The gay gene has stood up well. Hamer has replicated his findings, and no studies have yet contradicted them. Still, the gene itself remains at large, its function unknown. It might be involved in the development of the hypothalamus, a part of the brain that has been shown to differ between homosexual and heterosexual men. He also looked for a comparable X-linked marker for sexual orientation in lesbians, but had little luck.
Female homosexuality does run in families, but there's no clear indication that it is genetic.
He suspects that women's sexual preferences may be less genetically programmed than men's. Many studies have also looked at the sexual preference in animals. Some of these homosexual activities appear to boost reproduction. In other cases, same-sex affairs may help reproduction indirectly, by promoting the general fitness of a group or individual. Researchers interested in animal behavior and sexual selection have long held that the main function of homosexual endeavors is to ensure that one's genes get passed along.