Bonobo communication shares compositional similarities with human language
Summary author: Walter Beckwith
American Association for the Advancement of Science (AAAS)
Wild bonobos – our closest living relatives – communicate using vocal calls organized in compositionally complex semantic structures that mirror key features of human language, according to a new study. The findings challenge long-held assumptions about the uniqueness of human language and open new avenues for understanding the evolution of communication. A hallmark characteristic of human language is its ability to combine discrete elements to form more complex, meaningful structures. This principle, known as compositionality, allows for the assembly of morphemes (the smallest unit of language with meaning) into words and words into sentences; the meaning of the whole is determined by its constituent parts and their arrangement. Compositionality can take two forms: trivial and nontrivial. In trivial compositionality, each word maintains its independent meaning. Nontrivial compositionality involves a more complex, nuanced relationship where meaning is not simply a direct sum of the words involved. Compositionality may not be unique to human language; studies in birds and primates have demonstrated that some animals are capable of combining meaningful vocalizations into trivially compositional strucutres. However, to date, there is no direct evidence that animals use nontrivial compositionality in their communication.
Here, Mélissa Berthet and colleagues report strong empirical evidence that wild bonobos (Pan paniscus) use nontrivial compositionality in their vocal communication. Berthet et al. analyzed 700 recordings of bonobo vocal calls and call combinations and documented over 300 contextual features associated with each utterance. Employing a method derived from distributional semantics – a linguistic framework that measures meaning similarities between words – the authors analyzed these contextual features to infer the meanings of individual bonobo vocalizations and quantify their relationships. Then, to assess whether bonobo call combinations follow compositional principles, they applied a multi-step approach previously used to identify compositionality in human communication. Berthet et al. discovered that bonobo call types integrate into four compositional structures, three of which exhibit non-trivial compositionality, suggesting that bonobo communication shares more structural similarities with human language than previously recognized.
Journal
Science
Article Title
Extensive compositionality in the vocal system of bonobos
Article Publication Date
4-Apr-2025
Bonobos combine calls in similar ways to human language
University of Zurich
audio:
A bonobo whistling in the forest, to coordinate group movements over larger distances.
view moreCredit: Mélissa Berthet
Bonobos – our closest living relatives – create complex and meaningful combinations of calls resembling the word combinations of humans. This study, conducted by researchers at the University of Zurich and Harvard University, challenges long-held assumptions about what makes human communication unique and suggests that key aspects of language are evolutionary ancient.
A new study has investigated the vocal behavior of wild bonobos in the Kokolopori Community Reserve (Democratic Republic of Congo). Researchers at the University of Zürich and Harvard University used novel methods borrowed from linguistics to demonstrate for the first time that, similarly to human language, bonobo vocal communication relies extensively on compositionality.
Compositionality is the capacity to combine meaningful words into phrases whose meaning is related to the meaning of the words and the way they are combined. In more trivial compositionality, the meaning of the combination is the addition of its parts: for example, “blond dancer” refers to a person who is both blond and a dancer. However, in more complex, nontrivial compositionality, one part of the combination modifies the other. For example, “bad dancer” does not refer to a bad person who is also a dancer: “bad” in this case does not have an independent meaning but complements “dancer”.
A bonobo dictionary
In a first step, the researchers applied a method developed by linguists to quantify the meaning of human words. “This allowed us to create a bonobo dictionary of sorts – a complete list of bonobo calls and their meaning,” says Mélissa Berthet, a postdoctoral researcher at the Department of Evolutionary Anthropology of UZH and lead researcher of the study. “This represents an important step towards understanding the communication of other species, as it is the first time that we have determined the meaning of calls across the whole vocal repertoire of an animal.”
Compositionality is not unique to humans
After determining the meaning of single bonobo vocalizations, the researchers then moved on to investigating call combinations, using another approach borrowed from linguistics. “With our approach, we were able to quantify how the meaning of bonobo single calls and call combinations relate to each other,” says Simon Townsend, UZH Professor and senior author of the study. The researchers found numerous call combinations whose meaning was related to the meaning of their single parts, a key hallmark of compositionality. Furthermore, some of the call combinations bore a striking resemblance to the more complex nontrivial compositional structures in human language. “This suggests that the capacity to combine call types in complex ways is not as unique to humans as we once thought,” says Mélissa Berthet.
Older than previously thought
An important implication of this research is the potential light it sheds on the evolutionary roots of language’s compositional nature. “Since humans and bonobos had a common ancestor approximately 7 to 13 million years ago, they share many traits by descent, and it appears that compositionality is likely one of them,” says Harvard Professor Martin Surbeck, co-author of the study. “Our study therefore suggests that our ancestors already extensively used compositionality at least 7 million years ago, if not more,” adds Simon Townsend. The findings also indicate that the ability to construct complex meanings from smaller vocal units existed long before human language emerged, and that bonobo vocal communication shares more similarities with human language than previously thought.
Literature
Berthet et al., (2025) Extensive Compositionality in the Vocal System of Bonobos, Science, doi: 10.1126/science.adv1170
Mia, a young bonobo female from the Fekako community, vocalizing in response to distant group members.
Credit
Martin Surbeck, Kokolopori Bonobo Research Project
Tupac, a young male bonobo scratching its head.
Olive, a fist time bonobo mother from the Ekalakala community, vocalizing toward distant group members.
Credit
Lukas Bierhoff, Kokolopori Bonobo Research Project
combination peep whistle [AUDIO] |
A bonobo emits a subtle peep before the whistle, to denote tensed social situations. (Here, the bonobo is performing a display in front of the other group members by dragging a branch.)
Credit
Mélissa Berthet
Science
Method of Research
Observational study
Subject of Research
Animals
Article Title
Berthet et al., (2025) Extensive Compositionality in the Vocal System of Bonobos
Article Publication Date
3-Apr-2025
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