316 THE TREND OF THE RACE 
mothers (20 or less) are shorter ‘and lighter than the children of 
mothers a few years older. In mothers over 25 the height and 
weight of children diminished with advancing'age. A somewhat 
similar relationship is seen in children at 13.5 years. The data of 
Professor Ewart, since they deal with only a few hundred cases of 
mixed stocks, are entirely inadequate to solve the problem of how 
age of parents affects the offspring in later years. In such an 
investigation there are several sources of fallacious conclusions. 
Consider for instance the presence of a number of Italians in the 
population studied. The Italians are characterized by short 
stature and they are prone to marry early. The children of 
young mothers would be apt to include a relatively large propor- 
tion of Italian stock. Now if we compare the height of these 
children in later life with the average height of children of older 
parents we might be misled into attributing to parental age a 
characteristic really dependent upon race. Children of older 
parents are, other things equal, members of larger families than 
children of young parents. Large families tend to characterize 
stocks in the lower walks of life in which the surroundings are less 
hygienic and in which conditions for growth are less favorable 
than among people with small families. By taking a random lot 
of children begotten by old parents we should get a proportion- 
ately large number of children from large families, especially since 
the relatively recent reduction of the birth rate has occurred 
mainly through preventing the arrival of those who would be later 
born children. Selecting the children of old parents, therefore, 
incidentally involves also a selection of stocks and to a certain 
degree also a selection of environments. These sources of erro- 
neous interpretation of statistics,—to say nothing of others— 
must be borne in mind in the study of our problem. 
Mr. Redfield has reported investigations on the influences 
of parental age on longevity of offspring which led him to con- 
clude that children begotten when their parents are old live 
longer, on the average, than children who are the product of their 
parents’ earlier years. He has calculated the length of life of all 
the great men of whom he could obtain a record of the birth 
