hen its mother dies at the age of 69; the
child herself was probably married long before the death of the mother.
Nor is it credible that the death of the father takes bread from the
child's mouth, leaving it to starve to death in the absence of a pension
for widowed mothers, if the father died at 83, when the "child" herself
was getting to be an old woman. The early death of a parent may
occasionally bring about the child's death for a reason wholly
unconnected with heredity, but the facts just pointed out show that such
cases are exceptional. The steady association of the child death-rate
and parent death-rate _at all ages_ demonstrates that heredity is a
common cause.

But the reader may suspect another fallacy. The cause of this
association is really environmental, he may think, and the same poverty
or squalor which causes the child to die early may cause the parent to
die early. They may both be of healthy, long-lived stock, but forced to
live in a pestiferous slum which cuts both of them off prematurely and
thereby creates a spurious correlation in the statistics.

We can dispose of this objection most effectively by bringing in new
evidence. It will probably be admitted that in the royal families of
Europe, the environment is as good as knowledge and wealth can make it.
No child dies for lack of plenty of food and the best medical care, even
if his father or mother died young. And the members of this caste are
not exposed to any such unsanitary conditions, or such economic pressure
as could possibly cause both parent and child to die prematurely. If the
association between longevity of parent and child mortality holds for
the royal families of Europe and their princely relatives, it can hardly
be regarded as anything but the effect of heredity,--of the inheritance
of a certain type of constitution.

Dr. Ploetz studied the deaths of 3,210 children in European royalty,
from this viewpoint. The following table shows the relation between
father and child:

LENGTH OF LIFE OF FATHERS AND CHILD-MORTALITY OF THEIR CHILDREN IN
ROYAL AND PRINCELY FAMILIES, PLOETZ' DATA

At
Year of life in which fathers died Years all
ages
16-25 26-35 36-45 46-55 56-65 66-75 76-85 86 up

No. of children. 23 90 367 545 725 983 444 33