No abstract

Personality dimensions capturing individual differences in behavior, cognition, and affect have been described in several species, including humans, chimpanzees, and orangutans. However, comparisons between species are limited by the use of different questionnaires. We asked raters to assess free-ranging rhesus macaques at two time points on personality and subjective well-being questionnaires used earlier to rate chimpanzees and orangutans. Principal-components analysis yielded domains we labeled Confidence, Friendliness, Dominance, Anxiety, Openness, and Activity. The presence of Openness in rhesus macaques suggests it is an ancestral characteristic. The absence of Conscientiousness suggests it is a derived characteristic in African apes. Higher Confidence and Friendliness, and lower Anxiety were prospectively related to subjective well-being, indicating that the connection between personality and subjective well-being in humans, chimpanzees, and orangutans is ancestral in catarrhine primates. As demonstrated here, each additional species studied adds another fold to the rich, historical story of primate personality evolution.

Kin selection promotes the evolution of social behavior that increases the survival and reproductive success of close relatives. Among primates, maternal kinship frequently coincides with a higher frequency of grooming and agonistic aiding, but the extent to which paternal kinship influences adult female social relationships has not yet been investigated. Here, we examine the effect of both maternal and paternal kinship, as well as age proximity, on affiliative interactions among semifree-ranging adult female rhesus macaques, Macaca mulatta. Kinship was assessed by using both microsatellites and DNA-fingerprinting. Our study confirms that the closest affiliative relationships characterize maternal half-sisters. We provide evidence that adult females are significantly more affiliative with paternal half-sisters than with nonkin. Furthermore, paternal kin discrimination was more pronounced among peers than among nonpeers, indicating that age proximity has an additional regulatory effect on affiliative interactions. We propose that kin discrimination among cercopithecine primates emerges from ontogenetic processes that involve phenotype matching based on shared behavioral traits, such as inherited personality profiles, rather than physiological or physical characteristics. Kin selection promotes the evolution of social behavior that increases the survival and reproductive success of close relatives (1, 2). Hamilton (ref. 1, p. 22) proposed that one possible mechanism mediating kin selection could be ''familiarity of appearance. . . being [that] relatives must tend to look alike. . . ''. Kin discrimination can arise if individuals classify relatives on the basis of shared family traits (3, 4), i.e., phenotype matching, or if individuals identify relatives on the basis of frequent association patterns (5, 6), i.e., familiarity, but whether these two mechanisms are mutually exclusive or overlapping is unclear (7).Evidence of kin discrimination has been reported for a variety of vertebrate species, e.g., Cascades frog tadpoles, Rana cascadae (8), long-tailed tits, Aegithalos caudatus (9), house mice, Mus musculus (10), white-footed mice, Peromyscus leucopus (11), spiny mice, Acomys cahirinus (12), Belding's ground squirrels, Spermophilus beldingi (3, 13), beavers, Castor canadensis (14), golden hamsters, Mesocricetus auratus (15), and chimpanzees, Pan troglodytes (16). Although most studies of kin recognition have focused on the discrimination of kin versus nonkin, only a few have been able to distinguish paternal half-siblings from nonkin, e.g., Belding's ground squirrels (17), peacocks, Pavo cristatus (18), and savanna baboons, Papio cynocephalus (19). Although Wu et al. (20) concluded that pigtailed macaques, Macaca nemestrina, exhibit kin recognition in the absence of familiarity, based on their finding that unfamiliar juvenile peers prefer to sit closer to their paternal half-siblings than to nonkin, all subsequent studies of cercopithecine primates have failed to replicate the original findings (21-24), which ...