Do Apes Laugh When Tickled?
Apes often make weird sounds when they're tickled, and some researchers now say these pants and hoots truly are related to human laughter.
That's the conclusion of a new study in the journal Current Biology that analyzed the "tickle-induced vocalizations" of infant and juvenile apes as well as human infants.
One of the scientists, Michael Owren of Georgia State University in Atlanta, says he was initially skeptical that the panting sounds made by tickled chimps had anything to do with the distinctive "ha ha ha" of human laughter.
"I was reluctant to think of the chimpanzee pantlike vocalizations as being laughter," Owren says. "And I did not necessarily believe that there was a common origin between those sounds and human laughter."
But then a researcher named Marina Davila Ross, of the University of Portsmouth in the United Kingdom, came to his lab with recordings she had collected of 21 infant and juvenile orangutans, gorillas, chimpanzees and bonobos, as well as three human babies.
Davila Ross says going to zoos and watching the apes being tickled was an amazing experience, because they really seemed to love being tickled and, even though their sounds were odd, they looked like they were cracking up.
"That was absolutely fascinating, how they responded to the caretakers when they were tickled," Davila Ross says.
But the question is, she says, when you listen to these ape sounds, "how can one really know that this is laughter?"
To try and find out, she and Owren analyzed 11 different acoustic features in the recordings of tickled apes.
Then, along with Elke Zimmermann, of the University of Veterinary Medicine in Hannover, Germany, they compared what they'd found to the known evolutionary relationship between these apes and humans. They discovered a revealing pattern of similarities and differences among these five related species.
"The results suggest that the evolutionary origins of human laughter can be traced back at least 10 to 16 million years to the last common ancestor of humans and modern great apes," they write in their research report.
The primordial laughlike sound of that common ancestor probably had long, slow, noisy calls. Specific features of these sounds then got exaggerated or changed over evolutionary time, as the different apes emerged.
"All these sounds do seem to have a common origin, evolutionarily speaking," says Owren, "and I am now comfortable calling them all laughter."
This raises a question: If these sounds are all laughter, what made humans develop our distinctive "ha ha ha" instead of something more like the panting of a chimp? "If human laughter has evolved in a somewhat different direction, then why did it do that? And why these features in particular?" asks Owren.
He says learning more about that could help reveal the function of laughter in human relationships. After all, people don't just laugh when they're tickled.
Robert Provine, a neuroscientist at the University of Maryland, Baltimore County who studies laughter, notes that dogs pant in a certain way when they're playing, and rats are known to chirp.
So he thinks the roots of laughter might go even further back and would like to see more studies like this one that compare different animals' playful sounds.
"I think that it's about time we get out there, start tickling the dogs and the cats, and the pigs, the rats, as well as the chimpanzees," Provine says. "I think we'll learn a lot about what we have in common, as well as our differences."
Play-associated sounds have hardly been studied in animals, says Provine. "What about whales?" he asks. "You know, do whales have some form of laughter? People really haven't looked into this."
In general, Provine says, laughter hasn't gotten a lot of attention from scientists, because it's such an everyday thing that it often goes unnoticed.
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MELISSA BLOCK, host:
From NPR News, this is ALL THINGS CONSIDERED. I'm Melissa Block.
ROBERT SIEGEL, host:
I'm Robert Siegel.
And this next story is about something very pleasant: tickling babies. Once an infant is a few months old, you hear something like this if you go kitchy-kitchy-koo.
(Soundbite of baby laughing)
SIEGEL: But if the baby being tickled is a gorilla or a chimpanzee, you'll hear something a little different.
NPR's Nell Greenfieldboyce reports on some new research into the origins of laughter.
NELL GREENFIELDBOYCE: Marina Davila Ross is a researcher at the University of Portsmouth in the United Kingdom. She recently went around to zoos in Europe and recorded the sounds that apes made as they were tickled by their caretakers. One of her videos shows a man tickling the big feet of a hairy gorilla. The gorilla makes these rumbling, breathy sounds and squirms around. It looks like he's cracking up and loving it.
(Soundbite of tickled gorilla)
Ms. MARINA DAVILA ROSS (Researcher, University of Portsmouth): And that was absolutely fascinating, you know, how the relationship was between caretakers and the apes and how they responded to the caretakers when they were tickled.
GREENFIELDBOYCE: She didn't just record gorillas, she recorded bonobos being tickled.
(Soundbite of tickled bonobo)
Orangutans.
(Soundbite of tickled orangutan)
And chimps.
(Soundbite of tickled chimpanzee)
All of these great apes share a common ancestor with humans, but are their tickle-induced sounds really related to this?
(Soundbite of baby laughing)
Ms. DAVILA ROSS: Now, how can one really know that this is laughter?
GREENFIELDBOYCE: To try to find out, Davila Ross took her recordings to the lab of Michael Owren of Georgia State University who has studied the acoustics of human laughter. He says humans tend to go ha-ha-ha, while chimps' so-called laughter is more like panting.
(Soundbite of tickled chimpanzee)
Almost like they're just exerting themselves.
Professor MICHAEL OWREN (Psychology and Neuroscience, Georgia State University): I was reluctant to think of the chimpanzee pant-like vocalizations as being laughter, and I did not necessarily believe that there was a common origin between those sounds and human laughter.
GREENFIELDBOYCE: But then, the researchers analyzed various acoustic features in the recordings of tickled apes - things like how many sounds were made in a burst, whether sounds were made on the exhale or the inhale or both and how the vocal chords vibrated. And here's what they found.
Owren says there's a revealing pattern of similarities and differences between these five related species. He says it seems likely that the origins of laughter go back at least to their last common ancestor, 10 to 16 million years ago. That ancestor had a primordial, laughter-like sound and specific features of this sound then got exaggerated or changed over evolutionary time as different apes emerged.
Prof. OWREN: All these sounds do seem to have a common origin, evolutionarily speaking, and I am now comfortable calling them all laughter.
GREENFIELDBOYCE: All of them?
Prof. OWREN: All of them.
GREENFIELDBOYCE: He says this raises a question. If these sounds are all laughter, what made humans develop our distinctive ha-ha-ha instead of something more like the panting of a chimp?
Prof. OWREN: If human laughter has evolved in a somewhat different direction, then why did it do that? And why these features in particular?
GREENFIELDBOYCE: He says understanding that could help us learn more about the function of human laughter. After all, we don't just laugh when we're tickled.
The results are reported in the journal Current Biology. Robert Provine is a neuroscientist at the University of Maryland who studies laughter. He thinks the roots of laughter might go even further back. He'd like to see more studies like this one that compare different animals' playful sounds.
Professor ROBERT PROVINE (Psychology; Neuroscientist, University of Maryland): I think that it's about time we get out there, start tickling the dogs and the cats and the pigs, the rats, as well as the chimpanzees. I think we'll learn a lot about what we have in common, as well as our differences.
GREENFIELDBOYCE: He says dogs pant in a certain way when they're having fun, and rats chirp, but lots of other animals haven't been studied.
Prof. PROVINE: What about whales? You know, do whales have some form of laughter? People really haven't looked into this.
GREENFIELDBOYCE: In general, he says, laughter hasn't gotten a lot of attention from scientists. He says it's such an everyday thing that it basically goes unnoticed.
Nell Greenfieldboyce, NPR News. Transcript provided by NPR, Copyright National Public Radio.
