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International audience; It was long assumed that only humans can distinguish the living from the dead. Renewed interest in this question over the last decade has led several authors to assert that non-human primates are also aware of death. We investigate this issue by comparing the behaviours of monkeys and great apes toward helpless conspecifics, basing our analysis on published reports. We first examine the behaviours of mothers towards the body of their dead offspring. They may carry the corpse for days or more before abandoning it. They groom, inspect and protect it, sometimes allowing group members to explore it, and rare cases of cannibalism have been reported. No significant difference is observed in the way that monkeys and great apes treat the bodies of infants. We then examine responses to collapsed (still able to move and react) and inanimate (unresponsive or dead) conspecifics. Monkeys and great apes guard, care for and inspect their helpless partners, and also manipulate and mobilise them. Through these actions, individuals may inform themselves about the state of their partners, test their responsiveness and/or attempt to rouse them. It appears that only chimpanzees and gorillas show violent action such as display behaviours and the rough treatment of bodies. They can also make distress calls, and periods of "stunned silence" sometimes occur in chimpanzees, indicating that they are experiencing intense emotion. Finally, we argue that while both monkeys and great apes detect body dysfunction through the victims' inability to wake up and move, only great apes can understand that something serious has happened. The signs of emotional disturbance reported in them indicate that they may believe that inanimate conspecifics have entered a state of "dormancy", meaning that they are unlikely to regain wakefulness. However, there is no evidence that any non-human primates are aware of mortality.

This work was supported by grants from the Agence Nationale de la Recherche (ANR-08-412 BLAN-0042-01) and the European Science Foundation (Compcog Exchange Grant N°3648). Many studies investigate the decisions made by animals by focussing on their individual attitudes towards risk, i.e., risk seeking, risk neutrality or risk aversion. However, little attention has been paid to how far individuals understand the different odds of outcomes. In a previous gambling task involving up to 18 different lotteries (Pelé et al., 2014), non-human primates used probabilities of gains and losses to make their decision. Although the use of complex mathematical calculation for decision-making seemed unlikely, we applied a gradual decrease in the chances to win throughout the experiment. This probably facilitated the extraction of information about odds. Here, we investigated whether individuals would still make efficient decisions if this facilitating factor was removed. To do so, we randomized the order of presentation of the 18 lotteries. Individuals from four ape and two monkey species were tested. Only capuchin monkeys differed in their gambling behaviour, playing even when there was nothing to win. Randomising the lottery presentation order leads all species to predominantly use a maximax heuristic in which individuals gamble as soon as there is at least one chance to win more than they already possess, whatever the risk. Most species also gambled more as the frequency of larger rewards increased. These results suggest the occurrence of optimistic behaviour. The maximax heuristic is sometimes observed in human managerial and financial decision-making, where risk is ignored for potential gains, however low they may be. Our results suggest a shared and strong propensity in primates to rely on heuristics whenever complexity in evaluation of outcome odds arises. Postprint Postprint

International audience; In species that move in cohesive groups, animals generally reach decisions through socially distributed processes, and individual knowledge is expected to influence collective decision making. Pooling of information should not be considered a general rule, however, since conflicts of interest may occur between group members. When resources are limited or highly attractive, higher-ranking individuals can prevent others from accessing food, and subordinates may have an interest in withholding information about its location. We investigated the role individual knowledge may play in recruitment processes in four groups of horses (Equus caballus). Animals were repeatedly released in a food search situation, in which one individual had been informed about the location of a preferred food, while another was a naïve control subject. Horses that were informed about the location of the feeding site were seen to approach the food source more steadily and were followed by a higher number of group members than their uninformed counterparts. Recruitment processes appeared mostly passive. Among the informed subjects, lower-ranking individuals were overall less followed than the higher-ranking ones. Most lower-ranking horses arrived alone at the feeding site. Non-followed informed subjects spent less time in active walk and used direct paths less frequently than followed animals, and they were joined by fewer partners at the attractive food source and spent more time feeding alone. This indicates that the influence of informed individuals on the behavior of other group members was a mixed process. Some horses brought nutritional benefits to their conspecifics by leading them to food supplies, whereas the behavior of others might be functionally deceptive

Individual-based computer models show that different mechanisms, proximity-based or emotional bookkeeping, can lead to reciprocation. By comparing social networks from different computer models with those of empirical data, we show that the models’ social networks bear limited resemblance with some features of the observed social networks. This indicates that additional social processes (third-party awareness) may be needed in these models to represent more accurately the social behavior and interaction patterns observed in group-living animals.

Observations of animals' responses to dying or dead companions raise questions about their awareness of states of helplessness or death of other individuals. In this context, we report the case of a female Tonkean macaque (Macaca tonkeana) that transported the body of her dead infant for 25 days and cannibalized its mummified parts. The mother appeared agitated in the first 2 days after the birth. She then took care of her infant's corpse, which progressively dried and became mummified. In a third stage, the mother continued to transport the corpse as it started disintegrating, and she gnawed and consumed some parts of the remains. Our observations suggest that mummification of the body favored persistence of maternal behaviors by preserving the body's shape. The female gradually proceeded from strong attachment to the infant's body to decreased attachment, then finally full abandonment of the remains.

International audience; Among nonhuman primates, the evolutionary underpinnings of variation in social structure remain debated, with both ancestral relationships and adaptation to current conditions hypothesized to play determining roles. Here we assess whether interspecific variation in higher‐order aspects of female macaque (genus: Macaca ) dominance and grooming social structure show phylogenetic signals, that is, greater similarity among more closely‐related species. We use a social network approach to describe higher‐order characteristics of social structure, based on both direct interactions and secondary pathways that connect group members. We also ask whether network traits covary with each other, with species‐typical social style grades, and/or with sociodemographic characteristics, specifically group size, sex‐ratio, and current living condition (captive vs. free‐living). We assembled 34–38 datasets of female‐female dyadic aggression and allogrooming among captive and free‐living macaques representing 10 species. We calculated dominance (transitivity, certainty), and grooming (centrality coefficient, Newman's modularity, clustering coefficient) network traits as aspects of social structure. Computations of K statistics and randomization tests on multiple phylogenies revealed moderate‐strong phylogenetic signals in dominance traits, but moderate‐weak signals in grooming traits. GLMMs showed that grooming traits did not covary with dominance traits and/or social style grade. Rather, modularity and clustering coefficient, but not centrality coefficient, were strongly predicted by group size and current living condition. Specifically, larger groups showed more modular networks with sparsely‐connected clusters than smaller groups. Further, this effect was independent of variation in living condition, and/or sampling effort. In summary, our results reveal that female dominance networks were more phylogenetically conserved across macaque species than grooming networks, which were more labile to sociodemographic factors. Such findings narrow down the processes that influence interspecific variation in two core aspects of macaque social structure. Future directions should include using phylogeographic approaches, and addressing challenges in examining the effects of socioecological factors on primate social structure.

