I. SELECTION AND MUTATION. 



In his theory of Selection Darwin combined two 

 principles relating to the origin of species ; and he laid 

 stress sometimes on the one, and sometimes on the other, 

 according to the nature of the available evidence or to 

 the objections of his critics. One was the principle on 

 which the controversy over the origin of species turned 

 in pre-Darwinian days. It was the supposition of a 

 progress by steps in nature, by means of which a new 

 species arose suddenly from a former one. Such a phe- 

 nomenon was called a Mutation. If the new form was 

 distinguished from its parents by a single character the 

 mutation was obviously a relatively simple process. And 

 those who believed in the "sub-species" always regarded 

 the matter in this simple way, even when they questioned 

 the possibility of such mutations on the ground that they 

 never saw them. This was the attitude of the French 

 school in the middle of the XlXth century. They rec- 

 ognized individual variation, and described it time after 

 time; but they saw no connection between it and the 

 origin of species. 



It always seems an extraordinary thing to me that 

 the occurrence of mutations should have escaped the 

 notice of the workers of that time. For they occur both 

 in the cultivated state where they have been called single 

 variations, and also in nature, where as I hope to show 



nOFERTT LIBRARY 



N. C. State College 



