Experimental evidence for yawn contagion in orangutans (Pongo pygmaeus)

Evy Van Berlo,Mariska E Kret,Alejandra P Díaz-Loyo,Oscar E Juárez-Mora,Jorg J M Massen

doi:10.1038/s41598-020-79160-x

Abstract

Yawning is highly contagious, yet both its proximate mechanism(s) and its ultimate causation remain poorly understood. Scholars have suggested a link between contagious yawning (CY) and sociality due to its appearance in mostly social species. Nevertheless, as findings are inconsistent, CY’s function and evolution remains heavily debated. One way to understand the evolution of CY is by studying it in hominids. Although CY has been found in chimpanzees and bonobos, but is absent in gorillas, data on orangutans are missing despite them being the least social hominid. Orangutans are thus interesting for understanding CY’s phylogeny. Here, we experimentally tested whether orangutans yawn contagiously in response to videos of conspecifics yawning. Furthermore, we investigated whether CY was affected by familiarity with the yawning individual (i.e. a familiar or unfamiliar conspecific and a 3D orangutan avatar). In 700 trials across 8 individuals, we found that orangutans are more likely to yawn in response to yawn videos compared to control videos of conspecifics, but not to yawn videos of the avatar. Interestingly, CY occurred regardless of whether a conspecific was familiar or unfamiliar. We conclude that CY was likely already present in the last common ancestor of humans and great apes, though more converging evidence is needed.

Highlights

Yawning is highly contagious, yet both its proximate mechanism(s) and its ultimate causation remain poorly understood
Orangutans are more likely to yawn in response to yawning videos rather than to control videos, but only when the yawning individual is a ‘real’ orangutan, and are less likely to yawn in response to the avatar
To investigate whether the likelihood of contagious yawning (CY) differed with regard to familiarity with the ‘real’ orangutan stimuli, we ran an additional binomial model on a reduced dataset that excluded all trials with the avatar

Summary

Introduction

Yawning is highly contagious, yet both its proximate mechanism(s) and its ultimate causation remain poorly understood. Some scholars argue that CY taps into the same PAM as emotion contagion (e.g.6,7,31,32), which is the tendency to automatically synchronize emotional states with another individual[33] Following this line of thought, CY can potentially be a proxy for empathy (i.e. the CY-empathy hypothesis)[6,9,12,18,31,34,35]. The hypothesis predicts that individuals who are socially, and emotionally close are more likely to yawn contagiously in response to each other[15,16,18,19,34,46,47]. In a recent study investigating auditory yawn contagion in humans, yawns were most contagious between family and friends while controlling for the potential effects of increased attention to socially close others using a non-visual stimuli[34]. While it is likely that CY is a social phenomenon, its exact mechanisms remain an active field of investigation

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