Ingroup-outgroup bias in contagious yawning by chimpanzees supports link to empathy
Campbell and de Waal, PLoS ONE, 2011. Twenty-three chimpanzees from two groups watched videos of familiar and unfamiliar individuals yawning or at rest; they yawned more at familiar yawns than at control or unfamiliar yawns.
Campbell and de Waal, PLoS ONE, 2011. Twenty-three chimpanzees from two groups watched videos of familiar and unfamiliar individuals yawning or at rest; they yawned more at familiar yawns than at control or unfamiliar yawns.
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PLoS ONE. doi:10.1371/journal.pone.0018283 https://doi.org/10.1371/journal.pone.0018283