I’ve written here before about the theory that gay men are influenced by a gene that causes both women and men to be strongly attracted to men. A new study released today seems to confirm this.
Homosexuality in males may be caused in part by genes that can increase fertility in females, according to a new study
Homosexuality in males may be caused in part by genes that can increase fertility in females, according to a new study.
The findings may help solve the puzzle of why, if homosexuality is hereditary, it hasn’t already disappeared from the gene pool, since gay people are less likely to reproduce than heterosexuals.
A team of researchers found that some female relatives of gay men tend to have more children than average. The scientists used a computer model to explain how two genes passed on through the maternal line could produce this effect.
In 2004 the researchers studied about 200 Italian families and found that the mothers, maternal aunts and maternal grandmothers of gay men are more fecund, or fruitful, than average. Recently, they tried to explain their findings with a number of genetic models, and found one that fit the bill.
“This is the first time that a model fits all our empirical data,” said Andrea Camperio-Ciani, an evolutionary psychologist at the University of Padova in Italy who led the study. “These genes work in a sexually antagonistic way — that means that when they’re represented in a female, they increase fecundity , and when they’re represented in a male, they decrease fecundity. It’s a trait that benefits one sex at the cost of the other.”
The researchers detail their findings in the June 18 issue of the journal PLoS ONE.
If this scenario turns out to be true, it could help explain the seeming paradox of hereditary homosexuality. Since gay people are less likely to reproduce than heterosexuals, many experts have wondered why, if homosexuality is caused by genetic factors, it wouldn’t have been eliminated from the gene pool already.
But if the same genes create both homosexuality in men and increased fertility in women, then any losses in offspring that come about from the males would be made up for by the females of the family.
I’ve also mentioned the “older brother effect”.
“I think it’s almost beyond a doubt that genes have some influence,” said Ray Blanchard, a researcher at the Centre for Addiction and Mental Health in Toronto, who studies the effect of birth order in predicting whether a male will be born homosexual. “My personal view is that there is probably more than one biological mechanism contributing toward homosexuality. I think it’s also safe to say that there is at least one non-genetic influence.”
Blanchard found that with each older brother in a family, the odds increase by about a third that a boy born later will be gay. This effect is not thought to be caused by genetics, but rather by antibodies produced by the mother’s immune system during pregnancy.
Loving men
Camperio-Ciani and his team hypothesize that the genes they modeled may cause people of both sexes to be extremely attracted to men, which would lead men with the genes to pursue relationships with other men, while causing women with the genes to have more sexual partners, and become pregnant slightly more often than an average woman.