International audience; Whereas most experiments indicate that monkeys have no theory of mind, a study carried out by Wood and collaborators (2007) claimed that they can make inferences about the intentions of another individual. We applied the experimental procedure devised by these authors to investigate whether monkeys can recognize goal-directed actions. We tested 16 Tonkean macaques (Macaca tonkeana) and 12 tufted capuchin monkeys (Sapajus apella). Each subject was submitted to 24 trials in randomized order. The experimenter presented 2 containers, 1 of which was potentially baited with a food reward. After the experimenter had either intentionally or accidentally made an action on 1 of the containers, the subject was asked to select 1 of them. We found that individuals in both species failed to distinguish between accidental and intentional actions. However, they displayed a significant preference for the container touched by the experimenter in the hand conditions, and not in the elbow conditions. These results do not support those reported by Wood and collaborators, but they are consistent with other studies concluding that monkeys are not capable of mind reading

International audience; Social bonds between group members affect individual fitness and wellbeing. While the impact of bond strength is well studied, the consequences of bond predictability and equitability are often overlooked. Similarly, whether bonds reflect short-term contingencies and/or long-term social strategies remains understudied. We investigated these questions in female crested macaques, Macaca nigra, which display a tolerant social style within a nepotistic hierarchical social structure. We analysed the structure of social bonds by testing whether similarity within dyads (in kinship, dominance and age) predicted the strength, predictability and equitability of bonds. We then tested the value of social bonds by analysing the effect of their characteristics on three fitness-related behaviours: coalitionary support, feeding-in-proximity and aggression. We found that the bond characteristics of females differed substantially from those of other species with comparable data: bonds were of average strength, of moderate endurance and relatively balanced. Stronger bonds were more equitable but less predictable than weaker bonds. Closely ranked females, but not kin or age peers, had stronger, more predictable and more equitable bonds than others. Coalitionary support was not related to any of the bond characteristics, feeding-in-proximity was positively associated with strength and predictability and aggression was positively linked to strength and negatively to equitability. These results highlight the complex picture of the benefits of social bonds in this species. They reflect the degrees of freedom tolerant macaque females can express in their social relationships within their stable social structure, a pattern that may not be given enough consideration in stable nepotistic hierarchical societies. Comparative research is necessary to establish whether these patterns are more general than previously thought or a specific feature of tolerant macaques. Investigating various characteristics of bonds together is paramount to appreciate the dynamics of social relationships and to better understand the social components of fitness.

Males living in multi-male groups are both strong rivals and potential allies. In several primate species they regularly interact through ritualized exchanges known as greetings. We studied five captive groups of Tonkean macaques (Macaca tonkeana) to test five hypotheses regarding the social function of greetings. We found that greetings were mostly reciprocal interactions, and that they often involved physical contact and facial displays. Although they were mostly initiated by the higher-ranking individual in each dyad, subordinates could initiate approximately one-third of greetings, which indicates that greetings do not serve as a formal acknowledgement of dominance relationships. Although greeting frequencies were negatively correlated to the frequency of supplantations and conflicts, they were not significantly influenced by age and dominance status, showing that greetings are not used to appease partners or decrease tension between males. Males most frequently greeted partners with whom they spent more time in proximity and body contact, and this is consistent with the hypothesis that greetings play a role in reinforcing social relationships. Lastly, greetings increased in frequency between individuals involved in challenges for rank, lending support to the hypothesis that males assess the state of their social relationships through greetings. Am. J. Primatol. 76:989–998, 2014. © 2014 Wiley Periodicals, Inc.

International audience; Species comparisons of personality structure (i.e., how many personality dimensions and the characteristics of those dimensions) can facilitate questions about the adaptive function of personality in nonhuman primates. Here we investigate personality structure in the brown capuchin monkey (Sapajus apella), a New World primate species, and compare this structure to those of chimpanzees (Pan troglodytes), orangutans (Pongo spp.), and rhesus macaques (Macaca mulatta). Brown capuchins evolved behavioral and cognitive traits that are qualitatively similar to those of great apes, and individual differences in behavior and cognition often reflect differences in personality. Thus, we hypothesized that brown capuchin personality structure would overlap more with great apes than with rhesus macaques. We obtained personality ratings from seven sites, including 127 brown capuchin monkeys. Principal-components analysis identified five personality dimensions (Assertiveness, Openness, Neuroticism, Sociability, and Attentiveness), which were reliable across raters and, in a subset of subjects, significantly correlated with relevant behaviors up to a year later. Comparisons between species revealed that brown capuchins and great apes overlapped in personality structure, particularly chimpanzees in the case of Neuroticism. However, in some respects (i.e., capuchin Sociability and Openness) the similarities between capuchins and great apes were not significantly greater than those between capuchins and rhesus macaques. We discuss the relevance of our results to brown capuchin behavior and the evolution of personality structure in primates. (PsycINFO Database Record (c) 2013 APA, all rights reserved).

The clumped distribution of food resources promotes food defensibility and can lead to the monopolizing of resources by high-ranking individuals. However, the balance of power is set at different levels according to societies, meaning that resource partitioning should vary between them. This study investigates whether dominance asymmetry and resource partitioning are related in non-human primates by comparing two species with contrasting social styles, namely rhesus macaques (Macaca mulatta) which display strong social intolerance and a steep gradient of dominance, and Tonkean macaques (Macaca tonkeana), which exhibit higher levels of tolerance and more balanced dominance relationships. Study groups were kept in semi-free ranging conditions. Animals were provided with fruit in three different clumped conditions during 30-min trials. We found that higher-ranking rhesus macaques had priority for the access to fruit: these individuals spent longer in the feeding area in the first 10-min period of trials, while lower-ranking individuals had diminished access to fruit under the most clumped condition; this was associated with sustained agonistic interactions. Dominance effects were weaker in Tonkean macaques. They exhibited co-feeding between high- and low-ranking individuals in the first period; there was no significant effect of dominance even in the most clumped condition; and frequencies of agonistic interactions remained moderate relative to the number of individuals present in the feeding area. These results show that food resources were more equitably distributed among group members in tolerant macaques than in their intolerant counterparts. Dominance gradient and social tolerance may be considered as two aspects of the same phenomenon.

