Birth Order and Sexual Orientation

Incredible as it might seem, birth order, some studies suggest, has an influence on whether men and women become homosexuals. In men, studies have indicated that later-born males are more prone to become homosexuals than first-born male children. Further, these studies are not confined to one country, such as the United States. They have been done in different countries, but the results are remarkably similar and indicate later-born males are far more likely to become homosexuals.
Birth Order and Sexual Orientation Studies
However, one theory is that male homosexuals who are willing to participate in studies are "liberal" about their sexual orientation. Most are later-born children, which might or might not skew the result of such studies. Unfortunately, similar studies of women have been less frequent, and those that have been conducted indicate there is no relation between a girl's birth position in the family and her later tendency to become a lesbian. The few studies that have been done do indicate a definite correlation between the female's position by birth in the family and her later choice of sexual orientation.
Birth Order and Women
Further, women who say they are attracted to other women generally report that they were taught by a brother about sex. As they grew into adulthood, this earlier influence led them to seek relationships with other women, rather than with men. One theory on this says that women who were taught about sex by their brothers above and beyond what their parents taught them ended up with more "masculine" tendencies, to imitate their brothers, and thus seek out a same-sex relationship.