ence of heredity
regardless of the surroundings in which it is placed, has been shown by
the study of long-lived families to be unjustified. It was found that
even those who inherited exceptional longevity usually did not live as
long as their inheritance gave them the right to expect. If they had had
more euthenics, they should have lived longer.

But this illustration certainly gives no ground for a belief that
euthenics is sufficient to prolong one's life _beyond_ the inherited
limit. A study of these long-lived families from another point of view
will reveal that heredity is the primary factor and that good
environment, euthenics, is the secondary one.

For this purpose we augment the 100 families of the preceding section by
the addition of 240 more families like them, and we examine each family
history to find how many of the children died before completing the
fourth year of life. The data are summarized in the following table:

CHILD MORTALITY IN FAMILIES OF LONG-LIVED STOCK, GENEALOGICAL RECORD
OFFICE DATA

Size of No. of families No. of families Total no.
family investigated showing deaths of deaths
under 5 years

1 child 6 0 0
2 children 6 0 0
3 " 38 4 5
4 " 40 6 7
5 " 38 4 4
6 " 44 12 13
7 " 34 8 11
8 " 46 13 18
9 " 31 14 20
10 " 27 14 14
11 " 13 6 9
12 " 13 9 16
13 " 1 0 0
14 " 2 0 0
17 " 1 1 2
--- --- ---
340 91 119

The addition of the new families (which were not subjected to any
different selection than the first 100) has brought down the child
mortality rate. For the first 100, it was found to be 7.5%. If in the
above table the number of child deaths, 119