HISTORICAL SPECULATIONS 15 



They are accidents, it is true, but they are causal 

 accidents. 



In his famous book on Animals and Plants under 

 Domestication, Darwin dwells at great length on 

 the nature of the conditions that bring about varia- 

 tions. If some of his views seem to us today at times 

 vague, at times problematical, and often without a 

 secure basis, nevertheless we find, in every instance, 

 that Darwin was searching for the ijhysical causes 

 of variation. He brought, in consequence, conviction 

 to many minds that there are abundant indications, 

 even if certain proof is lacking, that the causes of 

 variation are to be found in natural processes. 



Today the belief that evolution takes place by 

 means of natural processes is generally accepted. It 

 did not seem probable that we should ever again have 

 to renew the old contest between evolution and spe- 

 cial creation. 



But this is not enough. We can never remain satis- 

 fied with a negative conclusion of this kind. We must 

 find out what natural causes bring about variations 

 in animals and plants; and we must also find out 

 what kinds of variations are inherited, and how they 

 are inherited. If the circumstantial evidence for or- 

 ganic evolution, furnished by comparative anatomy, 

 embryology and paleontology is cogent, we should 

 expect to observe evolution going on at the present 

 time, i.e., w^e should be able to observe the occurrence 

 of variations and their transmission. This has actu- 



