Conflict, sticks and carrots: war increases prosocial punishments and rewards

Unlike most species, humans cooperate extensively with group members who are not closely related to them, a pattern sustained in part by punishing non-cooperators and rewarding cooperators. Because internally cooperative groups prevail over less cooperative rival groups, it is thought that violent intergroup conflict played a key role in the evolution of human cooperation. Consequently, it is plausible that propensities to punish and reward will be elevated during intergroup conflict. Using experiments conducted before, during and after the 2006 Israel-Hezbollah war, we show that, during wartime, people are more willing to pay costs to punish non-cooperative group members and reward cooperative group members. Rather than simply increasing within-group solidarity, violent intergroup conflict thus elicits behaviours that, writ large, enhance cooperation within the group, thereby making victory more likely.     

Cooperation and conflict: field experiments in Northern Ireland

The idea that cohesive groups, in which individuals help each other, have a competitive advantage over groups composed of selfish individuals has been widely suggested as an explanation for the evolution of cooperation in humans. Recent theoretical models propose the coevolution of parochial altruism and intergroup conflict, when in-group altruism and out-group hostility contribute to the group''s success in these conflicts. However, the few empirical attempts to test this hypothesis do not use natural groups and conflate measures of in-group and unbiased cooperative behaviour. We conducted field experiments based on naturalistic measures of cooperation (school/charity donations and lost letters'' returns) with two religious groups with an on-going history of conflict—Catholics and Protestants in Northern Ireland. Conflict was associated with reduced donations to out-group schools and the return of out-group letters, but we found no evidence that it influences in-group cooperation. Rather, socio-economic status was the major determinant of cooperative behaviour. Our study presents a challenge to dominant perspectives on the origins of human cooperation, and has implications for initiatives aiming to promote conflict resolution and social cohesion.     

Duration and outcome of intergroup conflict influences intragroup affiliative behaviour

Theoreticians have long suggested that the amount of intergroup conflict in which a group is involved could influence the level of cooperation or affiliation displayed by its members. Despite the prevalence of intergroup conflicts in many social animal species, however, few empirical studies have investigated this potential link. Here, I show that intragroup allopreening rates are highest in green woodhoopoe (Phoeniculus purpureus) groups that have the greatest involvement in intergroup conflict. One reason for this relationship is a post-conflict increase in allopreening, and I demonstrate for the first time that both conflict duration and outcome influence subsequent allopreening rates: group members allopreened more following long conflicts and those they lost compared with short conflicts and those they won, perhaps because the former are more stressful. The increase in affiliative behaviour was the result of more allopreening of subordinate helpers by the dominant breeding pair, which may be because the breeders are trying to encourage helpers to participate in future conflicts; relative group size influences conflict outcome and helpers contribute more to conflicts than do the breeding pair. These results emphasize that our understanding of cooperation and group dynamics can be enhanced by investigations of how intergroup interactions affect intragroup processes.     

Exaggerated Intergroup Bias in Economical Decision Making Games: Differential Effects of Primary and Secondary Psychopathic Traits

Psychopathic personality traits are linked with selfish and non-cooperative responses during economical decision making games. However, the possibility that these responses may vary when responding to members of the in-group and the out-group has not yet been explored. We aimed to examine the effects of primary (selfish, uncaring) and secondary (impulsive, irresponsible) psychopathic personality traits on the responses of non-offending participants to the in-group and the out-group (defined in terms of affiliation to a UK University) across a series of economical decision making games. We asked a total of 60 participants to act as the proposer in both the dictator game and the ultimatum game. We found that across both tasks, those who scored highly for secondary psychopathic traits showed an elevated intergroup bias, making more generous offers toward members of the in-group relative to the out-group. An exaggerated intergroup bias may therefore represent a motivational factor for the antisocial behavior of those with elevated secondary psychopathic traits.     

