CHAPTEE I. 

 INTRODUCTORY REMARKS. 



Among, the current phrases which the flood of litera- 

 ture on the theory of natural selection has brought 

 to the surface, there is scarcely one more frequently 

 used, and perhaps also misused, than "the preserva- 

 tion of advantageous varieties." These words do in 

 truth sum up the whole theory, and there is nothing 

 in the theory itself which can be made a reason- 

 able ground of objection to them. The questions, 

 however, which lie at the base of this theory remain, 

 and will long remain, open to discussion — the ques- 

 tion, that is, as to " the primary cause of individual 

 varieties," and further, the question as to "the ad- 

 vantages derivable from any given peculiarity in an 

 organism." 



It appears to me to be urgently necessary that instead 

 of indulging in oft -repeated, wide -branching, theo- 

 retical discussions on the preservation of advantageous 

 varieties, we should make the establishment of the 



