“…Active mechanisms include those in which cooperative individuals behave conditionally to avoid free-riding-for instance, by determining whether to cooperate based on others' shared genes [43], reputations [44][45][46][47], tags [48], or wealth [49][50][51]. Such active mechanisms also include conditional behavior either to sanction defection (e.g., via punishment [14,[52][53][54][55][56][57][58][59], reciprocating defection with defection [36,60], or discontinuing play [61][62][63]) or to repay cooperation (e.g., via reciprocal altruism and rewards [60,64,65]). An adjacent literature, moreover, has recently generalized from the problem of cooperation to consider moral preferences more widely [66] and ofers a new active mechanism for study in the literature on cooperation.…”