Bonobos, one of humanity’s closest relatives, appear to string together vocal calls in ways that mirror a key feature of the human language, a new study carried out in the forests of the Democratic Republic of the Congo has found.
While bonobos (Pan paniscus) produce grunts, peeps, whistles and hoots, they also combine these calls to create new meanings, researchers found, suggesting they may share a trait once deemed uniquely human: a complex language structure called nontrivial compositionality.
In human language, this would be akin to how we understand “broken heart” where “broken” means one thing and “heart” another, but when combined produce a third meaning that isn’t the literal joining of the two. By contrast, “sleeping cat” joins an object with an action and doesn’t produce a distinct third meaning.
“Our results indicate that nontrivial compositionality is not limited to humans,” the study’s authors write. “Bonobos, our closest living relative, also engage in [it].”
The researchers recorded 700 vocalizations from wild bonobos in Kokolopori Bonobo Reserve, a community-managed protected area where the apes are accustomed to human presence. For each call, the team tracked its contextual details, including what the bonobos were doing when they produced the sounds and how others responded to them.
Using this language map, the researchers attempted to infer each sound’s meaning.
For example, the bonobos used a “peep” as a suggestion, a kind of “I would like to,” while a “yelp” was more of a demand, like “Let’s do that.” A single whistle seemed to mean “Let’s stick together.”
But the bonobos also seemed to join the distinct sounds to create a third meaning: for instance, they paired an “I would like to” peep with a “let’s stick together” whistle during copulation or specific displays of assertion.
The researchers say these findings may be a clue toward how early human language began to develop. “One interpretation of the data could be that nontrivial compositionality can be traced as far back as the last common ancestor of bonobos and humans, 7 million to 13 million years ago,” the authors write.
It could also mean that many more forms of life communicate in this way but have not been studied before.
Klaus Zuberbuehler, a specialist in the origins of language at the University of St Andrews, U.K., who wasn’t involved in the study but previously supervised two of the authors as Ph.D. students, said the study was “highly valuable” due to the extensive data collected in the field, but added there were limitations to the study.
“[The authors] do not have any direct information on the meaning of the calls they have recorded,” Zuberbuehler said. “In the end, it will be necessary to ask the bonobos themselves whether they agree with the proposed dictionary and the meaning compositions identified by the authors.”
Banner image: Bonobos in the DRC’s Kokolopori Bonobo Reserve. Image courtesy of Maud Mouginot.
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