Internalizing cooperative norms in group-structured populations

Social norms play a crucial role in human behavior, especially in maintaining cooperation within human social groups. Social norms might be self-enforcing or be enforced by the threat of punishment. In many cases, however, social norms are internalized and individuals have intrinsic motivations to observe norms. Here, we present a model for how intrinsic preferences to adhere to cooperative norms can evolve with and without external enforcement of compliance. Using the methodology of preference evolution, we model how cooperative norms coevolve with the intrinsic motivations to follow them. We model intrinsic motivations as being provided by guilt, a kind of internal “punishment” that individuals feel for falling short of cooperative norms, and show that the shape of this internal punishment function plays a crucial role in determining whether and how much internalization can evolve. We find that internal punishment functions that eventually level off with the deviation from the norm can support internalization without external punishment. In contrast, internal punishment functions that keep escalating with the deviation from the norm require external punishment, but yield stronger norms and more cooperation when external punishment is present. By showing how different preference mechanisms can enhance or limit norms that stabilize cooperation, these results provide insights into how our species might have evolved the norm psychology that helps us maintain such complex social and cultural institutions.