Context-Dependent Gestural Laterality: A Multifactorial Analysis in Captive Red-Capped Mangabeys.

Abstract

Simple SummaryIn vertebrates, each of the two hemispheres of the brain controls the opposite side of the body. Consequently, lateralized actions in animals may reflect that one hemisphere processes particular functions underlying the behavior. In humans, for instance, the left-brain hemisphere is specialized for language functions. In several species of non-human primates, communicative gestures are preferentially produced with the right hand. It has been hypothesized that the human language lateralization has common evolutionary origins with a left-hemispheric specialization for gestures in African-Asian primates. Therefore, it is particularly interesting to describe the gestural laterality of non-human primates to understand the evolutionary history of intentional communication. Previous studies reported different factors affecting the gestural laterality of great apes, but this has rarely been investigated in more distant species of monkeys. In the present study, we observed the manual gestures produced by captive mangabeys. We found that, although monkeys were not lateralized when considering their gestures, on the whole, they preferentially gesture with their right hand in contexts of aggression or submission, and that the position of their receiver also affected the hand used. As for chimpanzees, gorillas, or humans, the gestural laterality of mangabeys depends on the context in which they communicate.Catarrhine primates gesture preferentially with their right hands, which led to the hypothesis of a gestural origin of human left-hemispheric specialization for language. However, the factors influencing this gestural laterality remain understudied in non-hominoid species, particularly in intraspecific contexts, although it may bring valuable insights into the proximate and ultimate causes of language lateralization. We present here a preliminary investigation of intraspecific gestural laterality in catarrhine monkeys, red-capped mangabeys (Cercocebus torquatus). We described the spontaneous production of brachio-manual intentional gestures in twenty-five captive subjects. Although we did not evidence any significant gestural lateralization neither at the individual- nor population-level, we found that mangabeys preferentially use their right hands to gesture in negative social contexts, such as aggressions, suggesting an effect of emotional lateralization, and that they adapt to the position of their receiver by preferentially using their ipsilateral hand to communicate. These results corroborate previous findings from ape studies. By contrast, factors related to gesture form and socio-demographic characteristics of signaler and receiver did not affect gestural laterality. To understand better the relationships between gestural laterality and brain lateralization from an evolutionary perspective, we suggest that the gestural communication of other monkey species should be examined with a multifactorial approach.