Intergroup Aggression Research Articles

Intra- and interindividual differences in the costs and benefits of intergroup aggression in female vervet monkeys

In social species, fighting in intergroup conflicts is one of the riskiest cooperative activities group members engage in, particularly for individuals of the smaller sex. In a number of species, female group members are significantly smaller than males, so the costs associated with intergroup aggression outweigh the potential benefits and females avoid participating. Studies conducted on species in which females are active participants have consistently found that they fight to defend access to food resources and that high-ranking females tend to be more active than low-rankers. However, additional factors may modulate the costs and benefits of participation, creating differences between individuals and variability within individuals over time. In this study, we investigated costs and benefits that potentially affect female vervet monkey, Chlorocebus aethiops pygerythrus, participation in intergroup conflicts. We observed the participation of 35 females in three groups, during 115 intergroup conflicts. Our findings suggest that female vervet monkeys defend access to valuable food resources, as well as to areas that are intensely used in the long term; however, rank also influenced female participation indicating that the potential benefits gained from resource defence vary with one's priority of access to these resources. We found that females were more likely to participate aggressively when they did not have an infant, and when they received more male support throughout the intergroup conflict, suggesting these factors influence the perceived risk, or costs, of intergroup aggression. Because we observed considerable temporal variability in both the proportion of female group members with infants and the number and identity of male group members (i.e. amount of male support provided), the relative fighting ability of neighbouring groups will inevitably fluctuate. Thus, our findings may help explain the lack of stable intergroup dominance relationships observed in many studies of intergroup conflict.

Male food defence as a by-product of intersexual cooperation in a non-human primate.

Males in a number of group-living species fight in intergroup conflicts to defend access to food resources, a seemingly paradoxical behaviour, given that this resource does not usually limit male fitness directly. We investigated the mechanism(s) driving apparent male food defence in wild vervet monkeys (Chlorocebus aethiops pygerythrus) by testing the effect that female resource access, and female audience size and activity had on the response of focal males during simulated intergroup encounters. Males do not appear to defend food to increase the reproductive success of female group members because their response was not influenced by the presence of provisioning boxes that only females could access. Female audience size was also unimportant, suggesting males do not participate in intergroup encounters to advertise their quality to potential mates. However, focal males almost always followed/supported female group members who initiated an approach towards simulated intruders, supporting that male participation largely functions to gain status as a cooperative group member, and that apparent male food defence in this species arises as a by-product of intersexual cooperation. Our study highlights that considering audience composition and activity can reveal the presence of social incentives and illuminate the evolutionary mechanism(s) promoting joint action in intergroup aggression.

Cross-Cultural Sex Differences in Post-Conflict Affiliation following Sports Matches

The nature of ancestral human social structure and the circumstances in which men or women tend to be more cooperative are subjects of intense debate. The male warrior hypothesis proposes that success in intergroup contests has been vital in human evolution and that men therefore must engage in maximally effective intragroup cooperation [1-3]. Post-conflict affiliation between opponents is further proposed to facilitate future cooperation [4], which has been demonstrated in non-human primates [5] and humans [6]. The sex that invests more in post-conflict affiliation, therefore, should cooperate more. Supportive evidence comes from chimpanzees, a close genetic relative to humans that also engages in male intergroup aggression [7]. Here we apply this principle to humans by testing the hypothesis that among members of a large community, following a conflict, males are predisposed to be more ready than females to repair their relationship via friendly contact. We took high-level sports matches as a proxy for intragroup conflict, because they occur within a large organization and constitutesemi-naturalistic, standardized, aggressive, and intense confrontations. Duration or frequency of peaceful physical contacts served as the measure of post-conflict affiliation because they are strongly associated with pro-social intentions [8, 9]. Across tennis, table tennis, badminton, and boxing, with participants from 44 countries, duration of post-conflict affiliation was longer for males than females. Our results indicate that unrelated human males are more predisposed than females to invest in a behavior, post-conflict affiliation, that is expected to facilitate future intragroup cooperation.

Alcohol consumption increases bias to shoot at Middle Eastern but not White targets

Alcohol has been implicated in intergroup aggression and hostility. The effect of consuming alcohol relative to a placebo on hostile cognitive biases toward a social category typically stereotyped as threatening and hostile (i.e., Middle Eastern men) was tested. Undergraduates ( N = 81) consumed either an intoxicating dose of alcohol (BrAC = .05% by vol.) or placebo. Then, they played a shooter game in which they were asked to shoot at targets holding guns, but not at targets holding harmless objects. Half of the targets were White and half were Middle Eastern. As predicted, alcohol consumption, relative to a placebo, increased participants’ bias to shoot Middle Eastern targets, but did not affect the shooter bias against White targets. Findings suggest that alcohol may heighten aggressive biases toward outgroups stereotyped as threatening and hostile.

