1890 ON PHYSIOLOGICAL SELECTION 251 



evolving any of the adaptive mechanisms in organic 

 nature. 



It is for these reasons that in my forthcoming 

 lectures I carefully and expressly follow Darwin in 

 holding ' that there must be a life and death 

 question to make natural selection.' No doubt your 

 principle, if it works, l accumulates variation by 

 mere elimination of competitors ' ; but in so doing 

 it does not i make for righteousness ' in the sense 

 of improvement. 



Therefore I say, it is not, properly speaking, < a 

 form of natural selection.' On the other hand, I 

 think it is a form of physiological selection. For, 

 as you observe, physiological selection depends for its 

 action on i some change in the organs concerned.' 

 But is it not precisely to explain such a change that 

 your principle is suggested ? As I understand it, 

 your principle is put forward as one possible (or more 

 or less probable) cause of increasing sterility of first 

 crosses between two sexually segregating sections of 

 a hitherto (or previously) uniform species. Now, if 

 this be so, is not your suggestion a suggestion to 

 explain the causation of the particular physiological 

 variation on the occurrence of which my theory 

 depends ? Unless you can show any reason for 

 answering this question in the negative, I can only 

 continue to regard your principle (which I think a 

 most interesting one) as belonging to the category of 

 physiological selection. For, if you turn to p. 354 of 

 my paper, you will see that immediately after stating 

 tltc theory, I say : 



'First, let it be observed that if this particular 



