The Maintenance of Cooperation Through Discriminator Norms: A Review of Significant Discussions in Indirect Reciprocity

Abstract

Indirect reciprocity is a powerful mechanism that maintains cooperation in a population where individuals are tempted to be selfish. The use of reputation distinguishes indirect reciprocity from other cooperation models, as it allows cooperation between unrelated individuals meeting for the first time. This reputation is determined through norms: a set of rules that outlines when someone is good or bad. Numerous studies have investigated the evolutionary dynamics of different norms, and whether they sustain cooperation in a population of unconditional cooperators and unconditional defectors. This review identifies the general trend in the discourse of norm study: the identification of a norm, an analysis of why it struggles to maintain cooperation under specific parameters, proposal of new norms that overcome such struggles, and finally the identification of new parameters to be studied. More specifically, major topics such as the scoring dilemma posed by the image scoring model, derivation of the leading eight, the punishment dilemma brought up by the introduction of private assessment, and the stability of lenient norms under private assessment are discussed. This paper also identifies some remaining challenges. Notably, the modeling of polymorphic populations with multiple norms has been difficult, yet necessary to better represent interactions between those of different backgrounds in human society. In addition, the discussion of different degrees of goodness remains sparse, and variation in donation options remains uninvestigated. Such parameters should be included in modeling to depict reputation assignment and cooperation decisions of more cognitive populations that are more sophisticated in moral evaluation.