Emotion and aggressive intergroup cognitions: The ANCODI hypothesis.

Previous research has suggested an important role for the emotion of hatred in intergroup aggression. Recent theoretical and empirical work has strongly suggested that the combination of anger, contempt, and disgust (ANCODI) comprise the basic elements of hatred, and are the key emotions associated with intergroup aggression. No study, however, has provided evidence that these emotions cause hostile cognitions about specific groups. We report two studies that provide initial evidence. In both, participants were members of ideologically motivated groups and were primed with ANCODI. In Study 1 participants primed with ANCODI produced more aggressive cognitions relative to their opponent outgroup than a neutral outgroup; this effect did not occur for participants primed with fear-sadness. In Study 2 participants primed with ANCODI engaged in more competitive decision making against their opponent outgroups than a neutral outgroup; this effect did not occur for participants primed with disgust only. These findings contribute to the literature on the role of emotion in intergroup aggression and hostility, and provide a more nuanced view of the role of emotions in intergroup relations, possibly identifying the basic emotional elements of hatred. Aggr. Behav. 43:93-107, 2017. © 2016 Wiley Periodicals, Inc.

Going to extremes for one's group: the role of prototypicality and group acceptance

AbstractTo explore who goes to aggressive and antisocial extremes on behalf of their group we primed perceptions of (a) group prototypicality (peripheral vs. central) and (b) ease of acceptance by the group. Participants were members of self‐significant groups—fraternities and sororities (N = 218). Drawing on social identity theory, uncertainty‐identity theory and the social identity theory of influence through leadership, we found, as predicted, that peripheral members who believed it was easy to be accepted were most likely to intend to engage in and support antisocial and aggressive intergroup behaviors. This effect was somewhat stronger among males than females, and strengthened among the most highly identified participants. The research's potential for understanding socially harmful intergroup violence is noted.

The effect of intergroup competition on intragroup affiliation in primates

Researchers from various disciplines have hypothesized a positive correlation between the level of intergroup contest competition (IGCC) and the evolution of behavioural traits, such as cooperation, altruism and friendship, which promote intragroup affiliation. Empirical support for this hypothesis is, however, scarce and mainly available from humans. We tested whether the level of IGCC affects intragroup affiliation (i.e. intragroup grooming exchange) among male and female nonhuman primates. To quantify intragroup affiliation, we used social network measures and a grooming index. Our measure of IGCC combined frequency of intergroup encounters and proportion of aggressive encounters and was calculated separately for males and females. We ran our analyses on 27 wild groups of primates belonging to 15 species (13 Cercopithecinae, one Colobinae and one Cebinae). Our analyses reveal a clear pattern of correlated evolution between grooming network density and interindividual variation in the number of grooming partners on the one hand and the intensity of IGCC on the other in females, but not males. Thus, our results suggest that the exact nature of the relationship between IGCC and intragroup affiliation is sex specific. These results may be explained by the differential costs and benefits males and females experience during aggressive intergroup confrontations and by sex-specific differences in intragroup affiliation.

Networks of Violence in the Production of Young Women's Trajectories and Subjectivities

This paper focuses on the deployment and interdependence of different expressions of gendered and classed violence in shaping the choices, trajectories and subjectivities of young women on vocational beauty therapy courses. It takes as its premise the understanding that, far from simply being an aberrant expression of interpersonal or intergroup aggression, violence is embedded in social life in multiple and complex ways, reverberating through women's lives to reproduce disadvantage and subordination. The paper draws on theoretical and empirical investigations of the interrelationships between structural, direct and symbolic expressions of violence and asks what this literature can offer in challenging normative, often individualised, conceptions of violence. Drawing on an ethnographic case study of National Vocational Qualification (NVQ) beauty therapy courses and the young women undertaking them, I explore the accounts of students and their tutors on becoming and being ‘beauty girls’. I consider what these accounts might tell us about how forms of symbolic and interpersonal violence intersect with, reproduce and legitimise the violence involved in unequal and unjust socio-economic structures. I argue that the ways in which different forms of violence mutually reinforce each other at a micro-level produce an embodied ‘sense of limits’ that ultimately reproduces the structural violence of gendered and classed inequalities. The examples given illustrate both a ‘chronology of violence’ in young women's lives, and the way in which those lives can be understood, at least in part, as embedded in and shaped by networks of violence. Finally, I briefly consider examples of dissent and resistance, the conditions under which they might be possible and the ways in which, through the interplay of different forms of violence, they might also be curtailed.

