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While the FBOE is usually used to talk about the origins of male homosexuality, it could just as well be seen as suggesting that a particular womb environment is likely to produce babies who will grow up to be heterosexual men. In other words, the FBOE suggests that it is likely that many straight men were born inclined to be straight. Note this wouldn't be because of these straight men having been born with a "straight gene." They would be born inclined-straight following complex interactions of maternal and fetal genes.

Is there any evidence for "straight genes," other than the rather indirect evidence of the large number of people who identify as straight? Researchers have looked at sexual orientation among monozygotic twins -- that is, twins who are genetically identical -- versus dizygotic twins. Monozygotic twins are more likely than dizygotic to have the same sexual orientation (to both be straight or both be gay), but even they are not always matched. Bailey concludes that the data are "consistent with some genetic influence" for sexual orientation but that the data are "not overwhelming." He goes so far as to say "the evidence from twin studies for innateness of sexual orientation is pretty weak."

That said, Bailey does see some other evidence for an innate component to sexual orientation, at least in males. He points to cases where genetic males have been surgically and hormonally turned into girls in infancy, either because of childhood accidents that obliterated their penises or because they were born without penises and thus doctors subjected them to sex change. As adults, these folks are typically attracted to females. Says Bailey, "if you can't make a genetic male be attracted to other males by rearing him as a girl from early in life, how likely is any socialization theory of homosexuality or heterosexuality? I think not likely," at least for males.

Raymond Hames, a cultural anthropologist at the University of Nebraska, has been working with his students to survey the preponderance of homosexuality in various cultures. His team finds that, in more cultures than Americans might guess, same-sex encounters take the form of adult males obligating boys to sexually pleasure them. Many children don't appear to enjoy this; they do it because it is required as a kind of rite of passage. Importantly for this discussion, these kinds of cultures don't seem to produce many men who are attracted to men. In other words, these early same-sex experiences don't seem to "turn" the boys gay.

While it has been asserted by some that abuse at the hands of men might incline girls to be more likely to ultimately become lesbians, the evidence for this claim is weak. Boston Children's Hospital public health researcher Bryn Austin and her colleagues have documented that lesbian and bisexual women report having suffered higher rates of physical and sexual abuse in childhood and adolescence, a finding borne out by other teams' investigations. But we can't show any kind of clear causal link between the experience of childhood abuse (sexual or physical) and adult sexual orientation.

For abuse to push children toward straight or gay orientations they might otherwise not have had, it would have to be the case that children's sexual orientations can be shifted in direction, intentionally or unintentionally, and the truth is that the evidence for that is thin at best.


Finally, a related question: Given that we don't know if they are really all "born that way," should straight-identified people be allowed to marry?

Personally, I think it makes sense to let straight-identified people marry, not because they were necessarily born that way, but because it seems silly, in this day and age, to get in the way of their desire to marry and/or to have sex with whatever consenting adults they wish. Given the challenges of attempting a lifetime partnership with a person who will be, on average, fundamentally sexually different from oneself, it seems the least we can do for straight people is to let them get married if they want.