Weismannism tip to date (1893). 159 



minimizing the possible range of congenital variation 

 due to the action of external conditions on a non- 

 absolutely stable substance of heredity, Weismann 

 is making a wholly gratuitous assumption, for the 

 sole purpose of saving what remains of his theory 

 of evolution — i. e., the doctrine of the immense im- 

 portance of amphimixis. 



We have already seen in the foregoing chapter, 

 that his original assumption of the absolute stability 

 of germ-plasm was a gratuitous one, made for the 

 purpose of supplying a foundation for constructing 

 his theory of evolution. But still more gratuitous 

 is the assumption which he has now substituted, for 

 the purpose of saving as much of this theory as 

 is left — the assumption, namely, that germ-plasm, 

 although universally unstable, nevertheless everywhere 

 presents only a certain low degree of instability, 

 which serves to accommodate his modified theory 

 of heredity on the one hand, and all that is possible 

 of his previous theory of evolution on the other. His 

 original assumption, untenable though it was, fur- 

 nished at least a logical basis for the necessan/ con- 

 clusion that amphimixis was the only possible cause 

 of congenital variations. But there is not so much as 

 any logical sequence in the now substituted assumption, 

 that (A) all congenital variations are ultimately due 

 to the universal instability of germ-plasm, and (B) that 

 nevertheless they are all more proximately due to such 

 a high degree of stability of germ-plasm as necessitates 

 amphimixis as the only means whereby variations can 

 be made " perceptible.' 5 These statements are as 

 independent of one another as any two statements 

 can well be ; and, therefore, if the second of them is to 



