Lethal gang attacks, in which multiple aggressors attack a single victim, are among the most widespread forms of violence between human groups. Chimpanzees (Pan troglodytes), as well as wolves (Canis lupus), spotted hyaenas (Crocuta crocuta), and lions (Panthera leo), perform gang attacks during raids. In raids, a few individuals of a group enter another group's territory and attack its members if found in numerical disadvantage. Current theory predicts that raids and gang attacks are linked to fission-fusion dynamics, i.e. the capacity of a group to split into smaller subgroups of variable size and composition. However, over the last decade, research on social mammals without fission-fusion societies nor raiding have shown that they may also be involved in intergroup lethal gang attacks. Thus, neither fission-fusion dynamics nor raiding are required for gang attacks to evolve. Based on our first-ever reports of intergroup gang attacks in the crested macaque (Macaca nigra), combined with the synthesis of earlier observations of such attacks in several species living in stable groups, we develop a new hypothesis about the proximate causes leading to lethal intergroup aggression. We propose that the ability to estimate numerical odds, form coalitionary bonds, and show hostility towards outgroup individuals may suffice to trigger intergroup gang attacks when the conditions favour an imbalance of power between victims and attackers.

中文翻译：

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组间致命帮派袭击不需要裂变融合动力学来发展

致命团伙袭击是多个群体之间最普遍的暴力形式，其中多个侵略者攻击单个受害者。黑猩猩（Pan troglodytes）以及狼（Canis lupus），斑点鬣狗（Crocuta crocuta）和狮子（Panthera leo），在突袭中进行帮派袭击。在突袭中，一个小组中的几个人进入另一个小组的领土，并在数量上处于不利地位时攻击其成员。当前理论预测，突袭和帮派袭击与裂变融合动力学有关，即一个小组分裂成可变大小和组成的较小子小组的能力。然而，在过去的十年中，对没有裂变融合社会也没有突袭的社会哺乳动物的研究表明，它们也可能参与了集团间的致命帮派袭击。因此，帮派攻击的发展既不需要裂变融合动力学也不需要突袭。根据我们关于凤头猕猴（Macaca nigra）的团伙团伙袭击的首次报道），再结合对稳定群体中几种物种的此类攻击的早期观察结果的综合，我们得出了导致致命的群体间侵略的最接近原因的新假说。我们建议，当条件有利于受害者和攻击者之间的力量不平衡时，估计数字几率，形成联盟关系以及对外来群体表现出敌意的能力可能足以引发群体间的帮派袭击。