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.
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