Ingroup-Outgroup Bias in Contagious Yawning by Chimpanzees Supports Link to Empathy

Abstract

Humans favor others seen as similar to themselves (ingroup) over people seen as different (outgroup), even without explicitly stated bias. Ingroup-outgroup bias extends to involuntary responses, such as empathy for pain. However, empathy biases have not been tested in our close primate relatives. Contagious yawning has been theoretically and empirically linked to empathy. If empathy underlies contagious yawning, we predict that subjects should show an ingroup-outgroup bias by yawning more in response to watching ingroup members yawn than outgroup. Twenty-three chimpanzees (Pan troglodytes) from two separate groups watched videos of familiar and unfamiliar individuals yawning or at rest (control). The chimpanzees yawned more when watching the familiar yawns than the familiar control or the unfamiliar yawns, demonstrating an ingroup-outgroup bias in contagious yawning. These results provide further empirical support that contagious yawning is a measure of empathy, which may be useful for evolutionary biology and mental health.

Chimpanzees empathize with group mates and humans, but not with baboons or unfamiliar chimpanzees

“…We analysed the results using SPSS STATISTICS v. 20.0 for Macintosh (IBM) based on our previous rationale [44]. Looking at all of our data on yawn contagion [13,37] (this study), we see an approximately normal distribution and the presence of an outlier. The outlier is a consistently high performer in our studies of CY, so we do not believe that these data are anomalous and need to be discarded.…”

“…The difference in response to the gelada baboon yawn and control videos was non-significant, however (t 18 figure 1). Incorporating previous data on the response to ingroup versus outgroup chimpanzees [13] allows us to compare yawning rates across the five classes of video. We first calculated a yawning index for each individual within each class by subtracting the rate in the control sessions from the rate in the yawning sessions (figure 2).…”

“…Previously, we studied 23 chimpanzees in 20 min sessions [13], and in this study (black bars) we worked with 19 chimpanzees in 10 min sessions. The data for [13] have been sampled and restricted to match the current parameters (the same 19 chimpanzees for 10 min), thus a side-by-side comparison with the graphs from [13] will not match. The response to familiar humans, strange humans and ingroup chimpanzees was significantly greater than the response to outgroup chimpanzees and gelada baboons (p ¼ 0.003).…”

Young Children Display Contagious Yawning When Looking at the Eyes

“…Although contagious yawning occurs commonly in adulthood in human and non-human primates [2][3][4][5], infants and pre-schoolers seem less susceptible to the social influences of yawning [6]. Whereas spontaneous yawning is present from before birth [7], several authors have reported that contagious yawning is uncommon in children before the age of 4 or 5 years, at which age susceptibility to yawn contagion increases dramatically [6,8,9].…”

Sub-adult Ravens Synchronize their Play: A Case of Emotional Contagion?

“…Synchronization of yawning has been suggested to imply emotional contagion: the alignment of one's emotions with the other is a process believed to be a foundation of empathy (Preston & de Waal, 2002). This assumption has been strengthened by results showing that yawns are more contagious between familiar than unfamiliar individuals (e.g., Campbell & de Waal, 2011). Human psychology regards emotional contagion as a fundamental part of human sociality and cognition essential for developing "mind-reading" skills (e.g., Hatfield, Rapson, & Le, 2009) -making it of great interest whether, and in what forms, emotional contagion occurs in non-human animals.…”