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The Science of Gaydar

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EXAMPLE D: Hand Dexterity (Male)
Gay men and lesbians have a 50 percent greater chance of being left-handed or ambidextrous than their straight counterparts.  

Ironically, AIDS had also given LeVay opportunity. Before the epidemic, cadavers available for dissecting came with scant personal background besides age and cause of death. But because AIDS was still largely a gay disease, it was possible for the first time to do detailed neuroanatomical studies on the bodies of known gay men. (Being lucky enough to have no proprietary cause of death, lesbians were excluded from the study.)

LeVay decided to make the first detailed comparison of the brain’s hypothalamus, a small region at the base of the brain responsible for regulating everything from blood pressure and body temperature to hunger and wake-sleep cycles. And because it’s awash in more hormones than any other part of the brain, it also helps control emotions and sex drive and enjoys a reputation among neurologists, as LeVay noted in his book The Sexual Brain, for being “haunted by animal spirits and the ghosts of primal urges.”

LeVay suspected the secret to sexual orientation might lurk there as well. It was already known that in (presumably straight) men, a cell cluster in the hypothalamus called INAH3 is more than twice the size of the cluster in (presumably straight) women, a distinction probably created during fetal development when male hormones begin acting on boy fetuses and the two genders embark on different biological courses. LeVay designed a study to see if there were any size differences inside gay brains. His results were startling and unexpected. In gay men, INAH3 is similar in size to straight women’s.

This finding challenged a lot of what scientists believed. “The brain was considered pretty hardwired,” says Roger Gorski, a neurobiologist at UCLA who researches sexual differentiation. “It was male or female, period. Then Simon’s study shows that there could be intermediates. That wasn’t just a watershed—it pushed the water over the waterfall.”

At the time, LeVay presented his findings with caution, acknowledging that HIV or AIDS medications might have been responsible for altering brain structure. But more recently, an important study of sheep brains has replicated his findings. Sheep are among 500 animal species where homosexuality has been documented. They are also among the few who practice exclusive homosexuality, like many humans. In any population of sheep, about 8 percent of males show exclusive homosexual behavior. Little is known about the romantic life of Sapphic sheep because ewes tend to express their sexual interests by standing entirely still, yielding no clues about their partner preferences.

Slicing open the brains of ten ewes, eight female-oriented rams, and nine males who preferred other rams, researchers in the Oregon Health and Science University School of Medicine found nearly the same variations in hypothalamus that LeVay first noticed. Male sheep who were attracted to females had a significantly larger hypothalamus dimension than females or male-oriented males.

A second study in humans also found size differences, though less dramatic, in the hypothalamus cluster identified by LeVay. “There’s now more reason to think my results are right, that the gay brain has this distinction,” he says.

If LeVay’s research suggested that biology—not environment, vice, or sinfulness—was likely responsible for male homosexuality, the geneticist Dean Hamer, an author and molecular biologist at the National Institutes of Health, hoped to pinpoint the exact biological mechanism responsible. He scanned gene groups in pairs of gay siblings looking for sites where the relatives had inherited the same DNA more frequently than would be expected on the basis of chance. In 1993, he located a region in the human genome, called Xq28, that appeared to be associated with gayness, a finding that has generated some controversy among researchers who have not fully confirmed the results.

A large-scale study within the next year is expected to determine more conclusively if a gene (or genes) is linked to sexual orientation. Alan R. Sanders, a psychiatrist from Northwestern University, is enrolling 1,000 pairs of gay brothers in one of the largest sexual-orientation studies ever undertaken. With the experiment, funded by an NIH grant of over $1 million, Sanders will attempt to map genes that influence sexual orientation.

Why has it taken fourteen years to carry out such an investigation? Hamer says there is very little research money, and almost no glory, to be gained in the hunt for gayness. “At about the same time as Xq28 came out, we found another gene involved in anxiety—the target gene for Prozac, and since that time, there have been now almost 800 peer-reviewed publications on that gene. Whereas for the gay gene, every experiment has been done by three or four students, most of them my students.”

One of the riddles still vexing geneticists is why only 50 percent of gay identical twins share a sexual orientation with their sibling, despite being genetically identical. “We know from all sorts of research that it’s not your upbringing, not relationship with parents or siblings, not early-childhood sexual experiences and whether you go to a Catholic school or not,” says Sven Bocklandt, a geneticist at UCLA. “What I believe is that it is the ‘epigenetics environment,’ meaning the environment on top of our DNA—meaning the way that the gene is regulated. If you have identical twins, the genes are identical, but they are used differently. Every man and every woman has all the genes to make a vagina and womb and penis and testicles. In the same way, arguably, every man and woman has the genetic code for the brain networks that make you attracted to men and to women. You activate one or the other—and if you activate the wrong one, you’re gay.”


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