Prejudice is a universal social issue that has frequently led to massive discrimination and even genocide. Simply stated: equality is impossible so long as prejudice exists. Several decades of research has improved our understanding about the psychology of prejudice, yet important questions remain unanswered. Specifically: Is prejudice uniquely human? Are we born to be prejudiced or is it learned? What is the function of prejudice? Potential answers for these questions are characterised by an absence of evidence; subsequently, improving our understanding of the natural history of prejudice is something requiring urgent attention. Here I will discuss how a primatological perspective may better inform us in such a quest. Prospective experiments involving primates will be outlined along with some possible ramifications for the current debate concerning the validity of competing psychological theories of prejudice.

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[in Japanese]

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Social vocal learning in nonhuman primates is a matter of vivid discussion, especially due to early evidence of innately guided vocal production. However, socially determined flexibility is found when the debate is moved from vocal structure to vocal usage. Recent studies suggest that the appropriate context of call utterance, notably concerning call exchange rules, may be the result of a socially-guided development process. For example, young Campbell's monkeys and Japanese macaques break more often the turn-taking rule than adults. Among those rules, call-matching is found to be of primary importance in a growing number of species including Japanese macaques, with interacting females matching the frequency contour of their own call with another female's preceding call. Here, we tested for the ability of different age-class subjects to discriminate between vocal exchanges following or not the matching rule. We performed playback experiments in 10 adult and 10 one year-old captive Japanese macaque females at the Primate Research Institute, Kyoto University. Each subject was successively exposed to two stimuli, a pair of calls respecting call-matching (i.e. two calls from two individuals with matched frequency modulations) and another pair of calls that did not. Behavioural responses of subjects were video-recorded. Only adults displayed different levels of interest when hearing playbacks respecting or not the matching rule. The latency to look towards the direction of the loudspeaker was shorter and the duration of the directed gaze was longer after the playback of vocal exchanges that did not respect the matching rule in adults, but not in youngsters. Our findings support the conclusion that the matching rule is cognitively relevant for adults, whereas it does not seem to make any sense for socially inexperienced young monkeys. In Japanese macaques, the ability to produce and appropriately use social calls, but also to perceive vocal rules seems to require social experience, suggesting that a socially-guided learning process may be involved.

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Primate societies can be described by networks constructed from many different types of dyadic interactions or relationships, which combined produce the complex dynamics we observe. Of particular interest is the relationship between status signaling and aggression networks, as formalized dominance relationships established via status signals are a strategy to mitigate conflict in groups, guiding prioritization of access to resources thereby reducing deleterious aggression. In Rhesus macaques, Silent Bared Teeth Displays given in peaceful contexts (pSBT) are consistently unidirectional signals given from subordinate to dominant that are thought to represent formalized long-term dominance relationships. We compare the use of these signals to dominance probability as calculated from outcomes of aggressive interactions by a Beta Random Field Percolation and Conductance method to test the prediction that dyads connected via both direct and indirect pathways in a pSBT network have greater dominance certainty. We collected data on all occurrences of dominance interactions (aggression, submission, displacements, and SBT) in seven groups of captive rhesus macaques, each containing between 80-150 individuals, at the California National Primate Research Center between June 2008 and December 2009. All pSBT networks showed perfect transitivity, and multilevel generalized linear regression models revealed that dyads with any pSBT path (direct or indirect) had significantly more certain dominance relationships than dyads with no signaling pathway. Compared to dyads that did not have any SBT signal pathway, dyads with a 1-step path (p< 0.01), a 1-step path plus a longer signaling pathway (p< 0.01), a 2-step path (p< 0.01), a 2-step path plus a longer pathway, and a 3-step path (p<0.05) all had higher dominance certainty. Further, dyads with multiple pathways between them showed either the same level of dominance certainty or greater dominance certainty than dyads with only a single path. This demonstrates that, in addition to their value as alternative mechanisms of direct interaction for indicating subordination, the redundant combination of having both direct and indirect signaling pathways may also act to increase the robustness of dominance relationships. These results highlight the connection between two levels of rhesus macaque society - that pathways in a pSBT network exist between individuals that have greater directional consistency in aggression. We argue that pSBT networks are critical for understanding dominance relationships and the maintenance of stability in these complex monkey systems.

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The Rock-Paper-Scissors (RPS) game is the simplest example of intransitive dominance, where “P” beats “R”, “R” beats “S”, and “S” beats “P”. In order to investigate the learning process of the circular relationship in chimpanzees, seven chimpanzees were trained with tests that have two figures representing two of the three elements respectively in each trial, in the order that first “PR” a session, “RS” a session, “SP” a session, and then mixed pairs in one session. Four chimpanzees had high performances in the single trial sessions, while two chimpanzees were stuck at the third pair, “SP” for long. The results suggest that chimpanzees could have the ability of learning the intransitive relationship, but they showed some difficulty to finalize “circularity” of the relationships among the three items. We incidentally started from “PR”, but the same results will be obtained if we started from “SP”. This study may facilitate the understanding of chimpanzees' cognitive abilities in intransitive relationships, as well as the origin of that in human mind.

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Mother-infant relationship represents the strongest social bond in wild orangutans. Comparing to other ape species, orangutans have the longest immature period and longest inter-birth interval (IBI) that might be explained by their solitary lifestyle. Sumatran individuals have an estimated IBI of 8.25-9.25 years, while the IBI for Bornean subspecies stands between 6.1-7.7 years. During the long-term attachment, the mother provides the primary care and contributes to the development of the repertoire of social and other behaviors in her offspring. So far, infant development and mother-infant behavior studies are mainly focused on Sumatran individuals. Therefore, the subspecies occurring in Borneo remains the least studied. This study aims to understand how ecological factors and hormonal status of the mother influence her behavior towards the offspring; which motherhood variables are more relevant for the development and independence of the infant and in which stage during their development, Bornean orangutans acquire the skills/competence/independence to survive in their environment. The study site, where the data collection took place, comprehends an area of approximately 2 km² (of total area of 438km²) in Danum Valley Conservation Area, where 57 orangutans were identified since the beginning of an ongoing project started in 2004. The observations were conducted in 2013, from April to June and September to December, and, in 2014, from February to December. We collected data using a combination of continuous and instantaneous sampling. The data collected comprised activity budget of mother-offspring dyads and independent immature individuals, diet and food sharing behaviors, play behavior, mother-offspring proximity and contact, association and interaction with other individuals. Alongside with behavioral data, urine and fecal samples were collected for hormonal analysis to investigate the influence of mother's hormonal patterns across the different developmental stages of their offspring. The results will provide insight into Bornean orangutan development and the role of the mother during the process. By comparing with existent data from other field sites, we will have a better understanding of how the ecological factors may link to potential differences between species or subspecies, and ultimately understand differences across other primate species.

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