Is Homosexuality Inherited? 1993 Gay Gene Discovery Intensifies Search For Origins Of Gayness

Roger Gorski, a neurobiologist from the University of California at Los Angeles, recalls when he recently spoke at a seminar for Mormon parents of gay children in Salt Lake City:

“I felt like I was talking in a vacuum, with every word sucked up. It was the parents who were coming out,” he says.

Such meetings are all in a day’s work for Gorski. He welcomes the chance to tell angst-ridden parents a few biological facts: Homosexuality is a normal genetic variant, it is not a lifestyle choice, a disease or a mental illness, and in all probability it was passed down from the person’s mother.

Dean Hamer, a molecular geneticist from the National Institutes of Health near Washington, D.C., who, in 1993, discovered where in the genome the gay gene nestles, can also pat himself on the back for fostering a sense of vindication for gays.

Gorski has also contributed to the idea that gayness is biological in origin. In 1992, he showed that the anterior commissure, a bundle of nerves that connects a small region of the right and left sides of the brain’s cortex, is larger in gay men than in straight.

All the same, Gorski is the first to acknowledge that, in the name of community spirit, the scientific fellowship is quietly blending fact with biological theory. For in reality, today’s scientists are about as baffled by homosexuality as they have ever been.

In the intervening three years, Hamer’s spectacular finding has started to look shaky. Some geneticists have poked holes in his original methodology, and others have failed to confirm the existence of the gay gene with their own studies. But those disappointments have done nothing to dull the intense scientific and public interest in what triggers gayness.

The facts so far

That gayness is at least partly genetic is just about indisputable. A man with a gay identical twin brother - that is a brother who shares all his genes - has a 52 percent chance of being gay, and a man with a gay nonidentical twin only a 22 percent chance, according to a 1991 study from psychologist J. Michael Bailey at Northwestern University in Evanston, Ill.

In their study, Hamer’s team showed that specific genetic markers on a region of the X chromosome called Xq28 were shared by 33 of 40 pairs of gay brothers.

Hamer concluded that within a region of 4 million DNA base pairs on the tip of the long arm of the X chromosome lies a locus related to sexual orientation. He calls this locus GAY-1.

Despite these findings, however, biologists such as Harvard University’s Evan Balaban loathes the oversimplification of the gay gene topic by both scientists and journalists that accompanied Hamer’s original identification of GAY-1.

“I wish that some of the work was done a bit more carefully and presented more conservatively,” Balaban says. “It can only lead to misunderstanding and disappointment.”

But even if Hamer is right, and GAY-1 does contain the key to male homosexuality, the work is far from over. GAY-1 contains several hundred genes, and only by teasing out the gene or genes responsible for sexual orientation will there be a chance of working out the biochemical basis of why some men are turned on by other men.

Other theories

Over the past decade, scientists from Amsterdam to California have been picking through brain matter in their search for structures that differentiate gay men from their straight brothers.

Most researchers agree that biology, in the shape of genes, hormones and brain structures, correlates with gayness in some men.

Daryl Bem, a psychologist from Cornell University in Ithaca, N.Y., is not impressed by that insight.

“Correlation is not cause,” he says. “Sexual orientation is not transmitted by genes.”

Instead, Bem argues that when it comes to sexual orientation, a child is born with a clean slate. Genetic inheritance affects the child’s temperament and behavior, and that in turn molds their final sexual orientation.

Bem takes his cue from a 1981 study of about 1,000 gay men and women, and 500 straight men and women living in the San Francisco Bay area. That study, which was run by researchers at the Kinsey Institute for Research in Sex, Gender and Reproduction in Bloomington, Ind., found that 63 percent of gay men reported that as children they disliked “boys’ games,” such as football, compared to 10 percent of straight men.

On the flip side, 48 percent of gay men had enjoyed “girls’ games,” such as playing house, compared to 11 percent of straight men. Those findings have been confirmed by studies that look at boyhood play, and then note sexual orientation later in subjects’ lives, and also by a massive “meta-analysis” that pooled the data from 48 separate studies.

Bem speculates that a boy who enjoys more aggressive, traditionally male-associated play will detach himself from the gentler, more introspective world of little girls and will come to regard females as dissimilar and exotic. This sentiment is translated into “physiological tingles and jolts” in the presence of the opposite sex which at first seem offensive, but which during adolescence fire up sexual desire.

Genes may help hard-wire a boy’s brain so that he acts in a fashion that doesn’t conform to his gender. He becomes distanced from other boys and later finds them sexually attractive.

Curious but cautious biologists are treating Bem’s theory with a mixture of caution and curiosity.

Meanwhile, whether Bem, and the eclectic bunch of geneticists, neuroanatomists and psychologists who are studying gayness will ever completely understand the forces that dictate sexual orientation remains to be seen.

The following fields overflowed: CREDIT = Vittoria d’Alessio New Scientist