MARY LOUISE KELLY, HOST:
This next story could not be introduced by a chimpanzee, unfortunately, but chimps do possess some of the building blocks of spoken language. NPR's Jon Hamilton reports on two new studies that hint at the evolutionary roots of human speech.
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JON HAMILTON, BYLINE: One critical element of spoken language is rhythm, so scientists have been studying the beats produced by wild chimps in the African rainforest. Cat Hobaiter is from the University of St. Andrews in Scotland. She says, in the rainforest, the roots of many trees extend outward from the trunk above ground.
CAT HOBAITER: And what the chimps do is they take advantage of those 'cause they make fantastic resonant drumming surfaces.
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HOBAITER: They're actually drumming often with their feet, so they're using their hands to hold onto those roots, and then they're kind of dancing. And sometimes they're jumping between the roots and getting all of those different beat structures down, throwing a hand in if you want to get a little syncopated.
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HAMILTON: Chimps use drumming to communicate over long distances. Hobaiter was part of a team that analyzed hundreds of recorded drumming episodes from several different chimp communities. She says the analysis confirmed something field scientists had long suspected.
HOBAITER: Not only do chimpanzees have rhythmic structure in their drumming, but actually, different populations of chimpanzees - the Eastern and the Western subspecies - they use different rhythmic structures.
HAMILTON: The findings, which appear in the journal Current Biology, suggest that rhythmic structures were already around when the first humans appeared. And Hobaiter says rhythm isn't just for music and dance.
HOBAITER: It's present in the back and forth of a conversation and the timing of a kind of - you know, a slow country drawl or a fast-talking city kind of, you know, accent or something.
HAMILTON: Spoken language also combines a limited number of vocal sounds to create an unlimited number of meanings. So another group of scientists studied the call combinations used by 53 wild chimps in Cote d'Ivoire. Catherine Crockford of the French National Center for Scientific Research says the team would begin observing the chimps each day at dawn.
CATHERINE CROCKFORD: We stay with them through the day, collecting everything they do - every activity change, every social interaction, every vocalization - until they go to bed at night.
HAMILTON: The team recorded and analyzed more than 4,000 utterances. These included examples of about a dozen different calls. Sometimes the calls were used on their own and sometimes in combinations. Crockford says for this analysis, they focused on two call combinations known as bigrams.
CROCKFORD: What we found then is that there is some shifts in meaning when the single calls are embedded into these bigrams and that their meaning can change in several ways.
HAMILTON: For example, a hoo call on its own...
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HAMILTON: ...Often means a chimp is resting. A pant call on its own...
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HAMILTON: ...Usually means a chimp is playing. But when the two calls are combined...
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HAMILTON: ...Chances are, one or more chimps is building a nest. Previous research has found these call combinations when a chimp is sounding an alarm about something dangerous, like a snake. Crockford says it makes sense that chimps also use this ability for other purposes.
CROCKFORD: It probably didn't evolve just because once in a while we see a predator. It probably evolved because we need to somehow navigate our social world.
HAMILTON: Crockford says the finding, which appears in the journal Science Advances, does not mean that chimp calls are like human words. But she says the presence of rhythmic structures and complex calls in one of our closest relatives could help explain how human language emerged. Jon Hamilton, NPR News.
(SOUNDBITE OF MUSIC) Transcript provided by NPR, Copyright NPR.
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