Patterns of reconciliation among captive gelada baboons (Theropithecus gelada): A brief report

Animals that live in groups are frequently exposed to conflict situations and must in some way maintain group cohesion. One mechanism that appears to restore social relationships after they have been disrupted by conflict isreconciliation. This study investigated reconciliatory behavior in the gelada baboon,Theropithecus gelada. The subjects were 11 adult geladas, housed in a large outdoor enclosure at the Bronx Zoo/Wildlife Conservation Park, New York. Five-minute focal animal samples following spontaneous aggression were compared with 5-min matched-control samples. The results of this study were: (1) geladas reunited in a friendly way after aggression; (2) former opponents were attracted to one another rather than dispersed from one another after a conflict; (3) most post-conflict reunions occurred within the first 2 min of the post-conflict period; and (4) geladas do not have any specific types of behavior associated with post-conflict reunions as do chimpanzees and macaques. The results of this study support the hypothesis that gelada baboons reconcile after aggression.     

Decision Rules and Group Rationality: Cognitive Gain or Standstill?

Recent research in group cognition points towards the existence of collective cognitive competencies that transcend individual group members’ cognitive competencies. Since rationality is a key cognitive competence for group decision making, and group cognition emerges from the coordination of individual cognition during social interactions, this study tests the extent to which collaborative and consultative decision rules impact the emergence of group rationality. Using a set of decision tasks adapted from the heuristics and biases literature, we evaluate rationality as the extent to which individual choices are aligned with a normative ideal. We further operationalize group rationality as cognitive synergy (the extent to which collective rationality exceeds average or best individual rationality in the group), and we test the effect of collaborative and consultative decision rules in a sample of 176 groups. Our results show that the collaborative decision rule has superior synergic effects as compared to the consultative decision rule. The ninety one groups working in a collaborative fashion made more rational choices (above and beyond the average rationality of their members) than the eighty five groups working in a consultative fashion. Moreover, the groups using a collaborative decision rule were closer to the rationality of their best member than groups using consultative decision rules. Nevertheless, on average groups did not outperformed their best member. Therefore, our results reveal how decision rules prescribing interpersonal interactions impact on the emergence of collective cognitive competencies. They also open potential venues for further research on the emergence of collective rationality in human decision-making groups.     

Explaining the evolution of parochial punishment in humans

Humans usually favour members of their own group, ethnicity or culture (parochial cooperation), and punish out-group wrongdoers more harshly (parochial punishment). The evolution of parochial cooperation is mainly explained by intergroup conflict, as restricting cooperation to in-groups can provide a relative advantage during conflict. However, explanations for the evolution of parochial punishment are still lacking. It is unclear whether conflict can also explain parochial punishment, because conflict is expected to lead to full hostility towards out-groups, irrespective of their behaviour. Here, we use an agent-based simulation to explore which conditions favour the evolution of parochial third-party punishment. We show that when groups interact and then engage in conflict with each other, third-party punishment is not parochial but spiteful, and directed towards all out-groups. A parochial bias in punishment decisions evolves (i) without conflict, when groups compete against nature and enforcing cooperation requires many punitive actions, and (ii) with conflict, when groups come into conflict with a group other than one they previously interacted with. Our findings suggest that intergroup conflict does not always lead to parochial punishment, and that stable collaborative relations between groups is a key factor promoting third-party parochial punishment. Our findings also provide novel predictions on how punishment and intergroup conflict influence in-group bias in human societies.     

Oxytocin Motivates Non-Cooperation in Intergroup Conflict to Protect Vulnerable In-Group Members

Intergroup conflict is often driven by an individual''s motivation to protect oneself and fellow group members against the threat of out-group aggression, including the tendency to pre-empt out-group threat through a competitive approach. Here we link such defense-motivated competition to oxytocin, a hypothalamic neuropeptide involved in reproduction and social bonding. An intergroup conflict game was developed to disentangle whether oxytocin motivates competitive approach to protect (i) immediate self-interest, (ii) vulnerable in-group members, or (iii) both. Males self-administered oxytocin or placebo (double-blind placebo-controlled) and made decisions with financial consequences to themselves, their fellow in-group members, and a competing out-group. Game payoffs were manipulated between-subjects so that non-cooperation by the out-group had high vs. low impact on personal payoff (personal vulnerability), and high vs. low impact on payoff to fellow in-group members (in-group vulnerability). When personal vulnerability was high, non-cooperation was unaffected by treatment and in-group vulnerability. When personal vulnerability was low, however, in-group vulnerability motivated non-cooperation but only when males received oxytocin. Oxytocin fuels a defense-motivated competitive approach to protect vulnerable group members, even when personal fate is not at stake.     

