mentioned and those that followed. The fact of evolu- 

 tionary descent had been established long before, while 

 even some of the special points of Darwin's theories as to 

 method had been anticipated. Had Darwin never lived, 

 I believe that evolution would still be accepted and 

 taught at the present day. But Darwin rendered two 

 immortal services to science. During the twenty years 

 that elapsed between the first conception of his theories 

 and the date of their publication, he marshalled in orderly 

 array all the biological data obtainable which proved the 

 transformation of species, including the previously un- 

 recognized body of evidence afforded by the domesticated 

 animals. In the second place, in his doctrine of natural 

 selection he presented for the first time a partial consistent 

 program of nature's method of accomplishing evolution. 

 Darwin did not believe that this explanation was final or 

 even complete, whatever his opponents of the time or 

 critics of the present might contend. 



What now, is the doctrine of natural selection, as Darwin 

 propounded it? All animals vary; every individual differs 

 from others of its kind, even from its closest kin and from 

 its parents in some or many particulars and to different 

 degrees. Whatever the causes, the fact of variation stands 

 unquestioned. Some variations are of course due to direct 

 environmental influence, and to these Buff on attributed an 

 excessive importance; other deviations from the parental 

 or average specific type are no doubt due to indirect effects 

 of the environment, as Lamarck contended. But there are 

 countless other variations that cannot be so explained, 

 some of them indeed appearing before an individual is sub- 

 jected to the action of the environment, and these are the 

 congenital variations due to some constitutional even if 

 unknown causes. These seemed to Darwin to be the most 

 important in evolution. 



The second element of the doctrine is that over-produc- 



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