Abstract
Political polarization continues to divide people across the world, threatening the safety of individuals and of democracy. We propose a theoretical account of the emergence and maintenance of political polarization as a social identity phenomenon, driven by moral values as an ingroup norm representation. Norms play a crucial role in intergroup processes as a representation, both supporting signaling and inference of ingroup membership, and approximating a shared concept of the group that needs to be inferred and updated itself. Yet, little work on political polarization has addressed the role of norms, despite a large literature on its social identity mechanisms. Here, we argue that moral values are highly suitable as an ingroup norm representation and implement this as a formalized computational account of echo chamber formation. In this model, we also account for the cyclical interaction between these social identity pressures on moral values and moral cognitive processes such as moral disengagement and moral drift. When simulating this model under different conditions (Study 1 and 2), we find systematic differences in how liberals and conservatives form groups, corresponding to empirical investigations of interactions with people and news online. We discuss how the resulting polarization emerges as an interaction between the structure of liberal and conservative moral values, observed in empirical data, and their role as an ingroup norm representation. Finally, we consider how this moral mechanism of political polarization influences how we study political polarization, and we posit that liberals and conservatives may have different pathways to political polarization.