Conflict and competition between model-based and model-free control

A large literature has accumulated suggesting that human and animal decision making is driven by at least two systems, and that important functions of these systems can be captured by reinforcement learning algorithms. The “model-free” system caches and uses stimulus–value or stimulus–response associations, and the “model-based” system implements more flexible planning using a model of the world. However, it is not clear how the two systems interact during deliberation and how a single decision emerges from this process, especially when they disagree. Most previous work has assumed that while the systems operate in parallel, they do so independently, and they combine linearly to influence decisions. Using an integrated reinforcement learning/drift-diffusion model, we tested the hypothesis that the two systems interact in a non-linear fashion similar to other situations with cognitive conflict. We differentiated two forms of conflict: action conflict, a binary state representing whether the systems disagreed on the best action, and value conflict, a continuous measure of the extent to which the two systems disagreed on the difference in value between the available options. We found that decisions with greater value conflict were characterized by reduced model-based control and increased caution both with and without action conflict. Action conflict itself (the binary state) acted in the opposite direction, although its effects were less prominent. We also found that between-system conflict was highly correlated with within-system conflict, and although it is less clear a priori why the latter might influence the strength of each system above its standard linear contribution, we could not rule it out. Our work highlights the importance of non-linear conflict effects, and provides new constraints for more detailed process models of decision making. It also presents new avenues to explore with relation to disorders of compulsivity, where an imbalance between systems has been implicated.     

When to diversify,and with whom? Choosing partners among out-group strangers in lowland Bolivia

Evidence from the ethnographic and archaeological records reveals that humans often rely on out-group relationships for access to non-local resources and resource buffering. However, little is known about how actors choose out-group cooperative partners. The existing literature suggests that (in-group) partner choice is based on characteristics associated with greater cooperation (e.g., trustworthiness and productivity). Is out-group partner choice based on the same criteria as in-group? Because out-groups may be unique sources of resource access, we suggest that out-group partner choice should track characteristics of both the candidate partner and the partner's group that are associated with benefits for the actor. To assess partner choice, we employed a non-anonymous, one-shot economic game where participants could allocate money towards in-group and out-group strangers. Participants were from three populations of Bolivian horticulturalists (n = 200) that range in their market integration and their mobility, thus capturing variation in potential benefits to out-group cooperation. We find that individual-level qualities of prospective partners, such as wealth and trustworthiness, affect allocation behavior differently for in-group vs out-group prospective partners. While we find no consistent effects of perceived group qualities on a donor's giving to in-group and out-group members, the relevance of out-group market resource access for Tsimane' donors' allocations suggests that, at least when it comes to dividing a limited resource, qualities associated with a group can affect partner preference. Taken together, results provide insight into patterns of intergroup relationship building that have been crucial in the human lineage.     

Implications of armed conflict for maternal and child health: A regression analysis of data from 181 countries for 2000–2019

