New Working Paper
Humans reciprocate intentional harm by discriminating against group peers
By David Hugh-Jones, Itay Ron and Ro'i Zultan
Abstract:Cycles of intergroup revenge appear in large scale conflicts. We experimentally test the hypothesis that humans practice group-based reciprocity: if someone harms or helps them, they harm or help other members of that person’s group. Subjects played a trust game, then
allocated money between other people. Senders whose partners returned more in the trust game gave more to that partner’s group members. The effect was about half as large as the effect of direct reciprocity. Receivers’ allocations to group members were not affected by their partners’ play in the trust game, suggesting that group reciprocity was only triggered when the partner’s intentions were unequivocal.