| The evolution of large-scale cooperation among genetic strangers is a fundamental unanswered question in the social sciences. Behavioral economics has persuasively shown that so called ‘strong reciprocity’ plays a key role in accounting for the endogenous enforcement of cooperation. Insofar as strongly reciprocal players are willing to costly sanction defectors, cooperation flourishes. However, experimental evidence unambiguously indicates that not only defection and strong reciprocity, but also unconditional cooperation is a quantitatively important behavioral attitude. By referring to a prisoner’s dilemma framework where punishment (‘stick’) and rewarding (‘carrot’) options are available, here we show analytically that the presence of cooperators who... |
