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de Waal, F. B. (2000). Primates--A natural heritage of conflict resolution. Science, 289(5479), 586–590.
Abstract: The traditional notion of aggression as an antisocial instinct is being replaced by a framework that considers it a tool of competition and negotiation. When survival depends on mutual assistance, the expression of aggression is constrained by the need to maintain beneficial relationships. Moreover, evolution has produced ways of countering its disruptive consequences. For example, chimpanzees kiss and embrace after fights, and other nonhuman primates engage in similar “reconciliations.” Theoretical developments in this field carry implications for human aggression research. From families to high schools, aggressive conflict is subject to the same constraints known of cooperative animal societies. It is only when social relationships are valued that one can expect the full complement of natural checks and balances.
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Wolf, M., van Doorn, G. S., Leimar, O., & Weissing, F. J. (2007). Life-history trade-offs favour the evolution of animal personalities. Nature, 447(7144), 581–584.
Abstract: In recent years evidence has been accumulating that personalities are not only found in humans but also in a wide range of other animal species. Individuals differ consistently in their behavioural tendencies and the behaviour in one context is correlated with the behaviour in multiple other contexts. From an adaptive perspective, the evolution of animal personalities is still a mystery, because a more flexible structure of behaviour should provide a selective advantage. Accordingly, many researchers view personalities as resulting from constraints imposed by the architecture of behaviour (but see ref. 12). In contrast, we show here that animal personalities can be given an adaptive explanation. Our argument is based on the insight that the trade-off between current and future reproduction often results in polymorphic populations in which some individuals put more emphasis on future fitness returns than others. Life-history theory predicts that such differences in fitness expectations should result in systematic differences in risk-taking behaviour. Individuals with high future expectations (who have much to lose) should be more risk-averse than individuals with low expectations. This applies to all kinds of risky situations, so individuals should consistently differ in their behaviour. By means of an evolutionary model we demonstrate that this basic principle results in the evolution of animal personalities. It simultaneously explains the coexistence of behavioural types, the consistency of behaviour through time and the structure of behavioural correlations across contexts. Moreover, it explains the common finding that explorative behaviour and risk-related traits like boldness and aggressiveness are common characteristics of animal personalities.
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Bell, A. M. (2007). Evolutionary biology: animal personalities (Vol. 447).
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Flack, J. C., Krakauer, D. C., & de Waal, F. B. M. (2005). Robustness mechanisms in primate societies: a perturbation study. Proc Biol Sci, 272(1568), 1091–1099.
Abstract: Conflict management mechanisms have a direct, critical effect on system robustness because they mitigate conflict intensity and help repair damaged relationships. However, robustness mechanisms can also have indirect effects on system integrity by facilitating interactions among components. We explore the indirect role that conflict management mechanisms play in the maintenance of social system robustness, using a perturbation technique to 'knockout' components responsible for effective conflict management. We explore the effects of knockout on pigtailed macaque (Macaca nemestrina) social organization, using a captive group of 84 individuals. This system is ideal in addressing this question because there is heterogeneity in performance of conflict management. Consequently, conflict managers can be easily removed without disrupting other control structures. We find that powerful conflict managers are essential in maintaining social order for the benefit of all members of society. We show that knockout of components responsible for conflict management results in system destabilization by significantly increasing mean levels of conflict and aggression, decreasing socio-positive interaction and decreasing the operation of repair mechanisms.
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Grosenick, L., Clement, T. S., & Fernald, R. D. (2007). Fish can infer social rank by observation alone. Nature, 445(7126), 429–432.
