NATURAL SELECTION 127 



tiniies even although the average may for a while 

 be increased. JNIore tall men mav be produced by 

 selection of this kind, but the tallest men are not 

 necessarily any taller than the tallest in the ori^rinal 

 population. 



Selection, then, has not produced anything new, 

 l)ut only more of certain kinds of individuals. Evo- 

 lution, however, means jDroducing new things, not 

 more of what already exists. 



ft 



Darwin's interpretation as to the effect of con- 



100 



10 11 



Fig. 61. — Diagram ilustrating the re- 

 sults of selecting for extra bristles in 

 Drosophila melanogaster. Selection at 

 first produces rapid effects, which soon 

 slow down and then cease. {After 

 MacDoweU.) 



