Italian scientists have come up with an explanation for the puzzle as to why homosexuality, if it is hereditary, has not been eliminated from the gene pool to date, despite the fact that gay people are less likely to reproduce than heterosexuals.
Andrea Camperio-Ciani, an evolutionary psychologist at the University of Padova, says that homosexuality in males may be caused in part by genes that can increase fertility in females.
He says that a study on about 200 Italian families conducted in 2004 showed that mothers, aunts, and maternal grandmothers of gay men were more fecund than average.
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.
If the same genes lead to both homosexuality in men and increased fertility in women, any loss in offspring that come about from the males would be made up for by the females of the family.
He believes that the genes his team modelled might cause people of both sexes to be extremely attracted to men, thereby causing men to pursue relationships with other men, and women to have more sexual partners and become pregnant slightly more often than an average woman.
Such a phenomenon could not lead to homosexuality in women.
"We're still working on lesbianism, but were not getting to the same result, and possibly we'll come out with a completely different explanation," he said.