200 The Origin of Species by Mutation. 



One of the greatest faults of those who hold the cur- 

 rent theories of selection is that they have focussed their 

 attention much too exclusively on the phenomena of se- 

 lection and individual variation and much too little on 

 mutations. There can be no doubt th^it this is one of the 

 chief causes of the depth of our ignorance of the facts 

 of mutation. 



This circumstance explains how it is that we can do 

 no more in the matter of testing the hypothesis of indis- 

 criminate mutal^ility by the facts at our disposal, than 

 find out how far the special hypotheses put forward by 

 various authors are in harmony with fundamental and 

 undisputed Darwinian principles. 



Nor is this task an easy one. The question is ob- 

 viously : what share in the origin of the larger or collec- 

 tive species is to be ascribed to mutability and what to 

 the natural elimination of elementary species. Many 

 authors have suggested that altered conditions of life 

 exert a direct influence on animals and plants in such a 

 way that new characters are developed which render their 

 possessors better fitted to their new environment. The 

 environment has, according to them, the power of directly 

 evoking in the organism an adaptive response. 



But this assumption seems to be no more than a 

 begging of the question we are trying to answer. Dar- 

 w^in's idea was that mutability took place in all directions 

 and that the most favorable mutations were preserved. 

 And this view of the matter will, it seems to me, remain 

 the simplest and most probable answer to the question 

 imtil such time as we have collected sufficient experi- 

 mental evidence to decide whether this mutability exists 

 or not. 



We must now discuss in some detail the views of W. 



