144 WHAT EVOLUTION IS 



what the moving forces behind this 

 great natural process are, no one is 

 in a position to state. Lamarckism 

 may be one of these. Darwinism 

 alone, or supplemented by the muta- 

 tion idea, seems quite clearly another 

 though perhaps a subordinate one. 

 Others still are probably to be dis- 

 covered, for it is unlikely that a proc- 

 ess so intricate, so many-sided, and 

 so far-reaching as organic evolution 

 should depend for its energizing on 

 only one source. 



