Indirect Reciprocity (IR) is possibly the most elaborated and cognitively demanding mechanism of cooperation discovered so far. It involves status and reputations and has been heralded as providing the biological basis of our morality. Most theoretical models employed to date have studied how IR can lead to the emergence and sustainability of cooperation in infinite populations. However, it is known that cooperation, norms, reciprocity and the art of managing reputations, are features that date back to primitive, small-scale societies, when interactions mostly occurred within tribes. In small populations, stochastic finite size effects are not only important, but may even render infinite populations analyses misleading. Thus, it remains an open question which norms prevail in small-scale societies and their influence in the evolutionary dynamics of IR. With the current extended abstract, we would like to offer a new analysis of this problem. In Santos et al. (2016) we show that population size strongly influences the merits of each social norm, while proposing a new formal tool to assess the evolutionary dynamics of reputation-based systems in finite populations. We show that a single social norm (Stern-Judging) emerges as the leading norm in small-scale societies. That simple norm dictates that only whoever cooperates with good individuals, and defects against bad ones, deserves a good reputation.

This content is only available as a PDF.
This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.