Six adult female chimpanzees were shown video scenes of chimpanzees repeatedly yawning or of chimpanzees showing open-mouth facial expressions that were not yawns. Two out of the six females showed significantly higher frequencies of yawning in response to yawn videos; no chimpanzees showed the inverse. Three infant chimpanzees that accompanied their mothers did not yawn at all. These data are highly reminiscent of the contagious yawning effects reported for humans. Contagious yawning is thought to be based on the capacity for empathy. Contagious yawning in chimpanzees provides further evidence that these apes may possess advanced self-awareness and empathic abilities.

Contagious yawning is a common phenomenon affecting upwards of 60% of healthy humans. It has also been observed, at a lesser rate, in great apes and other primates. Here I summarize the suggestion that contagious yawning is a primitive expression of social cognition, namely empathy. Susceptibility to contagious yawning is correlated with the speed in recognizing one's own face, theory of mind processing, and is also associated with activation in regions of the brain that have been associated with social cognitive processes. This suggests that contagious yawning may be an evolutionarily old process that begot a higher level of social cognition in certain species.