The facts observed by many reputable breeders of domestic animals lead to the following conclusion, - that the most vigorous, the most prepotent parent at the time of conception is more likely to govern the sex of the offspring than the less vigorous parent. This is only saying that the stronger is superior to the weaker; but this general law can be discovered only by being put to an extensive test, - such as when a large number of animals are bred under similar conditions. Some extended experiments in France indicate that, when sheep were observed, the first lambs were largely males. As the yeaning season progressed, the number of male and of female lambs were about equal, while at the close of the lambing season the female lambs greatly predominated. In my own experience with five hundred American Merino ewes, I found that about nine-tenths of the first quarter of the total crop of lambs were males. Then the sexes began to even up, while, in almost every case, the last quarter of the lambs dropped were largely females. Where large flocks of sheep are kept, it is usual to separate the rams from the flock for three or four months preceding the rutting period. They are fed liberally with such foods as experience has shown will produce unusual vigor. At the same time the ewes are kept under normal conditions or those somewhat less productive of vigor, since the flock is usually large and the pasturage and food somewhat limited. It is evident that under these circumstances the males, when first turned into the flock, will be more vigorous than the females. As the season advances, there being but few of the males, they become depleted in vigor so far as to fall below the vigor of the ewes. Many instances of like experience with flocks of sheep could be cited.
My friend who owns an island off the coast of South Carolina which is stocked with cattle and swine that roam at will, with no care from the owners, states that they show marked sex-variations in different seasons. After a hard winter and scarcity of food, male pigs predominated. As they were hunted for food during encampment on the island, it was seldom that a female pig could be secured. The males, not being depleted by nourishing young the year before, passed through the winter with powers less impaired than the female. This is the explanation that he gave me for the facts observed. When food became abundant in other years and conditions were improved, the sex of those pigs which were slaughtered was about evenly divided. Were it appropriate, many facts could be cited to substantiate this theory in the human family.
However, before leaving this subject, it should be said that either the male or the female may be propotent in color alone or some other characteristic and not prepotent in sex characteristics, or either one may be prepotent in sex characteristics alone. We are acquainted with many animals which persist in bearing offspring of one sex though bred to different males, and with some that persist in producing one sex as long as mated with the same male, but when another male is used the sex of the offspring is changed.
Many theories have been advanced which sometimes have appeared to indicate a law; but as yet no law has been discovered for governing the sex of offspring which holds uniformly true or which is workable. We may sometimes change conditions or change the mating of the animals and arrest the prepotent factor of sex or any other potent factor, and at other times no change of food or mating accomplishes the desired result. We conclude then that the stronger characteristic, whatever it may be, is superior to the weaker. The difficulty consists in determining them. If any one had discovered a method of controlling sex, he would have taken out letters patent on it long ere this.