Collective conflicts among humans are widespread, although often highly destructive. A classic explanation for the prevalence of such warfare in some human societies is leadership by self-serving individuals that reap the benefits of conflict while other members of society pay the costs. Here, we show that leadership of this kind can also explain the evolution of collective violence in certain animal societies. We first extend the classic hawk−dove model of the evolution of animal aggression to consider cases in which a subset of individuals within each group may initiate fights in which all group members become involved. We show that leadership of this kind, when combined with inequalities in the payoffs of fighting, can lead to the evolution of severe intergroup aggression, with negative consequences for population mean fitness. We test our model using long-term data from wild banded mongooses, a species characterized by frequent intergroup conflicts that have very different fitness consequences for male and female group members. The data show that aggressive encounters between groups are initiated by females, who gain fitness benefits from mating with extragroup males in the midst of battle, whereas the costs of fighting are borne chiefly by males. In line with the model predictions, the result is unusually severe levels of intergroup violence. Our findings suggest that the decoupling of leaders from the costs that they incite amplifies the destructive nature of intergroup conflict.

人与人之间的集体冲突很普遍，尽管通常具有很高的破坏性。在某些人类社会中普遍存在这种战争的经典解释是，通过自助服务的个人来领导，他们从冲突中获利，而其他社会成员则为之付出了代价。在这里，我们表明，这种领导也可以解释某些动物社会中集体暴力的演变。我们首先扩展动物侵略性进化的经典鹰鸽模型，以考虑以下情况：每个小组中的一部分人可能发起战斗，而所有小组成员都参与其中。我们表明，这种领导能力与战斗的收益不平等相结合，会导致严重的群体间侵略行为演变，对人口平均适应性产生负面影响。我们使用来自野生带状猫鼬的长期数据测试了我们的模型，该带状猫鼬的特征是频繁发生群体间冲突，对男性和女性群体成员的适应性后果非常不同。数据显示，群体之间的激战是由女性发起的，女性在战斗中与群外男性交配会获得健身的好处，而战斗的费用主要由男性承担。与模型预测一致，结果是群体间暴力异常严重。我们的发现表明，领导者与他们所引发的成本脱钩，加剧了群体间冲突的破坏性。数据显示，群体之间的激战是由女性发起的，女性在战斗中与群外男性交配会获得健身的好处，而战斗的费用主要由男性承担。与模型预测一致，结果是群体间暴力异常严重。我们的发现表明，领导者与他们所引发的成本脱钩，加剧了群体间冲突的破坏性。数据显示，群体之间的激战是由女性发起的，女性在战斗中与群外男性交配会获得健身的好处，而战斗的费用主要由男性承担。与模型预测一致，结果是群体间暴力异常严重。我们的发现表明，领导者与他们所引发的成本脱钩，加剧了群体间冲突的破坏性。