New research casts doubt on the idea that same-sex sexual attraction evolved as a consequence of increased sociability in humans and other animals.
The study, published in Personality and Individual Differences, used data from an international survey with more than 4,000 participants to examine how dark personality traits were related to various manifestations of sexuality. The data provided researchers with the opportunity to test various hypotheses regarding the evolution of sexual orientations.
“In particular, we were interested in testing the prosociality hypothesis by Brian Hare that is heavily inspired by his work on bonobos,” explained study author Peter Karl Jonason, an associate professor of psychometrics at the University of Padua.
Hare and his colleagues have suggested that homosexuality may have evolved as a result of increased sociability in humans, noting that both same-sex and opposite-sex intercourse plays an important role in bonobo social bonding.
Jonason and his colleague, Severi Luoto, also tested the gender shift hypothesis, which holds that homosexual men tend to have personalities more similar to heterosexual women and that homosexual women tend to have personalities more similar to heterosexual men.
“It seemed like a way to move the study of these traits into a new area of research (although at least two studies were already done, but not paid much attention to), thereby inspiring more research,” Jonason added. “And we had for one of the first times sufficiently large enough numbers of non-heterosexual individuals to allow us to simply understand potential differences in sexual orientation.”
Of the entire sample, 3,675 identified as heterosexual, 115 as homosexual, 233 as bisexual, and 34 as “other.” The participants completed a scientific questionnaire known as the Dark Triad Dirty Dozen, which measures Machiavellian, psychopathic, and narcissistic personality traits.
But, contrary to the prosociality hypothesis, the researchers found no evidence that non-heterosexual individuals tended to have less of these anti-social personality traits. Instead, they found that, overall, bisexual and homosexual participants tended to be slightly more Machiavellian than heterosexual participants.
The results only provided limited support for the gender shift hypothesis. Since men tend to score higher on Dark Triad measures compared to women, non-heterosexual women should have scored higher than heterosexual women and non-heterosexual men should have scored lower than heterosexual men.
Among female participants, bisexual women tended to be slightly more Machiavellian, psychopathic, and narcissistic. The findings are in line with previous research, which found higher levels of dark personality traits among bisexual college women compared to their heterosexual and homosexual counterparts.
But the current study found no statistically significant differences between homosexual men and heterosexual men, or between homosexual women and heterosexual women.
“The results may be more consistent with a life history model and/or with observations about minority stress, suggesting that with greater experienced harshness of sexual minorities (i.e., non-heterosexuals), engaging in Dark Triad trait approaches to life might help non-heterosexual people stay safe, avoid detection, and get what they want from their lives,” the researchers said.
According to life history theory, early life experiences can shape an individual’s behavior toward relationships and life in general. Those faced with unpredictable childhoods develop a fast life strategy that emphasizes insecure attachments, immediate gratification, and risky behaviors. Those with a more stable childhood, on the other hand, develop a slow life strategy that emphasizes long-term goals, greater investments, and reduced aggression.
“Those who are not heterosexual may experience challenges in life that lead them to engage in behaviors consistent with a fast life history strategy as found in the Dark Triad traits,” Jonason told PsyPost.
However, Jonason noted that the study was limited by the fact that it had “grossly imbalanced numbers of non-heterosexual individuals, which while logical, may lead to biased estimates of the Dark Triad traits.”
“We are not diagnosing any one,” he added. The Dark Triad Dirty Dozen measures a spectrum of personality traits, not clinical disorders. “The major caveats in the study are already noted in the limitations section which, because it comes late in the study, may simply not get read before people are upset with the findings.”
The study, “The dark side of the rainbow: Homosexuals and bisexuals have higher Dark Triad traits than heterosexuals“, was authored by Peter K. Jonason and Severi Luoto.