Can men and women be just friends ?

We tested evolution-based hypotheses about (1) sex differences in perceived benefits and costs of opposite-sex friendship and (2) differences in perceived benefits of same-sex friendships and opposite-sex friendships. In the Preliminary Study (N = 400), an act nomination procedure was used to identify the benefits and costs of same-sex friendships and opposite-sex friendships. In Study 1, a total of 231 participants (100 men, 131 women) evaluated the frequency of occurrence of 100 benefits and costs in their closest same-sex friendship or opposite-sex friendship. In Study 2, a total of 229 participants (92 men, 137 women) evaluated how beneficial and how costly each would be if it were to occur in their closest same-sex friendship or opposite-sex friendship. Results supported several key hypotheses. Men perceived sex with their opposite-sex friends as more beneficial than did women. Women reported receiving protection from their opposite-sex friends more often than did men, and they perceived the protection as highly beneficial. Both men and women reported receiving information from opposite-sex friends about how to attract mates, and they perceived this information as beneficial. The discussion focuses on whether these benefits reflect an evolved psychology of opposite-sex friendship, or instead are incidental by-products. Much of human social interaction occurs within the context of enduring relationships, such as kinships, mateships, and friendships. From an evolutionary perspective, kinships and mateships are important because of their direct links with inclusive fitness (Hamilton, 1964): kin carry copies of our genes, and mates are our reproductive partners. Friendships, however, are more puzzling from an evolutionary perspective. Friends do not share copies of our genes,nor do we generally reproduce with our friends. Around the world, however, people form friendships that last for days, years, and even a lifetime. This requires explanation. The authors thank Barry Friedman, Martie Haselton, and Todd Shackelford for their helpful comments on earlier versions of this article. Portions of this article were presented at the annual convention of the Human Behavior and Evolution Society, Tucson, Arizona, June 1997. Address correspondence to April L. Bleske, Department of Psychology, University of Texas, Austin, TX 78712. E-mail: [email protected]. In principle, friendships can provide a bounty of benefits that historically may have been linked directly or indirectly with reproduction. Friends may offer us food and shelter or take care of us when we are ill, thus helping to solve adaptive problems of survival. Friends may introduce us to potential mates, helping to solve an adaptive problem of reproduction. Friends may also inflict costs on us by betraying our confidences to enemies, competing for access to the same resources, and even competing for the same mates. As illustrated by Brutus and Caesar, friends can cost us our lives. One of the complexities of friendship is that some characteristics of friendship are perceived as both beneficial and costly. The friendship literature, for example, is inconsistent on the role of sexuality in oppositesex friendship. More than half of men and some women report sexual attraction to their friends (Kaplan & Keys, 1997), and both sexes experience ambiguity about the sexual boundaries in their opposite-sex friendships (Swain 1992). Monsour, Beard,