BackgroundArmed conflicts have major indirect health impacts in addition to the direct harms from violence. They create enduring political instability, destabilise health systems, and foster negative socioeconomic and environmental conditions—all of which constrain efforts to reduce maternal and child mortality. The detrimental impacts of conflict on global maternal and child health are not robustly quantified. This study assesses the association between conflict and maternal and child health globally.Methods and findingsData for 181 countries (2000–2019) from the Uppsala Conflict Data Program and World Bank were analysed using panel regression models. Primary outcomes were maternal, under-5, infant, and neonatal mortality rates. Secondary outcomes were delivery by a skilled birth attendant and diphtheria, pertussis, and tetanus (DPT) and measles vaccination coverage. Models were adjusted for 10 confounders, country and year fixed effects, and conflict lagged by 1 year. Further lagged associations up to 10 years post-conflict were tested. The number of excess deaths due to conflict was estimated. Out of 3,718 country–year observations, 522 (14.0%) had minor conflicts and 148 (4.0%) had wars. In adjusted models, conflicts classified as wars were associated with an increase in maternal mortality of 36.9 maternal deaths per 100,000 live births (95% CI 1.9–72.0; 0.3 million excess deaths [95% CI 0.2 million–0.4 million] over the study period), an increase in infant mortality of 2.8 per 1,000 live births (95% CI 0.1–5.5; 2.0 million excess deaths [95% CI 1.6 million–2.5 million]), a decrease in DPT vaccination coverage of 4.9% (95% CI 1.5%–8.3%), and a decrease in measles vaccination coverage of 7.3% (95% CI 2.7%–11.8%). The long-term impacts of war were demonstrated by associated increases in maternal mortality observed for up to 7 years, in under-5 mortality for 3–5 years, in infant mortality for up to 8 years, in DPT vaccination coverage for up to 3 years, and in measles vaccination coverage for up to 2 years. No evidence of association between armed conflict and neonatal mortality or delivery by a skilled birth attendant was found. Study limitations include the ecological study design, which may mask sub-national variation in conflict intensity, and the quality of the underlying data.ConclusionsOur analysis indicates that armed conflict is associated with substantial and persistent excess maternal and child deaths globally, and with reductions in key measures that indicate reduced availability of organised healthcare. These findings highlight the importance of protecting women and children from the indirect harms of conflict, including those relating to health system deterioration and worsening socioeconomic conditions.

Mohammed Jawad and co-workers report on a global analysis of maternal and child health outcomes in situations of armed conflict.     

Steeling Ourselves: Intragroup Communication while Anticipating Intergroup Contact Evokes Defensive Intergroup Perceptions

Two experiments investigated the role of intragroup communication in intergroup conflict (de-)escalation. Experiment 1 examined the effects of intragroup communication (vs. individual thought) and anticipated face-to-face intergroup contact (vs. no anticipated face-to-face intergroup contact). The group discussions of stigmatized group members who anticipated face-to-face intergroup contact revolved more around intergroup hostility. This boosted ingroup identification and increased social creativity but also led to steeling (a hardening of perceived intergroup relations). In Experiment 2, new participants listened to the taped group discussions. The discussions of groups anticipating face-to-face intergroup contact evoked more intergroup anxiety-related discomfort than discussions of groups not anticipating face-to-face intergroup encounters. Together, these results support the idea that steeling is a defensive reaction to prepare for an anxiety-arousing intergroup confrontation. Although steeling is also associated with positive consequences such as increased ingroup solidarity and social creativity, this hardened stance may be an obstacle to conflict de-escalation.     

Conflict and post-conflict behavior in a small group of chimpanzees

Chimpanzee research plays a central role in the discussions of conflict negotiation. Reconciliation, or the attraction and affiliation of former opponents following conflict, has been proposed as a central element of conflict negotiation in chimpanzees and various other taxa. In an attempt to expand the database of chimpanzee conflict resolution, conflict and post-conflict behavior were recorded for a small group of socially housed chimpanzees at the Chimpanzee and Human Communication Institute, at Central Washington University. Data were collected over six 6-week periods between 1997 and 2000, for a total of 840 hours of observation, resulting in a substantial post-conflict (PC) and matched control (MC) data set. The data demonstrate this group’s tendencies to maintain visual contact and closer proximity after conflicts. Dyadic corrected conciliatory tendencies ranged between 0 – 37.5% and averaged 17.25% across all dyads. Individual corrected conciliatory tendencies ranged between 5.8 and 32%. The results of this study combined with recent publications on captive and free-ranging chimpanzee post-conflict behavior suggest that variation in post-conflict behavior may be important to our understanding of chimpanzee conflict negotiation, and may also have implications for the design and management of captive chimpanzee enclosures and social groups, respectively.     

