A. O. Powys' careful
study[170] of the admirable vital statistics of New South Wales showed
that the mothers who lived longest were those who bore from five to
seven children.
4. The age at which men and women should marry has not yet been
sufficiently determined, on biological grounds. Statistics so far
compiled do not indicate that the age of the father has any direct
influence on the character of the children, but the age of the mother
undoubtedly exercises a strong influence on them. Thus it is now well
established[171] that infant mortality is lowest among the children of
young mothers,--say from 20 to 25 years of age,--and that delay in
child-bearing after that age penalizes the children (see Fig. 44). There
is also some evidence that, altogether apart from the infant mortality,
the children of young mothers attain a greater longevity than do those
of older women. More facts are needed, to show how much of this effect
is due to the age of the mother, how much to her experience, and how
much to the influence of the number of children she has previously
borne.
5. Assortative mating, consanguineous marriage, the inheritance of a
tendency to disease, longevity, sex-linked heredity, sex-determination,
the production of twins, and many other problems of interest to the
general public as well as to the biologist, are awaiting the collection
of fuller data.
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