People often explain friendship in terms of present-day benefits, such as emotional support, shared interests or practical help. New research suggests that our choices may also be shaped by much older pressures linked to survival and cooperation in ancestral environments.
A study published in Evolution & Human Behavior suggests that preferences for same-sex friends are partly grounded in evolved mechanisms for choosing reliable cooperative partners. In early human groups, selecting the right allies could influence access to resources, protection and reproductive success.
Evolved signals of a good ally
The research team, led by Adar B. Eisenbruch, proposed that people continue to value traits that once signaled a strong cooperative partner. These include prosocial behavior, social status, physical attractiveness, dominance, nurturance and signs of survival-related skills or productivity.
From this perspective, such traits are not simply useful in modern life. Historically, they may have indicated who could share food, provide help during conflicts, care for children and offer social support, potentially embedding them in human psychology as markers of valuable friends.
Inside the first friendship experiment
In the first study, 156 U.S. university students were paired with unfamiliar same-sex partners for a structured 30-minute conversation. Afterward, each participant privately rated how desirable their partner seemed as a potential friend.
Participants evaluated their partners on dimensions including ancestral productivity, prosociality, dominance, social status, attractiveness to the other sex, nurturance and academic success. Researchers also measured physical strength using bicep circumference, grip strength and chest strength.
As a behavioral measure of interest, participants could choose whether to share their email address with their conversation partner. Contact information was exchanged only when both people agreed, providing a real-world indicator of willingness to pursue a new friendship.
The results showed that participants were more interested in becoming friends with people perceived as more ancestrally productive, prosocial, dominant, higher in status, attractive and nurturing. When all factors were considered together, attractiveness, prosociality and dominance emerged as the strongest unique predictors of friend desirability.
Men were more likely than women to offer their contact information despite not rating their partners as more desirable overall. This suggests possible sex differences in how people act on friendship interest, although the sample size limited firm conclusions.
Do current goals fully explain it?
The second study involved 444 U.S. adults recruited online. Participants first identified their most important current goal, such as advancing their career, improving their health or strengthening family relationships.
They then viewed photographs of unfamiliar same-sex faces and rated how much they would like to become friends with each person. Afterward, they evaluated which characteristics in a new friend would help or hinder their ability to achieve their chosen goal.
A separate group of raters assessed the same faces on characteristics including Big Five personality traits, attractiveness, intelligence, trustworthiness, aggressiveness, competence and ancestral productivity. This allowed researchers to compare friend desirability with perceived usefulness for participants’ current goals.
The analysis showed that friendship preferences could not be fully explained by present-day goals. Attractiveness and ancestral productivity were stronger predictors of friend desirability than their reported relevance to participants’ specific goals would suggest.
This pattern supports the idea that some friendship preferences may reflect underlying evolved biases rather than only conscious calculations about who can help with immediate priorities. Participants appeared drawn to traits that historically could have signaled valuable cooperative partners even when those characteristics did not clearly support their current goals.
Limits of the findings and wider context
The authors acknowledge that the first study’s relatively modest sample limited their ability to examine sex differences in detail. The second study, which relied on judgments of photographs, also cannot capture the full complexity of how friendships develop in real-life situations.
They also note that friendship preferences may be influenced by multiple current goals, including some that are less conscious or difficult to articulate. Cultural norms, personal history and social environments can further shape how particular characteristics are perceived and valued.
Still, the combined findings suggest that friendship choices may emerge from both immediate practical concerns and longer-term evolutionary pressures. People appear to favor individuals who seem kind, capable, socially well-positioned and attractive — traits that may once have provided concrete survival advantages.
The research contributes to a growing body of evolutionary psychology examining how ancestral challenges may continue to influence modern social life. By exploring why people are drawn to particular friends, it highlights the deep roots of human cooperation and the subtle cues that can guide our closest social bonds.
