In the first systematic study of a non-human primate language, scientists from St. Andrew's University have deciphered the meaning of 66 wild chimpanzee sign language gestures. Ranging from flirting requests to grooming instructions, the gestures may reveal how language evolves.
Top image: Catherine Hobaiter
The study, which now appears in Current Biology, shows that wild chimpanzees use at least 66 gestures, such as arm raises, ground slaps, and foot stomps, to intentionally communicate 19 meanings. This dictionary, or "lexicon," was compiled by researchers Catherine Hobaiter and and Richard Byrne after observing over 80 wild chimps in the rainforests of Uganda, and then examining over 4,500 individual cases to decipher true (i.e. non-playful) meanings for the various gestures; the researchers isolated non-playful uses because in play, gestures are not always used with their 'real' meaning.
Hobaiter claims that only humans and chimps have a system of communication in which deliberate messages are sent from one individual to another. But that's debateable. Dolphins, through their complex use of clicks, burst-pulses, and whistles, may be utilizing a primitive form of language. And according to Sue Savage-Rumbaugh, bonobos have innate language skills, which suggests they may have their own yet-to-be deciphered lexicon of their own.
Undoubtedly, however, this new study is the first to formally describe the natural use of specific chimp gestures (as distinguished from vocal calls, say, to warn a group about a nearby predator). Although it's been known for some time that apes use gestures to communicate, no one has, until now, taken the time to work out the actual meanings.
"There is abundant evidence that chimpanzees and other apes gesture with purpose," noted Byrne in a statement. "Apes target their gestures to particular individuals, choosing appropriate gestures according to whether the other is looking or not; they stop gesturing when they get the result they want; and otherwise they keep going, trying out alternative gestures or other tactics altogether."
Hobaiter and Byrne found that gestures have the same meaning (or meanings) across individual signalers, and that the flexible use of several gestures for the same goal increases during negotiations.
Graphic via BBC.
So, when a chimp taps or grabs another it means "stop that." Used in another context, it can mean "climb on me." A hand fling or the slapping of an object means "move away." Chimps can convey "I want that" or "give me that" by raising an arm.
Fascinatingly, the act of leaf clipping — where a chimp very obviously takes small bites from leaves — is used to elicit sexual attention.
Image: Catherine Hobaiter
"Just as with human words, some gestures have several senses, but importantly the meanings of chimpanzee gestures are the same irrespective of who uses them," added Hobaiter. "Chimpanzees may use more than one gesture for the same purpose — especially in social negotiations, where the final outcome may be a matter of some give and take."
The next steps will involve the researchers investigating possible variations in meaning behind certain chimpanzee gestures.
Image: Patrick Rolands/shutterstock
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