The fact that men and women experience sexual attraction toward their opposite-sex friends has been evidenced in various studies. It has also been shown that there is a close parallel between preferences for opposite-sex friends and mate preferences, i.e., that men prioritize physical attractiveness of their OSFs, while women prioritize their male friends' ability to provide protection and economic resources. Although this mating activation hypothesis has been validated to an extent, there is hardly any research that points to moderating factors which would define the boundary conditions for these effects. We present two studies that involved heterosexual participants who were in a committed relationship and at the same time had a heterosexual opposite-sex friend. We investigated how both the qualities of one's current partner and the qualities of one's opposite-sex friend shape sexual interest in opposite-sex friends for men and women. Results mostly support the mating activation hypothesis. We show that within actual cross-sex friendships: 1) physical attractiveness of opposite-sex friends predicts sexual interest toward them, and this effect is stronger for men than women, 2) current partner's attractiveness, provided support, and relationship satisfaction moderate this effect only for women, and not men, 3) perceived financial resources of opposite-sex friends predict sexual interest toward them for highly sexually unrestricted women, and, surprisingly, for those who are in committed relationships with high-income men. The results reaffirm previous evidence indicating that perceptions of opposite-sex friends can be viewed as a manifestation of evolved human mating strategies.
Keywords: back-up mates; evolutionary psychology; mate-switching; opposite-sex friends; sexual interest.