If true, a biological explanation is good news for homosexuals and their advocates.
Our own research has shown that male sexual orientation is substantially genetic. Over the last two years, we have studied the rates of homosexuality in identical and non-identical twin brothers of gay men, as well as adoptive brothers of gay men. Fifty-two percent of the identical twin brothers were gay, as against 22 percent of non-identical twins and 11 percent of the adoptive, genetically unrelated brothers.
In contrast, research on social factors has been fruitless. [:-)...rjw] Despite many attempts, there has been no clear demonstration that parental behavior, even a parent's homosexuality, affects children's sexual orientation. Cultures tolerant of homosexuals do not appear to raise more of them than do less permissive societies.
Homophobes sometimes justify their prejudice against homosexuals by alleging that homosexuality is contagious -- that young homosexuals become that way because of older homosexuals and that homosexuality is a social corruption. Such beliefs form the core of the organized anti-homosexual movement. If homosexuality is largely innate, this would prove that these claims are groundless.
Given these implications, it may seem surprising that the biological studies disturb many gay and lesbian advocates. Misunderstanding them, the advocates often suggest that the search for a biological cause is motivated by an assumption that homosexuality is an illness. Behavioral scientists, however, have long searched for biological underpinnings of traits such as extraversion and intelligence, which no one considers to be negative. Furthermore, a biological explanation of homosexuality simultaneously explains heterosexuality.
This leads to a more pertinent fear of gays and lesbians, that people will assume that answers to moral questions hinge on the results of scientific study. Should a benevolent view of homosexuality depend on the assumption that it is innate? Are gays and lesbians to be tolerated only if they are "born that way"?
Regardless of what causes sexual orientation, there is no plausible justification for oppressing homosexuals. Reasons that have long been offered -- that homosexuals disproportionately molest children, convert heterosexuals to homsexuality, are mentally ill, betray their country -- have been shown to be false.
But homophobia remains the one form of bigotry that respectable people can express in public. If the long-overdue national debate on homosexuality took place, the poverty of the anti-homosexual case would become readily apparent.
If scientific study of the origins of sexual orientation would not directly resolve the public issue, why do it?
First, in can inform public debate. But equally important is the value of discovery, particularly self-discovery. A gay man with a heterosexual identical twin, both of whom we studied, put it this way: "I accepted being gay years ago, so that's not why I want to know. But sexual orientation is such an important part of my life -- anyone's life -- that I'm still curious why I turned out gay and my brother straight." How could anyone not be curious?
Michael Bailey is assistant professor of psychology at Northwestern University. Richard Pillard is associate professor of psychiatry at Boston University School of Medicine.