A series of two studies published in Evolutionary Psychology examined how the characteristics of the current romantic partner and those of an opposite-sex friend predict sexual interest in the opposite-sex boyfriend for both men and women. The findings largely supported the mating activation hypothesis.
Friends of the opposite sex can be a way to seek close and long-term intimate romantic relationships. This possibility suggests that it may be an evolutionary adaptive strategy to initiate and maintain opposite-sex friendships (i.e., potential reproductive success).
Study authors Aleksandra Szymkow and Natalia Frankowska write, “If natural selection has formed psychological mechanisms that motivate individuals to seek friendships, then we should expect a strategic search for specific friends, which should also be different for women and men.” Several studies suggest that forming opposite-sex friendships may be a way to gain short-term sexual access to the opposite sex, protection, long-term partners, and even backup partners.
Men and women can seek out friends of the opposite sex for the general purpose of making friends. However, under certain circumstances, such friendships can be for finding a partner for the short or long term. The backup mate hypothesis posits that cultivating potential replacement partners could have been an effective solution to several adaptive problems (eg, decline in partner’s partner value). In ancestral environments, the lack of a backup partner could have put women at risk in terms of protecting and providing resources for children. So having friends of the opposite sex could have served as ‘partner insurance’.
Prior research has observed parallels between opposite-sex friends’ preferences and partner preferences, with men prioritizing physical attractiveness in friends, and women prioritizing physical protection and economic resources. But these preferences are flexible, indicating their adaptability; for example, “unrestricted sociosexual orientation predicted greater priority of physical prowess in females but not males, while couples predicted that OSF economic resources would be prioritized higher in females and lower in males.” As such, sexual interest in friends of the opposite sex can be an adaptive response to cues such as environmental conditions and personal qualities, and a means of solving adaptive problems.
Study 1 included a total of 146 sex couples of friends who were in committed heterosexual relationships. The variable of interest in this study was sexual attraction to one’s friend of the opposite sex. The participants were asked to visualize that person and gave ratings to cognitive, affective, and behavioral items such as: “I have sexual fantasies about my boyfriend”† “Do you get sexually aroused when you are with your boyfriend”, or “If your boyfriend wanted to have a friends-with-benefits relationship with you, would you agree?” on a scale of 1 (never) to 7 (very often). Predictor variables include participants’ current partner and physical attractiveness, resources, and support from a friend of the opposite sex. The degree of overall satisfaction with the romantic relationship, the length of the romantic relationship, and friendship were also measured.
Study 2 included 161 female heterosexual participants in committed romantic relationships who maintained a friendship with a heterosexual male. As in Study 1, the researchers assessed sexual attraction to a friend of the opposite sex. Predictor variables included the perceived financial resources of the romantic partner and boyfriend, romantic relationship satisfaction, and sociosexual orientation. Sociosexual orientation refers to “participants’ attitudes to, history of, and desire for non-commitment sex.”
These studies sought to provide additional support for the mating activation hypothesis, particularly the moderating role of a current partner’s qualities and the qualities of friends of the opposite sex in shaping sexual interest in friends of the opposite sex. The results revealed support for this hypothesis, such that the physical attractiveness of one’s friend of the opposite sex positively predicted sexual interest in this friend. This effect was greater in men than in women. This effect was stable for men because it was not moderated by any of the current partner’s qualities; for women, however, there was flexibility depending on the characteristics of their current partner. When a woman’s partner was highly attractive, supportive, or very satisfied with her romantic relationship, the physical attractiveness of an opposite-sex friend no longer predicted sexual interest in him.
Finally, the perceived financial means of opposite-sex friends predicted sexual interest toward them for highly sexually unrestricted women and women in romantic relationships with high-income men.
The authors emphasize that different moderators shape the sexual interest of men and women in friends of the opposite sex. They conclude: “Among them are qualities of the current partner, qualities of friends of the opposite sex, as well as individual characteristics of participants. Finally, our study proves the predictive value of an evolutionary psychological approach to understanding friends of the opposite sex.”
The study, “Moderators of Sexual Interest in Opposite-sex Friends,” was written by Aleksandra Szymkow and Natalia Frankowska.