the same period, they have again found[57] that
"for both sexes a heavy death-rate in one year of life means a markedly
lower death-rate in the same group in the following year of life." This
lessened death-rate extends in a lessened degree to the year following
that, but is not by the present method easy to trace further.

"It is difficult," as they conclude, "to believe that this important
fact can be due to any other source than natural selection, i. e., a
heavy mortality leaves behind it a stronger population."

To avoid misunderstandings, it may be well to add to this review the
closing words of the Elderton-Pearson memoir. "Nature is not concerned
with the moral or the immoral, which are standards of human conduct, and
the duty of the naturalist is to point out what goes on in Nature. There
can now be scarcely a doubt that even in highly organized human
communities the death-rate is selective, and physical fitness is the
criterion for survival. To assert the existence of this selection and
measure its intensity must be distinguished from an advocacy of high
infant mortality as a factor of racial efficiency. This reminder is the
more needful as there are not wanting those who assert that
demonstrating the existence of natural selection in man is identical
with decrying all efforts to reduce the infantile death-rate." A further
discussion of this point will be found in a later chapter.

The conclusion that, of the infants who die, a large number do so
through inherent weakness--because they are not "fit" to survive--is
also suggested by a study of the causes of death. From a third to a half
of the deaths during the first year of life, and particularly during the
first month, are due to what may be termed uterine causes, such as
debility, atrophy, inanition, or premature birth. Although in many
cases such a death is the result of lack of prenatal care, in still more
it must be ascribed to a defect in the parental stock.

In connection with infant mortality, it may be of interest to point out
that the intensity of natural selection is probably greater among boys
than among girls. There is a steady preponderance of boys over girls at
birth (about 105 to 100, in the United States), while among the
stillborn the proportion is 158 to 100, if the Massachusetts figures for
1891-1900 may be taken as general in application. Evidently a large
number of weak males have been eliminated before birth. This elimination
continue