38 THEORY OF EVOLUTION 



bring about variations. If bis views seem to us 

 today at times vague, at times problematical, 

 and often witbout a secure basis, nevertbeless 

 we find in everv instance, tbat Darwin was 

 searching for the physical causes of variation. 

 He brought, in consequence, conviction to 

 many minds that there are abundant indica- 

 tions, even if certain proof is lacking, that the 

 causes of variation are to be found in natural 

 processes. 



. Today the belief that evolution lakes place 



/by means of natural processes is generally ac- 



jcepted. It does not seem probable that we 



shall ever again have to renew the old contest 



between evolution and special creation. 



But this is not enough. We can never re- 

 main satisfied with a negative conclusion of this/' 

 kind. We must find out what natural causes 

 l)ring a])out variations in animals and plants; 

 and we must also find out what kinds of varia- 

 tions are inherited, and liow they are inherited. 

 If the circumstantial evidence for organic evo- 

 lution, furnished by comparative anatomy, 

 embryology and paleontology is cogent, we 

 should be able to observe evolution going on at 



