Page:Popular Science Monthly Volume 65.djvu/253

Rh species: "I hold that these supernumerary digits are, at their first appearance, nothing but accidental variations. . . . But these variations once well established (confirmées) through a sufficient number of generations in which both sexes have had them, constitute (fondent) species; and it is perhaps thus that all species have multiplied." In fact, for Maupertuis the difficulty lay in explaining, not how species are transformed, but why they arc so stable.

It will be seen that Maupertuis puts forward his theory of transformation only as a likely hypothesis, not as a settled truth. But it is an hypothesis for which he clearly enough indicates his own preference; and it is certain, from a passage of Diderot's which I shall presently quote, that his contemporaries looked upon him as the typical representative of the doctrine of the descent of all species from a primitive type. Yet the significance and originality of the work of Maupertuis lie not so much in his explicit enunciation of the theory of descent, as in the fact that he (1) insistently called the attention of naturalists to the problems connected with the genesis and transmission of variations; (2) framed a conception of the processes involved in embryogeny and heredity which made the mutability of species seem antecedently the more natural and more probable hypothesis; (3) indicated a program for systematic observation and experimentation with reference to heredity and to the effects of interbreeding, which, if carried out, would have transformed zoology; (4) intimated that Nature produces a far greater number of types and of individuals than she can maintain, and that among all these variant types there is constantly taking place a process of natural selection whereby those unfitted to the conditions of their life are exterminated; (5) explained the adaptation of animals to their environment solely as the result of these conjoint processes of variation and selection.