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There are few one-offs in life on Earth—rarely can a single species boast a trait or ability that no other possesses. But human language is one such oddity. Our ability to use subtle combinations of sounds produced by our vocal cords to create words and sentences, which when combined with grammatical rules, convey complex ideas.

There were attempts in the 1950s to teach chimpanzees to “speak” some words, but these failed. And with no other living relatives able to communicate as we do, it has made understanding the origins of language a knotty problem.

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But Adrien Meguerditchian, a primatologist at the French National Centre for Scientific Research and Aix-Marseille University, believes that gestures could be a key landmark in the evolution of language—and these are something we do have in common with other primates.

Gestures are more important to language than linguists used to believe.

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Many primate species use gestures to communicate with others in their groups. Wild chimpanzees have been seen to use at least 66 different hand signals and movements to communicate with each other. Lifting a foot toward another chimp means “climb on me,” while stroking their mouth can mean “give me the object.” In the past, researchers have also successfully taught apes more than 100 words in sign language. “The idea is to look at language, not just as speech, but seeing it as a constellation of many cognitive properties,” says Meguerditchian.

Most language properties involve asymmetric organization of the human brain between the two hemispheres. Given that gestures in primates seem to involve several key properties that underpin spoken language, Meguerditchian wants to see if primates undergo similar brain asymmetry when they gesture to each other. “If you want to understand the origins of language, you need to understand not only animal cognition and communication but also its brain specialization in comparison with humans, and that is what we do in primate species,” he says.

Given both primates and humans can communicate through gestures, it provides a way of comparing how gestures are related to brain asymmetry for language and to unravel whether there are differences in how each species communicate. Meguerditchian is studying both adult and baby baboons to see which gestures they learn and the parts of their brains that might be involved. “When baboons invite someone to play, they will use their hands,” he says. “Baboons are also able to point to food they want and use gaze, like children can.”

In human babies, which learn to gesture at objects before they can speak, the left side of their brain seems to be engaged when they do so. Certain regions on the left side of our brain, such as Broca’s area, are especially important when we speak. Meguerditchian is using magnetic resonance imaging to study baboon baby brains to see if they use a similar part of their brain when they learn to gesture. “The questions is, if language is mostly in the left hemisphere in humans, what about gesture in non-human primates? If it is the same system, which was used by a common ancestor between us, gesture in baboons might also be related to this left hemisphere specialization of the brain in baboons.”

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So far, early results from 27 brain scans of baby baboons suggest that his hypothesis is correct, and apes use similar asymmetric brain areas when they gesture as humans do when they gesture and speak.

By comparing these results in baboons with other primates, including humans, gorillas, chimps, and monkeys, Meguerditchian hopes to unravel whether they too share a similar asymmetric system in the brain for communication. This might help discern where on our evolutionary tree gesture communication, and the brain structures needed for it, first arose and perhaps sowed the seeds for our spoken language.

But he is not alone in thinking that some of the earliest forms of language in our species may well have been gestural rather than vocal. “For some reason, speech won out evolutionarily,” says Wendy Sandler, a linguist at the University of Haifa, Israel. “We have not discovered any community of hearing people who happen to use sign language as their main mode of communication.”

Apes and humans use similar brain areas when they gesture and speak.

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Sandler is exploring the relationship between physical communication and the composition of human language. She believes sign languages can provide some clues to the structure of human language and how language may have emerged in our ancestors. Unlike all spoken languages, which are thousands of years old and descended from other ancient languages, sign language can be born whenever a group of deaf people have an opportunity to meet and communicate.

“The visual aspect of language is much more important than linguists used to believe,” says Sandler, who is leading a project called the Grammar of the Body (GRAMBY). Part of the work has involved studying the complexity of newly emerging sign languages and sign language in a number of different cultures. “Different parts of the body convey different linguistic functions,” she says. “The hands convey words, but the intonation, so the rise and fall of voice, is conveyed in sign language by facial expressions and different tilts of the head.”

She and her colleagues also studied video footage of chimp displays at a Zambian wildlife orphanage to see if they use combinations of facial and gestural signals to convey complex meanings. Humans can knit together smaller elements of meaning according to known rules to form composites, which gives us the ability to communicate an infinite number of messages. Sandler offers the example of “train station,” which we know is a station for trains because of the words and rules we know apply in English. She has also studied the expression of extreme emotion in athletes who have won and lost a competition. Taking her studies together, she concludes that humans are “compositional communicators.”

“This means we can express complex messages by reorganizing the same units according to their meanings and the rules of our language,” Sandler says. This compositional complexity is critical in human communication.

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Can chimps stack meaning like this to create a higher meaning? So far the answer is no in our nearest relatives. However, Sandler discovered that chimps can separate and recombine some gesture and facial expressions, which “is a stepping stone to the compositionality of human language.”

Scientists still do not know how or when language arose in our ancestors, a crucial mystery in unravelling our uniqueness. But a better understanding of how humans use gestures and our closest primate relatives communicate may reveal more about how and when we learned to speak.

Anthony King is a freelance science journalist based in Dublin, Ireland.

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Originally published on Horizon, the E.U. research & innovation magazine.

Lead image: namatae / Shutterstock

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