THEORY OF EVOLUTION 161 



realized the importance of the condition or 

 not is uncertain — curiously he laid no em- 

 phasis on it in the first edition of his "Elemente 

 der exakten Erblichkeitslehre". 



It has since been pointed out by Jennings 

 and by Pearl that a race that reproduces by 

 self-fertilization as does this bean, automati- 

 cally becomes pure in all of the factors that 

 make up its germ plasm. Since self-fertiliza- 

 tion is the normal process in this bean the pur- 

 ity of the germ plasm already existed when 

 Johannsen began to experiment. 



How Has Selection in Domesticated 



Animals and Plants Brought;^ About 



Its Results? 



If then selection does not bring about trans- 

 gressive variation in a general population, how 

 can selection produce anything new? If it 

 can not produce anything new, is there any 

 other way in which selection becomes an agent 

 in evolution? 



We can get some hght on this question if we 

 turn to what man has done with his domesti- 

 cated animals and plants. Through selection. 



