(Internat. Centralbl. f. d. Physiol. und Patholog. der Harn- und Sexual-Organe, Band ii., Heft 3 und 4.)
The relation of the number of males to the number of females born is a constant one as regards man, animals, and plants.
In man the numerical relation of male to female is 106 to 100. In horses, male and female, it is 100 to 98.
This relationship in man is subject to variation to a certain extent. For example, during war male births predominate. The absence of a considerable number of men exerts this certain influence. In favorable times not alone are a greater number of children born, but girls preponderate.
In unfavorable times fewer female children are born and more boys.
Among the first births in the human species there are relatively many males.
This excess is especially seen in the children of those mothers who are advanced in age when they become pregnant, and is attributable to the nutrition of the mother not being up to normal.
From the author's foregoing explanations, it is concluded that the sex is not inherited, but results from a combined action of causes. These factors act not only at the time of impregnation, but at various times after. From the beginning the ovule has a tendency to the development of a certain sex, and the semen possesses the same tendency; both combine at the time of impregnation to constitute one tendency, which determines the sex. Long after impregnation, when the embryo is already developed, the nutrition is still of influence, and can cause a change of tendency even if the sexual organs have begun to develop: as for example the occurrence in the mother of a poor state of nutrition may arrest the development of the female and bring about the development of the male organs.
When this late reactionary influence remains absent or is not exerted strongly enough to cause a change in the development of the sexual organs, then the sex is definitely decided.
F. Tilden Brown
J Cutan Genito-Urin Dis.
Dusing C. The Relation of Sexes. Arch Dermatol. 1991;127(2):171. doi:10.1001/archderm.1991.01680020031003