Abstract: Transitive inference (TI) involves using known relationships to deduce unknown ones (for example, using A > B and B > C to infer A > C), and is thus essential to logical reasoning. First described as a developmental milestone in children, TI has since been reported in nonhuman primates, rats and birds. Still, how animals acquire and represent transitive relationships and why such abilities might have evolved remain open problems. Here we show that male fish (Astatotilapia burtoni) can successfully make inferences on a hierarchy implied by pairwise fights between rival males. These fish learned the implied hierarchy vicariously (as 'bystanders'), by watching fights between rivals arranged around them in separate tank units. Our findings show that fish use TI when trained on socially relevant stimuli, and that they can make such inferences by using indirect information alone. Further, these bystanders seem to have both spatial and featural representations related to rival abilities, which they can use to make correct inferences depending on what kind of information is available to them. Beyond extending TI to fish and experimentally demonstrating indirect TI learning in animals, these results indicate that a universal mechanism underlying TI is unlikely. Rather, animals probably use multiple domain-specific representations adapted to different social and ecological pressures that they encounter during the course of their natural lives.
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Palagi, E., Paoli, T., & Tarli, S. B. (2004). Reconciliation and consolation in captive bonobos (Pan paniscus). Am. J. Primatol., 62(1), 15–30.
Abstract: Although reconciliation in bonobos (Pan paniscus) has previously been described, it has not been analyzed heretofore by the postconflict (PC) match-control (MC) method. Furthermore, although reconciliation has been investigated before in this species, consolation has not. In this study we analyzed agonistic and affiliative contacts in all sex-class combinations to clarify and reevaluate the occurrence of reconciliation in bonobos via the PC-MC method. We also investigated the occurrence of consolation by analyzing the victims' triadic contact tendency (TCT), the influence of the sex of victims, and the relative occurrence of consolation and reconciliation. We collected 167 pairs of PC-MC observations in a captive group of bonobos (in Apeldoorn, The Netherlands). The conciliatory tendency (CCT) we obtained was tendentially lower than the mean value previously found for Yerkes captive chimpanzees. Close relationships, which were present in all female-female (FF) and some male-female (MF) dyads, positively affected reconciliation rates. When only adult PC-MC pairs (157) were considered, the mean TCTs and CCTs did not differ significantly. When we focused on types of PC affiliative contact, in the case of consolation we found a striking preference for sociosexual patterns. As to the relative occurrence of consolation and reconciliation, the highest level of the former was found in the absence of the latter. When reconciliation took place, consolation generally preceded it, suggesting that consolation may be a substitutive behavior. Our findings suggest that even if reconciliation remains the best option, consolation may be an alternative substitute for reconciliation that is used to buffer the tension originating from an unresolved conflict. Reconciliation and consolation are complex phenomena that are probably related to the life history of a group. Given that few studies have been conducted on this subject, we can not at this time make any generalizations regarding conflict resolution in certain species by comparing results among studies.
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Gruter, C. C. (2004). Conflict and postconflict behaviour in captive black-and-white snub-nosed monkeys (Rhinopithecus bieti). Primates, 45(3), 197–200.
Abstract: Black-and-white snub-nosed monkeys (Rhinopithecus bieti) have almost never been the subject of any behavioural observations in captivity. This study was aimed at providing preliminary information about agonistic and reconciliation behaviour in a group kept at the Kunming Institute of Zoology in China. Established procedures were used for this investigation (i.e., the postconflict/matched-control method and the time-rule method). Intra-group aggression rates were quite low. Postconflict affiliation as well as selective attraction of former opponents to each other following conflicts was demonstrated. Former opponents contacted each other earlier in postconflict periods than in matched-control periods. The average conciliatory tendency of all focal individuals combined was 54.5%. After an agonistic interaction, the first affiliative contact between former aggressors usually took place within the first minute. The behaviours most often shown as first affiliations after a conflict were body contact, mount, touch, and “hold-lumbar”, of which the latter is an explicit reconciliatory gesture. Furthermore, the adult male intervened non-aggressively in 84% of all conflicts (n=25) among the adult females. Overall, the patterns of aggression and reconciliation observed in R. bieti bear many of the traits that characterise tolerant primate species.
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Rogers, L. J. (2000). Evolution of hemispheric specialization: advantages and disadvantages. Brain Lang, 73(2), 236–253.
