Guest Blogger

Why Gay? ...female strategy for fecundity?

Filed By Guest Blogger | June 29, 2008 7:30 PM | comments

Filed in: Living
Tags: Camperio Ciani, chemistry.com, evolution of homosexuality, Helen Fisher

Editors' Note: Guest blogger Dr. Helen Fisher is the founder and Chief Scientific Advisor to Chemistry.com. Dr. Fisher has been posting every Sunday evening for the past month, so I hope someone fixed her a plate.

Dr-Helen-Fisher.jpgI was fascinated with everyone¹s response to my blog on the evolution of homosexuality via kin selection. Thank you.

Here¹s another theory offered to explain the genetic diffusion of male homosexuality. It is based, foremost, on the work of Camperio Ciani and colleagues, published in 2004, who reported that females in the maternal line of male homosexuals are particularly fertile.

Hence the genes that contribute to male homosexuality are maintained at a low and stable frequency in the population because they promote female fecundity.

This process is known as "sexually antagonistic selection" because it jeopardizes the fecundity of one sex (men) while it gives a reproductive advantage to the other (women).

This type of selection is found in other creatures, including insects, birds and other mammals. But if the above theory is correct, male homosexuality would be the first trait selected by this method in people.

I have no comment on this theory. But long ago I came to believe that most of our dramatic human traits--as well as our remarkable variety--evolved for MANY reasons working in tandem with one another, not just one.

Anyway, that¹s the current buzz. Have a great July 4th. I¹ll be finishing my book on who we choose to love, due July 7th to the publisher. And as time goes on, I hope to share with you what I have discovered about gays and lesbians -- particularly how similar we ALL are in the ways we love.

"Come as you are" to Chemistry.com if you are looking for the one. And happy days, Helen.


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Dr. Fisher,
I joined Chemistry.com two days ago and I sent out 5 inquiries, but no response. I really loved your extensive questionnaire. I would have never even checked it out if it wasn't for your posts here. I hope I can find that special someone.

Brynn Craffey Brynn Craffey | June 29, 2008 9:04 PM

Dr. Fisher, for some reason I have a particularly hard time when it comes to figuring out these family/hereditary theories...so what you're saying is that my brother is gay (as am I) and hence, according to this theory, our mother should be particularly fertile? Likewise, any females born to her?

The theory doesn't seem to address if those born female, would also be likely or not be gay?

I know these sorts of theories only really hold true on a statistically large scale. But I was trying to translate it into terms I can better understand.

Thanks (in advance)!

I'm afraid I'm a little lost too, Brynn.

...females in the maternal line of male homosexuals are particularly fertile.

Hence the genes that contribute to male homosexuality are maintained at a low and stable frequency in the population because they promote female fecundity.

This process is known as "sexually antagonistic selection" because it jeopardizes the fecundity of one sex (men) while it gives a reproductive advantage to the other (women).

I understand that gay men's maternal line is particularly fertile. I'm the youngest of 5 children born to my mother. Gotcha. Check.

But why are they maintained because they promote fertility. Is this a case of chicken and the egg? (no pun intended) I thought the female fertility "caused" homosexuality, not homosexuality cause fertility.

I can see how it "jeopardizes the fecundity" of men. Gay men don't usually have children. But how does it give an advantage to the women? Now they have one less person to mate with; doesn't that give them a disadvantage too?

battybattybats battybattybats | June 30, 2008 10:42 AM

"Now they have one less person to mate with; doesn't that give them a disadvantage too?"

Yes! And thats the way it works in some ants too (ok, I admit it, I like ants).

Ok in ants where a Queen mates with multiple males before founding the colony their should be an even distribution of bloodlines of the half-sisters. Some will be turned into Queens as they develop. However some genes lead to a greater chance of becoming a queen giving the female descendants of that male an edge over others but if it works too well it will destabilise the population so it is curtailed somewhat by such collapses and adapts to be weak. Being more successful but not too successful is often better than being very successful. Or rather it is having better long-term success.

So if this theory is correct in this case it would be expected to be weak in its effect so as to not disrupt too greatly the population.

Diseases are a good example. A very lethal disease does not work well, it is too effective in the short term and too likely to kill the host before it can spread. It exists to spread it's genes not to kill. Thats why many new diseases actually become weaker over time as they adapt to effectively spread before they can kill their hosts or better yet don't kill their hosts enabling them to keep spreading.

While the number of available men will be reduced by such a gene it will have an edge over other women, so long as they don't dominate the gene pool too much to cause collapse. The gene will likely then become a stable proportion of the population, too effective to die out, not too effective though so it doesn't wipe itself out.

But why are they maintained because they promote fertility. Is this a case of chicken and the egg? (no pun intended) I thought the female fertility "caused" homosexuality, not homosexuality cause fertility.

Neither - the idea is that a (set of) gene causes both increased female fertility and an increased chance of being a homo. (I think you're referring to a separate study, the one about the youngest brothers being more likely to get into the same sex lovin'.)

I don't see how this is sexually antagonistic, because the idea that male homosexuality can reduce male fecundity is culturally specific. There are people from other cultures who would be described as gay in modern America who have wives and children and sex with men on the side (what am I saying, that's still happening in our culture!).

And it's not just closetedness. The ancient Greeks were pretty down with the gay love, and most of those people still had children.