THE REPRODUCTIVE FACTOR IN EVOLUTION. 281 



elements, — that is to say, affecting the offspring. If the reproductive 

 elements, in spite of the close connection between all parts of the 

 body, or even between cell and cell (see fig. p. 280), do lead such a 

 charmed physiological life within the organism that they are unaffected 

 directly by changes in the other parts of the body, then an optimism 

 of heredity is demonstrable. How far we believe it from being so can 

 not be here discussed, but the consequences of Weismann's conclusion 

 to the general theory of evolution must be re-emphasized. If 

 individually acquired characters are of importance only to the 

 individual body, they are obviously of no account in the evolution of 

 the species, — above the level of the Protozoa at least; and, as Weis- 

 mann 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 

 fertilization is the sole fountain of variation; a view which 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 quantitative rather than 

 qualitative. But, even if none but constitutional 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 many 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 " constitutional 

 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 selection, for which indeed, if variations be strictly definite, 

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

 the organism not merely under the molding influence of its functions, 

 nor solely as the product of environmental hammering, least of all as 

 the survivor from a crowd of unsuccessful competitors, but as the 

 expression of an internal fate, no longer mystical, but expressible in 

 terms of the dominant chemical constitution. 



II. The Reproductive Factor. — Without further discussion of 

 the still open controversy as to the various factors of evolution. 



