372 READINGS IN EVOLUTION, GENETICS, AND EUGENICS 



512, the theoretical number. Nevertheless this calculation will serve 

 to show how widespread our ancestral lines are, and how nearly related 

 are all people of the same race. 



Davenport concludes that no people of Enghsh descent are more 

 distantly related than 30th cousins, while most people are much more 

 closely related than that. If we allow three generations to a century, 

 and calculate that the degree of cousinship is determined by the num- 

 ber of generations less two, since first cousins appear only in the third 

 generation, the first being that of the parents and the second that of 

 the sons and daughters, we find that 30th cousins at the present time 



Parents 



Grand Pts 



Gt Gd Pts 



Gt g\ Gd P\s 



Fig. 65. — Diagram of Galton's "Law of Ancestral Inheritance." 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 each ascending 

 generation while its area is halved. {From Conklin, after Thomson.) 



would have had a common ancestor about one thousand years ago or 

 approximately at the time of William the Conqueror. As a matter of 

 fact most persons of the same race are much more closely related than 

 this, and certainly we need not go back to Adam nor even to Shem, 

 Ham, or Japheth to find our common ancestor. 



2. The Law of Filial Regression is the second principle which 

 Galton deduced from his statistical studies, or it may be called the 

 tendency to mediocrity. He found that, on the average, extreme 

 peculiarities of parents were less extreme in children. Thus "the 

 stature of adult offspring must on the whole be more mediocre than 

 the stature of their parents, that is to say more near to the mean or 

 mid of the general population"; and again, "the more bountifully a 



