Chimps, bonobos and other great apes speak sign language, but what are they saying? You might know

In a turn around for science, researchers in the UK have discovered that humans are quite good at interpreting the sign language used by some apes. Mostly, research has been done to see if apes can understand humans.

Using videos – which anyone can try – they found that chimp and bonobo sign language can be largely understood by humans, despite the fact we no longer use the hand gestures ourselves.

Great ape hand gestures were the first recorded evidence of intentional communication outside of our human language. Now, over 80 hand signals have been identified, many of which are shared across non-human apes. There are even similarities between the signs of distantly related apes such as chimpanzees and orangutans – living on opposite sides of the globe.

Of course, we humans are ourselves gestural creatures. As a Mediterranean boy, I know this very well: 🤌🏽

But our hand signs are thought to no longer incorporate the apes’ gestures despite humans being more closely related to chimpanzees and bonobos. Humans and chimpanzees are thought to have a common ancestor which lived about 6 to 7 million years ago.

Is it possible that humans could have retained some understanding of ape hand gestures?

University of St Andrews, UK, research suggests that the answer is yes.

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The researchers tested people on the 10 most common gestures used by chimpanzees (Pan troglodytes) and bonobos (Pan paniscus). Over 5,500 viewed 20 short videos of ape gestures in an online game. They were then tasked with selecting the meaning of the gesture from four possible answers.

The human participants did better than pure chance alone, correctly identifying the meaning more than 50% of the time. Providing context to the signs increased success marginally.

Normally, such video playback experiments have been used to test language comprehension in non-human primates. In this study, the tables were turned, testing our ability to understand our closest relatives for the first time.

You can take a quiz version of the experiment at this link. No data are collected from this quiz.

Indeed, pet owners will tell you (even if you didn’t ask) that they can understand their dog, cat, horse or other domesticated beast. But this “understanding” is inference built up over time. The results of the test of our ability to understand ape hand gestures indicates a different kind of understanding.

While we no longer use these gestures, the experiment suggests we may have retained an understanding of this ancestral communication system.

The authors are unsure whether our ability to understand great ape signs is inherited. It may also be the case that humans and other great apes share an ability to interpret signals because of similar intelligence, physical appearance, and social goals.

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“All great apes use gestures, but humans are so gestural – using gestures while we speak and sign, learning new gestures, pantomiming – that it’s really hard to pick out shared great ape gestures just by observing people,” says co-lead researcher Dr Kirsty E Graham. “By showing participants videos of common great ape gestures instead, we found that people can understand these gestures, suggesting that they may form part of an evolutionarily ancient, shared gesture vocabulary across all great ape species including us.”

The research is published in the journal PLOS Biology.

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