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

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.

Inferring Humor Styles Through Men’s Formidability

Men’s formidability is inferred multimodally through various facial and bodily features. Such inferences frequently provide downstream perceptions of various traits and motivational states that inform subsequent affiliative decisions. Within these inferences could be an implicit understanding of men’s preferred humor styles. Across four studies, this research considered perceptions of men’s proclivity to employ each of the four humor styles through different formidability cues: upper body strength (Study 1), body muscularity (Study 2), facial width-to-height ratio (Study 3), and neck musculature (Study 4). Results indicated a relatively consistent perception of formidable features being diagnostic of men’s interest in aggressive humor. Additional findings indicate certain formidability cues connote a disinterest in self-defeating and self-enhancing humor. Facial and bodily cues finally connoted affiliative humor in different capacities. We frame findings from an evolutionary perspective based on perceptions of the various benefits and costs of different formidability features.