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This is something that Marina Davila-Ross, a psychologist at the University of Portsmouth, UK, can attest to. She has dealt with her share of giggling chimpanzees.
Tickling can be a lot of fun
By enlisting zookeepers and mothers to tickle their ape and human baby charges, respectively, she has explored the links between laughter in human and non-human apes.
"We used the acoustic data [of laughter] similarly to how a geneticist uses genetic data in order to reconstruct evolutionary relationships," she says.
This work, published in 2009, appeared to confirm that human laughter developed from vocalisations found in the common ancestors we share with apes.
While the gorillas and bonobos in Davila-Ross's research produced more human-like sounds, the more distantly-related apes made noises that, out of context, would not be recognisable as laughter. However, by constructing a family tree of these sounds, she demonstrated the progression from brief grunts into the chuckles and guffaws made by humans.
This research traces the evolutionary history not only of laughter, but of tickling too. "An ape would not watch other apes playing or doing something funny, and laugh," says Davila-Ross. "They do not produce vocalisations free from behavioural context."
For an ape to find something funny, they need to be actively playing with their fellows. Tickling is part of the rough-and-tumble play carried out by all young apes, including humans. That kind of play can leave you breathless, and this breathlessness is what resulted in laughter as we know it.
"The 'ha-ha' of laughter is what I call the ritualisation of the sound of laboured breathing from rough-and-tumble play. If you tickle a chimpanzee, its laughter is a panting sound," says Provine, making panting noises down the phone to emphasise his point. "This is a way for the chimpanzee to indicate 'this is play, I'm not attacking you'. It's one of the clearest cases of where a vocalisation comes from."
For social animals like primates, tickling is a great way of reinforcing friendships in a controlled way. While human laughter is far more elaborate, this is where Provine thinks it originated.
