338 Darwin, and after Darwin. 



Weismann, on the other hand, can only suppose that this 

 intensely specialized instinct had its origin in fortuitous varia- 

 tions in the psychology of the species. But, neglecting the 

 consideration that, in order to become fixed as an instinct 

 by natural selection, the particular variation required must 

 have occurred in many different individuals, not only in the 

 first, but also in the sequent generations, the chances against 

 its occurring only once, or in but one single individual case, are 

 many thousands if not millions to one. 



