258 THE TREND OF THE RACE 



marry into a stock which produces less children. Jenks recognizes 

 this fact and has calculated the expected size of the family re- 

 sulting from mixed marriages. 



In speaking of Dutch families he says "Not only is the Dutch 

 half-breed family much less fecund than the Dutch pure-bred 

 family, but the average for the Dutch half-breed families is notice- 

 ably lower than the expected average for said families. This 

 expected average is computed from the fourteen ethnic groups 

 composing the i8i Dutch half-breed families. The expected 

 average is 2.4 children per family, while the actual average is 

 only 1.83 children — the fact of amalgamation apparently being 

 the cause for reduced fecundity." Just how the expected size of 

 the family is calculated is not explained in detail, but apparently 

 the author has calculated the average fecundity of the stocks into 

 which any given group marries and taken the mean between 

 this and the average size of the pure-bred Dutch family. But 

 however he computes the expected averages of cross-bred families, 

 why can we say that any numerical expression represents the 

 expected number of children from a given cross mating? The 

 proceeding involves the assumption that the size of the families of 

 the stocks in question is an index of their natural fecundity. If 

 this is not the case, the argument becomes vitiated. If the aver- 

 age size of the pure-bred Dutch families is 3.53 and the size of the 

 American family is 1.52 are we justified in expecting that the 

 average size of the Dutch- American family is the mean of these 

 two numbers, or 2.5? Take a stock in which birth restriction is 

 an ingrained custom and suppose that marriages occur between 

 its members and those of a people which does not practice artifi- 

 cial restriction of the family. Who can say what is the "ex- 

 pected" number of children? It seems not improbable that 

 the size of the family would be nearer that of the stock with a tra- 

 dition of family limitation, because one member, at least, would 

 be familiar with the practice. There are various social influences 

 also which might affect the size of the cross-bred groups, and it is 

 not improbable that those who marry with people of alien stock 

 may not be typical of the general average of their group. Much 



