Social Identity,Heterogeneous Groups,and The Evolution Of Cooperation

Cooperation is a ubiquitous phenomenon in economical and social life. The under-standing of cooperation has become a significant issue in current social science. The s-tudies from behavioral experiments have discovered the salience of in-group favoritism in human cooperation, showing that individual preferences are significantly subject to group and social identity. The relationship between social identity and human behavior makes the development of identity economics (or economics of identity)urgent and en-courage the scholars to create novel theories which have more explanatory power. On the basis of these theories, behavioral and neural experiments not only have discovered the context-dependency of in-group favoritism, but also have found its innate nature. How to understand these findings under a unified framework is a key question in further researches. Evolutionary theories can provide a unified perspective which allows us to conquer the paradoxes in the previous researches. The most important insight from evolutionary theories is that they can help us to understand the functional and fitness values of social identity, which are constantly emphasized in previous studies. Tag-mediated cooperation is a special evolutionary theory which states that cooperation can emerge by the individual tags and their conditional behaviors. In tag-based models, the function of identity and groups can be explained, but in the previous models, the researchers have not emphasized the meaning of their results in the explanation of iden-tity phenomenon. This is because the purpose of these models is mainly to explain the emergence of cooperation but not social identity, thus they are not necessarily suitable to discuss identity itself. On the basis of this context, this thesis tries to explore social identity problems using tag-based models.This thesis, which is inspired by the problem of identity-dependency in human cooperation, uses evolutionary theories and computational methods to study the two basic problems in identity economics:why individuals can have identities and divide themselves into groups, and how different individuals form a group which shares the same identity.We explore three main problems:the function and origin of the consciousness of identity and prejudice, the problem of identity uncertainty, and the evolutionary prob- lem of identity perception. We find that if individuals have moderate prejudice, high levels of cooperation can emerge, indicating the social function of the consciousness of identity and prejudice. However, the social function does not directly imply that prejudice can be favored by natural selection, by considering heterogeneous prejudices which is subject to selection and mutation, our results show that moderate prejudice can actually be favored by natural selection in the process of evolution. This observation can explain the origin of the consciousness of identity and prejudice. In the discus-sion of identity uncertainty, we find that identity uncertainty can play a crucial role not only in the evolution of cooperation but also in the emergence of group polarization. Identity uncertainty can affect the cooperation levels, and the evolution of cooperation also allows the individuals to enhance their identities through social interactions. The results demonstrate that self-uncertainty reduction may be the basic motivation of so-cial identification. Lastly, in the investigation of the evolutionary problem of identity perception, we realize that even if the individuals incur costs by the tag perception, partial perception still emerges and serves as a means of promoting cooperation. This observation can deepen our understanding of the cognitive foundation of social identity. Through the exploration of these problems, we can improve our understanding of the meaning of social identity in real economic life.