Ethiopian Monkey Study Offers Clues Into How Human Speech Evolved

Apr 18, 2016
Originally published on April 18, 2016 5:56 pm
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A new study finds that chatty monkeys in Ethiopia may offer clues into how the power of speech evolved in humans. NPR's Gregory Warner reports the reason has to do with something all of us do every day without noticing.

GREGORY WARNER, BYLINE: That something was first noticed in 1899 by a French laryngologist, which my French-speaking colleague, Ofeibea Quist-Arcton, will now demonstrate.

OFEIBEA QUIST-ARCTON, BYLINE: Always a pleasure.

WARNER: Ofeibea will say two French words with the same syllable, pa (ph).

QUIST-ARCTON: (Speaking French).

WARNER: The syllable tends to shorten as the word lengthens, so the pa in...

QUIST-ARCTON: (Speaking French).

WARNER: ...Is of a longer duration than the pa in -

QUIST-ARCTON: (Speaking French).

WARNER: This characteristic of language is known more broadly as Menzerath's law. It holds true from English to Greek to Mandarin Chinese. A paper published today in the Proceedings of the National Academy of Sciences says this law also operates in one non-human language.

(SOUNDBITE OF MONKEY CALL)

WARNER: This is the gelada monkey. It's found exclusively in the highlands of Ethiopia. It's also called the bleeding heart monkey, named so for the distinct splash flash of red on its chest and not for the elaborate soliloquies that the males deliver to the females.

(SOUNDBITE OF MONKEY CALL)

WARNER: This is a sound called the exhaled moan. And much like our French example from before, we're going to listen to Walter - he's a 10-year-old male - use that same moan in two sequences. So first, a short one of just two calls.

(SOUNDBITE OF MONKEY CALL)

WARNER: And then a longer, six-call sequence. You'll hear what happens to the moan.

(SOUNDBITE OF MONKEY CALL)

WARNER: The longer the sequence, the shorter the moan comes.

MORGAN GUSTISON: And the way I think about this - it's a general concept of compression.

WARNER: Morgan Gustison is lead author of the paper and a grad student at the University of Michigan. She says this finding gives clues not just to how monkeys talk, but how our primate ancestors may have evolved to speak.

GUSTISON: For the geladas, we think that because they're in such a talkative society where there's geladas vocalizing all the time, you want a way in which you can say what you want to say and not get interrupted.

WARNER: It's not clear whether the geladas are actually saying anything. There's no apparent words or grammar. But Gustison says that's actually the point. We use language as communication, so we might imagine that our primate ancestors evolved to do the same. But sometimes there's an evolutionary advantage just in holding the floor.

GUSTISON: Like, I - my favorite gelada, his name was Devil, and he was such a talker. And he's the one who would give these really, really, really long strings of calls all the time. And he had, like, one of the longest tenures I think we've seen.

WARNER: The longest tenure as a leader male making baby geladas. Not because he said anything witty or anything at all, but just because he'd learned to command attention and not get interrupted. Gregory Warner, NPR -

(SOUNDBITE OF MONKEY CALL)

WARNER: Gregory Warner, NPR News, Nairobi. Transcript provided by NPR, Copyright NPR.