Human sexuality is complex; most of us all fall somewhere on a spectrum with straight on one side and gay on the other. Yet, when it comes to female sexuality, women are perceived to be naturally fluid, or bi-curious. Now, researchers at the University of Nicosia in Cyprus suggest some women evolved to be lesbian or bisexual because of men's mating preferences.

The evolutionary origins of same-sex attraction in women is believed to develop from a man's intrinsic desire for a sexually fluid partner. According to the researchers, this stems from men wanting to secure their evolutionary success of passing on their genes. In other words, a female partner who sleeps with other women would ensure the certainty that he is the father of the offspring.

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“When this woman has sex with another woman she does not have sex with another man which translates into same-sex contact reducing the risk of cuckoldry," wrote the researchers, in their study, published in the journal of Personality and Individual Differences.

The Cypriot researchers surveyed over 1,500 heterosexual men and women in two online studies to test their theory on female same-sex attraction. About half of the men reported they would become sexually excited if their opposite-sex partners revealed they experienced same-sex attraction. Meanwhile, only eight percent of women saw same-sex male attraction as a turn on in their partners.

The study also analyzed the differences in men's preferences for sexually fluid partners between long and short-term relationships. Approximately 30 percent of heterosexual men would occasionally want their partner to have a sexual encounter with another woman. However, only 15 percent of men in long-term relationships reported the same preference.

"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," Menelaos Apostolou, study author, told IBTimes UK.

Apostolou's theory fails to consider one key element in men's desire for bisexual women — porn. The notion straight men like it when two women kiss, and do more, is a huge cultural influence of porn. This type of porn doubles up the visual cues men are most aroused by without the drama or emotional difficulty.

In a Pornhub and Vocativ study, both sites teamed up to find what terms Americans were searching for when they were on the adult site. “Lesbian” was found to be the most-searched term in the majority of the 50 states, and ranked highest in 30 states scattered across from east to west. The intrigue of women on women sexual encounters is shared among most porn viewers in the U.S.

Read More: Drinking Alcohol Makes Straight Men More Sexually Fluid

However, adding to Apostolou’s argument, previous research has found men are more lax if their female partner committed infidelity with another women. In the 2010 study, conducted at the University of Texas at Austin, psychologists noted this type of infidelity did not threaten the paternity of their offspring. They also theorized men view a woman's homosexual affair as an opportunity to have sex with more than one woman simultaneously, satisfying men's desire for more partners.

It's no surprise straight men are more likely to be sexually aroused by bisexual, or lesbian women. However, women's sexuality is much more complex than just satisfying a man's ego. A 2011 study on twins determined lesbianism is at least 25 percent genetic. In identical twin sisters, they are more likely to both be lesbians than are fraternal twin sisters, proving genes matter.

Apostolou admits his study has several limitations, which warrants more research to understand the complexity of same-sex attractions.

“The publication of my theory gives the opportunity for a fruitful academic dialogue, where another scholar may attempt to refute, alter, or expand it and replicate my findings," he told PinkNews.

The truth is female sexuality has yet to be fully and properly understood by science.

Source: Apostolou M, Shialos M, Khalil M et al. The evolution of female same-sex attraction: The male choice hypothesis. Personality and Individual Differences. 2017.

See Also:

Why Lesbian Porn And Threesomes May Be Popular Among Females

Men Who View X-Rated Content May Be Less Satisfied With Sex Life