Bonobos use a kind of syntax once thought to be unique to humans
The way bonobos combine vocal sounds to create new meanings suggests the evolutionary building blocks of human language are shared with our closest relatives
By Sophie Berdugo
3 April 2025
A female bonobo at Kokolopori Bonobo Reserve in the Democratic Republic of the Congo
Lukas Bierhoff, Kokolopori Bonobo Research Project
Bonobos combine their calls in a complex way that forms distinct phrases, a sign that this type of syntax is more evolutionarily ancient than previously thought.
Human language, often described as the hallmark of our species, is made up of many different building blocks. One core block is syntax, where meaningful units are combined into longer sequences, like words into sentences. This is made possible through compositionality, where the meaning of the whole is derived from the meaning of the parts.
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Compositionality in itself isn’t unique to humans. For example, chimpanzees combine calls to warn others of snakes. But, so far, only “trivial compositionality” has been identified in non-human animals, whereby each unit adds independently to the meaning of the whole. For example, the phrase “blonde dancer” has two independent units: a blonde person who is also a dancer. Humans were thought to be unique in also having “non-trivial compositionality”, where the words in a combination means something different to what they mean individually. For example, the phrase “bad dancer” doesn’t mean a bad person who also dances.
The issue was that biologists didn’t have the tools to assign a clear meaning to animal vocalisations, says Mélissa Berthet at the University of Zurich in Switzerland, so they couldn’t be certain if a combination was trivial or non-trivial.
Berthet and her colleagues spent years learning and tweaking methods from linguistics to try to find unambiguous evidence of non-trivial compositionality in our closest living relatives. This first involved spending five months following 30 adult bonobos in the Kokolopori Bonobo Reserve in the Democratic Republic of the Congo, recording almost 1000 instances when a bonobo called out. Of these utterances, roughly half were combinations where at least two different call types were paired together in quick succession.
