Emotional closeness as a mediator of the effect of genetic relatedness on altruism.

Inclusive fitness theory has been used to explain the overall pattern of altruistic behavior. However, this theory does not address the proximal causes of altruism. The purpose of the present study was to increase the understanding of altruism by testing a model that includes both ultimate and proximate causes. In particular, emotional closeness was tested as a mediator of the effect of genetic relatedness on altruistic behavior. This was accomplished by having college students choose which of their family members they would most likely provide with life-saving assistance. As expected, results showed that emotional closeness is an important proximal cause of altruism that partially mediates the effect of genetic relatedness on willingness to act altruistically.