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Chimpanzees use surprisingly complex vocal sequences

As the only species on earth known to use language, humans combine sounds to form words, and words to form hierarchically structured sentences. The origins and evolution of human language remain unknown. 

To retrace the evolutionary origins of human language, researchers often use a comparative approach with primates. In contrast to humans, primates often use single calls –referred to as call types – and rarely combine them with each other to form vocal sequences.

The communication used by primates appears less complex on the surface. Human language complexity comes from the way we combine sounds in a structured manner to form words and combine these words to form sentences to express an infinite number of meanings. To date, primate vocal sequences have not been analyzed in great detail and we may not have a full picture of how they communicate. 

Researchers at the Max Planck Institute for Evolutionary Anthropology and CNRS recorded thousands of vocalizations produced by three groups of wild chimpanzees in the Taï National Park in Ivory Coast. The experts identified 12 different call types and assessed how chimpanzees combine them to form vocal sequences. 

“Observing animals in their natural social and ecological environment reveals a previously undiscovered complexity in the ways they communicate,” said study first author Cédric Girard-Buttoz. 

“Syntax is a hallmark of human language and in order to elucidate the origin of this human ability it is crucial to understand how non-human primate vocalisations are structured,” said co-author Emiliano Zaccarella.

The study is the first documentation of diversity of vocal production in non-human primates. The results show that chimpanzees communicate by using hundreds of different sequences, combining up to ten call types. This highlights a communication system in chimpanzees that is much more complex than previously thought.

“By studying the rich complexity of the vocal sequences of wild chimpanzees, a socially complex species like humans, we expect to bring fresh insight into understanding where we come from and how our unique language evolved,” said study senior author Catherine Crockford.

As a next step, the experts are working to understand what these complex and structured vocal sequences mean and whether chimpanzees have a range of topics they can communicate about.

Overall, the evidence of structured vocal sequences in wild chimpanzee communication provides insights into human language evolution communication.

The study is published in the journal Communications Biology.

By Katherine Bucko, Staff Writer

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