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Show 200 DARWINIAN A. other naturalists in no wise essential .to th~ ~pecies, and may not have been the region of Its origin. · In Agassiz's view the habitat is supposed to mark ~he ori·g m· , an d to be a part of the character of th.e. s pecies. The habitat is not merely the place where It 1s, but a part of what it is. . . . Most naturalists recognize vaneties of spemes; and many, like De Candolle, have come to conclude that varieties of the highest grade, or races, so far partake of the characteristics of s~ec~es, and are so ~ar governed by the same laws, that It IS often very difficult to draw a clear and certain distinction between the two. Agassiz will not allow that varieties or races exist in Nature, apart from man's agency. Most naturalists believe that the origin of species is supernatural, their dispersion or particular geographical area, natural, and their extinction, when they disappear, also the result of physical causes. In the view of Agassiz, if rightly understood, all three are equally independent of physical cause and effect, are equally supernatural. In comparing preceding periods with the present and with each other, most naturalists and pa1ffiontologists now appear to ·recognize a certain number of species as having survived from one epoch to the next, or even through more than one formation, especially from the Tertiary into the post-Tertiary period, and from that to the present age. Agassiz is understood to believe in total extinctions and total new creations at each successive epoch, and even to recognize no existing species as ever contemporary with extinct ones, except in the case of recent exterminations. SPECIES AS TO VARIATION, ETC. 201 . These peculiar views, if sustaine~, will effectually d1spose of every form of derivative hypothesis. Returning for a moment to De Candolle's article we are disposed to notice his criticism of Linnffius'~ "definition" of the term species (Philosophia Botanica, No. 157) : "Species tot n~tJmeramus quot divers(J3 formw in prilncipio sunt creat(J3 "-which he declares illogical, inapplicable, and the worst that has been propounded. " So, to determine if a form is specific, it · is necessary to go back to its origin, which is impossible. A definition by a character which can never be verified is no definition at all." Now, as Linnffius practically applied the idea of species with a sagacity which has never been surpassed, and rarely equaled, and indeed may be said to have fixed its received meaning in natural history, it may well be inferred that in the phrase above cited he did not so much undertake to frame a logical a"efi;nition, as to set forth the idea which, in his opinion, lay at the foundation of species; on which basis A. L. J ussieu did construct a logical definition- " Nunc rectius definitur perennis individuorum similium suecessio continuata generatione renascentiun." The fundamental idea of species, we would still maintain, is that of a chain of which genetically-connected individuals are the links. That, in the practical recogniti~:ri of species, the essential characteristic has to be inferred, is no great objection-the general fact that like engenders like being an induction from a vast number of instances; and the only assumption being that of the uniformity of Nature. The idea of gravitation, that of the atomic ·constitution of matter, and the like, |