controlling factor in sex determination has been narrowed down to
three possibilities; it is inherited either from the single cell
contributed by the father or from the single cell contributed by the
mother, or it is determined by the effect these two cells have upon
each other at the moment when they unite. In most animal species the
weight of authority distinctly favors placing the whole
responsibility upon the male cell.

According to recent evidence, there are two kinds of male germinal
cells; one kind giving rise to female offspring and the other to
male. In all probability, at the time of the marital relation, these
varieties are deposited in the vagina in equal numbers; and,
moreover, the mode of their production is such as to place absolutely
beyond human control the possibility of changing this ratio. Since
only one spermatozoon enters the ovum, whether or not the child will
be a boy or a girl depends entirely upon which type gains entrance.
If this explanation is correct, and it is in accord with careful
biological observations, it removes from the mother all
responsibility for the sex of her child. Furthermore, since the facts
indicate that male-producing and female-producing spermatozoa are
present in equal numbers, it follows that practically there is an
even chance that an embryo will develop into a boy or a girl.

Birth statistics bear out this conclusion, as data gathered from many
countries indicate that when long periods of time are studied 105
boys are born with a surprising regularity for every 100 girls. Thus,
the records of Berlin, Germany, for a hundred years show that the
maximum difference occurred in 1820, when the males outnumbered the
females by 4.79 per cent.; the minimum difference, which was noted in
1835, was .64 per cent. in favor of boys.