Contagious Yawning In Chimpanzees as a Measure of Empathy: Potential Implications for Autism Research

Background:  Contagious yawning is hypothetically linked to empathy. Yawns are thought to be contagious for the same reason that smiles, frowns, and other facial expressions, like fear, are contagious. However, contagion of smiles, frowns, etc. can involve micro-expressions, which are too subtle to observe without technological assistance. The advantage of yawns is that they are fixed-action patterns which, once begun, go to completion. Since there are no ‘micro-yawns’, yawns are readily observable to the naked eye. The theoretical connection between contagious yawning and empathy has received empirical support in the form of positive correlations with performance on theory-of-mind tasks, self-face recognition (both important for complex forms of empathy), and social closeness. Importantly, negative correlations have been found with autism and schizotypy, two conditions associated with atypical empathy functioning. Chimpanzees (along with the bonobo) are humans’ closest living relatives. They share many aspects of complex human social behavior, including some forms of empathy, and therefore make for a suitable model for studying typical social development.

Objectives:  1) Confirm whether chimpanzees (Pan troglodytes) show contagious yawning, 2) test whether 3D computer animations can stimulate contagious yawning in chimpanzees, and 3) test whether contagious yawning is susceptible to ingroup-outgroup bias in chimpanzees, as predicted if empathy is the underlying mechanism.

Methods:  In two separate studies, 23 chimpanzees from two different groups watched videos of yawn or control stimuli. The first set of stimuli comprised computer-animated chimpanzees programmed to yawn or make other expressions, as controls. The second stimulus set comprised actual video of chimpanzees yawning or at rest (control) from the two groups. Sessions were videotaped and coded for the number of yawns and amount of attention paid to the stimuli by each subject.  

Results:  Chimpanzees yawned significantly more when watching yawn animations than control animations, and when watching familiar individuals yawn than controls. Video of unfamiliar individuals did not produce a significant difference between yawn and control conditions. Critically, the chimpanzees yawned more when watching familiar individuals yawn than unfamiliar individuals yawn. There were no correlations between the rate of attention and yawning for any stimulus set.  

Conclusions:  We confirmed that chimpanzees show yawn contagion through the robust response to two separate stimuli. The yawn contagion in response to the 3D animations suggests that animations can be used to stimulate a natural, involuntary response, and that the chimpanzees identified with the animations on some level. The measurable ingroup-outgroup bias provides further support for the hypothesis that empathy is the mechanism underlying contagious yawning. Contagious yawning is a low-cost, easy-to-implement test of involuntary behavioral/affective contagion that may be useful to autism research. Potential uses include assessments of the efficacy of interventions, exploring whether interventions enhance involuntary affective processes, and as a comparative measure for some nonhuman models.