Just seems that this recent finding could be confounded with that earlier finding – women with more male births could have this “younger-gay-sons” effect AND are more fecund (‘cuz they’ve HAD 2nd, 3rd, & 4th sons who are more likely to be gay).

Even if this model and its data provide a clue for understanding male homosexuality, where do lesbian women fit into the equation?

Well, of course we don’t study lesbians because they’re women and don’t count [end snark]

Seriously, I know I saw research some years ago that argued bisexual female primates were more favored by primate males because their children were more likely to survive into adulthood (because the female lovers would share food with one another’s children during times of stress/famine). Certainly we have seen the same attraction among straight men, and anecdotally it appears that women are far more likely to be bisexual than men. Thus, it is possible that lesbianism, while fulfilling many of the same supportive roles for human society, may be generated by a different mechanism, perhaps a gene for bisexuality that is expressed very strongly and elimates the attraction to men a bisexual woman would typically feel.

In general, though, I think the entire topic of the biological basis of human sexuality should be settled by a cursory examination of fetal development. We know that 1) all humans are 50% male and 50% female; 2) all embryos are basically the same; 3) a delicate dance of genes and hormones must occur in utero for a human baby to form. We also know that the physical process of fetal development can create intersexed people – who are physically, and often genetically, more of a mixture of the two genders than a typical human. Why then would it be shocking that some humans do not follow the strict male/female stereotypes?

I never say “Never”, as in psychological trauma “never” causes gays to happen

I highly doubt that significant numbers of men turn gay because of traumatic events. For instance a dad dies in a car wreck or a child goes through a messy divorce. But I wouldn’t count out some sort of general physical trauma at a very early age or in the womb. I don’t mean a konk to the head but possibly something as lame as a flu virus exposure or something like that.

Example:
Exposure to meningitis before the age of about 3 can switch kids from right to left handed. The earlier it happens and the worse the infection the more likely the brain will switch hand orientation from right to left. It sounds totally crazy but it happens.

Chapter 2 in this paper talks about that phenomenon.

But so far the evidence doesn’t support that. The latest Swedish twin study suggests that genes play a minor role.

“Overall, the environment shared by twins (including familial and societal attitudes) explained 0-17% of the choice of sexual partner, genetic factors 18-39% and the unique environment 61-66%. The individual’s unique environment includes, for example, circumstances during pregnancy and childbirth, physical and psychological trauma (e.g., accidents, violence, and disease), peer groups, and sexual experiences.”

To the best of my knowledge every twin study since 1991 suggests the same thing. Even Bailey’s 1991 twin study put concordence at just 50% and that was the high water mark. His 2000 study which he felt was much better dropped the concordence rate to 20%.

That doesn’t mean there aren’t dozens of genes that increase or decrease the odds someone will be gay. Those are certainly out there and scientists will eventually find them.

There could even be a rare mutation that makes someone gay all by itself. But rare is the key word.

Besides the fact that plenty of gays and lesbians do have children. The norm used to be, and still is in most of the world, that sex is mandatory for producing children or satisfying your husband and you don’t have to enjoy it or have a physical attraction to your partner. Alan Chambers and all the ex-gays who still appear gay are able to have kids.