that there is no
association; that from the age at which one dies, nothing whatever can
be predicted as to the age at which the others will die. Since it is
known that heredity is a large factor in longevity, such a finding would
mean that all deaths were due to some accident which made the
inheritance of no account.

In an ordinary population it has been found that the age at death of
brothers and sisters furnishes a coefficient of correlation of the order
of .3, which shows that heredity does determine the age at which one
shall die to considerable extent, but not absolutely.[190]

The index of correlation[191] between the lengths of life within the
fraternity in these 100 selected families, furnished a coefficient
of-.0163+-.0672, practically zero. In other words, if the age is known at
which a member of one of these families died, whether it be one month or
100 years, nothing whatever can be predicted about the age at which his
brothers and sisters died.

Remembering that longevity is in general inherited, and that it is found
in the families of all the people of this study (since one in each
fraternity lived to be 90 or over) how is one to interpret this zero
coefficient? Evidently it means that although these people had inherited
a high degree of longevity, their deaths were brought about by causes
which prevented the heredity from getting full expression. As far as
hereditary potentialities are concerned, it can be said that all their
deaths were due to accident, using that word in a broad sense to include
all non-selective deaths by disease. If they had all been able to get
the full benefit of their heredity, it would appear that each of these
persons might have lived to 90 or more, as did the one in each family
who was recorded by the Genealogical Record Office. Genetically, these
other deaths may be spoken of as premature.

In an ordinary population, the age of death is determined to the extent
of probably 50% by heredity. In this selected long-lived population,
heredity appears not to be responsible in any measurable degree
whatsoever for the differences in age at death.

The result may be expressed in another, and perhaps more striking, way.
Of the 669 individuals studied, a hundred--namely, one child in each
family--lived beyond 90; and there were a few others who did. But some
550 of the group, though they had inherited the potentiality of reaching
the average age of 90, actually died somewhere aroun