Differential Behavioural Effects of Silent Bared Teeth Display and Relaxed Open Mouth Display in Chimpanzees (Pan troglodytes)

Authors

  • Bridget M. Waller,

    1. Evolutionary Psychology and Behavioural Ecology Research Group, School of Biological Sciences, University of Liverpool, Liverpool, UK
    Search for more papers by this author
  • Robin I. M. Dunbar

    1. Evolutionary Psychology and Behavioural Ecology Research Group, School of Biological Sciences, University of Liverpool, Liverpool, UK
    Search for more papers by this author

Bridget M. Waller, Department of Psychology, King Henry Building, King Henry Street, University of Portsmouth, Portsmouth, UK, PO1 2DY. E-mail: bridget.waller@port.ac.uk

Abstract

This study examines the behavioural consequences of the silent bared teeth display (SBT) and the relaxed open mouth display (ROM) in the chimpanzee, and discusses functional similarities with smiling and laughing (respectively) in humans. Rates of affinitive behaviour increase (in relation to baseline levels) following SBT, suggesting that SBT is a signal of affinity. ROM is observed primarily during play, and dyadic play bouts are significantly longer when ROM is bidirectional, indicating that it may be a signal of play. Rates of affinitive behaviour also increased after ROM, suggesting that both displays may have a similar ultimate (evolutionary) function – social bonding; this could explain convergence of the two displays in humans.

Ancillary