What makes people gay?

 

Researchers may never locate a 'gay gene.' But according to The Boston Globe's Neil Swidey, the scientists hunting for the roots of homosexuality seem to be closing in on an answer.

 

With crystal-blue eyes, wavy hair, and freshly scrubbed faces, the boys look as though they stepped out of a Pottery Barn Kids cata­logue. They are 7-year-old twins. I'll call them Thomas and Patrick; their parents agreed to let me meet the boys as long as I didn't use their real names.

Spend five seconds with them, and there can be no doubt that they are identical twins—so iden­tical even they can't tell each other apart in photographs. Spend five minutes with them, and their profound differences begin to emerge.

Patrick is social, thoughtful, attentive. He repeatedly addresses me by name. Thomas is physical, spontaneous, a bit distracted. Just minutes after meeting me, he finds a reason to punch me in the upper arm. It's a hard punch. The twins horse around like typical brothers, but Patrick's punches are less forceful and his voice is higher. The differences are subtle, but they are there. When the twins were 3, Thomas blurted out that toy guns were his favorite things. Patrick piped up that his were the Barbie dolls he discovered at day care. When the twins were 5, Thomas wanted to be a monster for Halloween. Patrick said he was going to be a princess.

Their mother—intelligent, warm, and open-minded—found herself conflicted. She wanted Patrick—whose playmates have always been girls—to be himself, but she worried his feminine behavior would expose him to ridicule. She decided to allow him free expression at home while setting some limits in public. That approach worked until last year, when a school offi­cial called to say Patrick was making his classmates uncomfortable. He kept insisting that he was a girl.

Patrick exhibits behavior called child­hood gender nonconformity, or CGN. This doesn't describe a boy who has a doll somewhere in his toy collection or tried on his sister's Snow White outfit once, but rather one who consistently exhibits a host of strongly feminine traits and interests while avoiding boy-typical behavior like rough-and-tumble play. There's been con­siderable research into this phenomenon, particularly in males. The data suggest there is a good chance Patrick will grow up to be homosexual. Not all homosexual men show this extremely feminine behavior as young boys. But of the boys who do exhibit CGN, about 75 percent of them turn out to be gay or bisexual.

What makes the case of Patrick and Thomas so fascinating is that it calls into question both of the dominant theories in the long-running debate over what makes people gay: nature or nurture, genes or learned behavior. As identical twins, Patrick and Thomas began as genetic clones. From the moment they came out of their mother's womb, their environment was about as close to identical as possible—being fed, changed, and plopped into their car seats the same way, having similar relationships with the same nurturing father and mother. Yet before either boy could talk, one showed highly feminine traits while the other appeared to be "all boy."

"That my sons were different the second they were born, there is no question about it," says the twins' mother.

So what happened between their identi­cal genetic starting point and their births? They spent nine months in utero. In the hunt for what causes people to be gay or straight, that's now the most interesting and potentially enlightening frontier.

For much of the 20th century, the domi­nant thinking connected homosexuality to upbringing. Sigmund Freud speculated that overprotective mothers and distant fathers helped make boys gay. It took the American Psychiatric Association until 1973 to remove "homosexual­ity" from its manual of mental disorders.

Then, in 1991, a neuroscientist in San Diego named Simon LeVay announced he had found a key difference between the brains of homosexual and het­erosexual men. LeVay showed that a tiny clump of neurons of the anterior hypothalamus— which is believed to control sex­ual behavior—was, on average, more than twice the size in het­erosexual men as in homosex­ual men. LeVay's findings did not speak directly to the nature vs. nurture debate—the clumps could, theoretically, have changed size because of homo­sexual behavior. But that seemed unlikely, and the study ended up jump-starting the effort to prove a biological basis for homosexuality.

Later that same year, Boston University psychiatrist Richard Pillard and Northwestern University psy­chologist J. Michael Bailey announced the results of their study of male twins. While most reputable studies find the rate of homosexuality in the general population to be 2 percent to 4 percent, Pillard and Bailey found that, in identical twins, if one twin was gay, the other had about a 50 percent chance of also being gay. For fraternal twins, the rate was about 20 per­cent. Genetic makeup was believed to explain the difference.

In 1993 came the biggest news: Dean Hamer's discovery of the "gay gene." In fact, Hamer, a researcher at the National Cancer Institute, hadn't quite put it that boldly or imprecisely. He found that gay brothers shared a specific region of the X chromosome, called Xq28, at a higher rate than gay men shared with their straight brothers. Hamer suggested this finding would eventually transform our under­standing of sexual orientation.

That hasn't happened yet. But the clear focus of sexual-orientation research has shifted to biological causes, and there hasn't been much science produced to support the old theories tying homo­sexuality to upbringing.

As a 21-year-old college junior lies inside an MRI machine, she manipulates controls that allow her to indicate strong "likes" or "dislikes" of what she's seeing. Hundreds of pornographic images—in male-male and female-female pairings—flash before her eyes. Regardless of which buttons the student chooses to press, though, the MRI scans show her arousal level to each image, at its starting point in the brain.

