Humans reciprocate by discriminating against group peers

David Hugh-Jones, Itay Ron, Ro'i Zultan

Research output: Contribution to journalArticlepeer-review


Motivated by cycles of intergroup revenge in real-world 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 by strong norm violations. We discuss the role of group reciprocity in conflict among early humans.

Original languageAmerican English
Pages (from-to)90-95
Number of pages6
JournalEvolution and Human Behavior
Issue number1
StatePublished - 1 Jan 2019


  • Group identity
  • Intergroup conflict
  • Upstream reciprocity

All Science Journal Classification (ASJC) codes

  • Ecology, Evolution, Behavior and Systematics
  • Experimental and Cognitive Psychology
  • Arts and Humanities (miscellaneous)


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