We define social reciprocity as the act of demonstrating one's disapproval, at some personal cost, for the violation of widely-held norms (e.g., don't free ride). Social reciprocity differs from standard notions of reciprocity because social reciprocators intervene whenever a norm is violated...

The article suggests a new explanation for cooperation in large, unstructured societies that avoids the restrictions required in most previous attempts. Our explanation deals with the role of internalized norms. Even internalized norms, i.e. norms that alter the perceived utility from acting in...