Homosexuality in women evolved because it's a turn on for men, a controversial scientific paper has claimed.
It's estimated that about 15% of women are homosexual or bisexual. Exactly why so many women experience attraction to one another was a puzzle for Menelaos Apostolou at the University of Nicosia in Cyprus.
"Why does same-sex attraction happen in women, why did it evolve, and does it serve some purpose? A lot of men indicate a desire to have a partner who also experiences same-sex attraction," Apostolou told IBTimes UK.
According to a study by Apostolou, about 15% of heterosexual men in long-term relationships say that they would want their partner to have a sexual encounter with another woman. This figure goes up to about 30% of men in short-term relationships, according to the study published in the journal Personality and Individual Differences. The figures for heterosexual women who found same-sex attraction a turn on in their male partners were much lower in both types of relationship.
The male penchant for women who have sex with women drove the evolution of homosexuality in women, Apostolou argues. Men would chose female partners who experienced same-sex attraction, so those women would be more likely to have children with the men, leading to the evolutionary success of the trait, he says.
To say the least, the theory has been called a bit of a stretch.
"The paper totally ignores a lot of other possible hypotheses and makes claims that are really not supported by the evidence they provide," said Diana Fleischman, a psychologist at the University of Portsmouth.
One of the main points missed is that men have been shown to have much more relaxed attitudes when it comes to women's sexuality than women do about men.
"If you ask men about all kinds of sex fetishes their partner might have – so, how would you feel if a woman had a foot fetish – more men wouldn't care than if you asked women about male partners."
But even though men are typically more accepting of women's fluid sexuality, fetishes or paraphilia, women do not have higher rates of them than men do, Fleischman said, which introduces a bit of a hole in the hypothesis.
Another problem is that the study doesn't account for the effects of porn.
"I can't really see how cultural factors would make some men be turned on when their partners tell them I want to have sex with another woman," said Apostolou. "These kinds of sexual traits are more instinctive. It's a mechanism that has been selected to serve a purpose – to make you reproduce. For me, these things are expressions of old mechanisms.
"I'm not sure that factors like the media have an important effect. This is not something that is promoted, for instance, having a girlfriend who also has same-sex attraction. I don't see it there."
However, female same-sex activity is a very common theme in porn, which could be influencing men's stated preferences.
"I think this paper is showing the effect of pornography. Men see a lot of porn where a woman has sex with another woman, and then a man gets to have sex with that women," Fleischman said. "Two women having sex with one man is such a common theme in pornography that I think it is very difficult to parse out that particular variable."
The prevalence of this theme in porn isn't necessarily a reflection of an innate male attraction to female same-sex activity. Instead, it could be influencing men's preferences through repeated association with orgasm during masturbation while watching the porn.
"There's a big cultural influence of porn because men are more likely to form associations through classical conditioning and stimulation and sexual arousal," Fleischman said. "It only takes a few trials to get a man aroused at a piggy bank or a boot."
Apostolou acknowledges that more research will need to be done on some cultural factors to see whether they affect men's preferences. His next steps include seeing whether religion could be playing a role in either increasing or decreasing men's preference for women who are attracted to other women.