3o6 THE EVOLUTION OF SEX. 



are obviously of no account in the evolution of the species, — 

 above the level of the Protozoa at least ; and, as Weismann 

 himself says, the ground is thus taken from under the feet of 

 Buffonians, Lamarckians, neo-Lamarckians, &c. The ground 

 is left clear for natural selectionists, and the struggle for 

 existence acting on variations thus becomes the exclusive 

 factor in the mechanism of evolution. But what then starts 

 these variations which natural selection eliminates or fosters, as 

 the case may be ? Weismann's answer is clear and definite, the 

 intermingling of the sexual elements in fertilisation is the sole 

 fountain of variation ; a view w^hich certainly accents the 

 "Reproductive Factor in Evolution," though it seems to us 

 hardly to conform with the author's previously expounded 

 opinion, that the action of the sperm upon the ovum is quanti- 

 tative rather than qualitative. But, even if none but constitu- 

 tional or germinal variations are transmissible, we are not shut 

 up to the exclusive adoption of the natural selectionist position. 

 It is still open to the naturalist to demonstrate, that manj 

 adaptations at least are not explicable as the result of a long 

 process of fostering and eliminating selection among a host of 

 sporadic results of sexual interminglings, but are rather the 

 direct and necessary results of " laws of growth," of " constitu- 

 tional tendencies," or of the precise chemical nature of the 

 protoplasmic metabolism in the organisms in question. If 

 constitutional variations occur along a few definite lines, as 

 Eimer, Geddes, and others have shown to be true in certain 

 cases, then we can understand the origin, though not perhaps 

 the distribution, of species apart from any long process of selec- 

 tion, for which indeed, if variations be stictly definite, the 

 material must be vastly reduced. In other words, we can 

 think of the organism not merely under the moulding influence 

 of its functions, nor solely as the product of environmental 

 hammering, least of all as the survivor from a crowd of unsuc- 

 cessful competitors, but as the expression of an internal fate, 

 no longer mystical, but expressible in terms of the dominant 

 chemical constitution. 



§ 2. The Reproductive Factor. — Without further discussion 

 of the still open controversy as to the various factors of evolu- 

 tion, which would not be relevant to such a work as this, we 

 must summarily collate the more prominent opinions as to the 

 share reproduction has in the process. To most of these we 

 have already alluded in the body of the book. 



