8 Descent 



ations as the exclusive factor. Of late, however, 

 this point of view has been abandoned by many 

 investigators, especially in America. 



The actual occurrence of mutations is now 

 recognized, and the battle rages about the ques- 

 tion, as to whether they are be regarded as the 

 principal means of evolution, or, whether slow 

 and gradual changes have not also played a 

 large and important part. 



The defenders of the theory of evolution by 

 slow accumulation of slight fluctuations are di- 

 vided into two camps. One group is called the 

 Neo-Lamarckians ; they assume a direct modi- 

 fying agency of the environment, producing a 

 corresponding and useful change in the organ- 

 ization. The other group call themselves Dar- 

 winians or selectionists, but to my mind with 

 no other right beyond the arbitrary restriction 

 of the Darwinian principles by Wallace. They 

 assume fluctuating variations in all directions 

 and leave the choice between them to the sieve 

 of natural selection. 



Of course we are far from a decision between 

 these views, on the sole ground of the facts as 

 known at present. Mutations under observa- 

 tion are as yet very rare; enough to indicate 

 the possible and most probable ways, but no 

 more. On the other hand the accumulation of 

 fluctuations does not transgress relatively nar- 



