People may choose same-sex friends based in part on characteristics that would have made someone a valuable collaborative partner in their ancestral environment, according to a study published in . evolution and human behavior.
Friendship is often described through current usefulness. According to this view, people are attracted to potential friends who can help them pursue their current goals, such as by offering kindness, intelligence, support, common interests, or practical benefits. However, this explanation leaves open the question of whether people’s friend preferences are shaped solely by what is currently useful, or whether some preferences reflect older social pressures from the environment, where the selection of appropriate cooperation partners was important for survival and reproduction.
Adar B. Reisenbruch and colleagues investigated the possibility that same-sex friendship preferences partly reflect an evolved selection of cooperative partners. Human ancestors relied on long-term cooperation for tasks such as foraging, child rearing, social support, and conflict management, which may have led people to value friends who seemed able and willing to generate and share benefits. From this perspective, traits such as prosociality, social status, physical attractiveness, and traits perceived as survival-related skills may be attractive not only because they serve people’s current goals, but also because they have historically shown them to be valuable cooperative partners.
In Study 1, researchers recruited 156 students from a public university in the United States for a laboratory-based exchange study. Participants were paired with an unfamiliar same-sex partner and completed a 30-minute structured face-to-face conversation. They then personally rated how desirable their partner was as a potential friend and rated their partner on characteristics considered important for friendship, including ancestral productivity, prosociality, dominance, social status, attractiveness to the opposite sex, upbringing, and academic success.
The researchers also measured participants’ physical fitness individually using bicep circumference, grip strength, and chest strength. As a behavioral indicator of friendship interest, participants could choose whether to share their email address with their partner, but contact information was only exchanged if both members of the pair agreed.
In Study 2, 444 US participants recruited through Amazon Mechanical Turk first described their most important current goals. They then rated photos of unfamiliar same-sex faces based on how much they wanted to be friends with each person. They then judged the extent to which their new friend’s various characteristics were helpful or detrimental to achieving their stated goals.
A separate group of raters rated the same faces on traits such as the Big Five personality traits, attractiveness, intelligence, trustworthiness, aggression, competence, and ancestry productivity. This allowed the researchers to compare whether the traits that make a person look desirable as a friend are simply the same traits that participants think are helpful to their current goals.
In Study 1, participants were more interested in friendships with partners who appeared to be higher in ancestral productivity, prosociality, dominance, social status, attractiveness, and nurturance. When researchers considered these traits together, attractiveness, prosociality, and dominance emerged as the strongest unique predictors of friendliness. Men were also more likely than women to provide contact information, even though they rated their partners as less desirable.
Study 2 showed that friend preferences were not fully explained by current goal pursuit. Specifically, attractiveness and ancestry productivity predicted friend liking more strongly than expected based on the extent to which those traits were related to participants’ goals. This suggests that people’s preferences for same-sex friends may be shaped not only by their current usefulness but also by their preferences for characteristics that historically indicate them to be valuable cooperative partners.
The authors note that Study 1 was limited by sample size, especially when testing gender differences, and Study 2 cannot completely rule out the possibility that friend preferences are shaped by multiple or less consciously accessible current goals.
Taken together, these findings suggest that friendship choices may be shaped not only by people who are currently useful to us, but also by evolved preferences for people who appear like valuable and supportive partners.
The study, “What do people want in friends? Ancestral supportive partner values predict preferences for same-sex friends,” was authored by Adahl B. Eisenbrook, Rachel L. Grillot, and James R. Loney.
