One of the classic, politically charged "mysteries" of evolutionary biology (along with questions about the evolution of the female orgasm) is how genes for homosexuality propagate in a population. Gay sex, after all, doesn't lead to procreation. So genes for gayness should be on the short list for extinction, right? Explain that, Darwin! Gayness can't be genetic.
Well, here's one novel explanation: The same genetic factor that makes men like men might also make women like men (more). When this factor is expressed in men, they're more likely to be gay. When it's expressed in women, they're "hyper-heterosexual." They're really attracted to guys and end up having more kids. And they pass on to those kids, male or female, this gene for attraction to males. Boom. New Scientist has the details.