Altruism among relatives and non-relatives

The amount of their own monetary reward that undergraduate participants claimed they were willing to forgo, in order to give $75 to another person, decreased hyperbolically as social distance increased between the participant and the other person. Relatives tended to be ranked at closer social distances than were non-relatives. However, even at the same social distance, participants were willing to forgo significantly more money for the benefit of relatives than for the benefit of non-relatives. These results imply that altruism is determined by factors in addition to social distance