Is friendship akin to kinship?

Abstract

Although unrelated friends are genetically equivalent to strangers, several lines of reasoning suggest that close friendship may sometimes activate processes more relevant to kinship and that this may be especially true for women. We compared responses to strangers, friends, and kin in two studies designed to address distinct domains for which kinship is known to have functional significance: incest avoidance and nepotism. Study 1 examined emotional responses to imagined sexual contact with kin, friends, and strangers. Results revealed that women, compared to men, treated friends more like kin. Study 2 examined benevolent attributions to actual kin, friends, and strangers. Results revealed that women treated friends very much like kin, whereas men treated friends very much like strangers. The current findings support a domain-specific over a domain-general approach to understanding intimate relationships and raise a number of interesting questions about the modular structure of cognitive and affective processes involved in these relationships.

Fig. 1

Mean attributions of responsibility (and standard errors) for successful dyadic performance in Study 2. The dotted line represents an equal attribution of credit within a dyad. Ratings greater than 5 indicate relatively benevolent attributions, while ratings less than 5 indicate relatively self-serving attributions.

Fig. 2

A model of close relationships involving discrete mechanisms. This model conceptualizes close others as processed by distinct relationship modules, which, in turn, regulate distinct sets of programs related to altruistic behavior and sexual attraction for kin, friends, or mates. Positive associations are indicated by solid paths and negative associations by dotted paths, with the thickness of path lines indicating relative strength of association.

Fig. 3

A model of close relationships involving shared mechanisms. This model conceptualizes women’s interactions with friends as activating other close relationship modules (kinship most strongly), which, in turn, regulate general programs related to altruistic behavior and sexual attraction. For men, the process is similar, though interactions with friends are not presumed to activate a kin module. Positive associations are again indicated by solid paths and negative associations by dotted paths, with the thickness of path lines indicating relative strength of association.