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Show IJARWINIANA. siderable numbe~· of the lower forms of vegetable and animal life, and of a few of the higher plants from the Tertiary period to the present, tells even more directly for the limitless exist~nce o~ species. The. disappearance is quite compatible :Wit.h the latter :1ew; while the persistence of any species IS hardly exphcable upon any other. So that, even unde~ th.e co~n~o.n helief of the entire stability and essentialinflexlbihty of species, extiuction is more likely to ha~e been .accidental than predetermined, and the doctrme of mherent limitation is unsupported by positive evidence. On the other hand, it is an implication of the Darwinian doctrine that species are essentially unlimited in existence. When they die out-as sooner or later any species inay-the verdict must be accidental death, under stress of ad verse circumstances, not exhaustion of vitality; and, commonly, when the species seems to die out it will rather have suffered change. For the stock o'f vitality which enables it to vary an d survi.v e in changed forms under changed circumstances must he deemed sufficient for a continued unchanged existence under unaltered conditions. And, indeed, the advancement from simpler to more complex, which upon the theory must have attended the diversification, would warrant or require the supposition of increase instead of diminution of power from age to age. The only case we call to mind which, under the Darwinian view, might be interpreted as a dying out from inherent causes, is that of a species which refuses to vary, and thus lacks the capacity of ad~~tation t.o altering conditions. Under altering conditiOns, t~1s lack would be fatal. But this would be the fatahty DURATION OF SPECIES. 349 of some species or form in particular, not of species or forms generally, which, for the most part, may and do vary sufficiently, and in varying survive, seemingly none the worse, but rather the better, for their long tenure of life. The opposite idea, however, is maintained by M. N audin/ in a detailed exposition of his own views of evolution, which differ widely from those of Darwin in most respects, and notably in excluding that which, in our day, gives to the ubject its first claim to scientific (as distinguished from purely speculative) attention; namely, natural selection. Instead of the causes or operations collectively personified under this term, and which are capable of exact or probable appreciation, M. N audin invo_kes "the two principles of rhythm and of the decrease of forces in. Nature." He is a thorough evolutionist, starting from essentially the same point with Dan~·in; for he conceives of all the forms oi.· species of animals and plants "comme tire tout entier d'un protoplasma primordial, uniform, instable, eminemment plastique." Also in "!'integration croissante de la force evolutive a mesure qu'elle . se partage dans les formes produites, et la decroissance proportionelle de la plasticite de ces formes :1 rnesure qu'elles s'eloignent davantage de ·leur origine, et qu'elles sont mieux arretees." As they get older, they gain in fixity through the operation of the 1 "Les Especes affines et la Theorie de !'Evolution,'.' par Charles . Naudin Membre de l'Institut, in Bulletin de la Societe Botanique de France: tome xxi., pp. 240-272, 1874. See also Oomptes Rendus, September 27 and October 4, 18'75, reproduced in" Annales des Sciences Naturelles," 1876, pp. '73-81. |
