"The measure of the selective death-rate." says[53] Karl Pearson, to
whom this achievement is due, "is extraordinarily simple. It consists in
the fact that the inheritance of the length of life between parent and
offspring is found statistically to be about one-third of the average
inheritance of physical characters in man. This can only be due to the
fact that the death of parent or of offspring in a certain number of
cases is due to random and not to constitutional causes." He arrived at
the conclusion[54] that 60% of the deaths were selective, in the Quaker
families which he was then studying. The exact proportion must vary in
accordance with the nature of the material and the environment, but as
A. Ploetz found at least 60% of the deaths to be selective in the
European royal families and nobility, where the environment is
uniformly good, there is no reason to think that Professor Pearson's
conclusion is invalid.
Dr. Ploetz[55] investigated the relation between length of life in
parents, and infant mortality, in about 1,000 families including 5,500
children; half of these were from the nobility and half from the
peasantry. The results were of the same order in each case, indicating
that environment is a much less important factor than many have been
wont to suppose.
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