Latrine behaviour as a multimodal communicatory signal station in wild lemurs: the case of Hapalemur meridionalis

Latrine behaviour is the repeated use of specific sites for defecation/urination, and is common among most mammals, including carnivores, herbivores, marsupials and rodents. While rare among primates, latrine use has been observed among some lemurs. It has been hypothesized that group-living primates may use latrines to maintain intergroup spacing (i.e. territorial defence) and for female advertisement of sexual condition. To test these, we conducted focal follows of three neighbouring southern bamboo lemur, Hapalemur meridionalis, groups in Mandena littoral forest of southeast Madagascar. From January to December 2013, we recorded all occurrences of latrine behaviour and characterized latrine sites to determine what factors influenced returning to specific latrines. Additionally, we attempted to elucidate the functional role of scent marking at latrines. We assessed the degree of home range overlap between neighbouring groups, and recorded intergroup aggression. Overall, latrines were almost exclusively visually conspicuous sites and located in the core areas of group home ranges. Best-fit models indicated that multiply visited latrines occurred more often in core areas, and were influenced by both sexes. Glandular scent marking at latrine sites was driven by males, and occurred more during the nonmating season. Males overmarked female scent-marks less often during the mating season and more often when younger males were likely to disperse. Thus, overmarking at latrine sites may function as a mate-guarding strategy to deter new males. Latrine use supports the energy frugality hypothesis, which proposes that lemur social systems, known for female social dominance and low rates of agonism, evolved as responses to the low productivity of Malagasy forests. The deposition of olfactory cues (i.e. faeces, urine, glandular secretions) at visually conspicuous sites may convey information to neighbouring conspecifics, thus reducing the need for intergroup agonism. Overall, latrine behaviour acts as a multimodal means of intergroup communication.

Violent Rhetoric in Protracted Group Conflicts

How do messages from political elites interact with individual traits of citizens to spur intergroup aggression? Building on research in social psychology, we expect that in places of protracted conflict, violent rhetoric from elites will be enough to mobilize antagonism toward an outgroup, especially among those who are generally less apt to be hostile toward the outgroup. We present results from two large survey experiments, the first conducted with young Jewish-Israeli adults across Israel and the second with a nationally diverse sample of adults in India. The results show that mild “fighting” words (e.g. “battle,” “fight”), combined with a reference to the outgroup, provoke significantly greater support for policies that harm the outgroup among some citizens. This effect is largest among individuals low in outgroup prejudice and low in aggressive personality traits, people who are usually less inclined to support policies that hurt the outgroup. Effects of violent rhetoric persist even with policies and rhetoric to help the outgroup. This work highlights the importance of considering both individual traits and contextual factors together to understand their full impact in the study of intergroup conflict.

What makes people go to war? Defensive intentions motivate retaliatory and preemptive intergroup aggression

Although humans qualify as one of the most cooperative animal species, the scale of violent intergroup conflict among them is unparalleled. Explanations of the underlying motivations to participate in an intergroup conflict, however, remain unsatisfactory. While previous research shows that intergroup conflict increases individually costly behavior to the benefit of the in-group, it has failed to identify robust triggers of aggressive behavior directed at out-groups. Here, we present a controlled laboratory experiment which demonstrates that such aggression can be provoked systematically by manipulating the extent to which the own group is perceived to be on the offensive or the defensive side of a conflict. We find direct and causal evidence that the motivation to protect the in-group not only is a predictor of retaliatory aggression, but also promotes preemptive offensive actions against out-groups if they pose a potential threat. This finding improves our understanding of the escalation of intergroup conflicts and may have important implications for their prevention, as we find in our experiment that removing out-group threat substantially reduced intergroup aggression and led to full peace.

The development of bystander intentions and social-moral reasoning about intergroup verbal aggression.

A developmental intergroup approach was taken to examine the development of prosocial bystander intentions among children and adolescents. Participants as bystanders (N=260) aged 8-10 and 13-15years were presented with scenarios of direct aggression between individuals from different social groups (i.e., intergroup verbal aggression). These situations involved either an ingroup aggressor and an outgroup victim or an outgroup aggressor and an ingroup victim. This study focussed on the role of intergroup factors (group membership, ingroup identification, group norms, and social-moral reasoning) in the development of prosocial bystander intentions. Findings showed that prosocial bystander intentions declined with age. This effect was partially mediated by the ingroup norm to intervene and perceived severity of the verbal aggression. However, a moderated mediation analysis showed that only when the victim was an ingroup member and the aggressor an outgroup member did participants become more likely with age to report prosocial bystander intentions due to increased ingroup identification. Results also showed that younger children focussed on moral concerns and adolescents focussed more on psychological concerns when reasoning about their bystander intention. These novel findings help explain the developmental decline in prosocial bystander intentions from middle childhood into early adolescence when observing direct intergroup aggression.

