We know now that homosexuality is connected to genetics — and there's probably more than one gene involved. But why would that trait have been selected for strongly enough to make it present in 5-to-15 percent of the population?
At The Conversation, geneticist Jenny Graves presents an interesting theory that I'd never heard before. Homosexuality is evolutionarily adaptive, according to this idea, because the same genes that give you women who love women and men who love men also give you men who love women and women who love men. In fact, Graves suggests, it's better to think of these genes as "male loving" and "female loving" rather than "gay" or "lesbian" or "straight".
They may be common because these variant genes, in a female, predispose her to mate earlier and more often, and to have more children. Likewise, it would be surprising if there were not “female-loving genes” in lesbian women that, in a male, predispose him to mate earlier and have more children.
If [the] sisters, mother and aunts [of gay men] have more kids who share some of their genes, it would make up for the fewer children of gay males.
And they do. Lots more children. An Italian group showed that the female relatives of gay men have 1.3 times as many children as the female relatives of straight men. This is a huge selective advantage that a male-loving allele confers on women, and offsets the selective disadvantage that it confers on men.
This all puts an interesting twist on the whole "gay gene" conversation. A serious concern that plenty of queer people have about genetics research is the risk that, once specific genes for queerness are identified, people might start selectively aborting fetuses that have those genes or seeking out gene therapy to change them.
The good news is that the relationship between genetics and sexuality is probably more complicated than a simple, single-gene on/off switch. But it's also interesting to see that those complex genetics could be things that straight people, or at least some straight people, may share. If that's the case, it seems like it would make it a lot harder to stigmatize the minority for gene variants that occur across the population, or (at least) change how people thought about those gene variants.