Lead author, behavioural biologist Dr Marina Davila-Ross said:
"I didn't expect to find such prominent differences between responsive and spontaneous laughter in chimpanzees, but my biggest surprise was the results showing those in newer groups mimic their playmates more often than those in established groups where the chimpanzees know each other well. This suggests mimicking laughter might play a special role in strengthening social bonds."
The findings reveal important similarities with findings on humans, where both laugh cultures and mimicking cultures have been reported.
Dr Davila-Ross, of the University's Department of Psychology, said:
"Humans clearly use laughter as an important response in a wide range of social situations, but it is particularly interesting that chimpanzees seem to also use laughter to respond in such distinct ways. Great apes' ability to manage the sounds they make seems to be much more limited than humans and other animals, and even parrots. Nonetheless, their laughter might be partly managed and partly automatic. They do not just mimic the expressions of their playmates; they respond with their expressions in more complex ways than we were aware of before.
We found their responsive laughter shows a similarity to the conversational laughter of humans. Both are shorter than spontaneous laughter and both seem designed to promote social interaction.
These sorts of responses may lead to important advantages in cooperation and social communication - qualities that help explain why laughter and smiles have become integral tools of emotional intelligence in humans."
The researchers found that responsive laughter is also used differently across social groups of chimpanzees compared to their use of spontaneous laughter. It is not evident at such a young age as spontaneous laughter, it is shorter, and it seems to prolong play, which has a vital role in the physical, emotional, social and cognitive development of both chimpanzees and humans.
Dr Davila-Ross's study examined laughter in 59 chimpanzees living in four groups in the chimpanzee sanctuary Chimfunshi Wildlife Orphanage in Zambia. Two of the groups had been established for more than 14 years, and two groups had been living together for less than five years. All contained a mixture of ages and sexes. Nearly 500 play bouts were video recorded and in all cases, playing sessions lasted significantly longer when one playmate joined in the laughter of another.
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