All such problems will be illuminated, when more
genealogies are kept on a biological basis.
[Illustration: INFLUENCE OF MOTHER'S AGE
FIG. 44.--As measured by the percentage of infant deaths, those
children show the greatest vitality who were born to mothers between the
ages of 20 and 25. Infant mortality increases steadily as the mother
grows older. In this case the youngest mothers (those under 20 years of
age) do not make quite as good a showing as those who are a little
older, but in other studies the youngest mothers have made excellent
records. In general, such studies all show that the babies are penalized
if marriage is delayed beyond the age of 25, or if child-bearing is
unduly delayed after marriage. Alexander Graham Bell's data.]
Here, however, an emphatic warning against superficial investigation
must be uttered. The medical profession has been particularly hasty,
many times, in reporting cases which were assumed to demonstrate
heredity. The child was so and so; it was found on inquiry that the
father was also so and so: _Post hoc, ergo propter hoc_--it was
heredity. Such a method of investigation is calculated to bring genetics
into disrepute, and would hazard the credit of genealogy.
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