THEORY OF EVOLUTION 



153 



FIG. 78. Corn reared under different conditions. (After 

 Blakeslee.) 



it contains only a part of the truth. Any one 

 who repeats for himself this kind of selection 

 experiment will find that while his average class 

 will often change in the direction of his selec- 

 tion, the process slows down as a rule rather 

 suddenly (fig. 80). He finds, moreover, that 

 the limits of variability are not necesarily trans- 

 cended as the process continues even although 

 the average may for a while be increased. More 

 tall men may be produced by selection of this 

 kind, but the tallest men are not necessarily any 

 taller than the tallest in the original population. 



