Is human sexual orientation predetermined at birth or something that is learned? That question is not only part of the scientific inquiry into the nature of human sexual relationships but, to many, central to the political debate over gay rights.
If it's an innate characteristic like left-handedness or red hair, then arguments that homosexuality is “unnatural” or against God's plan become much harder to justify, as does treating sexual relationships — and the idea of love — between adults of the same gender differently than heterosexual relationships.
Since the “nature vs. nurture” question concerning sexual orientation is so fraught, some people will never accept the answer unless it coincides with their political or religious beliefs. But within the scientific community, a consensus has emerged.
“Most of today's psychologists view sexual orientation as neither willfully chosen nor willfully changed,” writes David Myers, a psychology professor at Hope College in Michigan in his textbook Psychology. “Sexual orientation is in some ways like handedness. Most people are one way, some the other. A very few are truly ambidextrous. Regardless, the way one is endures.”
A wide range of research has found biological connections to sexual orientation. Identical twins are more likely to share a homosexual orientation than fraternal twins. Another study found that a certain cell cluster in the hypothalamus of the brain is reliably larger in heterosexual men than in women or homosexual men. Hormonal activity in the womb also seems to have an effect on sexual orientation.
Several organizations, mostly religion-based, claim “corrective therapy” can reorient gays and lesbians toward heterosexual orientation. But studies by researchers have found that same-sex attractions typically persist, as do those of heterosexuals, who are no more capable of changing their sexual orientation.
Since the days of the ancient Greeks, whenever philosophers have argued against homosexual love, some have argued that it is against the natural order, in part because it was found nowhere else in the animal kingdom.
Scientists now know this is incorrect. Some birds, sheep, monkeys and more than 450 other species of animals have at least occasional same-gender sex. In some cases, animals form long-lasting same-sex relationships, even raising young together. Studies have found that roughly 8 percent of male sheep are sexually attracted only to other males — an example of an animal subpopulation that seems exclusively homosexual.
In his book The Science of Sexual Attraction, noted neurobiologist Simon LeVay examines same-sex animal behavior. “The bonobo monkeys are interesting, because they're fairly close to us (genetically),” he says, “and they're polymorphously perverse — they use sex for many interactions that aren't tied to procreation. As far as we know, you don't really have gay or straight … bonobos.”
LeVay discovered the difference in the hypothalamus between gay and straight men and published his results in Science in 1991. He initially found the results — some of the earliest evidence indicating biological differences between gay and straight men — startling.
The research briefly made him a scientific celebrity. “I was really shocked when I came in the day after it was published,” he says, “and saw satellite trucks waiting outside the office.”
Twenty years later, in the middle of a tour promoting The Science of Sexual Attraction — LeVay says the reaction has been far more muted. “There was no sense of shock with my book coming out as there was when my research came out,” he says. “I think a lot of people have come to accept that biology is relevant to sexual orientation.”
— Reed Karaim