A study of 400 gay men in the United States has shown that homosexuality in men is 30 to 40 percent determined by genetics, the Guardian reports. The unpublished study, the findings of which were presented by Northwestern University psychology professor Michael Bailey on Feb 13, focused on a section of the X chromosome called Xq28. Bailey found that while certain genetic markers in Xq28 do not make a man gay, and are not necessary for a man to be gay, they do have some influence on sexual orientation. Another section of chromosome 8 also appeared to be related to sexual orientation.
The study confirms the work of American researcher Dean Hamer, whose controversial studies in 1993 suggested that homosexuality is heritable.
Bailey says that genetics are definitely a factor in homosexuality but that it is impossible to test genetically. “Sexual orientation has nothing to do with choice,” he said. “We found evidence for two sets [of genes] that affect whether a man is gay or straight. But it is not completely determinative; there are certainly other environmental factors involved.”
The scientists believe that other factors in sexual orientation likely include hormonal influences in the womb.
“When people say there’s a gay gene, it’s an oversimplification,” researcher Alan Sanders said. “Whatever gene contributes to sexual orientation, you can think of it as much as contributing to heterosexuality as much as you can think of it contributing to homosexuality. It contributes to a variation in the trait.”