Bocklandt is quick to point out that most likely there is no single “gay gene”—no single switch for sexual orientation. Instead, there are probably a handful of genes that work in ways as yet unexplained. Still, he is confident that the genes involved are few enough that he can find them. Although sexual attraction between humans has its frills—the social dances, the fetishes, the preferred body types—it is still pretty fundamental. “If you’re breeding pigs, you can buy a little spray—spray it on a female and it will stand still as if it’s having sex,” Bocklandt says. “There’s nothing like that for humans. Obviously, the behavior is complex—there’s phone sex and of course porn—but genetically it’s simple. There are limits to what you can code on a genome.” He thinks it is likely that perhaps 5 to 15 genes explain sexual orientation in most people.
Ideally, Bocklandt would scan the genome of each individual, looking for a methylation pattern anywhere on any chromosome that shows up repeatedly in the gay member of each twin pair. Unfortunately, at the moment it costs about $10 million a person to map out every base pair of the 46 chromosomes, so Bocklandt is looking only where he suspects to unearth genetic gold. If he finds a pattern, then he will look at the DNA beneath the methylation.
Sex-determining
chromosomes
Image courtesy
of the National
Institute of Health
Actually, the whole genome can be mapped for less than $10 million if you are willing to forfeit the high degree of resolution Bocklandt is after. Alan Sanders, an associate professor of psychiatry at Northwestern, will be looking at the whole genome of about 1,000 gay brothers using the genetic marker technique that Hamer used. A sample that big should eliminate the statistical weaknesses that plagued Hamer. “There are a number of things that go into trying to figure out how much statistical power you have, but the only one that’s in your control is sample size—the bigger the better,” says Sanders. “So that’s what we’re doing.”
For several years Sanders has been collecting DNA from blood or saliva samples from families with two or more gay brothers. In addition to requesting their spit, Sanders’s team asks each individual a set of questions similar to those Hamer used in his study. Then he begins looking at the men’s chromosomal markers to see if the brothers are more similar than what chance would predict. Wherever there is a significant increase in sharing, Sanders plans to look at the genes that can be found near that particular marker. (When two brothers come from the same mother and father, about 50 percent of their genes should be identical.) Not only is the sample size bigger than Hamer’s, but there are now far more genetic markers available, allowing Sanders to zero in on specific genes much faster.
By setting up a stand at Gay Pride parades and approaching “gay friendly” groups like PFLAG (Parents, Families and Friends of Lesbians and Gays), Sanders has found more than 4,000 gay men with a brother who are interested in participating. He has already started mapping the first 500 and estimates that by mid-2008 the world will know where—if anywhere—to find the gay gene.
“We definitely should be able to put to rest one way or another whether the Xq28 finding is replicable,” says Sanders. “We should be able to address that to anyone’s satisfaction.”
The question of whether there is a gay gene—and if so, where it resides—is hardly the only question about sexual orientation that remains unanswered. If either Bocklandt or Sanders is lucky enough to spot the genes responsible for homosexuality, there will most likely be more questions raised than answered. “Frankly, the biggest problem of the genetic possibilities is the evolutionary problem,” says Michael Bailey, the researcher who found that women get turned on by anything, who is now working with Sanders. “And I don’t think that Dean [Hamer] has taken that problem seriously enough.” Men who like men are obviously less likely to procreate. Even if social pressures through the ages led some gay men to have some children, the significantly lower rate of reproduction would eventually lead to the disappearance of the gene (as Hamer does note in his book, The Science of Desire: The Search for the Gay Gene and the Biology of Behavior).
Possible explanations abound, but an ingenious one was recently put to the test. Perhaps, the theory goes, some genes, when found in men, make them more likely to be gay and when found in women make them more likely to have children. (“Fecund” is the word the researchers use.) The increased number of grandchildren that a parent might have through such a superfertile daughter would offset whatever loss of genetic posterity comes from having a gay son.
How such a gene might work is anyone’s guess. Perhaps the gene simply increases attraction to men, so a male with the gene comes out liking men, and a female with the gene comes out really liking men. Whatever the mechanism, it turns out that an Italian study found that women with gay family members have more children than women with all straight relatives. Andrea Camperio-Ciani, a professor of ethology and evolutionary psychology at the University of Padua, interviewed 98 gay men and 100 straight men and found that the mothers of gay men had an average of 2.7 children, while the mothers of straight men averaged 2.3.
That study has been criticized in some circles for the same old reason: The sample size was not big enough. But the man with the generous sample size hopes to answer that question too. “We’ll look at the offspring of female relatives of gay men—especially of sisters. How many do they have compared to the relatives of straight men?” asks Sanders. “We’re also trying to replicate that.”
Another way to pass on the seemingly nonreproducing gay gene would be for a nonreproducing gay man to have an extra interest in seeing that the offspring of his siblings survive. Biologist E. O. Wilson first put forward this idea of kin selection as an explanation for homosexuality in 1978, but for some time now it has been considered an unlikely scenario.
Michael Bailey conducted a study in 2001 to find out if gay uncles treat their nephews and nieces any better than straight uncles treat theirs. They did not. Thinking that Bailey did not control for the income level of the uncles surveyed—richer uncles tend to be more generous—Qazi Rahman, a professor of psychobiology at the University of East London, tried to replicate the study in England. In addition to looking at how they spent their money, Rahman tried to see if gay men had some kind of extra psychological generosity by asking questions like, “Assuming you had a million pounds, would you buy gifts for your family?” Again, Rahman found no difference between straight and gay men. He admits that looking at “presents and stuff” might seem a crude measure for an adaptation that was selected for thousands of years ago, but he sees no other way that such an impulse would manifest itself today.
