OTHER FACTORS OF EVOLUTION 115 



In order, however, to account for all the facts concerning 

 'sports' of all kinds, 'mutation' and 'correlated variability,' to 

 which we have just been referring, as well as to many other 

 difficulties besetting his exclusive doctrine concerning the all- 

 sufficiency of ' Natural Selection,' Prof. Weismann relies upon a 

 supplemental hypothesis which he calls ' Germinal Selection.' In 

 addition, he appeals to it to explain the existence of non-adaptive 

 characters in animals and plants ; as a means of starting and 

 increasing incipient variations till they can be made use of by 

 natural and sexual selection ; as a mode of accounting for the 

 influence of new external conditions in modifying organisms ; 

 as a means of bringing about the diminution and even total 

 disappearance of disused organs ; and finally as yielding an 

 " explanation of every heritable variation." ' 



In the last chapter we have seen how devoid of all foundation 

 in fact is his doctrine of the ' Continuity of the Germ Plasm,' and 

 what an extraordinary web of assumptions and hypotheses he 

 has made use of, in conjunction with this basal doctrine, in his 

 attempts to explain many known phenomena. And now all out- 

 standing difficulties, he seems to think, are to be explained away 

 by his supplemental hypothesis of ' Germinal Selection ' — that is, 

 by a process of selection occurring between the determinants of 

 each 'id' and going on in all of them simultaneously. 



In reference to this doctrine we have to bear in mind that the 

 cell itself is a body of microscopic minuteness ; that the bulk of 

 the nucleus is very much smaller still ; that the nucleus contains 

 several minute chromosomes ; that each chromosome is made up 

 of a number of granular bodies termed ids (only visible with very 

 high powers of the microscope) ; and that each granular id is 

 assumed to be composed of many thousands of imaginary bodies 

 named determinants — and that it is between these determinants 

 that the nutritional struggle, or ' selection,' is taking place. 



It is further assumed by Weismann that the rate of growth of 

 these imaginary determinants within the granular id will depend 

 "mainly on the amount of nourishment which reaches them" ; 

 and that there will be "unequal nutrition of the determinants 

 conditioned by the chances of the food-supply." Moreover, owing 

 to their different assimilative powers " while one determinant may 

 be slowly becoming weaker, its neighbour, on the other hand, may 



• See " The Evolution Theory," Vol. II, pp. 113-158. 



