How homosexuality may have evolved

THE evidence suggests that homosexual behaviour is partly genetic. Studies of identical twins, for example, show that if one of a pair (regardless of sex) is homosexual, the other has a 50% chance of being so, too. That observation, though, raises a worrying evolutionary question: how could a trait so at odds with reproductive success survive the ruthless imperatives of natural selection? Various answers have been suggested. However, they all boil down to the idea that the relatives of those who are gay gain some advantage that allows genes predisposing people to homosexual behaviour to be passed on collaterally.