According to lead researcher Dr Marina Davila Ross of the University of Portsmouth, "What is clear now is the building blocks of positive emotional contagion and empathy that refer to rapid involuntary facial mimicry in humans evolved prior to humankind."

The team came to the conclusion after analysing the way facial expressions were picked up and copied by a group of 25 orangutans at four primate centres around the world. When one of the orangutans displayed an open, gaping mouth -- the equivalent of laughter -- the researchers examined the response of its playmate.

Dr Ross explained that often the playmate displayed the same expression less than half a second later, suggesting the mimicry was an involuntary display.

According to Dr Ross, the findings shed new light on empathy and its importance for animals which live in groups. "It revealed that empathy of positive emotions or contagious laughter evolved before humans."