Punishing the individual or the group for norm violation.

It has recently been proposed that a key motivation for joining groups is the protection from consequences of negative behaviours, such as norm violations. Here we empirically test this claim by investigating whether cooperative decisions and the punishment of associated fairness-based norm violations are different in individuals vs. collectives in economic games. In the ultimatum game, participants made or received offers that they could reject at a cost to their outcome, a form of social punishment. In the dictator game with third-party punishment, participants made offers to a receiver while being observed by a punisher, or could themselves punish unfair offers. Participants made lower offers when making their decision as part of a group as compared to alone. This difference correlated with participants' overall mean offers: those who were generally less generous were even less so in a group, suggesting that the collective structure was compatible with their intention. Participants were slower when punishing vs not punishing an unfair offer. Importantly here, they were slower when deciding whether to punish or not to punish groups as compared to individuals, only when the offer concerned them directly in second party punishment. Participants thus take more time to punish others, and to make their mind on whether to punish or not when facing a group of proposers. Together, these results show that people behave differently in a group, both in their willingness to share with others and in their punishment of norm violations. This could be explained by the fact that being in a collective structure allows to share responsibility with others, thereby protecting from negative consequences of norm violations.