EVOLUTION IN NATURE 175 



explanation of all evolution. Mutation as a result 

 of the action of rays on the genes, followed by- 

 natural selection of an inconceivable extent, pro- 

 vides an explanation which is logically tenable 

 if one's mental processes are sufficiently elastic to 

 encompass it without serious distortion. To my 

 mind, and I advance this entirely as a personal 

 view, the idea demands too much credulity. The 

 close parallel between the adaptive processes in 

 individuals and the adaptations evident in species 

 suggests too strongly that adaptation of species is 

 not wholly haphazard at the outset, that it does 

 not depend wholly upon random mutations, but 

 that it is a part of the astonishing plasticity of the 

 living substance which, in spite of its tendency to 

 retain its fixed characteristics, has displayed such 

 versatility in meeting the conditions available over 

 the world. 



One cannot accept this view without admitting 

 the possible truth of Devaux's conclusion that 

 evolution is now at a low ebb and that, at one time, 

 living matter was in such a plastic state that many 

 species were formed as the many available habitats 

 on the sparsely populated earth were invaded. ^^ 

 This possibility, however, only complicates our 

 problem. If evolution is now at a low ebb, it will 

 be more difficult to demonstrate the method of its 

 progress. We need not expect that method to be 



26 Rev. gen. sci. pures et appL, 39 (10), pp. 299-306, 1928. 



