The Coevolution of Group Size and Leadership: An Agent-­Based Public Goods Model for Prehispanic Pueblo Societies

We embed a public-goods game in a realistic agent-based model of resource availability, acquisition, and settlement location set in the Pueblo societies of southwestern Colorado between AD 600 and 1280. The public-goods game provides a framework for a voluntaristic process in which members of a society can choose to live in a more hierarchically structured group, rather than a more egalitarian one, if leaders can reduce the likelihood of failures in cooperation due to free-riding or lack of coordination. We show that choosing to work under the supervision of a leader becomes an optimal decision for members of a society when cooperation as a group is potentially profitable, but group size exceeds that in which leaderless cooperation is viable. The emergence of leaders in the model matches that known from the reference archaeological series reasonably well.