Moderate tolerance promotes tag-mediated cooperation in spatial Prisoner’s dilemma game

Humans often behave discriminatorily towards others depending on their group membership. In this work, we establish a spatial Prisoner’s dilemma model to investigate the relation between tag-mediated discrimination and cooperation. By introducing tag-mediated selective interaction, we find that if tag length is sufficiently large and individuals have moderate tolerance, cooperation can be promoted. Interestingly, both too high or too low tolerance may inhibit the emergence and maintenance of cooperation, which means that individuals may benefit from moderate tolerance in society. It is also shown that the high levels of cooperation stem from the high heterogeneity and clear boundaries between clusters. Our work should be helpful to understand both the evolution of human cooperation and the science of social identity.