Heredity and Environment 



owing to the intermarriage of cousins of various degrees the 

 actual number of ancestors is much smaller than the theoretical 

 number. For example, Plate says that the late Emperor of Ger- 

 many, Wilhelm II, had only 162 ancestors in the loth ascend- 

 ing generation, instead of 512, the theoretical number. Neverthe- 

 less this calculation will serve to show how widespread our an- 

 cestral lines are, and how nearly related are all people of the 

 same race, 



Davenport concludes that no people of English descent are 

 more distantly related than 3Oth cousins, while most people are 

 much more closely related than that. If we allow three genera- 

 tions to a century, and calculate that the degree of cousinship is 

 determined by the number 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 3Oth cousins at the present time would have had a com- 

 mon ancestor about one thousand years ago or approximately at 

 the time of William the Conqueror. As a matter of fact most per- 



Parents 



Grand Pta 



Gt Gd Pts 

 (ft G\ Gd P\s 



FIG. 24. 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. (After Thompson.) 



