Last month, when the California Supreme Court declared same-sex marriage a constitutional right, it repeatedly invoked the precedent of interracial marriage. An attorney involved in the case protested, "There is no evidence to establish that a homosexual lifestyle is an immutable characteristic such as race."
He's wrong. There's lots of evidence. More of it just came out this week. It's been driving the gay rights debate all along, away from the clutches of religion and into the clutches of science. The trend is inexorable, but its implications are about to change. The culture war over homosexuality is dying—and a chemical war is threatening to take its place.
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Homosexuality used to be regarded as a lifestyle, something you freely chose or rejected. We discouraged, condemned, and punished it like any other sin.
Then along came science. Study after study found differences between gay and straight brains. Homosexuality came to be viewed less as a lifestyle and more as an orientation, too deeply rooted to be freely rejected. Gay activists embraced and trumpeted these studies. Public opinion shifted. Punishment and condemnation began to subside.
But the march of science into the gay brain hasn't stopped. It has continued, seeking to understand not just what doesn't cause homosexuality—playing with dolls, growing up with a strong mother, watching Will and Grace—but what does. And the more we understand these biological factors, the closer we get to being able to change them.
A new study, published Monday in Proceedings of the National Academy of Sciences, hints at what's coming. Previous gay-brain studies focused on structures or responses that might have been shaped by social interactions. To screen out social factors, authors of the new study relied on brain scans rather than behavioral responses, and they targeted structures known to form during or shortly after gestation. "That was the whole point of the study, to show parameters that differ, but which couldn't be altered by learning or cognitive processes," the lead author explains.
The sample consisted of 25 straight men, 25 straight women, 20 gay men, and 20 lesbians. In overall symmetry and amygdala activity, the brains of gay men resembled the brains of straight women, whereas the brains of lesbians resembled the brains of straight men. Previous work has connected such differences to fear, anxiety, aggression, and verbal, spatial, and navigational ability. It's not just a matter of preferring men or women. The broader implication, one expert argues, is that "in gay men, the brain is feminized."
Are the differences genetic? Not likely. "As to the genetic factors, the current view is that they may play a role in male homosexuality, but they seem to be insignificant for female homosexuality," the authors conclude. "Genetic factors, therefore, appear less probable as the major common denominator for all group differences observed here."
So, what's the common factor? If the study's design rules out learned influences, and if the results in women rule out genetics, that leaves what the authors call "hormonal influences" or noncognitive differences in the infant environment. According to the Guardian, the same research team has "begun another study to investigate brain symmetry in newborn babies, to see if it can be used to predict their future sexual orientation." If it can, that will scratch postnatal factors off the list, and the search will narrow to hormones in the womb. Already, the authors point to evidence that homosexuality may be caused by "under-exposure to prenatal androgens" in males and "over-exposure" in females.