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Think Tank

The Gay Gene: New Evidence Supports an Old Hypothesis

What's the Big Idea?

If a so-called "gay gene" exists, what is the evolutionary logic for it? After all, you would expect that homosexuals would have fewer children than heterosexuals, so that any genetic cause of homosexuality would have been selected out of the gene pool a long time ago. 

The answer, as you might expect, is a bit complicated (if it's even the right answer). 

A new study published in the Journal of Sexual Medicine has found a link between homosexuality and female fertility. The mothers and maternal aunts of gay men have "increased fecundity compared with corresponding maternal female relatives of heterosexual men," the authors of the study write. 

This study, which the authors note was based on a small sample and "would benefit from a larger replication," supports the so-called "balancing selection hypothesis." The gay gene -- or genes -- are thought to exist on the X chromosome, and "increase the reproductive value" of the female relatives. In other words, it makes the women more attractive to men, allowing them to produce more offspring. So while the 'gay gene' may not be passed down directly, it will survive over the course of many generations. 

Not only are the maternal relatives of gay men more attractive, more fertile and subject to fewer complications during pregnancy, the study also found these women are extroverts and generally happier. In other words, if you're the mother of a gay man, you're pretty awesome.

Can this idea survive scrutiny? 

Bryan Sykes, the author of the new book, DNA USA, tackled this subject in a previous work, Adam's Curse, and more recently in an interview with Big Think. 

According to Sykes, "there is some evidence that there is a genetic predisposition to male homosexuality." And yet, in Sykes's view, it is highly unlikely there exists "a simple gay gene" that you either have or don't have. To put it another way, the idea that a simple gay gene exists "as a kind of mutation" is downright ludicrous, according to Sykes. 

However, Sykes also points out that there is some evidence that suggests the possibility of a genetic association with homosexuality without the existence of a mutated gene. He tells us:

I think you could explain it by the way that mitochondria--that piece of DNA which I’m full of admiration for because they aren't interested in men at all--are inherited down the female line. And they have ways, I think, of getting rid of male embryos and making sure that they’re propagated at the expense of males. 

One way that mitochondria might do this, Sykes says, is to influence some male fetuses during early development so these fetuses "do not turn into heterosexual males." This controversial idea, according to Sykes, "would explain how you can have a genetic association without there being a mutant gene." But why would mitochondria act this way? While it may sound weird, Sykes says this type of activity has been observed in many other animal species. He tells us:

It’s the basis of how beehives work. There are bees working away for the queen bee with no hope of having their own DNA propagated in the next generation. I think there's a possibility, at least it’s something to argue about, that a similar thing is operating in humans as regards male homosexuality. 

What's the Significance?

If the existence of the 'gay gene' is ever proven conclusively, it is unlikely to have much of an impact on the beliefs of some people who reject homosexuality as a "lifestyle." After all, some of those people simply reject science. Indeed, there are some people who want to bury their heads in the sand, and that is an issue that impacts the field of genetics in general, gay gene or no gay gene. 

So what does genetics have to teach the rest of us about who we are? Quite a lot, says Sykes, if we're in fact willing to find out. The other significant question, of course, is how much is our behavior pre-programmed in our genes and to what extent can we change ourselves and grow after we are born? Sykes has a good answer. 

While it’s "perhaps too deterministic" to say that your genes determine everything you do, Sykes says your genes are like a deck of cards. You're dealt these cards, you're influenced by these cards, but the rest depends on what you do with them.

Watch the video here:

Image courtesy of Shutterstock

Follow Daniel Honan on Twitter @Daniel Honan

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