Abstract: Lateralization of the brain appeared early in evolution and many of its features appear to have been retained, possibly even in humans. We now have a considerable amount of information on the different forms of lateralization in a number of species, and the commonalities of these are discussed, but there has been relatively little investigation of the advantages of being lateralized. This article reports new findings on the differences between lateralized and nonlateralized chicks. The lateralized chicks were exposed to light for 24 h on day 19 of incubation, a treatment known to lead to lateralization of a number of visually guided responses, and the nonlateralized chicks were incubated in the dark. When they were feeding, the lateralized chicks were found to detect a stimulus resembling a raptor with shorter latency than nonlateralized chicks. This difference was not a nonspecific effect caused by the light-exposed chicks being more distressed by the stimulus. Instead, it appears to be a genuine advantage conferred by having a lateralized brain. It is suggested that having a lateralized brain allows dual attention to the tasks of feeding (right eye and left hemisphere) and vigilance for predators (left eye and right hemisphere). Nonlateralized chicks appear to perform these dual tasks less efficiently than lateralized ones. Reference is made to other species in discussing these results.
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Peake, T. M., Terry, A. M. R., McGregor, P. K., & Dabelsteen, T. (2002). Do great tits assess rivals by combining direct experience with information gathered by eavesdropping? Proc Biol Sci, 269(1503), 1925–1929.
Abstract: Animals frequently use signals that travel further than the spacing between individuals. For every intended recipient of a given signal there are likely to be many other individuals that receive information. Eavesdropping on signalling interactions between other individuals provides a relatively cost-free method of assessing future opponents or mates. Male great tits (Parus major) extract relative information from such interactions between individuals unknown to them. Here, we show that male great tits can take information gathering a stage further and obtain more information about a previously unencountered intruder, by the hitherto unknown capability of combining information gathered by eavesdropping with that derived from their own direct interaction with an individual. Prior experience with an intruder (A) was achieved by subjecting a focal male to different levels of intrusion simulated using interactive playback. This intruder (A) then took part in a simulated interaction with an unknown male (B) outside the territorial boundary of the focal males. In response to subsequent intrusion by the second male (B), focal males showed low song output in response to males that had lost to a male that the subject was able to beat. Males of known high quality, or those about which information was ambiguous, elicited a high level of song output by focal males. We discuss the implications of this finding for the evolution of communication and social behaviour.
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Baker, K. C., Seres, E., Aureli, F., & De Waal, F. B. (2000). Injury risks among chimpanzees in three housing conditions. Am. J. Primatol., 51(3), 161–175.
Abstract: Meeting the psychological needs of chimpanzees (Pan troglodytes) can be a challenge given their aggressiveness on the one hand and the complexity of their social lives on the other. It is unclear how to balance the need to provide opportunities for species-appropriate behavior against potential risks of injury chimpanzees may inflict on each other. This study evaluates the suggestion that simpler social environments protect chimpanzees from wounding. Over a two-year period all visible injuries to 46 adult males, 64 adult females, and 25 immature chimpanzees were recorded at the Yerkes Regional Primate Research Center. Approximately half of the subjects were mother-reared, and the rest were nursery-reared. Housing included compounds containing about 20 chimpanzees, interconnected indoor-outdoor runs for groups of up to 12 individuals, and smaller indoor-outdoor runs for pairs and trios. Annual wounding rates were calculated for serious wounds (extensive injuries and all those requiring veterinary intervention) as well as for minor wounds. Compound-housed chimpanzees incurred the highest level of minor wounding, but serious wounding levels were not affected by housing condition. Even with a period of dominance instability and elevated levels of wounding in one compound, compound chimpanzees were not injured more than those in smaller social groups over the long term. Nursery-reared females in moderate-sized groups were wounded more than mother-reared females. Also, nursery-reared males and females were wounded less often when paired with mother-reared companions. Overall, this study indicates that maintaining chimpanzees in pairs and trios would not be an effective means for reducing injuries. The management of wounding in chimpanzee colonies is influenced more by the sex and rearing composition of a colony.
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