Opposite-sex friendships (OSF’s) may be defined as a “voluntary, cooperative, non-romantic alliance between members of the opposite sex” (Bleske-Rechek et al. 2012, p.570). Although they are relatively common in humans (Monsour 2002) and in non-human primates (e.g., baboons; Goffe et al. 2016), the motives for pursuing OSFs have not been extensively researched. Interestingly, one study found that the characteristics that people prefer in the OSFs are more similar to those that they seek for in non-platonic relationships than in same-sex friendships (Sprecher and Regan 2002). According to evolutionary perspective, a close bond with an opposite-sex individual could benefit men by providing them sexual access to a female friend (Bleske-Rechek and Buss 2001). On the other hand, women may expect the benefit of physical protection from violence (the “Bodyguard hypothesis”; Bleske-Rechek and Buss 2001; Wilson and Mesnick 1997) or from other environmental threats (the “Environmental security hypothesis”; Reeve et al. 2019). In this study, our aim is to investigate the Bodyguard hypothesis in relation to women’s choice for opposite-sex friend characteristics that could be beneficial in providing protection.

According to the Bodyguard hypothesis, women may have an evolved preference for mates and male friends who are able to protect them from aggression from other men (Bleske-Rechek and Buss 2001; Buss and Schmitt 1993; Wilson and Mesnick 1997). Thus, women, more than men, should prefer OSFs that have characteristics indicative of better ability to offer protection (i.e., physical strength, aggressive and dominant personality traits; Bleske-Rechek and Buss 2001). However, associating with formidable men has apparent costs too, as women and their offspring are vulnerable to aggression from the “protector” (see, for example, Borras-Guevara et al. 2017). We would expect, then, that women’s preference for aggressive-formidable male friends depends on the level of external risk in the environment of the woman. In theory, women who live in dangerous areas should have a stronger preference for physical strength in opposite-sex friends (Bleske-Rechek and Buss 2001), because the benefits of the protection may outweigh the costs of aggression. However, the current literature has focussed on investigating women’s preference for romantic partners rather than non-romantic, platonic friends.

Previous research suggests that especially in dangerous neighbourhoods (Snyder et al. 2011), and under other environmental threats (Reeve et al. 2016), women prefer physically strong and/or dominant males as romantic partners. Interestingly, when investigating preference for formidable romantic partners, research has found that subjective fear of crime is a stronger predictor than the objective risk of crime (Snyder et al. 2011; Ryder et al. 2016). Fear of crime, in turn, is influenced by exposure to violent crime in childhood (Snyder et al. 2011), as well as crime in the current neighbourhood environment (Zhao et al. 2015). If platonic male friends are chosen because they provide protection, women who have elevated subjective fear of crime should prefer more aggressive and formidable men as their non-romantic friends.

In the present studies, we aim to add to the scarce literature on environmental influences on friendship selection by partially replicating the method used by Snyder et al. (2011), who studied the Bodyguard hypothesis in romantic partner preference. Based on previous literature on mate choice, we expect that both childhood and current neighbourhood objective crime rate relates not only to women’s preference for male friends who are aggressive and formidable, but also to higher manifestation of these traits in their actual male friends. Similarly, we expect that subjective fear of crime is positively associated with women’s choice of aggressive-formidable male friends, perhaps even more so than objective crime (see Snyder et al. 2011; Ryder et al. 2016 for similar findings in romantic partner preferences). In addition, we expect that fear of crime is unrelated to friend characteristics that are irrelevant in providing physical protection. Finally, we predict that any correlations between fear of crime and aggressive-formidability in actual and ideal friends will be stronger for women than for men, and within women, stronger for opposite, rather than same-sex friends.