SECTION V 



DISUSE OF ORGANS DEGENERATION PAMMIXIS 



IN the paper previously mentioned, " Eetrogression in Nature," 

 Weismann replies with greater detail and precision than on 

 previous occasions to the objections which may be made as 

 they have been made by me to his theory on account of the 

 facts of the degeneration of organs in consequence of disuse. 



Starting from the proposition that "the adaptation of 

 living beings in all their parts depends on the process of 

 natural selection," he infers that this adaptation must be 

 maintained by the same means by which it was produced, 

 and that it must again disappear as soon as this means, 

 natural selection, fails to act. 



In other words, he says : Through natural selection alone 

 forms have come to be what they are. By the continuation 

 of natural selection only are they maintained in their present 

 state. If selection ceases, they of necessity retrograde. But 

 selection with respect to a particular organ obviously ceases 

 as soon as that organ is no longer necessary (" the reverse 

 side of natural selection ") its cessation therefore produces 

 the degeneration of organs. 



It is, according to my view, self-evident that the cessation 

 of natural selection l can as little cause the retrogression of 



1 Weismann employs the expression Naturzuchtung (natural breeding) only in 

 the sense of Auslese (selection), herein following Darwinism in general. This use 



