The second scientific study the media have used to propagate the idea that homosexuality is genetically determined is the finding of a prevalence of homosexuality among twin and adopted brothers by homosexual psychiatrist Richard Pillard and psychologist/gay rights activist Michael Bailey.
The two researchers recruited the subjects for their study through homosexual publications that cater exclusively to the homosexual population. Thus, their study did not represent a randomized, non-biased selection. Nevertheless, they found that, of the brothers who responded, 52 percent of identical twins, 22 percent of fraternal twins, 11 percent of adoptive brothers, and 9 percent of non-twin brothers were homosexual. Bailey and Pillard theorized that the reason there was such a high percentage of homosexuality among identical twins was because of their identical genetic makeup. But here we also encounter problems.
Half of the identical twins were not homosexual; they were clearly heterosexual. How could this be, if they shared the same genes that supposedly predetermine homosexuality? In Perpetuating Homosexual Myths, Richard A. Cohen noted, “If a homosexual orientation is genetic, then 100 percent of all identical twin brothers should have been homosexual, but only half were. Therefore, it is easy to conclude that environmental factors, not genes, cause homosexuality.” Even Dr. Simon LeVay admitted that neither Bailey and Pillard’s study on twins nor his own brain research has proven that homosexuality is genetically determined. “At the moment it’s still a very big mystery. Not even my work nor any other work that’s been done so far really totally clarifies the situation of what makes people gay or straight….In fact, the twin studies, for example, suggest that it’s not totally inborn, because even identical twins are not always of the same sexual orientation.