by Mr. A. W. Bennett, of Mr. Mivart's Genesis of Species,' contains the following passage :

'It behoves, therefore, every Darwinian to satisfy himself that either Mr. Mivart's premisses or his line of argument is unsound.

'The objections brought forward by the author are summed up as follows:-(1) That Natural Selection is incompetent to account for the incipient stages of useful structures. (2) That it does not harmonize with the co-existence of closely similar structures of diverse origin. (3) That there are grounds for thinking that specific differences may be developed suddenly instead of gradually. (4) That the opinion that species have definite though different limits to their variability is still tenable. (5) That certain fossil transitional forms are absent which might have been expected to be present. (6) That some facts of geological distribution supplement other difficulties. (7) That the objection drawn from the physiological difference between "species" and "races" still exists unrefuted. (8) That there are many remarkable phenomena in organic forms upon which Natural Selection throws

no light whatever, but the explanations of which, if they could be attained, might throw light upon specific origination.

'If these objections are not new, they are at least sustained by new arguments. They are evidently of very unequal value. The third is very difficult of proof or disproof. The fifth may be true in our present state of knowledge, but would be very unsafe by itself as the basis of an argument. The first, second, and eighth are of greatest value, and are those which Mr. Mivart has most closely worked out1.'

The review containing the above passage did not appear till the present volume was on the very eve of publication. Even a hasty glance at Mr. Mivart's book is sufficient to show that Mr. Bennett has not over-estimated its importance and value. It is scarcely possible here to do more than make a few reflections upon its general scope, in reply to the challenge offered to Darwinians. The first objection, as it stands in the summary, wears the appearance of a misconception. It is almost certain to produce one. When Mr. Darwin attributes the origin of species to Natural Selection, he includes expressly, and where not expressly, by obvious implication, the principle of Variability. He never maintains that the first or any subsequent stage of a useful structure can be produced by Natural Selection. Natural Selection only operates to preserve. Without Variation it would have no sphere in which to operate, so that 1 Nature,' No. 65.

from one point of view Mr. Darwin may be said to attribute the origin of species to Variation rather than Natural Selection. He is, moreover, far from ignoring the influence of other principles, such as Inheritance, Reversion, and Correlation, upon the total result. He may be thought inconsistent with himself in laying stress at times upon the minuteness of the variations which he supposes to have slowly accumulated into specific differences, and at other times admitting the sudden appearance of variations which may be considered as large ones, and which are certainly striking. But in the first instance the great and almost overwhelming difficulty was to induce a belief that forms specifically different could be connected with one another by descent. By showing that a multitude of small differences accumulated would make a large total difference, he made as it were a bridge for the existing incredulity. It now appears that the gulf may be passed with easy strides instead of the little slow steps at first thought necessary. This fortifies the doctrine of the Transmutation of Species, in proportion as there are fewer missing links,' fewer transitional forms that need to be accounted for.

Of the coexistence of closely similar structures of diverse origin,' illustrated so forcibly by the instance of the eye, 'in at least three independent lines of descent, the Mollusca, the Annulosa, and the Vertebrata,' it can scarcely be denied that Natural Selection alone would be an inadequate explanation. But here again it should be observed that Darwinism does not attribute every

thing to Natural Selection. It assumes, what must be allowed, that variations occur. In obedience to what laws those variations themselves are produced is an interesting speculation, and a most important subject of inquiry. That such laws or conditions of Variation exist no one can doubt, unless he has been seduced by Ovidian metamorphoses to believe in trees bleeding human blood and human foreheads branching with the antlers of the stag. A knowledge of those conditions might fully explain the coexistence of similar structures of diverse origin, consistently with the principle of Natural Selection. The ignorance of them is scarcely a proof that such coexistence does not harmonize with it.

The objection that giraffes, which profited by long necks in a time of drought, would find them a disadvantage subsequently, as requiring a greatly increased size and strength of muscles to support them, overlooks the law of correlation, by assuming that the elongated neck would be out of proportion to the other conditions of the creature's fabric.

Mr. Mivart's fourth objection seems at least an extremely improbable opinion. He refers to Mr. Darwin's expression, that the goose appears to have a highly inflexible organization, as if he himself thought it possible for a species at length to attain to an organization completely inflexible. Such a view would imply two parents exactly like one another, producing offspring exactly like themselves; and of such exact likenesses no known families afford examples.

The seventh objection recalls the still unexplained physiological difference between species' and ' races,' unions between the former being sterile, and between the latter fertile. In this branch of the subject there is much scope still for inquiry. Some of the difficulty may be due to a trick played us by language. True species have been defined to be those that are not fertile together; and from the definition it follows that races which are fertile together are not true species. But the question is obscured by the use of the two different words 'races' and 'species,' the real issue being, whether races that are and races that are not fertile together can originate in the same way. The subject in its other bearings has been largely discussed by Mr. Darwin in his work on Animals and Plants under Domestication.'

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It remains only to say a few words on the argument from the calculation of chances which is supposed to reduce the survival by natural selection of any particular useful variation almost or altogether to an arithmetical impossibility. The advantage,' we are told, 'whatever it may be, is utterly outbalanced by numerical inferiority. A million creatures are born: ten thousand survive to produce offspring. One of the million has twice as good a chance as any other of surviving: but the chances are fifty to one against the gifted individual's being one of the hundred survivors. No doubt the chances are twice as great against any one other individual, but this does not prevent their being enormously in favour of some

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