By Jonathan Amos
Science reporter, BBC News, Liverpool
The consoling arm of a good friend
If you have just had a big falling out with a colleague, there is nothing better than the comforting and consoling arm of a good friend.
Chimps, it seems, feel the same way, according to a study at Chester Zoo.
The research is said to provide the first evidence that consolation in primates, such as hugging and stroking, can reduce stress levels after a fight.
The behaviour could indicate some level of empathy, Dr Orlaith Fraser told the British Association Science Festival.
"We can't actually say what's going on in a chimpanzee's mind; we can only deduce from their behaviour what's going on," the Liverpool John Moores University researcher said.
"Because this behaviour is actually reducing stress levels and it's being offered by a valuable partner, it seems likely that this is an expression of empathy."
A bit of sympathy
Dr Fraser and colleagues spent 18 months observing 22 adult chimps at Chester Zoo.
They watched closely what happened immediately after the animals had a scrap - perhaps a fight over food, a mate or simply where to sit.
In about 50% of cases, the victim in the fight would be consoled by another member of the group. The soothing was always done by a valuable - or best - friend, a chimp with whom the victim would routinely play or share food.
Feeling better after a kiss
The consolation usually took the form of a kiss or embrace, a grooming session or even play.
The scientists could see that this activity had the effect of reducing stress levels, indicated by the return to the animals' normal activities of self-scratching and self-grooming.
"Sympathetic concern" has also been observed in gorillas, bonobos, dogs and even rooks - but it is the calming effect that it had on the Chester Zoo chimps which is said to be a new observation.
"If these chimpanzees are actually motivated by empathy to console victims of aggression, they must first of all be able to recognise that the victim is distressed and then they must know what to do in order to act appropriately to respond to this distress," said Dr Fraser.
"This is something often thought to be a unique trait to humans, so understanding the link between consolation and stress reduction in chimpanzees is an important step towards understanding whether or not chimpanzees are capable of this level of empathy."
The results of the Chester Zoo study were recently published in the journal Proceedings of the National Academy of Sciences.