The formal hierarchy of rhesus macaques: An investigation of the bared‐teeth display

Abstract

Teeth-baring in a large captive rhesus monkey group (Macaca mulatta) was observed over a 30-month period. Its directional consistency among adults was significantly higher than that of aggression. The unidirectionality was so extreme that the facial display must be seen as a formal status indicator; ie, a signal of which the direction is independent of short-term contextual variation. As such, it seems adapted €or communication about the state of the relationship. Formal dominance relationships among adults could be arranged in a hierarchy which approached perfect linearity. Focal observations demonstrated that teeth-baring was associated with withdrawal. It was uncommon among foraging monkeys, perhaps because dominant animals paid less attention to their subordinates in this context. The speed of rank acquisition by young females, in terms of received teeth-baring, was highest among peers and lowest against the group's old matriarchs. The age at which dominance over unrelated adult females was achieved correlated negatively with the amount of affiliative contact with these females. This translates into a positive correlation between bonding and rank establishment, indicating that dominance processes may be indistinguishable from social integration.

Context modulates signal meaning in primate communication

“…Although the facial morphology of the display is similar across the macaque species in which it occurs, the social function of the display varies. In rhesus, stumptailed, Japanese, and longtailed macaques, the BT/SBT is unidirectional and is thought to communicate subordination/ submission (3,6,36). In Tonkean macaques, the SBT is not associated with dominance, it is bidirectional and is used by both individuals during greeting situations to signal peaceful intentions (37).…”

“…This signal is unidirectional: It is always emitted by the same individual in a pair (1)(2)(3). The sender emits the signal when a conflict arises once it has learned, based on its agonistic interaction history with its opponent, it is likely to lose contests with that opponent.…”

“…The signal additionally occurs in apparently peaceful contexts, during pass-bys and approaches in the absence of any overt aggression or threatening behavior by the receiver. Unfortunately, in those studies in which data on peacefully emitted SBTs have been collected, the data have been lumped with agonistic context data in the analyses (3,11).…”

Young children discriminate genuine from fake smiles and expect people displaying genuine smiles to be more prosocial

“…Some researchers have argued that human smiling could be a homologue to the silent-bare-teeth display found among nonhuman primates (Burrows, Waller, Parr, & Bonar, 2006;Marler & Tenaza, 1977;van Hooff, 1972). The social functions of this display, such as appeasement and reconciliation, have been well discussed in the literature (e.g., de Waal & Luttrell, 1985;Preuschoft & van Hooff, 1997;Waller & Dunbar, 2005). Human infants begin smiling in the womb; however, so-called "social smiles," which occur in response to social stimuli, develop…”

Not Growling but Smiling: New Interpretations of the Bared‐Teeth Motif in the Pre‐Columbian Caribbean

“…In primate species with a strict dominance hierarchy, such as rhesus macaques (Macaca mulatta), BT (see fig. 7C) is used by subordinate individuals when interacting with dominants and is a signal of submission (de Waal and Luttrell 1985). In contrast, in primate species with more flexible hierarchies, such as chimpanzees (Pan troglodytes), BT (see fig.…”