From the several foregoing cases we have some reason to believe that
infanticide practised in the manner above explained, tends to make a
male-producing race; but I am far from supposing that this practice in
the case of man, or some analogous process with other species, has been
the sole determining cause of an excess of males. There may be some
unknown law leading to this result in decreasing races, which have
already become somewhat infertile. Besides the several causes
previously alluded to, the greater facility of parturition amongst
savages, and the less consequent injury to their male infants, would
tend to increase the proportion of live-born males to females. There
does not, however, seem to be any necessary connection between savage
life and a marked excess of males; that is if we may judge by the
character of the scanty offspring of the lately existing Tasmanians and
of the crossed offspring of the Tahitians now inhabiting Norfolk
Island.
As the males and females of many animals differ somewhat in habits and
are exposed in different degrees to danger, it is probable that in many
cases, more of one sex than of the other are habitually destroyed. But
as far as I can trace out the complication of causes, an indiscriminate
though large destruction of either sex would not tend to modify the
sex-producing power of the species. With strictly social animals, such
as bees or ants, which produce a vast number of sterile and fertile
females in comparison with the males, and to whom this preponderance is
of paramount importance, we can see that those communities would
flourish best which contained females having a strong inherited
tendency to produce more and more females; and in such cases an unequal
sex-producing tendency would be ultimately gained through natural
selection. With animals living in herds or troops, in which the males
come to the front and defend the herd, as with the bisons of North
America and certain baboons, it is conceivable that a male-producing
tendency might be gained by natural selection; for the individuals of
the better defended herds would leave more numerous descendants. In the
case of mankind the advantage arising from having a preponderance of
men in the tribe is supposed to be one chief cause of the practice of
female infanticide.
In no case, as far as we can see, would an inherited tendency to
produce both sexes in equal numbers or to produce one sex in excess, be
a direct advantage or disadvantage to certain individuals more than to
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