Chimpanzees "catch" yawns from humans, scientists have discovered in one of the first examples of cross-species "yawn contagion".


Chimpanzees can "catch" yawns from humans as they grow older, according to scientists who say the behaviour is most likely an attempt to bond with their keepers.

'Contagious' yawning, which happens when one person's yawn sets off the same reaction in others, is thought to be a measure of empathy, or sharing others' emotions.

Humans are more likely to catch yawns from people they are close to, and the only previously documented example of contagion between humans and animals has been between dogs and their owners.

Now researchers from Lund University in Sweden have found that chimpanzees exhibit the same behaviour, according to a study in the PLOS ONE journal.

Like young human children, infant chimpanzees are unaffected by the yawning of others but pick up the habit at about the age of five, they concluded.

The researchers carried out their study on 33 juvenile orphaned chimpanzees, aged between 13 months and eight years, at the Tacugama Chimpanzee Sanctuary in Sierra Leone.

Each chimpanzee in turn played with a researcher who repeatedly yawned, gaped (opened her mouth without yawning) or wiped her nose, and their responses were recorded.

The results showed that yawning was contagious, but only in chimpanzees over the age of five, while the other behaviours were not contagious.

However, further tests surprisingly showed that the chimpanzees were equally likely to "catch" a yawn from an unfamiliar researcher as from one of their keepers, with whom they had a close relationship.

Dr Elainie Madsen, who led the study, said chimpanzees might apply "targeted empathy" towards other chimpanzees, meaning they would catch yawns only from those they were close to, but react in a more generalised way to humans.

"A reason for this may be that chimpanzees typically engage in competitive, even hostile, relationships with unfamiliar members of their own species, but rarely do so with humans, who they mostly experience as cooperative," she said.

"Alternatively, it is possible that younger chimpanzees switch from a 'generalised empathy' to all individuals - irrespective of species - to a more 'targeted empathy' as they mature into adults and possibly have stronger reasons to differentiate friends from foes."