HOW did human same-sex attraction come to be? At first glance it seems to be an evolutionary paradox. For a trait to evolve, it has to be passed on to children to whom it confers some sort of advantage. But as gay sex, of itself, cannot yield offspring, we should expect same-sex attraction to go extinct. Evolutionary biologists have long struggled with this paradox, but my colleagues and I believe that if you come to the puzzle from a different angle, the apparent contradiction disappears.