150 



THEORY OF EVOLUTION 



in wliicli they liave developed. This is a famil- 

 iar fact of almost every-day ohservation. It 

 is well shown in the following example. In 

 fiyure 76 the two hoys and the two varieties of 



+ 11 5 Fl 



Fi(i. 7,5. Students arrajiged according to size. (After 

 Blakeslee.) 



corn, which they are holding, differ in height. 

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

 pi-ohable that their lieight is largely inherited 

 and the two races of corn are known to l)elong 

 to a tall and a sliort race resj^ectively. Here, 

 tlien, the chief effect or difference is due to 

 heredity. On the other hand, if individuals of 

 the same race develoj:) in a favorable environ- 

 ment the result is different from the develop- 