Nonhuman primates show remarkable variation in several aspects of social structure. One way to characterize this variation in the genus Macaca is through the concept of social style, which is based on the observation that several social traits appear to covary with one another in a linear or at least continuous manner. In practice, macaques are more simply characterized as fitting a four-grade scale in which species range from extremely despotic (grade 1) to extremely tolerant (grade 4). Here, we examine the fit of three core measures of social style-two measures of dominance gradients (hierarchical steepness) and another closely related measure (counter-aggression)-to this scale, controlling for phylogenetic relationships. Although raw scores for both steepness and counter-aggression correlated with social scale in predicted directions, the distributions appeared to vary by measure. Counter-aggression appeared to vary dichotomously with scale, with grade 4 species being distinct from all other grades. Steepness measures appeared more continuous. Species in grades 1 and 4 were distinct from one another on all measures, but those in the intermediate grades varied inconsistently. This confirms previous indications that covariation is more readily observable when comparing species at the extreme ends of the scale than those in intermediate positions. When behavioral measures were mapped onto phylogenetic trees, independent contrasts showed no significant consistent directional changes at nodes below which there were evolutionary changes in scale. Further, contrasts were no greater at these nodes than at neutral nodes. This suggests that correlations with the scale can be attributed largely to species' phylogenetic relationships. This could be due in turn to a structural linkage of social traits based on adaptation to similar ecological conditions in the distant past, or simply to unlinked phylogenetic closeness.

International audience; Abstract Sexual competition is potentially disruptive for the cohesion of social groups because stress and conflicts can extend to other group members. The displays and interactions of sexual partners are liable to influence the behavior of groupmates, which may need to observe them to anticipate possible consequences. We studied 2 captive groups of Tonkean macaques (Macaca tonkeana) to test whether group-mates pay more attention to consort partners, modify their activities and social interactions, and exhibit signs of stress during periods of sexual consortships. We found that group-mates approached the top-ranking male more frequently and were more frequently oriented toward the consort pair at the time of consortship than at other times. Group-mates spent less time sleeping, and devoted less time to manipulating the environment and more time to monitoring during consortship. This indicates that consortships may incur costs in individuals not involved in sexual competition. However, Tonkean macaques did not exhibit any signs of increased stress during consortship periods, as their rates of scratching and yawning did not differ between consortship and nonconsortship periods. This study shows that not only direct competitors but also other individuals monitor the behavior of sexual partners. It is likely that group-mates obtain information this way about ongoing action, and take decisions accordingly.

International audience; Animals commonly face choices requiring them to wait and postpone action. The ability to delay gratification is a prerequisite for making future-oriented decisions. We investigated the ability of brown capuchins (Cebus apella) and Tonkean macaques (Macaca tonkeana) to delay benefits in several experiments. In exchange tasks, subjects had to return a piece of cookie after a given time lag to obtain a larger one from an experimenter. Capuchins could wait 10–40 s and macaques 20–80 s depending on subjects and the size of rewards. Both groups were able to anticipate delay durations, but unlike macaques, capuchins discounted all sizes of reward at the same speed, meaning that their delay-maintenance was not affected by the reward size. When the subjects could give the initial piece of cookie back immediately and then wait for the return, performances increased to 10–21 min for capuchins and 21–42 min for macaques, demonstrating the role of consumption inhibition in postponing gratification. In a further task, we presented subjects with an accumulation of food pieces added at short intervals until they seized them. On average, brown capuchins could wait 33–42 s and macaques 38–72 s before seizing the rewards. Our results confirmed that brown capuchins were more impulsive than Tonkean macaques in several tasks. We did not find significant differences between the waiting performances of the Tonkean macaques and those previously reported in long-tailed macaques. The contrasting performances of macaques and capuchins might be related to their different skills in the physical and social domains

International audience; Aggression is potentially disruptive for social groups. Although individuals witnessing a conflict are not directly threatened by aggressive interactions, the aftermath of aggression appears to be a period of social instability.We expected bystanders to respond to conflicts by affiliating with other group members and so reducing social tension. To test this hypothesis we collected data on two captive groups of Tonkean macaques, Macaca tonkeana. After an agonistic interaction, the behaviours of focal individuals uninvolved in the conflict were recorded over 5 min postconflict periods, for comparison with baseline periods. The results showed that bystanders were more likely to show affiliation during postconflict periods than in baselines. We found that affiliation occurred more frequently between individuals linked by friendship, whereas no significant effect of kinship appeared, which may be related to the open social relationships reported in Tonkean macaques. Females initiated affiliation sooner than males and conflicts involving physical contact were more quickly followed by affiliation between bystanders. Rates of scratching tended to decrease after the first affiliative interaction. None the less, few signs of anxiety were observed in bystanders. Our results reflect the high propensity of Tonkean macaques to appease others and stop aggression. This study demonstrates that postconflict affiliation occurs between bystanders in a species characterized by tolerant social relationships. It could be a pervasive means of social cohesion among primates.

International audience; Most studies about social play have focused on its function in aiding socialization. It is not known whether play patterns vary by species according to specific adult social relationships. To test whether there is covariation between the form of play interactions and adult relationships, we studied social play in Japanese macaques (Macaca fuscata) and crested macaques (Macaca nigra). Comparative studies have shown that whereas low levels of tolerance and strict hierarchies characterize Japanese macaques, crested macaques display greater tolerance and relaxed dominance. The results showed that the former prefer less risky games, with minimal physical contact, ease of escape and a small number of play partners. The play bouts of the latter species involve closer contact and more partners. We conclude that play patterns covary with specific social style. Play patterns could have been selected for to introduce youngsters to their future social environment.

International audience; By distinguishing the attentional cues of theirmates, animals can learn what part of their environment is ofpotential interest. However, recognizing the attentional statesof others through auditory perception appears to be difficult,since these states are generally not accompanied by ostensivesignals liable to reveal them. In this context, one study foundthat rhesus macaques withhold their action when unobserved,then concluding that they know what others can hear. Wereplicated this study by testing 18 Tonkean macaques in anexperimental setting where subjects had to choose betweentwo boxes containing a food reward. One box made a noisewhen opened, and the other opened silently. An experimenterwas present and could either have her back to subjects or befacing them. If subjects aimed to avoid attracting the experimenter’sattention, they were expected to select the silent boxwhile the experimenter’s back was turned. Results showedthat subjects did not discriminate between boxes,whatever theexperimenter’s position. We thus found no evidence thatTonkean macaques are able to take the auditory attentionalstates of a human into account. It is therefore premature toconclude that monkeys can establish a link between hearingand knowing.

