The biologist Martin Nowak has argued that the only way humans have been able to sustain cooperation is by developing cheap ways to punish misbehavior. To discourage A from hurting B, the reaction of C can be important, because if A knows that C will punish him for what he does to B, he might think twice before hurting B.
生物学家马丁·诺瓦克（Martin Nowak）指出，人类能够保持合作的唯一方式是找到惩罚不当行为的低成本方法。要让A不去伤害B，C的反应可能十分重要，因为如果A知道C会因为他对B做的事而惩罚他，他就会在伤害B之前三思。