CURIOUS: Female Same-Sex Attraction Revisited.

One idea that we can lay to rest here is the notion that female masculinization and SSA stem from prenatal exposure to male hormones. The way to test this idea is to look at females with a male fraternal twin (Fm) compared to women with female fraternal twins (Ff). If the Fm women were more masculine that Ff women, then it would imply prenatal hormones were at work. A massive review looking at such twin studies (Tapp, Maybery, and Whitehouse, 2011 [PDF]) found little support for this notion, particularly from the larger studies examined. Another recent twin study out of Denmark (Ahrenfeldt et al, 2015 [PDF]) found no such effect on women’s academic performance (Fm twins didn’t exhibit a more male-typical cognitive profile). . . .

Manly men beget manly daughters. Some of these alleles may serve to increase “gynephilia” (attraction to women), and they may have this effect in both sexes. This may be where SSA comes from in women. Unlike male SSA, female SSA appears to be continuously distributed – consistent with what we’d expect if it arose from the general load of various gynephilic alleles (resulting in pure lesbianism in the most extreme cases). The female SSA itself, being near selectively neutral, could reach high frequencies in women, just as masculinity in general has. However, the general suite of masculinized traits (e.g., sociosexuality, facial masculinity) was likely maladaptive in women, and was selected against, counteracting the positive selection in men. In other words, sexual antagonistic selection.