What does scientific research reveal about this question?
One of the web sites, among many that I researched, seemed to have the most unbiased opinion based upon research. Here are some of its views.
“There have been many articles published in various publications regarding homosexuality that do not reflect the scientific literature. In fact, their social advocacy suggests a greater reliance on politics than on science…Are men
and women born with a genetic propensity for same-sex attraction? Scientific attempts to demonstrate that homosexual attraction is biologically determined have failed. The major researchers have arrived at such conclusions.”
1. Dr. Dean Hamer, an American geneticist, director of the Gene Structure and Regulation Unit at the U.S. National Institute of Cancer, attempted to link male homosexuality to a stretch of DNA located at the tip of the X chromosome, the chromosome that some men inherit from their mothers. Regarding genetics and homosexuality Hamer concluded: “There is not a single master gene that makes people gay. I don't think we will ever be able to predict who will be gay."
2. Dr. George Rice of the University of Western Ontario duplicated the research and found “the genetic markers to be non-significant….Our data does not support the presence of a gene of large effect influencing sexual orientation.”
3. Dr. Simon LeVay, an American neuroscientist known for his studies about brain structures and sexual orientation, professor at University of Cambridge, at Harvard University and at Univ. of California, in his study of the hypothalamic differences between the brains of homosexual and heterosexual men, offered the following criticisms of his own research, "It's important to stress what I didn't find. I did not prove that homosexuality is genetic, or find a genetic cause for being gay. I didn't show that gay men are born that way…. Nor did I locate a gay center in the brain." LeVay observed, “…people who think that gays and lesbians are born that way are also more likely to support gay rights.”
4. Researchers J.M. Bailey and Richard C. Pillard, did a study which focused on twins. This study provides support for environmental factors, but not for genetic factors. If homosexuality were in the genetic code, however, all of the identical twins would have been homosexual.
5. Prominent research team William Byne and Bruce Parsons, as well as psychiatrists R. Friedman and J. Downey, reviewed the studies linking biology and homosexual attraction. They concluded that there was no evidence to support a biologic theory but rather that homosexuality could be best explained by an alternative model where "temperamental and personality traits interact with the familial and social milieu as the individual's sexuality emerges.” In other words it is a social and environmental issue, not a genetic issue.