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.

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