Abstract
The theory of inclusive fitness has transformed our understanding of cooperation and altruism. However, the proximate psychological underpinnings of altruism are less well understood, and it has been argued that emotional closeness mediates the relationship between genetic relatedness and altruism. In this study, we use a real-life costly behaviour (travel time) to dissociate the effects of genetic relatedness from emotional closeness. Participants travelled further to see more closely related kin, as compared to more distantly related kin. For distantly related kin, the level of emotional closeness mediated this relationship - when emotional closeness was controlled for, there was no effect of genetic relatedness on travel time. However, participants were willing to travel further to visit parents, children and siblings as compared to more distantly related kin, even when emotional closeness was controlled for. This suggests that the mediating effect of emotional closeness on altruism varies with levels of genetic relatedness.
Highlights
Inclusive fitness theory [1] has proved fundamental in explaining patterns of cooperation and altruism across a wide range of species [2,3], including humans [4,5] Hamilton’s rule of kin selection states that a behaviour or trait will be favoured by selection when r*B.C, where C is the fitness cost to the actor, B is the fitness benefit to the recipient and r is the coefficient of genetic relatedness – the probability that two individuals share the same genes by descent [1]
Other findings have led to suggestions that there may be a ‘kinship premium’ [12], in that kinship makes a significant unique contribution to altruism, even after controlling for the effects of emotional closeness
We examine whether emotional closeness mediates the relationship between genetic relatedness and investment in a kin relationship in the same way for kin with different levels of relatedness
Summary
Inclusive fitness theory [1] has proved fundamental in explaining patterns of cooperation and altruism across a wide range of species [2,3], including humans [4,5] Hamilton’s rule of kin selection states that a behaviour or trait will be favoured by selection when r*B.C, where C is the fitness cost to the actor, B is the fitness benefit to the recipient and r is the coefficient of genetic relatedness – the probability that two individuals share the same genes by descent [1]. Since the benefit of an action to the recipient is weighted by the coefficient of genetic relatedness, all other things being equal, more closely related individuals (with a higher r) are predicted to be favoured over less closely related individuals (with a lower r). In line with this theory’s predictions, people offer greater levels of support to more closely related kin members, both in hypothetical (e.g., [6,7,8]) and real-life situations (e.g., [9,10]). Other findings have led to suggestions that there may be a ‘kinship premium’ [12], in that kinship (as a purely linguistic label that correlates with true biological kinship) makes a significant unique contribution to altruism, even after controlling for the effects of emotional closeness (see [19])
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