Psychological Security of Two Generations in Latvia

The breakup of Soviet Union and transition from “well-developed socialism” to market economy led to the changes in the attitudes and the lifestyle of the people. Have these changes made human communication safer? The most important sociopsychological condition for such security is the absence of interpersonal and intergroup aggression, as well as the hatred that tends to provoke the explosions of such aggression. Has this condition changed in the life of generation educated in the market-economy society? Are these changes accompanied by the changes in mental variables that prevent the explosions of aggression, particularly in changes of experience of love and satisfaction with life? The aim of our study is the comparison of aggression, hate, love, and satisfaction with life that characterized the generation educated in Soviet Union (43–50 years old) and the same features of the younger generation (18-25 years old), educated after the breakup of Soviet Union in Latvia. Hypothesis on the existence of intergenerational distinctions on these variables was confirmed partly: distinctions were revealed in the inclination to aggression, satisfaction with life, and love passion. All these variables are higher in young generation, which could be explained more by age-specific features than by more general changes in the social-economic and social-political circumstances.

Social correlates of androgen levels in a facultatively monogamous ape (Symphalangus syndactylus): a test of the challenge hypothesis

The challenge hypothesis posits a correlation between male androgen levels and mating system, male–male aggression in a sexual context, and parental effort. This model has received support across a variety of taxa, including primates. Most primate studies have focused on multi-male societies characterized by relatively high levels of male–male aggression and limited paternal care. To expand this dataset, predictions of the challenge hypothesis were tested in a population of wild siamangs (Symphalangus syndactylus), small apes characterized by intense territoriality, monogamous/polyandrous grouping patterns, and varying amounts of paternal behavior. Behavioral data were collected on 11 study groups (five two-male groups and six one-male groups). Seven hundred thirty-four fecal samples were collected from 18 adult males to quantify concentrations of fecal immunoreactive androgens (fiA) by radioimmunoassay. As predicted by the challenge hypothesis, males involved in the aggressive replacement of a resident male had significantly higher fiA concentrations than control males, while males displaying active parental care had significantly lower fiA concentrations than average. Results showed no association between male androgen concentration and group composition, male rank, or rate of intragroup male–male aggression. These latter findings, seemingly inconsistent with the hypothesis, could be explained by the clear and stable dominance relationships between co-resident males: given the very low rates of physical aggression, a low baseline testosterone is to be expected. Furthermore, the effects of increased intragroup conflict experienced by males in two-male groups might be offset by the higher frequency of intergroup aggression experienced by males in one-male groups.

Myths about hunter-gatherers redux: nomadic forager war and peace

Purpose– The purpose of this paper is to critique several studies that claim to show that nomadic foragers engage in high levels of inter-group aggression. This is done through exploring four myths: nomadic foragers are warlike; there was a high rate of war mortality in the Pleistocene; the nomadic forager data support the “chimpanzee model” of lethal raiding psychology; and contact and state influence inevitably decrease aggression in nomadic forager societies.Design/methodology/approach– Using exact criteria, a sample of 21 nomadic forager societies is derived from the Standard Cross-Cultural Sample. This sampling method minimizes the chance of sampling bias, a shortcoming that has plagued previous studies. Only the highest quality ethnographic data, those classified as Primary Authority Sources, are used, which results in data on 148 cases of lethal aggression. The specifics of the lethal aggression cases are then discussedvis-à-visthe four myths to demonstrate the disjuncture between the data and the myths.Findings– All four myths are found to be out of step with actual data on nomadic forager war and peace. Overall, the default interaction pattern of nomadic foragers is to get along with neighbors rather than make war against them. The findings contradict both assertions that there was a high level of war mortality among nomadic foragers of the Pleistocene and the chimpanzee model's proposal that human males have a tendency or predisposition to form coalitions and make lethal attacks on members of neighboring groups.Research limitations/implications– Consideration of nomadic forager war and peace should be contextualized in terms of social organization, contact history (including ethnocide, displacement, and other factors), and the current situation faced by extant forager populations. As in other contexts, the introduction of alcohol at contact or subsequently has increased nomadic forager aggression.Practical implications– Propositions as to the aggressiveness of nomadic foragers should be viewed with skepticism because they are contradicted by data and a contextual view of nomadic forager social organization and ethnohistory.Social implications– The debate over nomadic forager war and peace is connected to larger debates in modern society about the nature of human nature and has real-world implications regarding foreign policy and political approaches toward war and peace.Originality/value– A critique of sampling, methodology, and theory is provided in this area.

