Perhaps if you read Dr. Hamer's study, you would see that he explicitly tests for that (by looking not only at the gay men's genetics, but at their mothers' and fathers' separately).
"Perhaps if you read Dr. Hamer's study, you would see that he explicitly tests for that (by looking not only at the gay men's genetics, but at their mothers' and fathers' separately)."
Genetics may not have anything to do with it.
Example: The DES (diethyle stilbestrol) daughters.
These girls exhibited a higher incidence of being lesbian than usual for females.
Example: Girls with CAH (congenital adrenal hyperplasia).
These girls experience some degree of masculinization of their genitals and behavior because of an over-active adrenal gland (within the womb). These girls are also much more likely to be lesbian.
There have been some twin studies run on incidence of homosexuality. There has been some corelation in pairs of twins, which could be explained by congenital effects, such as the hormonal environment in the womb.
It has been established the action of testosterone is necessary for the masculinization of the fetus, both in physical structure and behavior. If there is no testosterone, the default outcome for gestation is female. It does not matter if the fetus is XX or XY, without testosterone, the baby will look female and behave like a girl.
Example: Gonadal Agenesis.
This can have the genotype XO, XX, XY, or even be a chimera. No gonads, the external phenotype will be female, and the behavior will be female.
Example: Androgen Insensitivity Syndrome. The XY fetus does not respond to androgens. The result is a female phenotype and female behavior.
More research needs to be done on the effects of hormones and drugs on the fetal nervous system.