Laughter was not developed first by humans but by our close biological cousins the apes, according to new scientific research.
Scientists at the University of Portsmouth have found that orang-utans have a sense of empathy and mimicry which is an essential part of laughter.
Dr Marina Davila Ross, of the university's psychology department, studied the way facial expressions were picked up and copied by 25 orang-utans aged between two and 12 playing at four primate centres around the world.
Her team recorded the orang-utans playing with each other and when one of the orang-utans displayed an open, gaping mouth - the equivalent of laughter - the researchers examined the response of its playmate.
Dr Davila Ross explained that often the playmate displayed the same expression less than half a second later, suggesting the mimicry was an involuntary display.
She said that the findings have shed a new light on empathy and its importance for animals which live in groups.
She added that it also revealed that empathy of positive emotions or contagious laughter evolved before humans.
Dr Davila Ross said: "By mimicking emotional expressions of others, individuals are able to experience and understand the emotions of their social partners.
"Such mechanism of empathy is likely to help us to form and maintain social bonds.
"In humans, mimicking behaviour can be voluntary and involuntary. Until our discovery there had been no evidence that animals had similar responses."