Having older brothers increases the chance of a man being gay because of biological changes that happen when a woman becomes pregnant with a boy, according to a new study.
Canadian and American researchers sought to understand a previously established link that homosexual men tend to have a greater number of older brothers than heterosexual men.
In the study, published Monday in the journal PNAS, researchers found that mothers who have boys had higher instances of an antibody against a protein essential in the developing male brain.
The presence of the antibody — anti-NLGN4Y — is believed to play a role in determining sexual orientation while the fetus is developing.
The study consisted of 154 subjects that included men, women with no sons, mothers of heterosexual son, mothers of gay sons with no older brothers and mothers of gay sons with older brothers.
“Our results begin to explain one of the most reliable correlates of sexual orientation in men (i.e., Fraternal Birth Order) and provide evidence of a specific biological mechanism underlying men’s sexual orientation: a maternal immune response to a Y-linked protein important in male fetal brain development,” the authors wrote.
The researchers said that while results are promising, the findings need to be replicated in larger studies and only accounts for a small and specific portion of gay men.
“Sexual orientation is clearly a complex phenomenon with likely many factors influencing it,” they wrote.
• Laura Kelly can be reached at lkelly@washingtontimes.com.
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