Researchers at Northwestern University, outside Chicago, are doing this work as a follow-up to their studies of arousal using genital measurement tools. They found that while straight men were aroused by film clips of two women having sex, and gay men were aroused by clips of two men having sex, most of the men who identified themselves as bisexual showed gay arousal patterns. More surprising was just how different the story with women turned out to be. Most women, whether they identified as straight, lesbian, or bisexual, were significantly aroused by straight, gay, and lesbian sex.

"I'm not suggesting that most women are bisexual," says Michael Bailey, the psychology professor whose lab con­ducted the studies. "I'm suggesting that whatever a woman's sexual arousal pat­tern is, it has little to do with her sexual orientation." That's fundamentally differ­ent from men. "In men, arousal is orien­tation. It's as simple as that. That's how gay men learn they are gay."

These studies mark a return to basics for the 47-year-old Bailey. He says researchers need a far deeper understanding of what sexual orientation is before they can deter­mine where it comes from. Female sexual orientation is particularly foggy, he says, because so little research has been done.

But let's get back to Thomas and Patrick. Because it's unclear why twin brothers with identical genetic starting points and similar post-birth environments would take such divergent paths, it's helpful to return to the beginning.

Males and females have a fundamental genetic difference—females have two X chromosomes, and males have an X and a Y. Still, right after conception, it's hard to tell male and female zygotes apart, except for that tucked-away chromosomal differ­ence. Normally, the changes take shape at a key point of fetal development, when the male brain is masculinized by sex hor­mones. The female brain is the default. The brain will stay on the female path as long as it is protected from exposure to hor­mones. The hormonal theory of homosexu­ality holds that, just as exposure to circulat­ing sex hormones determines whether a fetus will be male or female, such exposure must also influence sexual orientation.

The cases of children born with disor­ders of "sexual differentiation" offer insight. William Reiner, a psychiatrist and urologist with the University of Oklahoma, has evaluated more than a hundred of these cases. For decades, the standard medical response to boys born with severely inadequate penises was to castrate the boy and have his parents raise him as a girl. But Reiner has found that nurture—even when it involves surgery soon after birth—cannot trump nature. Of the boys who were raised as girls, he says, "I haven't found one who is sexually attracted to males."

Sexual orientation, Reiner says, seems to be set before the sexual organs are formed. But he also says that exposure to sex hor­mones probably does not provide the com­plete answer. More likely, hormones are interacting with other factors.

Canadian researchers have documented a "big-brother effect," finding that the chances of a boy being gay increase with each additional older brother he has. So, a male with three older brothers is three times more likely to be gay than one with no older brothers. They argue that this results from a complex interaction involv­ing hormones, antigens, and the mother's immune system.

There is, in any case, substantial evi­dence showing correlation between sexual orientation and traits that are set when a baby is in the womb. Take finger length. In general, men have shorter index fingers in relation to their ring fingers; in women, the lengths are generally about the same. Researchers have found that lesbians gener­ally have ratios closer to those of males. Other studies have shown masculinized results for lesbians in inner-ear functions and eye-blink reactions to loud noises, and feminized patterns for gay men on certain cognitive tasks like remembering the place­ment of objects.

Considering the case of the twins, New York University researcher Lynn S. Hall speculates that Patrick, who was born a pound lighter than his brother, was some­how prenatally stressed, probably during the first trimester, when the brain is really developing.

Genes could be involved in the process, but, at the University of California, Los Angeles, Eric Vilain, an associate profes­sor of human genetics, and his colleague, Sven Bocklandt, aren't expecting to find a single "gay gene." Using gay sheep, trans-genic mice, and identical twin humans, they are hunting for several genes that together cause either attraction to men or attraction to women. Specifically, they are examining how these genes might be "turned up" or "turned down."

According to Bocklandt, it's not a ques­tion of what genes you have, but which ones you use. "I have the genes in my body to make a vagina and carry a baby," he says. "But I don't use them, because I am a man."

Vilain and Bocklandt are also testing an intriguing theory involving imprinted genes. Normally, we each have two identical copies of every gene, one from each parent. But an imprinted gene is a copy that is blocked from working, and the coding that keeps an imprinted gene shut down can vary between identical twins.

As researchers continue the hunt for the basis of sexual orientation, the mother of twins Patrick and Thomas has come to her own conclusions. She says Patrick's femi­nine behavior suggests he will grow up to be gay, and she has no problem with that.

She just worries about what happens to him between now and then.

After that fateful call from Patrick's school, she says, she "had no clue" how to counsel her son, but decided to tell him that although he could continue playing however he wanted at home, he had to stop telling his classmates he was a girl.

She asked him, "Do you think that you can convince yourself that you are a boy?"

"Yes, Mom," he said. "It's going to be like when I was trying to learn to read, and one day I opened a book and I could read."

At that, his mother's heart sank. She could tell that he wanted more than any­thing to please her. "Basically, he was say­ing there must be a miracle—that one day I wake up and I'm a boy. That's the only way he could imagine it could happen."

 

©2005 by The Boston Globe

 

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