Norm Enforcement: The Role of Third Parties

To be effective, norm enforcement often requires the participation of unaffected third parties. The logic of third-party intervention has, however, proven elusive because the costs always seem to outweigh the benefits. Using an evolutionary game theoretic approach, we posit that the intervention of unaffected bystanders is a triggered normative response and show that generalized punishment norms survive in one of the two stable equilibria subject to selection drift.