During the gay marriage debates, the claim was frequently made that children from gay families are not more likely than others to develop a same-sex orientation.
I was always skeptical of the claim because: 1) gay parents should at least make kids feel more comfortable about going with a gay identity; and 2) if the kids were biological offspring, they would probably face a higher risk of homosexual orientation via genes from a parent. In addition, I didn't rule out the possibility that gay parents might provide a more permissive environment for kids so they are more likely to have pleasant same-sex experiences when they are young and impressionable.
This new study shows that the claim about gay families was false. 76 adult biological offspring of a woman with a lesbian partner were matched demographically with 76 controls. Women from these families were: 1.5 times to be sexually attracted to other women; 2.4 times more likely to identify as lesbian or bisexual; and 1.4 times as likely to have same-sex experiences.
Compared to controls, men from lesbian families were: 3.1 times more likely to be sexually attracted to men; 4.3 times more likely to identify as gay or bisexual; and 3.8 times more likely to have had same-sex experiences.
There is no evidence here that lesbian parents have more impact on girls than boys, either by passing on genes that raise the risk of same-sex attractions for daughters but not sons, or by gender-specific socializing. In fact, the parent-child link seems to be stronger for males. (This could be due to the very high rates of same-sex attraction, identification, and experiences among the female controls. How do I make sense of this? I suspect women in their 20s in the past decade have lived in a pro-lesbianism culture which makes their numbers not that dissimilar from female peers from lesbian families.)
My guess would be that moms are passing on mutations on to sons and daughters that tend to disrupt heterosexual brain development. I suppose an encouraging environment could convince someone with same-sex attractions to pursue and embrace the identity, but I doubt this would explain such large differences. And I doubt that lesbians are providing a perinatal environment that raises the risk of the kind of infection posited by gay germ theory.
UPDATE: tantum (@QuasLacrimas) over at Twitter made a good point that these results do not support sexually antagonistic selection. According to the theory, genes that make a daughter more feminine and attractive and thus more reproductively successful will raise the risk that a son will develop a homosexual orientation. The daughter's success compensates for the son's reproductive failure so the genes are not weeded out. The logic is the same for lesbianism, with the advantage/disadvantage reversed.
Such a theory would predict that lesbians would be likely to have masculine, straight boys, but this study found that lesbians are much more likely to have gay sons.
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