Wild chimpanzees change the meaning of individual calls by combining them in different ways, a behavior that reflects how humans use language to create meaning through combining words.

Humans are the only species known to use full language, which involves combining sounds into words and words into structured sentences that convey infinite meanings. This process follows linguistic rules that determine how meaning changes with context.

For example, the word "ape" can be used in compositional ways to add meaning -- such as "the ape eats" or "big ape" -- or in non-compositional idioms like "go ape," which takes on a new meaning entirely. Syntax, the rule system that governs word order, is essential to this process. For instance, "go ape" and "ape goes" use the same words but convey different meanings due to their order.

One of the central questions in science is understanding the origin of this exceptional linguistic ability. Researchers often compare human language with the vocal behavior of other animals, especially primates, to explore how language evolved. Most non-human primates rely on individual call types and have only a few known call combinations, usually to warn about predators.

This has led to the belief that their vocal systems are too limited to be considered precursors of human language. However, we may be underestimating the communicative abilities of our closest relatives. New findings suggest that chimpanzees may use call combinations in more complex and meaningful ways than previously recognized.

Studying the meaning of chimpanzee vocalizations

Researchers from the Max Planck Institutes for Evolutionary Anthropology and for Cognitive and Brain Sciences in Leipzig, Germany, and from the Cognitive Neuroscience Center Marc Jeannerod (CNRS/Université Claude Bernard Lyon 1) and Neuroscience Research Center (CNRS/Inserm/Université Claude Bernard Lyon 1) in Lyon, France recorded thousands of vocalizations from three groups of wild chimpanzees in the Taï National Park in Ivory Coast.

They examined how the meanings of 12 different chimpanzee calls changed when they were combined into two-call combinations.

"Generating new or combined meanings by combining words is a hallmark of human language, and it is crucial to investigate whether a similar capacity exists in our closest living relatives, chimpanzees and bonobos, in order to decipher the origins of human language," says Catherine Crockford, senior author of the study.

"Recording chimpanzee vocalizations over several years in their natural environment is essential in order to document their full communicative capabilities, a task that is becoming increasingly challenging due to growing human threats to wild chimpanzee populations," says Roman Wittig, co-author of the study and director of the Taï Chimpanzee Project.

Chimpanzees' complex communication system

The study reveals four ways in which chimpanzees alter meanings when combining single calls into 16 different two-call combinations, analogous to the key linguistic principles in human language. Chimpanzees used compositional combinations that added meaning (e.g., A = feeding, B = resting, AB = feeding + resting) and clarified meaning (e.g., A = feeding or travelling, B = aggression, AB = travelling).

They also used non-compositional idiomatic combinations that created entirely new meanings (e.g., A = resting, B = affiliation, AB = nesting). Crucially, unlike previous studies which have mostly reported call combinations in limited situations such as predator encounters, the chimpanzees in this study expanded their meanings through the versatile combination of most of their single calls into a large diversity of call combinations used in a wide range of contexts.

"Our findings suggest a highly generative vocal communication system, unprecedented in the animal kingdom, which echoes recent findings in bonobos suggesting that complex combinatorial capacities were already present in the common ancestor of humans and these two great ape species," says Cédric Girard-Buttoz, first author on the study.

He adds: "This changes the views of the last century which considered communication in the great apes to be fixed and linked to emotional states, and therefore unable to tell us anything about the evolution of language. Instead, we see clear indications here that most call types in the repertoire can shift or combine their meaning when combined with other call types. The complexity of this system suggests either that there is indeed something special about hominid communication - that complex communication was already emerging in our last common ancestor, shared with our closest living relatives - or that we have underestimated the complexity of communication in other animals as well, which requires further study."

Reference: "Versatile use of chimpanzee call combinations promotes meaning expansion" by Cédric Girard-Buttoz, Christof Neumann, Tatiana Bortolato, Emiliano Zaccarella, Angela D. Friederici, Roman M. Wittig and Catherine Crockford, 9 May 2025, Science Advances.

DOI: 10.1126/sciadv.adq2879

Funding: Max-Planck-Gesellschaft, H2020 European Research Council, Deutsche Forschungsgemeinschaft