For more on this in relation to sexual orientation in particular, see:

http://wiringthebrain.blogspot.com/2010/07/sexual-orientation-wired-that-way.html

http://wiringthebrain.blogspot.com/2010/05/sexual-orientation-in-genes.html

Moreover, sexual interest is surely not as complicated as, say, hearing or vision, and thus should be a smaller mutational target – which implies that homosexuality should be rarer than blindness or deafness. But it’s much more common than genetic congenital deafness, which hits about 1 in 1500 kids.

That said, it is entirely possible than some small, maybe tiny fraction of homosexuality _is_ due to de novo mutations, and if anyone found such as a case, we could learn a lot from it. As we did with narcolepsy, in dogs.

A few years ago, I created a popular YouTube video that summarized the case that lesbianism, unlike male homosexuality, is not biologically driven. Then, I discovered a study that produced a high heritability estimate for women who sometimes engage in lesbians behaviors. I think anyone who is trying to invent a Viagra for women must believe that female sexuality is more complex than male sexuality. So, why isn’t a personality dimension incorporated into these kinds of discussions? It seems to me that male sexuality, like aggression, should be regarded as relatively elemental, whereas lesbianism should be regarded as a symptom of a personality profile that has a meaningful genetic component.

http://www.welmer.org/2008/07/14/the-chimera-hypothesis-homosexuality-and-plural-pregnancy/

Interesting theory.

http://en.wikipedia.org/wiki/Freemartin

The things you learn when you follow links.

I do agree that self-identiy is a problem in women, although I’m not sure it’s any better for men. For every hetero woman who claims to be lesbian or bi too be chique, there’s a non-hetero man who won’t self-identify as gay or bi because it’s “gross” or something.

Also, has it occurred to any researchers to use the Kinsey scale to measure sexual orientation instead of just “gay” or “straight”?

So far, no genes have been identified because there aren’t any (yeah, I know, some claim it’s a complex polygenic trait); some claim it’s all hormones in utero, but even if that’s so, they haven’t answered what in the world is affecting 2-4% of women’s male babies in the womb to come out, by today’s standards, sterile (and by yesterday’s standards sub-fit since there is no way imaginable I can believe a truly homosexual man who married had as many offspring as his heterosexual gene competitors); and, if there is some kind of pathogen involved in triggering it all, it stands to reason that its effects could happen before birth but wouldn’t have to since there are strong neonatal hormone bursts, since the brain keeps developing after birth, and since brain cells can be attacked at any time like any other cells.

All in all, I thought Pawlenty did just fine. Science hasn’t solved this riddle yet, and he makes clear that he knows that. Similarly, he seems to know that no gay genes have been identified which is a heck of a lot better than many of my progressive and supposedly well-educated friends who recall years ago that ” a gay gene was identified” and are surprised when I tell them that this isn’t so.

Yeah, the point about biological versus genetic is well-taken, but face it, the biological cause is still vague/unknown. If a Bill Clinton or a Barrack Obama had said, “I do believe people are born this way, that their genes have given them a homosexual orientation” they’d be no more “right” based on what we do and do not know, than is a Pawlenty.

1) i do provide links for that very reason so, at the wikipedia article the citations leads to: Genetic and Environmental Effects on Same-sex Sexual Behavior: A Population Study of Twins in Sweden:
There is still uncertainty about the relative importance of genes and environments on human sexual orientation. One reason is that previous studies employed self-selected, opportunistic, or small population-based samples. We used data from a truly population-based 2005–2006 survey of all adult twins (20–47 years) in Sweden to conduct the largest twin study of same-sex sexual behavior attempted so far. We performed biometric modeling with data on any and total number of lifetime same-sex sexual partners, respectively. The analyses were conducted separately by sex. Twin resemblance was moderate for the 3,826 studied monozygotic and dizygotic same-sex twin pairs. Biometric modeling revealed that, in men, genetic effects explained .34–.39 of the variance, the shared environment .00, and the individual-specific environment .61–.66 of the variance. Corresponding estimates among women were .18–.19 for genetic factors, .16–.17 for shared environmental, and 64–.66 for unique environmental factors. Although wide confidence intervals suggest cautious interpretation, the results are consistent with moderate, primarily genetic, familial effects, and moderate to large effects of the nonshared environment (social and biological) on same-sex sexual behavior.

2010 paper.

2) i’m frankly just suspicious of claims of female homosexuality heritability estimates in general before i see really clear ways of how they define lesbianism. many more avowed straight women seem to have a “lesbian” phase than straight men who have a “gay” phase in fact, i’ve never met a straight man who thought he was gay at some point in the past, and realized he wasn’t. i’ve known of men who have experimented with bisexuality, more or less.

I think what people want to say is whether there’s some easy way to stop. But the way they put it is quite odd. (I’d note that something similar happens in the debate about addictions – if one can’t just decide to stop it must be an addiction)

Ultimately the real problem is that people’s idea of biology is just woefully bad. I like the reference to Pinker’s Blank Slate in your post title. It was a pretty flawed book but the basic thesis was correct I think. Some old ideas from the dawn of modernism still dominate how we think about human behavior despite being falsified long ago.

Do you have a source for this claim? That’s not my understanding of the current state of evidence. Since women have been studied less than men in this regard, it’s hard to come to a conclusion. There a good overview of the available data here.

this discusses the male vs. female differences. Importantly, the famous Bailey, Pillard et al study did not find homosexuality less heritable in women than men. Kirk et al (2000) found that homosexuality is more, rather than less, heritable in females than males (see here).

Maybe a month might not be enough. Many gay persons have to live a life of heterosexuality, hiding it in some cases even from themselves… But then again, these are gay persons raised under a heavy cultural influence of being perceived as straight.

Wouldn’t that show up as a large difference between DZ and MZ twins though?

Skatr: I don’t see any particular error of understanding in Pawlenty’s answer.

The problem with Pawlenty and Gregory’s discussion is not what they say, but what they imply, i.e. that anything not genetic is necessarily a “choice”. One prime candidate for a homosexuality “cause” is hormonal balance in the mother’s womb. That’s not genetic, but that’s still biological – and that’s definitely not a choice.

I liked Greg Laden’s post, precisely because it did a good job of explaining these points to an audience for whom they might not be obvious.

He never really does that.

What does he mean by multiple “genders” – strict monogamists vs. serial monogamists vs. cads vs. polygamists etc? Or homosexual vs metrosexual vs couch potatoes vs hard-drinkers vs wife-beaters?

Wow – humans really evolved a rather shaky scaffold on which to ensure the reproduction of the species.