322 THE TREND OF THE RACE 
two years, and over twice as great when the interval was over 
two years. There was also a slightly greater death rate between 
the first and fifth years when the intervals between births were 
short, but the differences were slight. Ewart has adduced data to 
show that frequent births handicap offspring both physically and 
intellectually even at six years of age. The initial inferiority 
of children resulting from too frequent births is probably due 
in large part to the reduced vitality of the mother. The rela- 
tively poorer intellectual development which has been noted 
(and our data on this score are hardly sufficient to warrant a 
general conclusion) may be due largely to the selection of stocks. 
The people who exercise no control over the rapidity of their 
multiplication are not apt to produce children who excel in tests 
of intellectual development. 
It is uncertain that any of the agencies considered in the present 
rather unsatisfactory chapter cause any changes that may prop- 
erly be called hereditary. They may influence offspring, possibly 
throughout life, but it is probable that their effects are mostly 
purely somatic. It is possible that parental age, for instance, 
might influence selective fertilization, or the selective elimination 
of embryos. Since an old body affords an environment for the 
germ plasm different in many ways from that afforded by a young 
body, it is not improbable that this circumstance might be re- 
flected in the trend of germinal variability. It might be con- 
jectured that whatever causes the vitality of our bodies to run 
down with advancing years might also affect the germ plasm in 
a deleterious manner. But there is little use at present in indulg- 
ing in mere conjectures. Experiments on animals may throw 
light on some of these matters about which we are now in com- 
plete ignorance. 
REFERENCES 
Ansell, C. Statistics of Families, London, 1874. 
Auerbach, E. Kurzsichtigkeit und Erstgeburt. Arch. Rass. Ges. Biol. 9, 762-763, 
1912. 
Bell, A.G. The Duration of Life and the Conditions associated with Longevity. 
Washington, D. C., 1918. 
