Study: Link Between Having Older Brothers and Homosexuality

Posted on Jun 27, 2006

Having one or more older brothers boosts the likelihood of a boy growing up to be gay—an effect due not to social factors but biological events that occur in the mother’s womb, according to a study published Tuesday. More evidence—alas, Bible-thumpers still need it—that homosexuality has nothing to do with outside factors and has everything to do with biology.

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L.A. Times:

Having one or more older brothers boosts the likelihood of a boy growing up to be gay—an effect due not to social factors, but biological events that occur in their mother’s womb, according to a study published Tuesday.

In an analysis of 905 men and their siblings, Canadian psychologist Anthony Bogaert found no evidence that social interactions among family members play any role in determining whether a man is gay or straight.

The only significant factor was the number of times a mother had previously given birth to boys, according to the report in the Proceedings of the National Academy of Sciences.

Each older brother increases the chances by 33 percent. Bogaert said that assuming the base rate of homosexuality among men is 2 percent, it would take 11 older brothers to give the next son about a 50-50 chance of being gay.

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