WHAT EVOLUTION IS 69 



opinions, there arose a belief among 

 naturalists of the transformist school 

 that evolution was so slow and grad- 

 ual a process that no direct observa- 

 tion of it could ever be made. The 

 life of man was not long enough to 

 admit of even a glimpse at evolution- 

 ary change. This view was current 

 in Darwin's day and prevailed more 

 or less to the end of the nineteenth 

 century. It served as a most unfor- 

 tunate deterrent to scientific research, 

 for it discouraged investigators from 

 attempting any direct study of a proc- 

 ess whose operations seemed to be so 

 infinitely slow. 



With the advent of the twentieth 

 century a new phase in evolutionary 

 investigation appeared. Through the 

 work of Tschermak, of Correns, and 

 particularly of De Vries the subject 

 passed from the observational and 

 speculative stage to the experimental 



