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 181 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 
