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. After discussing Professor Pearson's work, he
continued:

It seems to me that a simpler result can be reached from our
material in the following way. Since the greater child-mortality of
each of our classes of children (divided according to the ages at
death of their parents) indicates a higher mortality throughout the
rest of their lives, the offspring of parents who die young will
therefore be eliminated in a higher degree, that is, removed from
the composition of the race, than will those whose parents died
late. Now the elimination can be non-selective, falling on all
sorts of constitutions with the same frequency and degree. In that
case it will of course have no connection with selection inside the
race. Or it may be of a selective nature, falling on its victims
because they differ from those who are not selected, in a way that
makes them less capable of resisting the pressure of the
environment, and avoiding its dangers. Then we speak of a selective
process, of the elimination of the weaker and the survival of the
stronger. Since in our examination of the various causes of the
difference in infant mortality, in the various age-classes of
parents, we found no sufficient cause in the effects of the
environment, which necessarily contains all the non-selective
perils, but found the cause to be in the different constitutions
inherited by the children, we can not escape the conclusion that
the differences in infant mortality which we observe indicate a
strong process of natural selection.

Our tables also permit us to get an approximate idea of the extent
of selection by death among children in the first five years of
life. The minimum of infant mortality is reached among those
children whose parents have attained 85 years of age. Since these
represent the strongest constitutions, the mortality of their
children would appear to represent an absolute minimum, mad