222 



HEREDITY AND ENVIRONMENT 



gram (Fig. 46). Pearson has somewhat 

 modified the figures given by Galton, holding 

 that in horses and dogs the parents contribute 

 1/2, the grandparents 1/3, the great grand- 

 parents 2/9, etc. 



Theoretically the number of ancestors 



cT 



c? 



d* 



d 1 



o* 



d 



in 



Parents 



Grand Pt$ 



g\ Gd P\s 

 Gt Ot Gd P'ts 



Fig. 46. Diagram of Galton's "Law of Ancestral Inheri- 

 tance." The whole heritage is represented by the entire rect- 

 angle; that derived from each progenitor by the smaller 

 squares; the number of the latter doubles in each ascending 

 generation while its area is halved. (After Thompson.) 



doubles in each ascending generation; there 

 are two parents, four grandparents, eight 

 great-grandparents, etc. If this continued to 

 be true indefinitely the number of ancestors in 

 any ascending generation would be (2) n , in 



