During the experiment, volunteers see 20 videos of chimpanzees and bonobos, each of which contains a single gesture. You see the action once in real time, and again in slow motion. Your job is to choose from four possible interpretations, and to rate how confident you are in your guess. In case it’s hard to work out what is happening, each video is accompanied by charming illustrations to show you what to look out for. (Graham, who did the stylized blocky drawings, calls them Bonobobots.)[...]
But chimp gestures are complicated, in much the same way human words are. Humans have successfully trained famous apes, like Koko the gorilla or Nim Chimpsky the chimp, to use sign language with us, but apes naturally use gestures to communicate with each other. In many ways, these actions are far closer to human language than the sounds coming from the animals’ mouths. The calls of great apes are typically emotive, like screaming in pain, whining in hunger, or hooting in happiness. Very rarely do such calls signal any meaning, and very rarely are they directed at a specific listener. [...]
In the 1980s, scientists began documenting a few dozen gestures by studying chimps in zoos. But captive animals turned out to have tiny vocabularies, as Hobaiter showed by tracking wild chimps in Uganda’s Budongo Forest Reserve. To do so, she had to keep pace with fast-moving, tree-living animals from the ground, while filming often subtle movements from weird angles and through obscuring foliage. And after that hard work, she had to pore over the footage, again and again, to note what the apes are doing and how their peers responded. [...]
Human gestures vary considerably between cultures, but ape gestures do not. Every individual uses the same gestures in the same ways, with apparently no room for idiosyncrasy. What’s more, different species of great apes use the same signals. While Hobaiter was watching chimps, Graham and other members of Richard Byrne’s team were observing bonobos, orangutans, and gorillas. And even though these animals have very different hands and styles of moving, they seem to share a common set of gestures. It seems likely that they inherited this repertoire from their common ancestor—and that we did too.
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