For years, researchers have pondered whether homosexual behavior plays a role in social affiliation—the innate desire to create and sustain connections with others. While previous findings have primarily been observational, recent studies provide clearer evidence suggesting that same-sex sexual interactions may serve as a form of social bonding.
Same-sex erotic encounters are surprisingly prevalent, often occurring among individuals who do not identify as exclusively homosexual. For instance, an evening conversation with a friend revealed that she had kissed one of her closest companions after sharing a particularly intimate moment. Young men, too, frequently engage in same-sex kissing; one study noted that 89% of heterosexual British men reported having kissed another man. This phenomenon is not exclusive to humans or Western societies; research from the 1950s indicated that a majority of cultures experienced some form of homosexual behavior, with 64% deeming it acceptable. Furthermore, our primate relatives exhibit similar behaviors: bonobos, often called pygmy chimpanzees, use sexual interactions to facilitate food sharing and reconcile after conflicts. Homosexual behavior that fosters alliances has also been observed in monkeys, baboons, and gorillas.
If sexual intimacy can enhance relationships, why should it only exist between opposite sexes?
The pleasurable sensations associated with sex are designed to motivate reproductive behavior, ensuring the continuation of our genes. However, individuals often find attraction toward those with whom they cannot reproduce. Most would argue that couples engage in sexual activity to strengthen their bond, which is vital for sustaining relationships through challenges. If sexual interactions help people connect, it begs the question: why limit this to opposite-sex encounters?
To examine the relationship between affiliation and homosexuality, we initially focused on progesterone, a hormone found in both genders. Research indicates that progesterone is linked to social bonding but does not correlate positively with sexual desire. Notably, levels of this hormone increase in response to social rejection and when individuals are given opportunities to connect with new acquaintances. In one study, women paired for a social task showed elevated progesterone levels, which predicted their willingness to sacrifice for their partners a week later.
In our lab, we collected saliva samples from women and posed questions aimed at gauging their interest in sexual interactions with other women, such as “Kissing a woman is sexually arousing to me” and “Women’s bodies are erotic.” Our findings revealed that women with elevated progesterone levels were more inclined to express a desire for erotic contact with other women.
If our evolutionary path has shaped a motivation for sexual interactions for both reproductive and social purposes, it stands to reason that trade-offs may exist between these motivations. For example, in many mammals, females consume fewer calories during ovulation while covering greater distances—an evolutionary strategy minimizing competition between the urge to eat and the urge to find mates.
Our research suggested a similar dynamic: while we didn’t establish a significant effect, there was a trend indicating that women might be less inclined to engage in homosexual behavior during ovulation.
Following this, we sought to determine whether progesterone and the drive for social bonding influenced men similarly. We invited men to the lab, collected saliva samples, and randomly assigned them to one of three conditions: affiliative, opposite-sex sexual, and neutral. Participants engaged in word puzzles designed to prime their thoughts; for instance, the sexual condition included filling in BR_ _ _ TS (Breasts), while the affiliative condition used FRI _ _ NDS (Friends).
The results were telling: men in the affiliative condition demonstrated increased homoerotic motivation, particularly when coupled with higher progesterone levels. Conversely, sexual primes did not enhance homoerotic motivation, possibly because they indicated the potential for reproductive success, thereby making same-sex interactions less advantageous at that moment.
What does this mean for individuals who identify as exclusively homosexual? The research raises questions about the existence of a “gay gene.” Some studies suggest that female relatives of gay men exhibit higher fertility rates, indicating that homosexuality might be an incidental byproduct of genes promoting female fertility. Our findings imply that if the motivation for same-sex sexual interactions is adaptive and rooted in social bonding, the notion of a singular “gay gene” is unlikely. Adaptive traits are typically governed by multiple genes, leading to variability in expression.
Like any trait that persists within a population, individuals will exist across a spectrum from strictly homosexual to exclusively heterosexual. In cultures where same-sex affection is frowned upon, we may not observe the full range of same-sex social interactions. However, as societal norms evolve, we are likely to witness a broader expression of these behaviors.
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In summary, our research sheds new light on the evolutionary role of homosexual behavior as a means to enhance social connections. The interplay between sexual motivation and social bonding suggests a complex relationship that transcends traditional binaries, with implications for understanding human sexuality in its entirety.