Mere Membership

Human social groups are central to social organization and pervasively impact interpersonal interactions. Although immensely varied, all social groups can be considered specific instantiations of a common and abstract ingroup-outgroup structure. How much of the power of human social groups stems from learned variation versus abstract commonality? I review evidence demonstrating that from early in development a wide range of intergroup phenomena, most prominently many ingroup biases, follow solely from simple membership in an abstract social collective. Such effects cannot be attributed to rich social learning, and thus (i) constrain theories seeking to explain or intervene on ingroup bias, and (ii) provide reason to think that our species is powerfully predisposed towards ingroup favoritism from early in development.