Evolution of warfare by resource raiding favors polymorphism in belligerence and bravery

From protists to primates, intergroup aggression and warfare over resources has been observed in several taxa whose populations typically consist of groups connected by limited genetic mixing. Here, we model the co-evolution between four traits relevant to this setting: (i) investment into common-pool resource production within groups ('helping'); (ii) proclivity to raid other groups to appropriate their resources ('belligerence'); and investments into (iii) defense and (iv) offense of group contests ('defensive and offensive bravery'). We show that when traits co-evolve, the population often experiences disruptive selection favouring two morphs: 'Hawks', who express high levels of both belligerence and offensive bravery; and 'Doves', who express neither. This social polymorphism involves further among-traits associations when the fitness costs of helping and bravery interact. In particular if helping is antagonistic with both forms of bravery, co-evolution leads to the coexistence of individuals that either: (i) do not participate into common-pool resource production but only in its defense and appropriation ('Scrounger Hawks'); or (ii) only invest into common pool resource production ('Producer Doves'). Provided groups are not randomly mixed, these findings are robust to several modelling assumptions. This suggests that inter-group aggression is a potent mechanism in favoring within-group social diversity and behavioural syndromes.

Opposite associations of collective narcissism and in-group satisfaction with intergroup aggression via belief in the hedonistic function of revenge

We investigated whether collective narcissism (i.e., believing that the in-group is exceptional but insufficiently recognized by others) and in-group satisfaction (i.e., believing that the in-group is a source of satisfaction) have opposite, unique associations with intergroup aggression via belief in the hedonistic function of revenge (i.e., an expectation of emotional reward from harming others in response to feeling oneself harmed). Results of two studies conducted in Poland (N = 675) found that collective narcissism is positively related to belief in the hedonistic function of revenge, whereas in-group satisfaction is negatively related, and both are related to intergroup aggression. These relationships were found only when the overlap between collective narcissism and in-group satisfaction was partialled out. The results shed a new light on the mechanisms linking in-group positivity to out-group derogation, and highlight the importance of investigating revenge motivations in the intergroup relations.

Intergroup lethal gang attacks do not require fission-fusion dynamics to evolve

ABSTRACTLethal 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.

Collective Narcissism and Its Social Consequences: The Bad and the Ugly

Collective narcissism is a belief that one’s own group (the in-group) is exceptional but not sufficiently recognized by others. It is the form of “in-group love” robustly associated with “out-group hate.” In contrast to private collective self-esteem (or in-group satisfaction, a belief that the in-group is of high value), it predicts prejudice, retaliatory intergroup aggression, and rejoicing in the suffering of other people. The pervasive association between collective narcissism and intergroup hostility is driven by a biased perception of the in-group as constantly threatened and out-groups as hostile and threatening. Collective narcissism is associated with hypersensitivity to provocation and the belief that only hostile revenge is a desirable and rewarding response. It arises when the traditional group-based hierarchies are challenged and empowers extremists as well as populist politicians. Instead of alleviating the sense of threat to one’s self-importance, it refuels it. The association between collective narcissism and intergroup hostility is weakened by experiences that fortify emotional resilience (e.g., positive identification with a community).

Collective narcissism and its social consequences: The Bad and the Ugly

Collective narcissism is a belief that one’s own group (the in-group) is exceptional but not sufficiently recognized by others. It is the form of ‘in-group love’ associated with ‘out-group hate’. In contrast to private collective self-esteem (a belief that the in-group is of high value), it consistently predicts prejudice, retaliatory intergroup aggression, and rejoicing in suffering of others. The pervasive association between collective narcissism and intergroup hostility is driven by a biased perception of intergroup situations that serves to protect undermined self-worth and frustrated personal entitlement invested in the in-group’s image. Collective narcissism is associated with hypersensitivity to provocation and the belief that only hostile revenge is a desirable and rewarding response. It arises when the traditional group-based hierarchies are challenged and empowers extremists as well as populist politicians. Instead of alleviating, it re-fuels a sense of threatened self-importance. The association between collective narcissism and intergroup hostility is weakened by experiences fortifying emotional resilience (e.g., positive identification with a community).