How do third parties help maintain cooperation? In a new Nature Human Behaviour paper, Manvir Singh et Zachary Garfield answer this question by studying responses to >400 transgressions (e.g., theft, adultery) among Mentawai horticulturalists in Indonesia.

They find no evidence of third-party punishment among the Mentawai. Most offenses were followed by a payment of resources from the offender's clan to the victim's clan. If an offender refused to pay and was punished, the punishment was always imposed by the victim.

At the same time, they find that third parties are frequently called to mediate, especially for conflicts occurring between clans. Approximately 75% of non-governmental mediators called were third parties, with people preferentially summoning shamans and elders.

This study helps clarify how justice works in small-scale societies. For the Mentawai, social order is decentralized. It emerges less through community enforcement and more as victims and offenders negotiate over how to restore cooperative relationships after transgressions.

You can learn more about the study in their "Behind the Paper" blog post here: https://socialsciences.nature.com/posts/how-justice-works-in-a-small-scale-society