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, 132 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.