To assess how brown capuchin monkeys (Cebus apella) delay gratification and maximize payoff, we carried out four experiments in which six subjects could exchange food pieces with a human experimenter. The pieces differed either in quality or quantity. In qualitative exchanges, all subjects gave a piece of food to receive another of higher value. When the difference of value between the rewards to be returned and those expected was higher, subjects performed better. Only two subjects refrained from nibbling the piece of food before returning it. All subjects performed two or three qualitative exchanges in succession to obtain a given reward. In quantitative exchanges, three subjects returned a food item to obtain a bigger one, but two of them nibbled the item before returning it. Individual differences were marked. Subjects had some difficulties when the food to be returned was similar or equal in quality to that expected.

International audience; Leadership is commonly invoked when accounting for the coordination of group movements in animals, yet it remains loosely defined. In parallel, there is increased evidence of the sharing of group decisions by animals on the move. How leadership integrates within this recent framework on collective decision-making is unclear. Here, we question the occurrence of leadership in horses, a species in which this concept is of prevalent use. The relevance of the three main definitions of leadership - departing first, walking in front travel position, and eliciting the joining of mates - was tested on the collective movements of two semi-free ranging groups of Przewalski horses (Equus ferus przewalskii). We did not find any leader capable of driving most group movements or recruiting mates more quickly than others. Several group members often displayed pre-departure behaviours at the same time, and the simultaneous departure of several individuals was common. We conclude that the decision-making process was shared by several group members a group movement (i.e., partially shared consensus) and that the leadership concept did not help to depict individual departure and leading behaviour across movements in both study groups. Rather, the different proxies of leadership produced conflicting information about individual contributions to group coordination. This study discusses the implications of these findings for the field of coordination and decision-making research.

International audience; Animals deal with predictable and unpredictable events on a daily basis. Yetour knowledge of the cognitive processes involved in decisions remains limited. Wetested capuchins, macaques and orang-utans in a food-gambling task to investigatewhether or not individuals estimate the chances of different outcomes. Resultshighlighted that gambling decisions were negatively induced by the probability oflosing and the frequency of previous losses, and positively induced by the probabilityof gaining. Actual decisions were consistent with first order stochastic dominance. Thestudy of second order stochastic dominance revealed that macaques were risk-pronewhereas capuchins and orang-utans were risk-adverse. We detected responses comparableto the hot-hand effect, a bias found in humans. Capuchins and orang-utansexhibited probability distortion and loss aversion, which were not systematically foundin macaques. Given the heterogeneity among individuals, we implemented mixture models and showed that attitudes towards risk and probabilities play complementary and different roles in the three species

International audience; Aggression can generate anxiety, create uncertainty about its aftermath and jeopardise social relationships. Postconflict interactions serve as conflict management strategies to mitigate these consequences. Whereas postconflict interactions are well characterized in many animals, their functions are still insufficiently investigated. Four functional hypotheses have been proposed: stress reduction, relationship repair, self-protection and benign intent. We aimed to test these hypotheses in females of a tolerant macaque species, the crested macaque, Macaca nigra, under natural conditions, for three postconflict interactions: reconciliation, affiliation and aggression with third parties. Our results provide meaningful contrasts compared with findings in other species. We found no evidence that aggression had consequences for individuals' behavioural indicators of anxiety, although it increased the likelihood of secondary aggression with third parties. There was little evidence for the stress reduction hypothesis as the occurrence of any of the three postconflict interactions investigated had little effect on the measured behavioural indicators of anxiety. Conflict and dyad characteristics also had limited influence on anxiety. The relationship repair function was only partly validated: dyads with stronger bonds or that exchanged more support did not reconcile more often, but dyads with attributes related to the symmetry, stability and predictability (i.e. security) within relationships did. Patterns of initiation and directionality of postconflict interactions in this study population suggest that reconciliation may constitute the signalling of appeasement and benign intent. Furthermore, we found that aggression towards third parties may serve as a source of self-protection and reassertion of the females' social status. The distinctive pattern of postconflict management strategies revealed in wild female crested macaques appears to be related to their typically tolerant social style. These results demonstrate the usefulness of concomitantly studying aggression, postconflict interactions and their functions, to understand conflict management strategies comprehensively, while taking into account the level of social tolerance characterizing the studied society.

International audience; The evolutionary study of social systems in non-human primates has long been focused on ecological determinants. The predictive value of socio-ecological models remains quite low, however, in particular because such equilibrium models cannot integrate the course of history. The use of phylogenetic methods indicates that many patterns of primate societies have been conserved throughout evolutionary history. For example, the study of social relations in macaques revealed that their social systems are made of sets of correlated behavioural traits. Some macaque species are portrayed by marked social intolerance, a steep dominance gradient and strong nepotism, whereas others display a higher level of social tolerance, relaxed dominance and a weaker influence of kinship. Linkages between behavioural traits occur at different levels of organization, and act as constraints that limit evolutionary responses to external pressures. Whereas these constraints can exert strong stabilizing selection that opposes the potential changes required by the ecological environment, selective mechanisms may have the potential to switch the whole social system from one state to another by acting primarily on some key behavioural traits that could work as pacemakers.

In primates, females typically drive the evolution of the social system and present a wide diversity of social structures. To understand this diversity, it is necessary to document the consistency and/or flexibility of female social structures across and within species, contexts, and environments. Macaques (Macaca sp.) are an ideal taxon for such comparative study, showing both consistency and variation in their social relations. Their social styles, constituting robust sets of social traits, can be classified in four grades, from despotic to tolerant. However, tolerant species are still understudied, especially in the wild. To foster our understanding of tolerant societies and to assess the validity of the concept of social style, we studied female crested macaques, Macaca nigra, under entirely natural conditions. We assessed their degree of social tolerance by analyzing the frequency, intensity, and distribution of agonistic and affiliative behaviors, their dominance gradient, their bared-teeth display, and their level of conciliatory tendency. We also analyzed previously undocumented behavioral patterns in grade 4 macaques: reaction upon approach and distribution of affiliative behavior across partners. We compared the observed patterns to data from other populations of grade 4 macaques and from species of other grades. Overall, female crested macaques expressed a tolerant social style, with low intensity, frequently bidirectional, and reconciled conflicts. Dominance asymmetry was moderate, associated with an affiliative bared-teeth display. Females greatly tolerated one another in close proximity. The observed patterns matched the profile of other tolerant macaques and were outside the range of patterns of more despotic species. This study is the first comprehensive analysis of females’ social behavior in a tolerant macaque species under natural conditions and as such, contributes to a better understanding of macaque societies. It also highlights the relevance of the social style concept in the assessment of the degree of tolerance/despotism in social systems. Am. J. Primatol. 75:361-375, 2013. © 2013 Wiley Periodicals, Inc.

