People often ignore material costs they incur when following existing social norms. Some individuals and groups are often willing to pay extremely high costs to enact, defend, or promulgate specific values and norms that they consider important. Such behaviors, often decreasing biological fitness, represent an evolutionary puzzle. We study theoretically the evolutionary origins of human capacity to internalize and follow social norms. We focus on two general types of collective actions our ancestors were regularly involved in: cooperation to overcome nature’s challenges and conflicts with neighboring groups. We show that norm internalization evolves under a wide range of conditions, making cooperation “instinctive.” We make testable predictions about individual and group behavior.
Human behavior is strongly affected by culturally transmitted norms and values. Certain norms are internalized (i.e., acting according to a norm becomes an end in itself rather than merely a tool in achieving certain goals or avoiding social sanctions). Humans’ capacity to internalize norms likely evolved in our ancestors to simplify solving certain challenges—including social ones. Here we study theoretically the evolutionary origins of the capacity to internalize norms. In our models, individuals can choose to participate in collective actions as well as punish free riders. In making their decisions, individuals attempt to maximize a utility function in which normative values are initially irrelevant but play an increasingly important role if the ability to internalize norms emerges. Using agent-based simulations, we show that norm internalization evolves under a wide range of conditions so that cooperation becomes “instinctive.” Norm internalization evolves much more easily and has much larger effects on behavior if groups promote peer punishment of free riders. Promoting only participation in collective actions is not effective. Typically, intermediate levels of norm internalization are most frequent but there are also cases with relatively small frequencies of “oversocialized” individuals willing to make extreme sacrifices for their groups no matter material costs, as well as “undersocialized” individuals completely immune to social norms. Evolving the ability to internalize norms was likely a crucial step on the path to large-scale human cooperation.