The effects of altruistic behavior in intergroup aggression

The effects of altruistic behavior in intergroup aggression

Homology across inheritance systems

Recent work on inheritance systems can be divided into inclusive conceptions, according to which genetic and non-genetic inheritance are both involved in the development and transmission of nearly all animal behavioral traits, and more demanding conceptions of what it takes for non-genetic resources involved in development to qualify as a distinct inheritance system. It might be thought that, if a more stringent conception is adopted, homologies could not subsist across two distinct inheritance systems. Indeed, it is commonly assumed that homology relations cannot survive a shift between genetic and cultural inheritance systems, and substantial reliance has been placed on that assumption in debates over the phylogenetic origins of hominin behavioral traits, such as male-initiated intergroup aggression. However, in the homology literature it is widely accepted that a trait can be homologous—that is, inherited continuously in two different lineages from a single common ancestor—despite divergence in the mechanisms involved in the trait’s development in the two lineages. In this paper, we argue that even on an extremely stringent understanding of what it takes for developmental resources to form a separate inheritance system, homologies can nonetheless subsist across shifts between distinct inheritance systems. We argue that this result is a merit of this way of characterizing what it is to be an inheritance system, that it has implications for adjudicating between alternative accounts of homology, and that it offers an important cautionary lesson about how (not) to reason with the homology concept, particularly in the context of cultural species.

Reducing aggressive intergroup action tendencies: Effects of intergroup contact via perceived intergroup threat

Two studies tested the prediction that more positive intergroup contact would be associated with reduced aggressive intergroup action tendencies, an effect predicted to occur indirectly via reduced intergroup threat perceptions, and over and above well-established effects of contact on intergroup attitudes. Study 1, using data based on a cross-section of the general population of eight European countries (France, Germany, Hungary, Italy, the Netherlands, Poland, Portugal, and the UK; N = 7,042), examined this hypothesis in the context of aggressive action tendencies towards immigrants. Study 2, using longitudinal data obtained from a general population sample in Northern Ireland, considered effects on aggressive action tendencies between ethno-religious groups in conflict. Both studies confirmed our predictions, showing that while perceived threat was associated with greater intergroup aggressive tendencies, positive intergroup contact was indirectly associated with reduced aggressive action tendencies, via reduced intergroup threat. Findings are discussed in terms of the theoretical contributions of this research for understanding the relationship between intergroup contact and intergroup aggression.

Sex‐specific participation in inter‐group conflicts within a multilevel society: the first evidence at the individual level

Inter-group conflicts are common among many group-living animals and involve potentially complex motivations and interactions. Mammals living in multilevel societies offer a good opportunity to study inter-group conflicts. This study is the first to explore the function of sex-specific participation during inter-group conflicts within a multilevel society at the individual level. The Sichuan snub-nosed monkey (Rhinopithecus roxellana) is an endangered seasonal breeding species living in a multilevel society. From Sep 2007 to May 2008 we recorded 290 inter-group conflicts of a free-ranging provisioned band of R. roxellana in the Qinling Mountains of China to investigate the function of individual aggression during inter-group encounters. Our findings show that adult males were the main participants in inter-group conflicts, while females took part in them only occasionally. The male participation rate during the mating season, when adult females were estrous, was significantly higher than that during the non-mating season. Furthermore, males directed their aggression to other males, and directed more intense aggression towards bachelor males than towards other resident males. For both sexes, the participation rate as initiators was higher in the winter than that in the spring; and there was a significant positive correlation between group size and the participation rate as initiators. Our results suggest that inter-group aggression in Sichuan snub-nosed monkeys is linked to both mate defense and resource defense.

Under multilevel selection: “When shall you be neither spiteful nor envious?”

In this paper, we study the egalitarianism-game in multilevel selection situation. The individuals form reproductive groups. In each group, an egalitarianism-game determines the number of juveniles of different phenotypes (spiteful, envious, neutral and donator). Before the juveniles form the next reproductive group, they have to survive either predators' attacks or a fight between two groups. We adopt the ESS definition of Maynard Smith to multilevel selection. Based on the “group size advantage” assumption (which claims that each juvenile's survival rate depends on the size of his own group, supposing that either the survival rate under predators' attacks is higher in larger groups, or in inter-group aggression usually the larger group wins) we found that when the survival probability has a massive effect on the average fitness, then “group fitness maximizing behavior” (in our case, either neutral or donator) has evolutionary advantage over “competitive behavior” (in our case, either spiteful or envious).