Co-evolution of cooperation and favoritism

 

FENG FU

HARVARD UNIVERSITY

 

Green beard, or similarity-based cooperation, has been suggested as a simple yet effective cooperation-promoter in recent years. Most previous studies are based on the predisposition of individual cooperation with like-minded ones and defection otherwise. This sort of contingent cooperation can be termed as in-group favoritism if group memberships depend on an individual’s “beard color” or phenotype in general. It is of significant interest to study how in-group favoritism arises in the first place. In this talk, I will first present a minimal model of in-group favoritism in homogeneous populations. The population is divided in groups according to each individual’s randomly assigned tag. Each individual has the same level of in/out group helping tendency. Individuals’ tags and behavioral strategies both are heritable traits that are subject to mutation and selection. Using coalescent theory, I will derive an analytical condition for cooperation to evolve under weak selection. I will show that the critical benefit-to-cost ratio reaches minimum when individuals only help in-group members and restrain from helping out-group members. Further, I will present the case where the tendency of in/out group severing behaviors coevolves with cooperation dynamics. In other words, there is no priori heuristic clue of cooperating with similar ones. I will show that under natural selection pressure, the whole population evolves towards the “biased” world, where each individual, if being a cooperator, shows strong discriminatin against out-group members. Cooperators have much higher tendency to help in-group members than out-group ones.