Chimpanzees Show a Developmental Increase in Susceptibility to Contagious Yawning: A Test of the Effect of Ontogeny and Emotional Closeness on Yawn Contagion

Elainie Alenkær Madsen,Tomas Persson,Göran Sonesson,Sara Lenninger,Tobias Deschner,Susan Sayehli

doi:10.1371/journal.pone.0076266

Abstract

Contagious yawning has been reported for humans, dogs and several non-human primate species, and associated with empathy in humans and other primates. Still, the function, development and underlying mechanisms of contagious yawning remain unclear. Humans and dogs show a developmental increase in susceptibility to yawn contagion, with children showing an increase around the age of four, when also empathy-related behaviours and accurate identification of others’ emotions begin to clearly evince. Explicit tests of yawn contagion in non-human apes have only involved adult individuals and examined the existence of conspecific yawn contagion. Here we report the first study of heterospecific contagious yawning in primates, and the ontogeny of susceptibility thereto in chimpanzees, Pan troglodytes verus. We examined whether emotional closeness, defined as attachment history with the yawning model, affected the strength of contagion, and compared the contagiousness of yawning to nose-wiping. Thirty-three orphaned chimpanzees observed an unfamiliar and familiar human (their surrogate human mother) yawn, gape and nose-wipe. Yawning, but not nose-wiping, was contagious for juvenile chimpanzees, while infants were immune to contagion. Like humans and dogs, chimpanzees are subject to a developmental trend in susceptibility to contagious yawning, and respond to heterospecific yawn stimuli. Emotional closeness with the model did not affect contagion. The familiarity-biased social modulatory effect on yawn contagion previously found among some adult primates, seem to only emerge later in development, or be limited to interactions with conspecifics. The influence of the ‘chameleon effect’, targeted vs. generalised empathy, perspective-taking and visual attention on contagious yawning is discussed.

Highlights

Contagious yawning (CY) is well-established in humans [1,2,3,4,5]
Yawn contagion has been reported in chimpanzees, Pan troglodytes spp. [6,7,8], bonobos, Pan paniscus [9], gelada baboons, Theropithecus gelada [10], domestic dogs, Canis lupus familaris [11,12] and budgerigars Melopsittacus undulatus [14]
The current study is the first to demonstrate the existence of cross-species contagious yawning in chimpanzees

Summary

Introduction

Contagious yawning (CY) is well-established in humans [1,2,3,4,5]. Viewing videos of others yawning elicits CY in approximately half of adults, and the thought [1] and sound [5] of yawning is sufficient to elicit contagion. Yawn contagion has been reported in chimpanzees, Pan troglodytes spp. While CY has been reported for stumptailed macaques, Macaca arctoides, elevated levels of concomitant selfdirected scratching, suggested that the yawns derived from tension, rather than contagion [15]. While the ultimate function of yawning remains disputed (for a review, see [17]), it has been suggested to carry thermorgulatory [18] and non-verbal communicative functions, and its contagiousness to serve the adaptive function of synchronizing group behaviour [19], with respect to arousal [20] and attention [21]. [22,23]), suggesting that yawn contagion allows individuals to automatically mimic and synchronise facial expressions and movements with others, and converge behaviourally and emotionally [24] The facial expressions that individuals adopt, tend to influence their emotional experiences (e.g. [22,23]), suggesting that yawn contagion allows individuals to automatically mimic and synchronise facial expressions and movements with others, and converge behaviourally and emotionally [24]

Methods

Results

Conclusion