Emergence of Communities and Diversity in Social Networks

Communities are common in complex networks and play a significant role in the functioning of social, biological, economic, and technological systems. Despite much interest in detecting community structures in complex networks and exploring the effect of communities on collective dynamics, a deep understanding of the emergence and prevalence of communities in social networks is still lacking. Addressing this fundamental problem is of paramount importance in understanding, predicting, and controlling a variety of collective behaviors in society. An elusive question is how communities with common internal properties could arise in social networks with great individual diversity. Here, we answer this question in virtue of the experiment of the ultimatum game that has been a paradigm to characterize altruism and fairness. We find that stable local communities with different internal agreements emerge spontaneously and induce social diversity into networks, which is in sharp contrast to the scenario of populations with random interactions. The diverse communities and social norms stem from the interaction between responders with inherent heterogeneous demands and rational proposers via local connections, where the former eventually becomes the leaders of communities. This indicates that networks are significant for the emergence and stabilization of communities and social diversity. Our experimental results also provide valuable information about individual strategies for the development of network models and theories of evolutionary games and social dynamics.