44 



Darwin, and after Darwin. 



deductions which were dealt with in the Examination 

 of Weismannism, while it is only his basal postulate 

 which has to be dealt with in the following chapters. 



So much, then, for the relations of Weismann's 

 system of theories to one another. It is, however, of 

 even more importance that we should gain a clear 

 view of the relations between his theory of heredity 

 to those of Darwin and of Galton, as preliminary to 

 considering the fundamental question of fact. 



As we have already seen, the theory of germ-plasm 

 is not only a theory of heredity : it is also, and more 

 distinctively, a theory of evolution, &c. As a theory 

 of heredity it is grounded on its author's fundamental 

 postulate the continuity of germ-plasm. But as a 

 theory of evolution, it requires for its support this 

 additional postulate, that the continuity of germ- 

 plasm has been absolute "since the first origin of 

 life." It is clear that this additional postulate is not 

 needed for his theory of heredity, but only for his 

 additional theory of evolution, &c. There have been 

 one or two other theories of heredity, prior to this one, 

 which, like it, have been founded on the postulate of 

 Continuity of the substance of heredity ; but it has 

 not been needful for any of these theories to postulate 

 further that this substance has been always thus 

 isolated, or even that it is now invariably so. For 

 even though the isolation be frequently invaded by 

 influences of body-changes on the congenital characters 

 of this substance, it does not follow that this principle 

 of Continuity may not still be true in the main, even 

 although it is supplemented in some degree by that 

 of use-inheritance. Indeed, so far as the pheno- 

 mena of heredity are concerned, it is conceivable that 



