Thus, our results show that the notion of strong reciprocity extends to the sanctioning behavior of ''unaffected'' third parties. In addition, these experiments suggest that thirdparty punishment games are powerful tools for studying the characteristics and the content of social norms.

QUESTION: What psychological mechanisms drive third-party punishment absent personal stakes? Is it empathy, moral outrage, or evolved group-selection pressure?

Ernst Fehr, Third-Party Punishment and …, loc. 2