In general it is true that, the more we learn of the characters and
histories of living beings, the more importance we attach to nature or
birth and the less to nurture or environment, vastly important though
the latter be. Thus to the student of heredity nothing could well seem
more improbable, at any rate amongst the higher animals, than that
characters so profound as those of sex should be determined by nurture.
He simply cannot but believe that the sex of the individual is as inborn
as his backbone, and as incapable of being created by varying conditions
of nurture. The causation of sex is therefore really a problem in
heredity; and we may most confidently assert, in the first place, that
the sex of every human being is already determined at the moment of
conception when, indeed, the new individual is created: determined then
by the nature and constitution of the living cells--or of one of
them--which combine to form the new being. Subsequent attempts to affect
the sex, as by means of the mother's diet and the like, are palpably
hopeless from the outset and always will be. This is by no means to say
that conditions affecting the mother--as, for instance, the
semi-starvation of a prolonged siege--may not affect the construction of
the germ-cells which she houses, and which are constantly being formed
within her from the mother germ-cells, as they are called. But any given
final germ-cell, such as will combine with another from an individual of
the opposite sex to form a new being, is already determined, once for
all, to be of one sex or the other.
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