ABSTRACT
In this paper, I accept the received view that the evolution of norm psychology in the hominin lineage coevolved with, and contributed to, the evolution of the extraordinary forms of cooperation in hominin life. But in contrast to other views in the literature, I do not think norm psychology was essential to the initiation of band-scale cooperation (which probably dates to the Early or Middle Pleistocene) and nor was it a reaction to the increase in the social scale of cooperation around the Pleistocene/Holocene boundary. Rather, I argue that norms, and especially explicit norms, were an adaptive response to changes in the economic foundations of cooperation in the last 100,000 years of the Pleistocene, as hominin social life transitioned from a forager economy largely based around collective action to one largely based around reciprocation. The chapter argues that reciprocation-based cooperation, while very profitable, was also cognitively and motivationally demanding. Its stability depended on new cognitive and social tools, and norms and normative guidance were among those tools.