Differences in Nutrient Requirements Imply a Non-Linear Emergence of Leaders in Animal Groups

Collective decision making and especially leadership in groups are among the most studied topics in natural, social, and political sciences. Previous studies have shown that some individuals are more likely to be leaders because of their social power or the pertinent information they possess. One challenge for all group members, however, is to satisfy their needs. In many situations, we do not yet know how individuals within groups distribute leadership decisions between themselves in order to satisfy time-varying individual requirements. To gain insight into this problem, we build a dynamic model where group members have to satisfy different needs but are not aware of each other''s needs. Data about needs of animals come from real data observed in macaques. Several studies showed that a collective movement may be initiated by a single individual. This individual may be the dominant one, the oldest one, but also the one having the highest physiological needs. In our model, the individual with the lowest reserve initiates movements and decides for all its conspecifics. This simple rule leads to a viable decision-making system where all individuals may lead the group at one moment and thus suit their requirements. However, a single individual becomes the leader in 38% to 95% of cases and the leadership is unequally (according to an exponential law) distributed according to the heterogeneity of needs in the group. The results showed that this non-linearity emerges when one group member reaches physiological requirements, mainly the nutrient ones – protein, energy and water depending on weight - superior to those of its conspecifics. This amplification may explain why some leaders could appear in animal groups without any despotism, complex signalling, or developed cognitive ability.     

Post-Conflict Affiliation in Barbary Macaques is Influenced by Conflict Characteristics and Relationship Quality, but Does Not Diminish Short-Term Renewed Aggression

Many group living primates have evolved mechanisms to repair their social relationships after conflicts ('reconciliation'). We analysed the post-conflict behaviour of female Barbary macaques, Macaca sylvanus , living in the enclosure 'La Forêt des Singes' at Rocamadour, France. Based on a sample of 914 conflicts, we investigated whether relationship (kinship, rank, affiliation, support and sex) and conflict characteristics (conflict intensity, context and duration) affected the quality and frequency of affiliative post-conflict interactions. Thirty-two per cent of all conflicts were followed by post-conflict affiliation. Rates of socio-positive interactions and support were better predictors of post-conflict affiliation than kinship or rank. Short conflicts were followed by post-conflict affiliation relatively more frequently, after a shorter latency, but only briefly, and such interactions were initiated by both parties equally frequently. The majority of affiliative post-conflict interactions occurred immediately after the end of the conflict. In sum, female Barbary macaques invest more in post-conflict affiliation with valuable partners, and they modulate their post-conflict behaviour in relation to conflict characteristics. Remarkably, affiliative post-conflict interactions increased the short-term probability of renewed aggression by the former aggressor to 16% compared with 9% for conflicts that were not followed by affiliative behaviour. Such renewed aggression after post-conflict affiliation occurred particularly frequently among females and after conflicts over food, suggesting that post-conflict affiliation sometimes falsely lures the former victim to stay in the vicinity, even at the risk of receiving renewed aggression.     

Aggression does not increase friendly contacts among bystanders in geladas (<Emphasis Type="Italic">Theropithecus gelada</Emphasis>)

Aggression within a social group may affect bystanders’ affinitive behaviour with other bystanders. After a conflict such affiliations, termed ‘quadratic’, may serve to reduce tension. This particular kind of conflict management has been found in hamadryas baboons. Following the classical and well-established approach for studying post-conflict behaviour [post-conflict/matched control method (PC/MC)], we collected behavioural data on a group of geladas (Theropithecus gelada) in order to check for the presence of quadratic affiliations. A total of 192 PC/MC pairs were collected on both adults and immature individuals. We did not find any increase of affiliation levels between bystanders during PC compared with MC condition. The distribution of affinitive quadratic interactions was not affected by either kinship or relationship quality of bystanders. Moreover, comparison of yawning and self-scratching behaviours (two of the typical non-primate displacement activities under stressful situations) recorded during PCs and MCs did not show any variation in the two conditions. Probably, due to the male tolerance and social cohesiveness in geladas, witnessing a fight does not necessarily induce a sufficient increase of tension in bystanders to be reduced by quadratic affiliation.     

