PHENOMENA OF INHERITANCE 3 2 3 



The average contribution of each ancestor was thus stated definitely, 

 the contribution diminishing with the remoteness of the ancestor. This 

 Law of Ancestral Inheritance is represented graphically in the accom- 

 panying diagram (Fig. 48). Pearson has somewhat modified the fig- 

 ures given by Galton, holding that in horses and dogs the parents con- 

 tribute Y%, the grandparents %, the great grandparents %, etc. 



Theoretically the number of ancestors doubles in each ascending 

 generation ; there are two parents, four grandparents, eight great-grand- 

 parents, etc. If this continued to be true indefinitely the number of 

 ancestors in any ascending generation would be (2) n , in which n rep- 

 resents the number of generations. There have been about 57 gen- 

 erations since the beginning of the Christian Era, and if this rule held 

 true indefinitely each of us would have had at the time of the birth of 

 Christ a number of ancestors represented by (2) 57 or about 120 quad- 

 rillions — a number far greater than the entire human population of the 

 globe at that time. As a matter of fact, 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 

 present Emperor of Germany had only 162 ancestors in the 10th as- 

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

 less 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 English 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 

 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 and Japhet, to find our common ancestor. 



2. The second principle which Galton deduced from his statistical 

 studies is known as the Law of Filial Regression, or what might be 

 called the tendency to mediocrity. He found that on the average ex- 

 treme peculiarities of parents were less extreme in children. " 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 parent 

 is gifted by nature, the more rare will be his good fortune if he begets 

 a son who is as richly endowed as himself." This so-called law of filial 

 regression is represented graphically in Fig. 49 in which the actual 



