PRINCIPLE OF NATURAL SELECTION. 21$ 



old doctrine of descent. But as he himself 

 remarked, a naturalist might be convinced by 

 affinities, embryology, distribution, etc., that 

 species are derived by descent; but the conclu- 

 sion, though correct, would be unsatisfactory 

 until it was shown how it was brought about. 



Lamarck had assigned causes for the modifi- 

 cation of species ; but Darwin insisted positively 

 that he derived no help whatever from him. 

 Logically, the failure of the former's doctrines 

 to win over the scientific world was due to his 

 connecting the doctrine of descent, which had 

 strong evidence in its favor, with hypothetical 

 causes which he did not subject to rigid de- 

 ductive tests in explanation of the facts. What 

 kept Darwin longest orthodox were the facts 

 of adaptation. No cause could be considered 

 adequate which did not account for the exqui- 

 site adaptation to environment found through- 

 out the animal and plant kingdoms. As he 

 said himself, " I had always been much struck 

 by such adaptation, and until these could be 

 explained it seemed to me almost useless to 

 endeavor to prove by indirect evidence that 

 species have been modified." 1 He distin- 

 guished clearly in his own mind between the 

 two propositions which he undertook to prove 



1 Life and Letters, Vol. I. p. 67. 



