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Apes sure love a good giggle, new research suggests.
Led by Marina Davila Ross, a primatologist at the University of Portsmouth in England, the research team tickled 22 young apes and three human babies to see how they would respond.
While none of the apes would make it onto a sitcom laugh track, the vocalisations were comparable to how humans respond to similar stimulus.
The study is the first to record laugh-like behaviour in apes, although there has been anecdotal evidence of such behaviour in the wild, said Michael J. Owren, a team member and associate professor of psychology and neuroscience at Georgia State University, in Atlanta.
The laughter "seemed like an expression of joy", said Davila Ross, a research fellow in the department of psychology. "It seemed to me that the subjects enjoyed the attention and the positive interaction with their caretakers, and did not show much attempt to leave when the tickling session was over."
How the research was done
The researchers, using more than 800 acoustic recordings, compared the laughter sounds of all four great ape species - chimpanzees, bonobos, gorillas and orangutans - and acoustically analysed and compared them to human laughter. Despite clear differences between ape and human laughter, the results showed that laughter is not a uniquely human trait, the scientists said.
The team then examined the sounds "phylogenetically" - that is, how they corresponded to well-established evolutionary similarities and differences between the different apes species and humans. The research provided strong evidence that laughter in great apes and humans has its origins with mankind's evolutionary ancestors.
In fact, the researchers point to the origin of laughter in a common primate ancestor that lived between 10 million and 16 million years ago. The findings were published online in the journal Current Biology.
"This is a very nice study which shows that when we sometimes compare the primate play-face with laughing, we're actually correct," said Frans B.M. de Waal, a professor of primate behaviour at Emory University, in Atlanta.
What the findings showed
"Some critics have argued that such terminology is anthropomorphic or that human laughing is a unique display in the animal world. But, in fact, there is a homology not just based on the facial expression, which we have suspected since Darwin, but also in the details of the breathing patterns and sounds of the display."
The study did not examine what - if any - connections exist between ape laughter and the development of humour, or precisely why the sounds evolved from short bursts into the voiced laughter of humans.
In a surprising finding, however, gorillas and bonobos were able to make laughter sounds while exhaling longer than expected. This ability was thought to be unique to humans and to have played an important role in the evolution of speech, the researchers said.
Scientists not involved with the research said they were intrigued by the study and predicted it would contribute to the evolving view of primates, especially those in captivity.
"This kind of behaviour does not surprise me," said Diana Reiss, professor of cognitive psychology at Hunter College in New York City, and an expert in animal communication. "We're finding much continuity between humans and the great apes. You see these behaviours and you see something you can relate to." – (HealthDay News, June 2009)
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