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Richerson et al. address two key changes in human evolution, the first being how cooperation could evolve in the small-scale Pleistocene societies of prehistoric times, and the second being how these small-scale societies successfully evolved into much larger and more complex societies during the Holocene. The authors' case for a role of cultural group selection (CGS) in the second transition is strong. However, we will argue that the adoption of cooperative breeding suffices to explain the origin of human hyper-cooperation in early forager societies, as it resulted in increased prosociality and social transmission and favored the emergence of language.
Richerson et al. mention cooperative breeding as a possible trigger of the process involving CGS, but argue that this alternative hypothesis is difficult to test independently. However, recent comparative work exploring the psychological and cognitive consequences of cooperative breeding in nonhuman primates now increasingly allows us to identify general patterns that reliably emerge whenever a primate species adopts cooperative breeding. It is thus most parsimonious to assume that such psychological and cognitive consequences also arose when our hominin ancestors, but none of the other great apes, started to engage in cooperative breeding (Hrdy 2009; Kramer 2010). Together, these consequences are likely to have paved the way for the emergence of CGS processes (van Schaik & Burkart 2010).
Proactive prosociality
The first and perhaps most important consequence of cooperative breeding...