The Days of a Man [1873 



ward joined the ranks of the evolutionists. For he 

 taught us to think for ourselves, not merely to 

 follow him. Thus, though i accepted his philosophy 

 regarding the origin and permanence of species 

 when I began serious studies in Zoology, as my work 

 went on their impermanence impressed me more and 

 more strongly. Gradually I found it impossible to 

 believe that the different kinds of animals and 

 plants had been separately created in their present 

 My forms. Nevertheless, while I paid tribute to Darwin's 

 "* t ~ marvelous insight, I was finally converted to the 

 z>TJL- tneor y of divergence through Natural Selection and 

 ism other factors not by his arguments, but rather by 

 the special facts unrolling themselves before my 

 own eyes, the rational meaning of which he had 

 plainly indicated. I sometimes said that I went 

 over to the evolutionists with the grace of a cat 

 the boy "leads" by its tail across the carpet! 



All of Agassiz's students passed through a similar 

 experience, and most of them came to recognize 

 that in the production of every species at least four 

 elements were involved - - these being the resident 

 or internal factors of heredity and variation, and 

 the external or environmental ones of selection and 

 segregation. 



In the original Penikese group, the man who most 

 interested me was William Keith Brooks, then 

 occupying a precarious professorship in a little 

 college at Niagara Falls. Very wise and self-con- 

 tained, he was especially sparing of words and keen 

 in all his conclusions. Later, as professor in Johns 

 Hopkins University, he came to be the most dis- 

 tinguished American biologist of his time, a true 



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