News: Men with older brothers more likely to be gay

Who knows how much merit this study has. I think this would be very difficult to predict. There are so many other environmental and genetic factors to take into account. In my own experience, I definitely feel the men I've dated who were the younger brother were perhaps more what we'd now label metrosexual but not gay. Then again, maybe I just attract the gentler ones.

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Men with older brothers more likely to be gay
Prenatal effect hinted for some gay men
By RANDOLPH E. SCHMID, AP Science Writer
Mon Jun 26, 6:27 PM ET


WASHINGTON - Men who have several older brothers have an increased chance of being gay — whether they were raised together or not — a finding researchers say adds weight to the idea that sexual orientation is based in biology.

The increase was seen in men with older brothers from the same mother, but not those who had stepbrothers or adopted brothers who were older.

"It's likely to be a prenatal effect," said Anthony F. Bogaert of Brock University in St. Catharines, Canada, who did the research. "This and other studies suggest that there is probably a biological basis" for homosexuality.

Bogaert studied four groups of Canadian men, a total of 944 people, analyzing the number of brothers and sisters each had, whether or not they lived with those siblings and whether the siblings were related by blood or adopted.

His findings are reported in a paper appearing in Tuesday's issue of Proceedings of the National Academy of Sciences.

S. Marc Breedlove, a professor in the neuroscience and psychology department of Michigan State University, said the finding "absolutely" confirms a physical basis.

"Anybody's first guess would have been that the older brothers were having an effect socially, but this data doesn't support that," Breedlove said in a telephone interview.

The only link between the brothers is the mother and so the effect has to be through the mother, especially since stepbrothers didn't have the effect, said Breedlove, who was not part of the research.

Tim Dailey, a senior fellow at the conservative Center for Marriage and Family Studies disagreed.

"We don't believe that there's any biological basis for homosexuality," Dailey said. "We feel the causes are complex but are deeply rooted in early childhood development."

There have been a number of attempts to establish a physical basis "and in every case the alleged findings have been severely challenged and questioned," he said.

"If it is indeed genetically based it is difficult to see how it could have survived in the gene pool over a period of time," Dailey added.

Bogaert said the increase can be detected with one older brother and becomes stronger with three or four or more.

But, he added, this needs to be looked at in context of the overall rate of homosexuality in men, which he suggested is about 3 percent. With several older brothers the rate may increase from 3 percent to 5 percent, he said, but that still means 95 percent of men with several older brothers are heterosexual.

The effect of birth order on male homosexuality has been reported previously but Bogaert's work is the first designed to rule out social or environmental effects.

Bogaert said he concluded the effect was biological by comparing men with biological brothers to those with brothers to whom they were not biologically related.

The increase in the likelihood of being gay was seen only in those whose brothers had the same mothers, whether they were raised together or not, he said.

Men raised with several older step- or adopted brothers do not have an increased chance of being gay.

"So what that means is that the environment a person is raised in really makes not much difference," he said.

What makes a difference, he said, is having older brothers who shared the same womb and gestational experience, suggesting the difference is because of "some sort of prenatal factor."

One possibility, he suggests, is a maternal immune response to succeeding male fetuses. The mother may react to a male fetus as foreign, but not to a female fetus because the mother is also female.

It might be like the maternal immune response that can occur when a mother has Rh-negative blood but her fetus has Rh-positive blood. Without treatment, the mother can develop antibodies that may attack the fetus during future pregnancies.

Whether that's what is happening remains to be seen, but it is a provocative hypothesis, said a commentary by Breedlove, David A. Puts and Cynthia L. Jordan, all of Michigan State.

The research was funded by the Social Sciences and Humanities Research Council of Canada.