Leader-biased teaching drives the evolution of egalitarian cooperation

Despite the voluminous body of work dedicated to understanding the evolution of cooperation, the role of teaching and the importance of leadership in the transmission of opaque cultural norms -- the foundations on which cooperative behaviors rely -- have not been thoroughly explored. Similarly, there is a sizable literature on the role of teaching in the evolution of instrumental culture (e.g., subsistence technology and behaviors, manufacture) but there has been relatively little attention dedicated to the important role of teachers in transmitting more opaque culture, such as social values, norms and institutions, cultural history, and proper behavior. The transmission of opaque culture is more likely to require teaching, as these cultural features are complex and not easily observable. We suggest socially influential individuals, i.e., leaders, are best positioned to transmit such cultural information. Given an egalitarian socio-ecology, leaders will be motivated to teach cooperative behaviors and prosocial norm-adherence among influenceable followers, given the benefits of living among cooperative group members that would accrue to themselves, their kin, their social partners, and their groups. We leverage comparative ethnographic data and introduce an empirically driven theory suggesting leader-biased teaching is a key cultural evolutionary process facilitating cooperation within more egalitarian social and cultural contexts. We draw on the *hunter-gatherer social learning data*, a cross-cultural ethnographic database based on 23 relatively egalitarian foraging societies, to identify relationships between teaching, leadership, and cooperative norms. We find that evidence for teaching is more often associated with the transmission of cultural values and kinship knowledge and less often associated with subsistence skill or manufacturing knowledge and is more closely linked to features of opaque culture and leadership. Based on our comparative analysis, we develop a formal model testing associated evolutionary dynamics and exploring the costliness of teaching by informed leaders and learning by naive followers in facilitating the evolution of cooperative norms. We suggest that leader-biased teaching is a critical mechanism in the evolution of cooperation, particularly in more egalitarian sociocultural contexts. Our leader-biased teaching theory for the evolution of cooperation suggests new avenues for research on social learning, social influence, and cooperative behaviors.