116 OTHER FACTORS OF EVOLUTION 



be varying on an ascending scale, just because the former is, on 

 account of its diminished power of assimilation, no longer able to 

 exhaust completely the food stream which flows to it " — that is, 

 within the very minute microscopic granular id. Some of these 

 assumed changes in rate of growth or nutritive vigour are believed 

 to be ' spontaneous,' while others are ' induced ' by changes in 

 external conditions. Weismann's doctrine necessitates, however, 

 the consideration of these other additional points: — "Each id 

 contains potentially the whole organism, though with some indi- 

 viduality of expression. The child is thus not determined by the 

 determinants of a single id, but by those of many ids, and the 

 variations of any part of the body do not depend upon the 

 variations of a single determinant X, but on the co-operation of 

 all the determinants X which are contained in the collective ids of 

 the relevant germ-plasm. Thus it is only when a majority of 

 the determinants have varied upwards or downwards, that they 

 dominate collectively the development of the part X and cause 

 it to be larger or smaller." 



It is not only, he tells us, that the determinants may " become 

 larger or smaller as a whole, but some kinds of the ' biophors ' 

 of which they are made up may increase more than others under 

 definite altered conditions, and in that case the determinants 

 themselves will vary qualitatively . . . consequently also qualita- 

 tive variations of the organs controlled by the determinants — the 

 determinates," will be caused.' 



Many persons will probably fail to find much security in these 

 complicated considerations — especially when they bear in mind 

 that the foundations on which they are based lie among shifting 

 and delusive sands rather than upon a bed of solid rock. H. M. 

 Vernon believes this hypothesis of ' Germinal Selection ' to be 

 absolutely at variance with an important body of well-established 

 facts. Thus he says,° "This theory, though plausible enough, is 

 absolutely opposed to fact in so far as it relates to the evolution 

 of more adaptive forms ... it is no more than an hypothesis, 

 which has not, and never can have, any experimental evidence 

 to support it." Haeckel also rejects it. He says : — " We may 

 admire the subtlety and depth of the speculations with which 

 Weismann has worked out his elaborate molecular theory. 

 But the nearer we get to its foundations the less solid we find 



■ Loc. cit., II, pp. 125 and IS^- 



' " Variation in Animals and Plants," 1903, p. 396. 



