It may be something else, anomalies in the hormonal bath the fetus is subjected to in the womb. Examples:
1. Girls with congenital adrenal hyperplasia. These girls have a much higher incidence of lesbianism, that the general female population. This is preseumably because of the exposure to testosterone during critical periods of fetal development.
2. There have been twin studies of male homosexual. Even when the boys are raised apart, there is an increased incidence of homosexuality in the other twin. This is presumably because of anomalies in the exposure to testosterone in the womb. Some researchers have even postulated the reason is additional exposure to testosterone in the womb, over the general male population. More research needs to be done.
Twin studies have long been disproven. You have to do better than that.