When I scroll through the biomedical research into how sexual orientation develops (don’t judge my hobbies), I notice three things. The first one’s obvious: Compared with, say, erectile dysfunction or male pattern baldness, there’s not much research into the biological origins of sexual orientation.
The second is a triumph of science. Researchers have figured out that men are more likely to be gay if they have older biological brothers from the same mother, or if they inherit certain genes from their mothers, some of which seem to be the same genes that make their female relatives more fertile.
But the third thing I notice is something that isn’t there. Where’s the research into how sexual orientation develops in women?
Twenty-two years after the first paper linked men’s orientation to genes on the X chromosome, researchers are starting to make progress on figuring out the biology behind orientation in women. This April, psychologist Qazi Rahman and Andrea Burri from King’s College London led a study into the genetics of women’s sexual orientation. By comparing patterns of orientation and sexual behavior in identical and fraternal twins, the researchers figured out that differences in genes must explain some (but not most) of how orientation develops in women. The exact genes—and the other, more important factors—are still a mystery.
But why are scientists only just focusing on the mystery of how women develop sexual orientation—a key part of identity with so many social and legal implications around the world?
Historically, scientists assumed gay women were like gay men: deviant. Late 19th-century researchers like the Viennese sexologist Richard von Krafft-Ebing thought that homosexual behavior came from a defect in healthy development. This belief evolved into the perception that gay people were a third sex of inverts—a perception that influenced research for decades, according to a recent paper by the geneticist Tuck Ngun of the University of California, Los Angeles.
But even as scientists moved beyond the “inversion paradigm,” they developed a new iteration of this old attitude: Women’s sexuality wasn’t behaving like it should. In other words, like men’s sexuality.
That’s not to say that human sexes are irreconcilably different. By the mid-1990s, scientists had figured out that being gay, like being tall or skinny, was partially heritable in men and women. And in 2000, American and Australian researchers found that 92 percent of men and 92 percent of women identify as exclusively straight on Alfred Kinsey’s seven-point scale of sexual orientation. The differences between the sexes popped up in the other 8 percent: Most non-straight men cluster at the far end of the Kinsey scale, as exclusively gay. Most non-straight women cluster close to the straight end, with only a tiny fraction exclusively gay.
Bolstered by early data showing that being gay was heritable, scientists looked for the link between sexual orientation and genes. They found a connection to the X chromosome in men, but not in women. They were further confounded when they looked at other aspects of sexuality—arousal, response, and especially self-identity. “The kind of answers that were coming out weren’t as straightforward as men’s answers,” says psychology professor Meredith Chivers of Canada’s Queens University. While men largely stay in the same orientation category—be it straight, bi, or gay—a study in 2003 found that women move between categories over their lifetime. Thanks largely to these and similar data on orientation fluidity in women, Ngun says there was “this perception that they’re choosing their sexuality.”
It was an endocrine disorder that first hinted at environmental factors—that is, nongenetic, biological factors—influencing women’s orientation. In congenital adrenal hyperplasia, a person overproduces masculinizing hormones like testosterone, starting when they’re a fetus. A boy with CAH could go through puberty very early, but the extra hormones don’t change how likely he is to be straight or gay. However, a girl with CAH is much more likely to identify as lesbian when she grows up. While CAH shows that women’s orientation can be altered by male hormones, scientists think that men’s orientation can be altered by the imprints older brothers leave on their mother’s immune system during her pregnancies. Although “there’s still a lot of uncertainty for the exact mechanisms,” says Malvina Skorska, who is one of the few researchers studying the biology of orientation and is doing so as part of her graduate work in psychology at Canada’s Brock University.
This persistent uncertainty isn’t surprising. Studying the biology of sexual orientation is hard. The science, says Ngun, is extremely complicated, with genetics and hormones and other factors playing parts—meaning that while being non-straight is the common destination, people get there through different biological routes. Also, it takes a lot of work to recruit enough research subjects, especially when subjects are a minority targeted for discrimination. But the “biggest roadblock in doing this kind of work,” says Chivers, “is institutional support” at the university and government level, especially in the United States. Researchers often have only enough money to study one sex. And they usually choose males, whether through unconscious bias, a desire to compare their results with past studies, or worry that the menstrual cycle will screw up their results.
These roadblocks—from different biology to empty wallets—help explain why there’s been more focus on men than on women. But I have another roadblock to suggest, which requires taking a step back and placing this field into a broader context.
The lack of research into women’s orientation is “a reflection of a broader pattern in science, and society in general,” says Ngun, “The default is the white male.” Historically, says Chivers, research into sexual orientation was “very much populated by male scientists”—and like much of biomedical science, it focused on male subjects. “You’re interested in your own sex to a certain degree,” says Skorska. Or, as British psychologist Rahman puts it, the “research is me-search.”
But why is it important to keep doing “me-search” (whether the “me” is a man or woman), now that we’re finally accepting homosexuality as a normal form of human sexuality, not a defect as von Krafft-Ebing once argued?
“Sexual orientation is a huge part of our identity,” says Skorska, and one with important implications for sexual health. And Rahman—who identifies as a gay man—agrees that understanding the biology behind sexual orientation will have health benefits. He and many advocates point out that prejudice causes many of “the very big mental health inequalities between heterosexual and LGBT individuals.” Research on people who are bisexual is even sparser than research on gay men and lesbians, but Rahman proposes—controversially—that biological differences might help explain why bisexual people seem to be more likely than gay or straight people to suffer from poor health.
But there’s another important reason to keep studying the biology of sexual orientation. Much of the momentum behind the gay rights movement, says Chivers, was founded on the idea that, whatever our orientation, we’re all “born this way”—a claim strongly supported by research into both men and women. Despite gains in parts of the West, prejudice and criminalization of homosexuality persist. As I scroll through the decades of work into sexual orientation, I continue to hope that more research will reduce that stigma, strengthen the movement’s momentum, and teach all of us more about a fundamental part of our identity.