International audience; Whether or not non-human animals can plan for the future is a hotly debated issue. We investigate this question further and use a planning-to-exchange task to study future planning in the cooperative domain in two species of monkeys: the brown capuchin (Cebus apella) and the Tonkean macaque (Macaca tonkeana). The rationale required subjects to plan for a future opportunity to exchange tokens for food by collecting tokens several minutes in advance. Subjects who successfully planned for the exchange task were expected to select suitable tokens during a collection period (5/10 min), save them for a fixed period of time (20/30 min), then take them into an adjacent compartment and exchange them for food with an experimenter. Monkeys mostly failed to transport tokens when entering the testing compartment; hence, they do not seem able to plan for a future exchange with a human partner. Three subjects did however manage to solve the task several times, albeit at very low rates. They brought the correct version of three possible token types, but rarely transported more than one suitable token at a time. Given that the frequency of token manipulation predicted transport, success might have occurred by chance. This was not the case, however, since in most cases subjects were not already holding the token in their hands before they entered the testing compartment. Instead, these results may reflect subjects' strengths and weaknesses in their time-related comprehension of the task.

International audience; Group-living animals travel together to collectively exploit the resources of their environment. This study investigates how social relationships and individual temperament traits affect movement orders in domestic cattle and sheep. We analysed spontaneous group movements occurring at pasture after a resting period in a group of 15 18-month-old Charolais heifers and a group of 19 1-year-old Romane ewe-lambs. For each species, animals had similar social experience and no kinship ties. Before that, animals were observed within the group to establish their social status (e.g. dominance and preferential relationships, and sociability), then in individual tests in order to assess their emotional traits. In both species, most individuals could initiate a group movement but some individuals were more successful than others in recruiting the rest of the group. Ewe-lambs, and to a lesser extent heifers, held preferential positions during travel. We did not find any significant correlations in either species between animal order and their position in the dominance hierarchy (heifers: P50.438; ewe-lambs: P50.574) while individuals linked by preferential bonds frequently followed each other during group movements (heifers: P,0.001; ewe-lambs: P,0.001). With regard to social traits, heifers with a low cohesion index, and with a lower number of partners with whom they develop frequent affinitive interactions, acted more frequently as ‘first movers' ( P50.040 and 0.023, respectively), as well as did ewe-lambs with a high spatial independency index ( P50.002). Ewe-lambs with the highest cohesion indices were more frequently observed in front of the group while moving halfway between departure and arrival ( P50.028). We did not find significant correlations between individual positions during group movements and emotional traits such as reactivity, boldness and fearfulness. We conclude that preferential bonds and individual traits related to social dependence were more influential in spontaneous group movements at pasture than were emotional traits and dominance status.

International audience; To investigate the rise of economic abilities during development we studied children aged between 3 and 10 in an exchange situation requiring them to calculate their investment based on different offers. One experimenter gave back a reward twice the amount given by the children, and a second always gave back the same quantity regardless of the amount received. To maximize pay-offs children had to invest a maximal amount with the first, and a minimal amount with the second. About one third of the 5-year-olds and most 7- and 10-year-olds were able to adjust their investment according to the partner, while all 3-year-olds failed. Such performances should be related to the rise of cognitive and social skills after 4 years.

International audience; Phylogenetic models of primate social behaviour posit that core social traits are inherent species characteristics that depend largely on phylogenetic histories of species rather than on adaptation to current socioecological conditions. These models predict that aspects of social structure will vary more between species than within species and that they will display strong phylogenetic signals. We tested these predictions in macaques focusing on dominance gradients, a relatively little studied, yet central, aspect of social structure.We used data from 14 social groups representing nine macaque species living in a variety of conditions. We examined proportions of counteraggression and two recently developed measures of dominance gradients (hierarchical steepness) for phylogenetic signals in nine phylogenetic trees constructed using (1) available genetic data sets and (2) Bayesian Markov Chain Monte Carlo (MCMC) and maximum likelihood algorithms. Hierarchical steepness and counteraggression showed significant variation between species but inconsistent variation within species. Both steepness and counteraggression showed evidence of phylogenetic signals, with results being particularly strong for one steepness measure and for counteraggression. Our results suggest that between-species variation in some core aspects of social structure are shaped by species' evolutionary relationships, despite differences in living conditions. As such, they provide broad support for the phylogenetic model.

Acquire and Share Few would argue with the stance that human social cognition supports an unequaled capacity to acquire knowledge and to share it with others. Dean et al. (p. 1114 ; see the Perspective by Kurzban and Barrett ) compared the extent to which these social and cognitive psychological processes can be elicited in children, capuchins, and chimpanzees through the use of a three-level puzzlebox task. Incentivized by improving rewards, 3- to 4-year-old children progressed from the first to the third level by imitating observed actions, taught other members of their social group how to solve the problem, and shared the rewards obtained. By contrast, neither the capuchins nor chimpanzees, very few of which ever reached the third level, exhibited these charactertistics.

International audience; The ability to wait for a reward is a necessary capacity for economic transactions. This 26 study is an age-related investigation of children's ability to delay gratification in an 27 exchange task requiring them to wait for a significant reward. We gave 252 children aged 28 2-4 a small piece of cookie, then offered them an opportunity to wait for a predetermined 29 delay period before exchanging it for a larger one. In a first experiment, the children had to 30 exchange the initial food item for rewards two, four or eight times larger. Results showed 31 that children aged 3-4 years old sustained longer time lags for larger rewards than for 32 smaller rewards. This effect was not found in 2-year-old subjects. In a second experiment, 33 a reward 40 times larger than the initial piece was offered to determine the maximum 34 waiting time that children could sustain. All age groups increased their performances. 35 Older children were more successful at waiting, but some children as young as 2 years 36 old were able to tolerate delays of up to 16 min. Older children who chose to give up wait- 37 ing earlier than their known capacity demonstrated anticipation skills which had not been 38 seen in younger children, showing that they had anticipated an increase in the time lag, 39 and that they had considered both time and reward value when making their decision. 40 Despite the age effect, we did not establish any limits for delaying gratification in children. 41 This study may have educational implications for dealing with behavioral misconduct, 42 which is known to be related to impulsivity control in young children

International audience; Play signals are viewed as important means by which animals inform each other that bites, strikes, and throws that occur during play fighting are indeed playful rather than serious. One such signal is the open mouth play face that is common in primates and many other mammals. Unfortunately, as most play fighting involves biting, it can be ambiguous as to whether any instance of opening the mouth is performed to communicate playful intent or is simply a preparation for biting. In this study, open mouths co-occurring with the bared-teeth display (teeth-baring) in Tonkean macaques were used to assess the context in which facial gestures only relevant for signaling (i.e., teeth-baring is not necessary for biting) are used during play. Two predictions arising from the hypothesis that play signals are used to facilitate playful contact were tested: that the open mouth with teeth-baring should (1) be most frequent preceding contact, and (2) that it should be performed most often when bites are directed at orientations that is visible to the recipient. The data only partially support these predictions. The open mouth with teeth-baring is also frequently used when a monkey withdraws from playful contact. Moreover, it is associated with bites to body targets, such as the rump, that offer little prospect for detection by the recipient; this supports the possibility that play signals may sometimes be emitted not to communicate with the partner but with the performer itself. Thus, play signals serve multiple functions during play fighting.

