THE STATISTICAL STUDY OF HEREDITY IN MAN 



473 



The same law was shown to hold also for mental characters, or 

 grades of mental ability. "The more bountifully a parent is gifted by 

 nature," says Galton, "the more rare will be his good fortune if he 

 begets a son as richly endowed as himself." Galton considered that 

 any law that applied to such diverse characters as stature, eye-color, 

 and mental ability must be a universal law of heredity. 



The problem then arose as to the reason why heredity between 

 parents and offspring is so imperfect. Let us remember that Galton 

 did all his work long before the rediscovery of Mendel's publications. 

 Had he known about Mendel's laws, about the difference between 



Parents 



Grand Pts 



Gt Gd Pts 



Gt G\ Gd Pts 



Fig. 8g. — Diagram to illustrate Galton's "Law of Ancestral Shares in Inheri- 

 tance." The whole heritage is represented by the entire rectangle; that derived 

 from each progenitor by the smaller squares; the number of the latter doubles in 



{From Conklin, after Thomson.) 



each ascending generation while its area is halved 



phenotypic and genotypic conditions, and that recessive characters 

 concealed for some generations crop out when two recessive genes meet, 

 he would have understood at once why offspring are not always as ex- 

 ceptional as parents. Without any of this background, Galton had to 

 solve the problem of imperfect heredity in his own way. 



He arrived at a conclusion not unlike that of Weismann, that 

 inheritance does not come from the bodies of parents but from a racial 

 "stirp," which is about the same as Weismann's "germ plasm." The 

 reason assigned for filial regression was that offspring do not get all 

 their hereditary characters from their immediate parents, but some of 

 it comes from the four grandparents, some from the eight great-grand- 

 parents, and some from more remote ancestors. Just how much each 

 of the different grades of ancestors contribute to the total heritage of 



