Adding to the growing mountain of scientific evidence that there is a strong biological component to being gay or lesbian, researchers in Canada have shown that boys with older brothers are slightly more likely to be gay than those without. "It's likely to be a prenatal effect," Anthony F. Bogaert of Brock University in St. Catharines, Canada, told the Associated Press. "This and other studies suggest that there is probably a biological basis for" homosexuality.
The finding, appearing in Tuesday's issue of Proceedings of the National Academy of Sciences, "absolutely" confirms a physical basis, added S. Marc Breedlove of Michigan State University. "Anybody's first guess would have been that the older brothers were having an effect socially, but this data doesn't support that," he told the AP. 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.
The effect of birth order on male homosexuality has been reported previously, but Bogaert's research, in which he studied four groups of Canadian men totaling 944 people, is the first designed to rule out social or environmental effects. One possibility for the result, he suggests, is a maternal immune response to succeeding male fetuses. (The Advocate)