Celebrations and bursts of communal joy can occur spontaneously in human communities based on mechanisms of emotional contagion. Some examples of similar collective excitement have been reported in animals when they reunite or anticipate rewards, but little is known about the processes and meaning of these multiple interactions. We experimen- tally studied such collective arousals in two captive groups of Tonkean macaques (Macaca tonkeana) within the context of reunions following the temporary separa- tion of two subgroups. We compared the behaviors of individuals after separation periods of 2 and 48 h with a control period with no separation. This study showed that it is possible to reproducibly induce bursts of friendly interactions in which groupmates run around over a period of several minutes, embracing and grasp- ing one another while displaying numerous affiliative vocalizations and facial expressions. The longer the pe- riod of separation, the higher and longer-lasting the rates of affiliative interactions were. Individuals affili- ated more frequently with groupmates from a previously separated subgroup than with those having stayed in their own subgroup. Collective arousal was followed by a quieter period characterized by high rates of contact-sit- ting and social grooming. These results point at the role of collective arousals in social cohesion; they could resolve social tension and renew social relationships. We propose that the emotional state experienced by Tonkean macaques during such events represents a disposition similar to that giving rise to what we humans call ''shared joy.'' Am J Phys Anthropol 146:457-464, 2011. V C 2011 Wiley-Liss, Inc.

International audience; In group-living species, individuals gain significant advantages from establishing an extensive network of social relationships. This results in complex organizations that are difficult to quantify in a comprehensive manner. In this respect, network analyses are an ideal means to pinpoint the overall properties of social structures, and the place of each individual within these structures. We used network measurements to investigate cross-species variations in the social style of macaques, and studied 12 groups from four species. Two species (Macaca mulatta, Macaca fuscata) were characterized by a relatively weak social tolerance, a steep gradient of dominance and a strong preference for kin. The other two species (Macaca nigra, Macaca tonkeana) were known to display higher levels of tolerance, relaxed dominance and low kinship bias. We used a centrality index based on eigenvector centrality to show that in a comparison of intolerant and tolerant species, top-ranking individualswere more central than other group members in the former species than the latter.We also found that networks had higher modularity in intolerant species, indicating that kinrelated partners interacted more frequently in subgroups of these species than in those of tolerant species. Consistently, the matrix of body contacts was more strongly correlated with the kinship matrix in intolerant species. This study demonstrates the efficiency of network methodology in detecting fine and overall contrasts in social structures, and also reveals novel dimensions in the social style of macaques.

International audience; Animals can maximize benefits but it is not known if they adjust their investment according to expected pay-offs. We investigated whether monkeys can use different investment strategies in an exchange task. We tested eight capuchin monkeys (Cebus apella) and thirteen macaques (Macaca fascicularis, Macaca tonkeana) in an experiment where they could adapt their investment to the food amounts proposed by two different experimenters. One, the doubling partner, returned a reward that was twice the amount given by the subject, whereas the other, the fixed partner, always returned a constant amount regardless of the amount given. To maximize pay-offs, subjects should invest a maximal amount with the first partner and a minimal amount with the second. When tested with the fixed partner only, one third of monkeys learned to remove a maximal amount of food for immediate consumption before investing a minimal one. With both partners, most subjects failed to maximize pay-offs by using different decision rules with each partner' quality. A single Tonkean macaque succeeded in investing a maximal amount to one experimenter and a minimal amount to the other. The fact that only one of over 21 subjects learned to maximize benefits in adapting investment according to experimenters' quality indicates that such a task is difficult for monkeys, albeit not impossible.

International audience; In the last two decades, it became largely accepted that monkeys show little, if any, copying fidelity. However, some recent studies have begun to challenge this notion. To explore reasons for such contrary findings, we designed a foraging apparatus so that in each of two experiments with capuchin monkeys (Cebus apella), a model would demonstrate one of two alternative methods to obtain food. The apparatus had a V-shaped track on which a panel could be slid up left or right from the center to reveal food. In Experiment 1, food was located in a cup directly behind the center panel. In Experiment 2, sliding the panel left or right revealed food either in left or right ends of the V-track. Since this sliding movement led directly to one food location exclusive of the other, we predicted capuchins would show greater copying fidelity in this second Experiment. Instead, subjects were significantly more faithful to the model's method in Experiment 1, which provided strong evidence of capuchins copying what they had observed. We suggest that the contrasting results of Experiment 1 may have occurred because capuchins prioritize exploratory behavior when alternative foraging locations are accessible.

International audience; The ability of animals to delay gratification is crucial for complex goal-directed action. It may help them in making effective decisions when facing a choice. We tested the ability of nine long-tailed macaques (Macaca fascicularis) to delay gratification in several experiments. In exchange tasks, subjects had to keep a small piece of cookie before returning it to an experimenter in order to get a larger food amount. Results showed that animals could wait between 10 s and 10 min depending on individual and sizes of reward. In another experiment, subjects could immediately give back the initial piece of cookie then wait for the return. Their performances more than doubled, demonstrating the role of consumption inhibition in postponing gratification. Such achievements underscore delays of gratification which until now were not thought possible in monkeys. Finally, subjects were presented with an accumulation of food pieces added at short intervals until they seized them. They mostly waited between 30 s and 1 min, which points at the consistency of our data, compared to those of other studies. Our results indicate that long-tailed macaques anticipated the duration of delays. We may account for their remarkable performances by their achievements in the social context.

