偏见从何而来——身份意识、异质群体与合作的演化

社会身份和偏见在合作的演化中扮演了重要的角色。文章提出了一种基于标签机制的空间囚徒困境博弈，以探讨身份、偏见和合作的关系问题。通过引入基于身份相似性的选择性交互，我们发现，假如个体拥有适度的偏见，高水平的合作就能够得到支持。无论是过低还是过高的偏见程度都不利于合作的演化，这意味着适度的偏见能为社会中的个体带来利益。由我们的分析可知，高水平的合作来源于群体异质性和群体之间的明确边界。借由群体异质性和群体边界，种群可以在背叛者侵入某个群体时将之淘汰，防止其进一步腐蚀整个种群。通过引入异质的偏见属性，我们还发现，适度水平的偏见可以在演化过程中得到自然选择的青睐。因此，文章既可以回答偏见的社会功能问题，又可以解释偏见从何而来的问题，为我们理解合作演化和人类的身份现象提供新的见解。

The Origin of Prejudice:Identity Consciousness,Group Heterogeneity and the Evolution of Cooperation

Social identity and prejudice are important in the evolution of cooperation. This study introduces a spacial prison's dilemma based on tag mechanism to investigate the relationships among identity, prejudice and cooperation. By applying selective interaction based on identity similarity, we find that high level of cooperation is possible if individuals have moderate level of prejudice. Neither lower nor higher level of prejudice is beneficial to the evolution of cooperation, which means that moderate level of prejudice is beneficial to individuals in the society. Our analyses indicate that high level of cooperation derives from group heterogeneity and the clear boundaries between groups, with which the population can eliminate the groups invaded by defectors to prevent further invasion. In addition, moderate level of prejudice is favored by natural selection in the evolution with heterogeneous prejudice. Therefore, this study can explain not only the social function of prejudice but also the origin of it, providing new sights for understanding the evolution of cooperation as well as the mechanism of human identity.