Cooperation during cultural group formation promotes trust towards members of out-groups

People often cooperate with members of their own group, and discriminate against members of other groups. Previous research establishes that cultural groups can form endogenously, and that these groups demonstrate in-group favouritism. Given the presence of cultural groups, the previous literature argues that cultural evolution selects for groups that exhibit parochial altruism. The source of initial variation in these traits, however, remains uninformed. We show here that a group''s economic production environment may substantially influence parochial tendencies, with groups formed around more cooperative production (CP) displaying less parochialism than groups formed around more independent production (IP) processes. Participants randomized into CP and IP production tasks formed cultural groups, and subsequently played hidden-action trust games with in-group and out-group trustees. We found CP to be associated with significantly greater sharing and exchanging behaviours than IP. In trust games, significant parochial altruism (in-group favouritism combined with out-group discrimination) was displayed by members of IP groups. By contrast, members of CP groups did not engage in either in-group favouritism or out-group discrimination. Further, we found the absence of out-group discrimination in CP to persist even following ‘betrayal’. Finally, belief data suggest that members of CP are not more intrinsically generous than IP members, but rather more likely to believe that out-group trustees will positively reciprocate. Our results have important implications for anyone interested in building cooperative teams, and shed new light on connections between culture and cooperation.     

Testing the function of reconciliation and third-party affiliation for aggressors in hamadryas baboons (Papio hamadryas hamadryas)

In social groups, agonistic conflicts can have different negative consequences. Several post-conflict interactions have been suggested as post-conflict management behaviors to mitigate those negative effects. In this study, we investigated the function of two post-conflict behaviors--reconciliation and aggressor-initiated third-party affiliation--on the aggressor's levels of post-conflict anxiety and aggression in a large colony of hamadryas baboons. We also examined variation in the aggressor's levels of post-conflict anxiety as a function of relationship quality between the opponents as predicted by the Integrated Hypothesis. We found that after conflicts hamadryas baboon aggressors showed increased rates of anxiety-related behaviors and that they were also more likely to be involved in renewed aggressive interactions. Although both reconciliation and aggressor-initiated third-party affiliation reduced the probability of receiving post-conflict aggression, only reconciliation reduced the rates of anxiety-related behaviors, suggesting that the aggressors' post-conflict anxiety might be owing mainly to the damage that the conflict causes to their relationship with the victim. Furthermore, aggressor's rates of post-conflict anxiety were higher after conflicts with individuals with whom they had a high-quality relationship, supporting the idea that levels of post-conflict anxiety mediate the occurrence of reconciliation depending on the quality of the relationship with former opponent as predicted by the Integrated Hypothesis.     

Asymmetry within social groups: division of labour and intergroup competition

Social animals vary in their ability to compete with group members over shared resources and also vary in their cooperative efforts to produce these resources. Competition among groups can promote within‐group cooperation, but many existing models of intergroup cooperation do not explicitly account for observations that group members invest differentially in cooperation and that there are often within‐group competitive or power asymmetries. We present a game theoretic model of intergroup competition that investigates how such asymmetries affect within‐group cooperation. In this model, group members adopt one of two roles, with relative competitive efficiency and the number of individuals varying between roles. Players in each role make simultaneous, coevolving decisions. The model predicts that although intergroup competition increases cooperative contributions to group resources by both roles, contributions are predominantly from individuals in the less competitively efficient role, whereas individuals in the more competitively efficient role generally gain the larger share of these resources. When asymmetry in relative competitive efficiency is greater, a group's per capita cooperation (averaged across both roles) is higher, due to increased cooperation from the competitively inferior individuals. For extreme asymmetry in relative competitive efficiency, per capita cooperation is highest in groups with a single competitively superior individual and many competitively inferior individuals, because the latter acquiesce and invest in cooperation rather than within‐group competition. These predictions are consistent with observed features of many societies, such as monogynous Hymenoptera with many workers and caste dimorphism.     

Social exchange and solidarity: in-group love or out-group hate?

Men exhibit a stronger tendency to favor the in-group over the out-group compared to women. We examined whether this male-specific “coalitional psychology” represents in-group love or out-group hate. One hundred thirty-three college freshmen played a prisoner's dilemma game with a member of their own group and a member of another group. Both groups consisted of same-sex participants. An in-group bias (cooperation with the in-group at a level higher than cooperation with the out-group) based on expectations of cooperation from the in-group was observed for both men and women. When such expectations were experimentally eliminated, women did not show any in-group bias, whereas men still exhibited an in-group bias. This male-specific in-group bias was found to be a product of intragroup cooperation (in-group love) rather than a product of intergroup competition (out-group hate). These findings suggest that the male-specific coalitional psychology caters more toward the promotion of within-group solidarity than aggression against the out-group.