International audience; In The Expression of the Emotions, Charles Darwin documents evolutionary continuity between animals and humans, emphasizing the universality of expressions in man. Most of the book addresses human behavior, and its influence on the study of animal behavior has been weak. The issue of natural selection is remarkably absent from this book, which relies on the inheritance of acquired characters rather than on a genuine Darwinian logic. Yet Konrad Lorenz considered Darwin to be a forerunner of behavioral biology. The reason was to be found in The Descent of Man and chapter VIII of The Origin of Species, where Darwin provides an explanation of behavior through selection, stating that the same mechanisms explaining morphological changes also account for gradual improvements in instincts. He assessed the accuracy of his evolutionary theory by directly studying animal behavior, hence laying the foundations of behavioral research for the next century.

International audience; Recent evidence suggests that female grooming kin bias in rhesus and Tibetan macaques varies within groups over time in a manner that is consistent with the time constraints model. Here we test the same hypothesis for Tonkean macaques, using data from a corral-living group collected between 1987 and 2002.We also use published data to ask whether time constraints can explain variation across the three macaque species and/or whether these species appear to show inherent differences in kin bias based on their species' social styles, as predicted by the phylogenetic model. Several predictions of the time constraints model were supported for Tonkean macaques: as the number of potential grooming partners increased, females groomed similar amounts, but displayed decreased per capita amounts of grooming, focused their grooming on a subset of potential partners, and displayed more intense grooming kin bias. Although numbers of potential partners affected all three species similarly, species differences in kin bias were sustained and were related to species social styles independently of numbers of potential partners.We suggest that grooming kin bias represents a social reaction norm, in which species display qualitatively similar, but inherently different ranges of response to the same current conditions.

International audience; Exchanges form the basis of human economies. Animals too can engage in reciprocal interactions but they do not barter goods like humans, which raises the question of the abilities necessary for trading to occur. Previous studies have shown that non-human primates can exchange food with human partners. Here, we tested the ability of brown capuchin monkeys and Tonkean macaques to reciprocate in a task requiring two conspecifics to exchange tokens in order to obtain rewards from an experimenter. We recorded 56 transfers between subjects in capuchin monkeys and 10 in Tonkean macaques. All transfers were passive in both species. Capuchins preferentially picked up tokens valuable for them in the partner's compartment. They tended to manipulate the partner-valued tokens more often than the no-value ones, leading to more opportunities for these tokens to end up within reach of the partner. Despite optimal conditions where values of goods were defined and known by partners, however, none of the pairs tested engaged in short-term reciprocal interactions. These results indicate that calculated reciprocity was difficult if not impossible in the animals tested.

Transfers and services are frequent in the animal kingdom. However, there is no clear evidence in animals that such transactions are based on weighing costs and benefits when giving or returning favours and keeping track of them over time (i.e. calculated reciprocity). We tested two orang-utans ( Pongo pygmaeus abelii ) in a token-exchange paradigm, in which each individual could exchange a token for food with the experimenter but only after first obtaining the token from the other orang-utan. Each orang-utan possessed tokens valuable to their partner but useless to themselves. Both orang-utans actively transferred numerous tokens (mostly partner-valuable) to their partner. One of the orang-utans routinely used gestures to request tokens while the other complied with such requests. Although initially the transfers were biased in one direction, they became more balanced towards the end of the study. Indeed, data on the last three series produced evidence of reciprocity both between and within trials. We observed an increase in the number and complexity of exchanges and alternations. This study is the first experimental demonstration of the occurrence of direct transfers of goods based on calculated reciprocity in non-human-primates.

International audience; Great apes appear to be the nonhuman primates most capable of recognizing trading opportunities and engaging in transfers of commodities with conspecifics. Spontaneous exchange of goods between them has not yet been reported. We tested gorillas (Gorilla gorilla), orangutans (Pongo pygmaeus), bonobos (Pan paniscus), and chimpanzees (Pan troglodytes) in a token-exchange task involving two conspecifics and a human experimenter. Tested in pairs, subjects had to exchange tokens with a partner to obtain food from the experimenter. We observed 4, 5, 264, and 328 transfers of tokens in gorillas, chimpanzees, orangutans, and bonobos, respectively. Most gifts were indirect in gorillas, chimpanzees, and bonobos, whereas most were direct in orangutans. The analysis showed no evidence of calculated reciprocity in interactions. A main finding of the study was the high rate of repeated gifts and begging gestures recorded in orangutans. This raises the question of the meaning of pointing in great apes and their ability to understand the communicative intent of others.

International audience; We addressed decision-making processes in the collective movements of two groups of Przewalski horses (Equus ferus przewalskii) living in a semi free-ranging population. We investigated whether different patterns of group movement are related to certain ecological contexts (habitat use and group activity) and analysed the possible decision-making processes involved. We found two distinct patterns; 'single-bout' and 'multiplebout' movements occurred in both study groups. The movements were defined by the occurrence of collective stops between bouts and differed by their duration, distance covered and ecological context. For both movements, we found that a preliminary period involving several horses occurred before departure. In single-bout movements, all group members rapidly joined the first moving horse, independently of the preliminary period. In multiple-bout movements, however, the joining process was longer; in particular when the number of decision-makers and their pre-departure behaviour before departure increased. Multiplebout movements were more often used by horses to switch habitats and activities. This observation demonstrates that the horses need more time to resolve motivational conflicts before these departures. We conclude that decision-making in Przewalski horses is based on a shared consensus process driven by ecological determinants.

International audience; For coordinated movement, group-living individuals have to reach consensus decisions through recruitment processes. Success in recruitment can depend on the spatial distribution and behaviour of animals before and/or after departure, and on their affinitive relationships. We tested the effect of such factors on recruitment processes in a group of 19 ewe lambs, Ovis aries, at pasture. Two observers continuously videotaped the behaviours of animals from a platform located in the centre of the field. Results showed that group orientation, group vigilance and activities such as head movements, stillness and number of steps increased before departure. Using general linear modelling we found that changes in most of these variables predicted the number of participants in movements. Similarly, activity of the first mover was modified in the last 2 min preceding departure, and at departure time the location and number of close neighbours of the first mover were especially influential in recruiting conspecifics. Animals first recruited were those that were close to the first mover and also its preferential partners. The behaviours of the second and third moving individuals could further influence the recruitment process. Moreover, there were clues that individuals were able to recruit others intentionally. Our findings emphasize that decision making in a group of domestic sheep was a continuous and distributed process. Recruitment depended both on group state and on the behaviour of individuals and their social relationships.

International audience; We investigated collective movements in a flock of domestic geese (Anser domesticus) to test the consistency of group orders and the influence of individual traits and social relationships on movement patterns. The subjects were 20 juvenile females kept in an herbaceous enclosure. Two observers continuously videotaped their movements. Although the positions of individuals might change during moves, the geese tended to hold predictable positions in different movements. We found that geese more reactive to unexpected noises more often held front positions. Moreover, the higher the associativity of a bird as measured by number of neighbors at rest, the more frequent the bird acted as first mover. The analysis did not evidence any influence of dominance status on the positions of geese during progression. In contrast, geese linked by close bonds clustered during progression. The structuring influence of social bonds in collective movements might be a general feature of animals gifted with individual recognition abilities.

