Experts decode chimp gestures

JARED Diamond, in his 1991 book The Third Chimpanzee, compared chimp biology with our own. Sharing 98.4% of their DNA with humans, chimps are more closely related to us than they are to the other great apes.

We are so similar to them genetically that, Diamond suggested, they belong with us in the genus Homo. Recent research has shown that the differences are greater than was previously thought but the chimps remain our closest animal relatives. Now, scientists from St Andrew’s University in Scotland claim that our hairy cousins use gestures of such complexity that they constitute a form of language. In the 1960s, philosopher and linguist Noam Chomsky declared that language is a uniquely human creation, a view which has prevailed ever since. Was he wrong? Catherine Hobaiter and Richard Byrne, writing in the journal Current Biology, think he was.

Chimps not only use tools, they are able to construct them. Have they also created their own language? When chimps interpret the calls and gestures of their peers, are they engaging in conceptual dialogue? Birds sing and display to attract mates and defend territories. These behaviours trigger responses from potential partners and rivals but they don’t necessarily have meaningful content. When you throw a switch to turn on a light, you are not communicating with the local power station. Similarly, a singing bird is just trying to trigger a response. Speaking to the BBC, Hobaiter gave this analogy; ‘..you pick up a hot cup of coffee. You scream and blow on your fingers. I can understand from that that the coffee was hot, but you didn’t necessarily intend to communicate that to me’.

Chimps use mostly visual, rather than vocal, signals. Hobaiter and Byrne tracked and filmed groups of chimps over 18 months in Uganda’s Budongo Forest, recording over 3,400 interactions. The footage appeared to show chimps deliberately sending messages to each other.

The role of a particular gesture only becomes apparent when there is an observable outcome. As in human discourse, most chimp dialogue doesn’t result in identifiable behaviours, so chimp language remains largely impenetrable. However, Hobaiter and Byrne catalogued 4,500 chimp gestures and worked out the meanings of 36 of them. They claim to have identified elements of chimp ‘vocabulary’. A mother might show the sole of its foot to a youngster; that’s an invitation to climb on her back. Presenting a shoulder or an arm is a request for grooming. Tearing leaves into strips is a sexual proposition. Stomping both feet expresses a wish to play. As in human language, there are ambiguities. Several gestures may convey the same meaning and signals can be used in combination.

According to the authors, this is the only known form of linguistic communication, apart from our own, recorded to date in the animal kingdom. Hobaiter believes ‘that there is another species out there that is meaningful in its communication, so that’s not unique to humans’.

This is an ambitious claim. Can a clear distinction be made between ‘intentional’ and more primitive forms of communication? Surely there are animal behaviours, more advanced than mating rituals, which approach in complexity the signals chimps send to each other? The cooperative hunting of lions and wolves, where victims are corralled into an ambush, must require elaborate intercommunication between the predators. The waggle-dances of bees returning to a colony convey detailed information on the locations of nectar and the distances to them. Is there not a continuous ‘cline’ of increasing behavioural sophistication between a plant turning towards the sun for light and Albert Einstein deriving the equations of General Relativity? Perhaps the outstanding value of this research is the light it throws on the evolution of human language. Our extraordinarily rich and flexible communication system, it suggests, is no recent invention but had its origins among our non-human ancestors, perhaps even those living before our evolutionary line separated from the one that led to the chimps, seven million years ago.

Catherine Hobaiter and Richard Byrne. The Meanings of Chimpanzee Gestures. In Current Biology, 2014.


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