In my previous articles about cross-sex friendships, I’ve written about their complexity, which makes them a very intriguing and rich topic to study. Evolutionary psychologists, including pioneers such as David Buss, have yet another perspective on this type of friendship. These researchers tend to view cross-sex friendship as an evolved reproductive tactic, or “sexual strategy.”1,2 In a nutshell, evolutionary processes have created differences between men and women with regards to sex—men are motivated to mate with an increased number of women, due to the low cost of sperm and lower parental investment, whereas women are motivated to be choosier about who they mate with, due to higher costs associated with childbirth and inability to reproduce with someone else when pregnant. Thus, men and women may have different motivations for becoming friends with the opposite sex.
A majority of men and women admit feeling somewhat attracted to an opposite-sex friend at some point, but men report such feelings significantly more often than women do.3 Men are also more likely to want female friends for the purpose of casual sex, and are more likely to befriend women they find physically attractive.4 Even if they are in a committed relationship, men admit that feelings of physical attraction and sexual desire are important for initiating cross-sex friendships (physical attractiveness matters less to women in choosing their male friends); men are also more likely to end the friendship if they are rejected or denied sex.5
In contrast, women report wanting male friends more for social and physical protection (a “buffer” from the potentially creepy/dangerous men in the dating pool), although women also report wanting this kind of protection from their female friends as well. Like men, women will end their friendships with men if these needs aren’t satisfied.4,5
Interestingly, women are often blind to the fact that their male friends are looking for sex to be part of the friendship—women underestimate the degree to which their male friends are attracted to them. In contrast, men overestimate the degree to which their female friends are attracted to them. This is part of what creates the confusion and ambiguity in cross-sex friendships. Men and women are often on different wavelengths in terms of their perceived romantic attraction.5,6 It’s also part of the reason why men are so protective and even violent when faced with a rival7 (illustrated on this episode of That 70s Show, when Eric confronts Donna’s male “friend” only to hear him openly admit that he does in fact have romantic feelings for her).
Overall, based on the research it’s fair to say that friendships between men and women are motivated by more than just shared interests and activities—there are definitely some biological and sexual factors at work in cross-sex friendships. But it’s also important to keep in mind that men and women are far more similar than different in their perception of these relationships. The authors of these studies clearly noted: “[Men and women] agreed that kindness, good conversation, and companionship were among the most important reasons for initiating an opposite-sex friendship. They both judged honesty, humor, and dependability as among the most desirable characteristics in an opposite-sex friend.”4
Researchers have also noted that sex is not the sole motivator for men in these situations, or even the strongest motivator: “For example, men rated companionship, self-disclosure, and gaining information about the opposite sex as higher in benefit than sex.”2 So, when the idea gets thrown around that men’s only interest in their female friends is for sex, even evolutionary psychologists would agree that is a very misguided stereotype.
Read more about cross-sex friendships here and here.
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1Buss, D.M. (2006). Strategies of human mating. Psychological Topics, 15, 239-260.
2Buss, D. M., & Schmitt, D. P. (1993). Sexual Strategies Theory: An evolutionary perspective on human mating. Psychological Review, 100, 204-232.
3Kaplan, D. L., & Keys, C. B. (1997). Sex and relationship variables as predictors of sexual attraction in cross-sex platonic friendships between young heterosexual adults. Journal of Social and Personal Relationships, 14, 191-206.
4Bleske, A. L., & Buss, D. M. (2000). Can men and women be just friends? Personal Relationships, 7(2), 131-151.
5Bleske-Rechek, A. L., & Buss, D. M. (2001). Opposite-sex friendship: Sex differences and similarities in initiation, selection, and dissolution. Personality and Social Psychology Bulletin, 27(10), 1310-1323.
6Koenig, B. L., Kirkpatrick, L. A., & Ketelaar, T. (2007). Misperception of sexual and romantic interests in opposite-sex friendships: Four hypotheses. Personal Relationships, 14(3), 411-429.
7Buss, D. M. (1988). From vigilance to violence: Tactics of mate retention in American undergraduates. Ethology & Sociobiology, 9(5), 291-317.
Dr. Dylan Selterman – Science of Relationships articles | Website/CV
Dr. Selterman’s research focuses on secure vs. insecure personality in relationships. He studies how people dream about their partners (and alternatives), and how dreams influence behavior. In addition, Dr. Selterman studies secure base support in couples, jealousy, morality, and autobiographical memory. 
