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Brain Study Shows Differences Between Gays, Straights
Savic and Lindstrom stressed that their findings need to be confirmed by additional research and that it remains unclear how the differences might affect behavior.
While other researchers agreed, some said the findings about the amygdala could help explain why gay men tend to respond to emotional situations more like women and gay women more like men, and could even play a role in their sexual orientation.
"This ancient structure is involved in 'orienting' our attention to biologically important stimuli in our environment (such as attractive partners . . .)," Qazi Rahman, who studies sexual orientation at Queen Mary, University of London, wrote in an e-mail.
Others said that that interpretation was highly speculative, but at the very least the findings support the idea that there tend to be fundamental differences in brain structure, supporting the idea that sexual orientation is inborn.
"This suggests that there's something going on during development that influences sexuality and the brain," LeVay said. "It points more persuasively to some early biological difference."
LeVay and other researchers said the findings fit with studies that found gay people tended to have different ratios in the lengths of their fingers and in the frequency of imperceptible clicking sounds in the ear.
"There's this cluster of interrelated findings," said Richard A. Lippa, a professor of psychology at California State University at Fullerton, who has found evidence that in gay men, the hair on the back of the head is more likely to curl counterclockwise than in straight men. "These are all biological markers that something must have gone on early in development."
These findings also fit with studies showing gay men tend to choose professions that typically attract women, such as teaching and social work, and have verbal and other cognitive skills that tend to be more like women's, he said.
"You get a sort of global shift in gender traits in gay people and straight people that affects not only their sexual orientation but other things as well," LeVay said.
Many researchers suspect that changes may be the result of the levels of hormones, such as testosterone, that fetuses are exposed to in the womb.
"We see the same asymmetries in the brains of rats and mice, and in rats and mice testosterone seems to be controlling it prenatally," said Marc Breedlove, a neuroscientist at Michigan State University.
But researchers say many questions remain about all this research. And there are as many differences within groups individuals of the same sexual orientation as between those of different orientation. Moreover, the new work involved adults, meaning there is no way to know with certainty when the structures and connections formed and why.
"It takes a snapshot of a group of people at a particular age," said Anne Fausto-Sterling, a professor of biology and gender studies at Brown University. "Even if there are reliable brain differences, it doesn't tell you anything about how those brain differences came into being."