150 



THEORY OF EVOLUTION 



in which they have developed. This is a famil- 

 iar fact of almost every-day observation. It 

 is well shown in the following example. In 

 figure 76 the two boys and the two varieties of 



:10 4:11 5.0 5:1 3:2 3:3 3:4 5:3 5:6 3:7 5:8 5:9 5:10 5:11 6:0 6:1 6:2 



FIG. 75. Students arranged according to size. (After 

 Blakeslee.) 



corn, which they are holding, differ in height. 

 The pedigrees of the boys (fig. 77) make it 

 probable that their height is largely inherited 

 and the two races of corn are known to belong 

 to a tall and a short race respectively. Here, 

 then, the chief effect or difference is due to 

 heredity. On the other hand, if individuals of 

 the same race develop in a favorable environ- 

 ment the result is different from the develop- 



