What Niche Did Human Cooperativeness Evolve In?

The Prisoner's Dilemma (PD) is widely used to model interaction between unrelated individuals in the study of the evolution of cooperativeness. Many mechanisms have been studied which allow for small founding groups of cooperative individuals to prevail even when all social interaction is characterised as a PD. Here, a brief critical discussion of the role of the PD as the most prominent tool in cooperation research is presented, followed by two new objections to such an exclusive focus on PD-based models. It is highlighted that only 2 of the 726 combinatorially possible strategically unique ordinal 2×2 games have the detrimental characteristics of a PD and that the frequency of PD-type games in a space of games with random payoffs does not exceed about 3.5%. Although this does not compellingly imply that the relevance of PDs is overestimated, in the absence of convergent empirical information about the ancestral human social niche, this finding can be interpreted in favour of a rather neglected answer to the question of how the founding groups of human cooperation themselves came to cooperate: Behavioural and/or psychological mechanisms which evolved for other, possibly more frequent, social interaction situations might have been applied to PD-type dilemmas only later.