Yawning can be as contagious between bonobos as it is among people, suggesting that the apes are capable of human-like empathy.
Scientists compared yawning behaviour in humans and bonobos, a cousin of the chimpanzee said to be the great ape closest to humans.
They found that yawning was equally catching in both species when "yawners" and "responders" were not friends or relatives.
Yawning contagion was already known to be a marker of empathy between individuals who share a close emotional bond.
Bonobos are the only animal known to share this trait with humans.
Over a period of five years, researchers led by Dr Elisabetta Palagi from the University of Pisa in Italy compared how often humans and bonobos responded to yawns, and how quickly.
They found that yawning was not necessarily more contagious in humans, as had previously been thought.
The researchers wrote in the journal PeerJ: "Between species, sensitivity to others' yawns was higher in humans than in bonobos when involving kin and friends but was similar when considering weakly-bonded subjects.
"Thus, emotional contagion is not always highest in humans."
Human empathy levels appeared to depend on the quality of relationships shared by individuals.
In situations where complex social bonds were less in evidence, humans and their ape cousins were on an empathic par.
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