The Social Brain Hypothesis and its Relevance to Social Psychology: R. I. M. Dunbar
H umans, like most mammals, are intensely social. In many ways, pri-mates’ success from an evolutionary perspective is a direct consequenceof that sociality. Primate societies are implicit social contracts that allow some of the problems of survival and reproduction to be solved co-operatively. Social contracts of this kind work because they allow relevant problems to be solved more eﬃciently by individuals collaborating in their solution. However, social contracts require individuals to be willing to forgo some of their more immediate personal interests in order to beneﬁt from greater returns later through group-level co-operation. If too many individuals act in their own selﬁsh interests, the cohesion of the group will be threatened, simply because others will end up paying the costs of sociality. When these costs become a burden and begin to outweigh the beneﬁts of co-operation, group stability is undermined, leading to the rapid collapse of the contract (and, of course, society). Gürerk, Irlenbusch, and Rockenbach (2006) provide some evidence to support this claim in the context of small group economic games: They showed that when punishment is prevented, individuals rapidly (within the time frame of repeatedencounters laboratory games) switch allegiance to another group where punishment is permitted. In eﬀect, free-riding does lead to the rapid breakdown of group cohesion.