BERNARD THIERRYHow would we know when a theoryhas to be given up? Nobody is able toanswer this question. Contrary to thePopperian thesis, some counterevi-dence is not enough to falsify a wholetheory. The history of science is lit-tered with examples demonstratingthat the core of a challenged theoryremains alive so long as it generates aproductive research program, not-withstanding additions and modifica-tions of auxiliary hypotheses.

International audience; Conflict resolution is an essential component of primate sociality that has been studied extensively within primate social groups, but few studies have examined how conflict resolution behaviours covary at evolutionary scales.We assembled a standardized data set on social interactions of sexually mature females to analyse patterns of conflict resolution in 15 groups of nine macaque species. Between-group comparisons revealed no significant difference in nonkin reconciliation levels between groups of the same species, whereas substantial interspecific differences were found.We tested for associations between four behavioural traits involving reconciliation and dominance asymmetry that play a central role in primate social systems. Regression analyses using group values indicated that these traits (conciliatory tendencies, proportions of explicit reconciliatory contacts, kin bias and levels of counteraggression) exist as an integrated suite of characters. We found strong phylogenetic signal in most traits, which further indicates that they evolved during the adaptive radiation of macaques. Using the method of independent contrasts, relationships between conciliatory tendencies and proportions of explicit reconciliatory contacts and between kin bias and levels of counteraggression remained consistent after controlling for phylogeny. This reveals that evolutionary change in one trait leads to correlated changes in other traits. Collectively, these results show how comparative studies of detailed behavioural interactions can be used to elucidate primate socioecology.

It has been reported that wild capuchin monkeys exhibit several group-specific behavioural traditions. By contrast, experiments have found little evidence for the social learning assumed necessary to support such traditions. The present study used a diffusion chain paradigm to investigate whether a novel foraging task could be observationally learned by capuchins ( Cebus apella ) and then transmitted along a chain of individuals. We used a two-action paradigm to control for independent learning. Either of two methods (lift or slide) could be used to open the door of a foraging apparatus to retrieve food. Two chains were tested ( N 1 =4; N 2 =5), each beginning with an experimenter-trained model who demonstrated to a partner its group-specific method for opening the foraging apparatus. After the demonstration, if the observer was able to open the apparatus 20 times by either method, then it became the demonstrator for a new subject, thus simulating the spread of a foraging tradition among ‘generations’ of group members. Each method was transmitted along these respective chains with high fidelity, echoing similar results presently available only for chimpanzees and children. These results provide the first clear evidence for faithful diffusion of alternative foraging methods in monkeys, consistent with claims for capuchin traditions in the wild.

Despite controversial expectations that animals achieve reciprocal altruism, it is unclear if nonhuman species possess the necessary cognitive abilities. For reciprocal altruism, individuals must anticipate the loss of a commodity and accept a delay before some return. The authors investigated the abilities of 5 chimpanzees (Pan troglodytes) to cope with increasing waiting duration in exchange tasks. Subjects had to keep a small cookie before returning it to a human partner to obtain a larger piece. For a piece 2, 4, or 8 times the size of the small piece, 3 of the 5 subjects waited for up to 4 min. For a piece 40 times larger, 4 of the 5 subjects waited up to 8 min. At long time lag, renouncement to wait occurred earlier than predicted by subjects' general waiting capacity, suggesting that the decision to wait was based on a trade-off between reward quantity and expected costs of the waiting duration. Chimpanzees could anticipate a delayed reward at a time scale of several minutes. If this reflects a cognitive limit in chimpanzees' anticipation capacity, reciprocal altruism by keeping track of costs and benefits over extended periods may be unlikely in chimpanzees.

International audience; The biological study of behavior was shaped by the divorce between ethology and behavioral ecology twenty years ago. Whereas the heirs of ethology promote a phenomenological study of behaviors, behavioral ecologists focus on their fitness consequences. I argue that both schools share the same blind spot about the link between evolutionary past and the making up of the individual because of their common acceptance of the dichotomy between ultimate and proximate causation. By maintaining a pan-selectionist view of evolution in the study of behavior, the dichotomy hampers exploring how epigenetic processes affect adaptive trade-offs. Giving up the dichotomy would give impetus to research programs that investigate how behavioral traits associate in clusters through development and evolution. It would further a comprehensive view of behavioral phenotypes, making the reunification of behavioral biology an attainable goal.

Delayed reciprocity is a potentially important mechanism for cooperation to occur. It is however rarely reported among animals, possibly because it requires special skills like the ability to plan a loss. We tested six brown capuchin monkeys ( Cebus apella ) in such skills. Subjects were studied in exchange tasks in which they had to retain a food item for a given time lag before returning it to an experimenter and obtaining a more desirable reward. Experiments showed that the subjects could wait for several minutes when allowed to return only part of the initial item. When required to return the full item intact, however, most subjects could not sustain a time lag longer than 10 s. Although the duration of waiting increased with the amount of return expected by subjects, in most cases it did not extend beyond 20 s even when the eperimenter offered a food amount 40 fold the initial item. The failure of capuchin monkeys to sustain long-lasting waiting periods may be explained by limited self-control abilities. This would prevent them achieving reciprocal altruism.

International audience; Post-conflict affiliation between former opponents and bystanders occurs in several species of non-human primates. It is classified in four categories of which affiliation received by the former victim, 'consolation', has received most attention. The hypotheses of cognitive constraint and social constraint are inadequate to explain its occurrence. The cognitive constraint hypothesis is contradicted by recent evidence of 'consolation' in monkeys and the social constraint hypothesis lacks information why 'consolation' actually happens. Here, we combine a computational model and an empirical study to investigate the minimum cognitive requirements for post-conflict affiliation. In the individual-based model, individuals are steered by cognitively simple behavioural rules. Individuals group and when nearby each other they fight if they are likely to win, otherwise, they may groom, especially when anxious. We parameterize the model after empirical data of a tolerant species, the Tonkean macaque (Macaca tonkeana). We find evidence for the four categories of post-conflict affiliation in the model and in the empirical data. We explain how in the model these patterns emerge from the combination of a weak hierarchy, social facilitation, risk-sensitive aggression, interactions with partners close-by and grooming as tension-reduction mechanism. We indicate how this may function as a new explanation for empirical data.