Why are there gay, lesbian, and bisexual people?

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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.

Image: Some Rights Reserved by Quinn Dombrowski

Notable Replies

  1. Because the universe would wither and die in despair if such fabulousness were not part of it.

  2. BB needs more science-y people. I <3 your posts, Maggie. The earlier post about evidence-based pregnancy, this one... gushes sorry.

  3. Point to consider: nature doesn't actually select /for/ things, only against them. The idea that nature would automatically be selecting against non-reproductive members of a species is readily disproven by the existence of ants, bees, etc.

  4. In their minds they were Turks and Muslims, despite coming from Christian European stock.

    Huh?! Belonging to one tribe or another is not at all comparable to innate sexual desire. Nobody has ever said "speaking Turkish" was a genetic trait, and a pale-skinned blonde Swede isn't going to turn dark-haired and swarthy from being raised by Turks; this is genetics, not Lamarck's "Transmutation of Species." Nevertheless, the sheer quantity of homosexuals who are raised among (and as) heterosexuals obviously disproves your point-- for centuries homosexuals were born in cultures where it was frowned upon, so any "nature vs. nurture" argument is moot here.

    (Sorry, originally posted this in reply to the wrong comment.)

  5. scav says:

    Now we need some research into why so many people think it is such a big fucking deal.

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