Uninvadable social behaviors and preferences in group-structured populations

Humans evolved in populations structured in groups that extended beyond the nuclear family. Individuals interacted with each other within these groups and there was limited migration and sometimes conflicts between these groups. Suppose that during this evolution, individuals transmitted their behaviors or preferences to their (genetic or cultural) offspring, and that material outcomes resulting from the interaction determined which parents were more successful than others in producing (genetic or cultural) offspring. Should one then expect pure material self-interest to prevail? Some degree of altruism, spite, inequity aversion or morality? By building on models in population biology we analyze the role that different aspects of population structure– such as group size, migration rates, probability of group conflicts, cultural loyalty towards parents– play in shaping behaviors and preferences which, once established, cannot be displaced by any other preference. In particular, we show that uninvadable preferences under limited migration between groups will consist of a materially self-interested, a moral, and an other-regarding component, and we show how the strength of each component depends on population structure.