Professor Jaak Panksepp says that animals other than humans exhibit play sounds that resemble human laughs. These include the panting sounds made by chimps and dogs when they play and chirping sounds observed in rats.
This suggests that the capacity for laughter may be a very ancient emotional response that predates the evolution of humankind, says Panksepp.
Professor Panksepp, of Bowling Green State University in Ohio, US, explains that neural circuits for laughter exist in "ancient" parts of our brain, whose general structure is shared amongst many animals.
"Such knowledge may help to reveal how joking and horsing around emerged in our expansive higher brain regions," Professor Panksepp writes.
Other researchers prefer to view laughter and joy as uniquely human traits.
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