The puzzle of human cooperation

Abstract

The claim by Johnson et al. that human cooperation in social-dilemma games violates rational-choice theory is not justified¹. If people have altruistic aims, altruistic behaviour is a rational means by which to achieve their proximate goals. From an evolutionary viewpoint, we need to explain why humans are often altruistic by strong reciprocity^2,3,4. Although kin selection, reciprocal altruism and indirect reciprocity explain relevant forms of human cooperation^5,6,7, they do not ultimately explain strong reciprocity⁸.

Fehr and Gächter reply

Kin selection would account for strong reciprocity if human behaviour were driven by rules that do not distinguish between kin and non-kin. But humans, like other primates, distinguish cognitively and behaviourally between the two^5,9, and generally feel stronger emotions towards kin. Likewise, reciprocal altruism could account for strong reciprocity if humans' behavioural rules did not depend on the probability of future interactions with potential opponents. But humans can distinguish long-term partners from people with whom future interaction will be less likely ('strangers'), and will cooperate more if they anticipate that interaction will be frequent⁶. Emotional responses may also be stronger towards a long-term partner than towards a 'stranger' (our unpublished results).

Reputation-based ultimate theories could account for strong reciprocity if our behavioural rules did not depend on our actions being observed by others. However, if reputation formation is ruled out, cooperation breaks down, whereas it flourishes if subjects gain in reputation⁷.

Early humans whose behaviour was fine-tuned to respond to kin or non-kin, partners or strangers, and gaining in reputation, probably had an evolutionary advantage because, contrary to common belief, they faced interactions where the probability of future encounters was sufficiently low as to make defection worthwhile. Ethnographic evidence indicates that humans had many encounters with individuals with whom they had little future interaction⁸. In addition, the costs of mistakenly treating unrelated individuals as kin, or treating strangers as partners, were high — for instance, a lack of vigilance with strangers could be fatal. Because of these costs, individuals who could adjust their behaviour to suit the their opponent's characteristics had greater fitness. The problem with any theory claiming that strong reciprocity is maladaptive in modern circumstances is that individuals understand the risks of exploitation in interactions with non-kin and strangers, and behave accordingly. An evolutionary explanation of strong reciprocity is needed that does not assume that individuals are maladapted^2,3.

A proximate mechanism of belief in supernatural punishment does not solve the evolutionary puzzle. How could such beliefs evolve if those who did not hold them defected and hence gained an advantage? Laboratory experiments do not support the claim that religion is important for cooperation. If other people in the group are expected to defect, then almost everyone else — religious or not — will defect too¹⁰. Moreover, in almost all religions, non-believers have been ostracized and have faced worldly punishment.

We do not agree that anonymity is a problem in the experiment: it rules out other, less costly forms of social punishment that are available in non-anonymous situations, such as workers' hostility towards strike-breakers and people's hostility towards wartime deserters. If non-anonymous punishment were lessened by being more costly, this could be just another example of how remarkable humans are at fine-tuning their behaviour to suit their circumstances.