Are gay people hard-wired that way? Rooting around in the brain is an obvious way to tackle this provocative question, but it has been fraught with difficulty.
A 1990s study seemed to show that the brains of gay men were more like those of women than men, but the science was questioned in the ensuing furore. This June, controversial brain scans gave us probably the best evidence yet that our brains are hard-wired before birth to be gay or straight, suggesting that nature not nurture governs sexual orientation.
The startling study by Ivanka Savic and Per Lindstr枚m of the Karolinska Institute in Stockholm, Sweden, showed that lesbians have asymmetric brains like straight men, while gay men have symmetric brains like straight women.
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So far, so clinical. But sexuality is as much about emotions as it is about biology. Enter the amygdala, the area of the brain that governs our every emotion, especially fear and anxiety. The amygdala of straight women and gay men connects mainly to areas of the brain that manifest fear as anxiety. In straight men and gay women though, the amygdala connects more to areas that trigger a fight-or-flight response.
So if we are hard-wired to be gay or straight, how could that arise? Perhaps our brains get too much or too little of a crucial hormone in the womb. Or maybe the answer lies in our genes. Gay and bisexual men, for example, often have unusually fertile female relatives 鈥� this could be how 鈥済ay genes鈥� get passed on, even though few gay men have babies themselves.
But Savic doesn鈥檛 think that being bathed in too much testosterone in the womb is what makes girls gay. She tested this by studying women with congenital adrenal hyperplasia, which can make female fetuses produce too much testosterone. She found that on the whole, their amygdala activity matched that of straight women. The brains of the women with the condition, most of whom happened to be straight, also responded as other straight women鈥檚 do to androstadienone, a male pheromone that attracts both straight women and gay men.
While evidence piles up that gay and straight brains might be different, the full explanation remains elusive. The debate is unlikely to end soon.
