A NEW THEORY OF THE ORIGIN OF SPECIES. 515 



almost every point. The Darwinian theory ha.s for its corner stone 

 indiyidual varitition; the new theory, specific mutation, 



Indiyidual variations are progressive, usually guided b}' adaptation 

 to the environment in a direction determined by the "survival of the 

 fittest." The}' are continuous — that is to say, they are produced at all 

 periods. Mutations are quite different. They are metamorphoses, 

 not determined by adaptation; they are produced in various wa3's, 

 without any direction; they are sometimes injurious, sometimes profit- 

 able, sometimes indifferent to the indiyidual — they appear only at cer- 

 tain periods of the life of the species. Besides, both of these transfor- 

 mations occur from the action of causes which are determinate but 

 whose nature is unknown. The first affect, more or less pro- 

 foundly, all parts of the organism; the others affect in a special waA' 

 the function of reproduction. In the Darwinian theory the first form 

 is separated from that which differs from it specific-all}' by a long suc- 

 cession of generations. According to Hugo de Vries the first form 

 which engenders another, and, ordinarily, many others, coexists side 

 by side with this daughter species. It is only after its formation that 

 the latter enters into competition with the species from which it 

 sprang, and circumstances decide which shall survive and which shall 

 disappear. Here the struggle for existence and selection suppresses 

 species ))ut it does not create them. In brief, the most characteristic 

 feature of nuitation is that it is a manifestation of a physiological 

 character, connected by special conditions with the function of repro- 

 duction. 



In one point only the two doctrines agree, viz, that very marked 

 differences in organization are the effect of the disappearance of inter- 

 mediate links. In the case of mutation the new form, although quite 

 markedly distinct from the parent one, does not necessarily show great 

 divergence from it. Its differences may sometimes be anatomically 

 very slight, although they are physiologically very marked, since they 

 inhibit any crossing. Great morphological divergences always result, 

 as in the theory of Darwin, from a series of repeated mutations. These 

 changes are, however, crowded together in a time relatively short, 

 since newly formed species are, at the very moment of their formation, 

 in their phase of plasticity, in their crisis of mutation. 



IV. 



We have now to state the evidence in favor of this doctrine and the 

 foundations on which it rests. We may count in its favor the advan- 

 tage of its reconciling the transformist hypothesis, which is neces- 

 sarily logical, with the inunutability of species, which is, according to 

 de Vries, a proved fact. It succeeds in doing this, as has been seen, 

 by supposing that there is in the life of the species a period of crisis, 

 so to speak — a temporary period of mutation which interrupts for 



