To these less general explanations of the origin of sex belong certain very startling theories dealing with the question before us. These notions are set forth at great length in theoretical explanations put in the shape of popular expositions. According to these views a single cell of the male or female reproductive glands is regarded as a sort of complicated compound structure that might be compared to a spherical world, in which thousands of primal individuals are contained, from whose powerful and secret activity results the formation of male or female individuals. (Hinz. Neusalz am Oder, 1897.)
Another very common opinion is that the seasons (Düsing), the climate, and other local circumstances, have an effect in determining the sex of the embryo. If the data supplied by Birelli, Berner, C. F. Vilson, and Felkin, and many other authors, be taken together, it appears that the different zones of the earth’s surface are not without influence in the reproduction of one sex rather than the other. More boys appear to be born in the north; in the warmer south more girls.
Felkin and Vilson adduce the following instance from the south of Egypt:—The Wagandas, a warlike race, kill the men and the old women of their conquered foes. The children, girls, and young women they lead into captivity. On one occasion 480 of the women gave birth to children on their march. Of the new-born 79 were boys, 403 girls. This incident led the author to pay further attention to the subject on the east coast of Africa and in the Soudan. Everywhere he found the anticipation of an excess of girls supported and confirmed. In fact his investigations of the phenomenon led him to formulate and advocate a law that the better nourished and superior parent tends to produce the opposite sex.
In this case the women are in an inferior position, and in consequence worse nourished and practically exhausted. Amongst other neighboring races, where they live peaceably and domestically, the difference between the number of new-born boys and girls is not a very great one, although a small average appears in favor of the girls. The influence of different phases of the moon has also been taken into consideration, and has been described as so effective that some have even attempted to prognosticate by these means the sex of a second child after the birth of a first. (Lioy.)
From Vilson’s statement that the sex of the worse-fed parent perpetuates itself, a theory has been deduced which has been described as cross-heredity of sex (Gekreuzte Geschlechtsvererbung). In accordance with this theory a prominent phenomenon would be that the individual parents were not in a position to propagate their own sex, but were yet under certain circumstances capable of reproducing the opposite sex. If the father were the stronger, a girl would result from the next impregnation; in the opposite case, a boy. A great number of authors of renown, most of whom are mentioned in works dealing with these questions, are supporters of this theory.
We have already mentioned that there are some who regard the act of generation as a conflict in consequence of which the sex of the elder parent, whether father or mother, will be reproduced, so that the sex in question may maintain its position. Similarly, in the case of the so-called cross-heredity of sex there seems to be a conflict for the preservation of the opposite sex. What conception we are to form of this conflict seems a difficult question. Any measure of the greater or less excitability of the centers during the act of generation (which might be determined in the case of animals) is not easily to be reached with any degree of probable correctness; and how much less any numerical index which would express the differences of excitability, of strength, and so forth, which might be developed during the conflict of the opposite sexes. The theory of the cross-heredity of sex rests upon the phenomenon that those female animals which are impregnated by sexually inferior and older males, whose capacity for reproduction must be considered as inferior to that of the females, produce more male than female individuals.