The chimps yawned more when they saw their group members yawning
Yawning is contagious not just for humans, but for our primate relatives, the chimpanzees, according to a study.
Researchers at Emory University in Atlanta, US, have used footage of yawning chimps to test the phenomenon in a group of the animals.
The chimps yawned more after watching the videos. And they were affected more by yawns of their group members than by those of unfamiliar chimps.
The findings are reported in the journal PLoS One.
Dr Matthew Campbell and Dr Frans de Waal showed the footage to 23 adult chimpanzees, which had been raised in two separate groups.
Each animal viewed several nine-second video clips of other chimpanzees either yawning or doing something else.
They yawned 50% more frequently in response to seeing members of their group yawn compared with seeing others yawn.
The findings suggest that contagious yawning is a good empirical measure of empathy.
The team says that it was this social connection rather than just how much attention the chimps paid to the videos that influenced the "contagiousness" of the yawns.
The researchers wrote in the journal: "The chimpanzees actually watched the videos of unfamiliar individuals more than the videos of familiar individuals.
"They [paid more attention] to the unfamiliar yawns, but yawned more to the familiar yawns," they explained.
"Given that chimpanzees exhibit both altruism and extreme violence toward others, studying how and when empathy is engaged may tell us about how humans switch between these two extremes as well.