Evidently a large
number of weak males have been eliminated before birth. This elimination
continues for a number of years to be greater among boys than among
girls, until in the period of adolescence the death-rates of the two
sexes are equal. In adult life the death-rate among men is nearly always
higher than that among women, but this is due largely to the fact that
men pursue occupations where they are more exposed to death. In such
cases, and particularly where deaths are due to accident, the mortality
may not only be non-selective, but is sometimes contra-selective, for
the strongest and most active men will often be those who expose
themselves most to some danger. Such a reversal of the action of natural
selection is seen on a large scale in the case of war, where the
strongest go to the fray and are killed, while the weaklings stay at
home to perpetuate _their_ type of the race.
A curious aspect of the kind of natural selection under
consideration,--that which operates by death without reference to the
food-supply,--is seen in the evolution of a wide pelvis in women. Before
the days of modern obstetrics, the woman born with an unusually narrow
pelvis was likely to die during parturition, and the inheritance of a
narrower type of pelvis was thus stopped.
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