Human language stands out for its ability to combine words into countless meanings—a feature that gives it its expressive power and separates it from the communication systems of other animals. Now, scientists have discovered a simpler version of this ability in bonobos, one of our closest living relatives. According to a study published this week in Science, bonobos can string together different vocal calls to express meanings that go beyond the sum of their parts.
“This is a pivotal study that could reshape the field,” says Maël Leroux, an evolutionary biologist at the University of Rennes who was not involved in the research. “It offers strong evidence for communication abilities once thought to be unique to humans.”
While earlier research has shown that some animals can combine sounds, these combinations are typically simple—each part just adds to the meaning. Human language, by contrast, often creates new meanings from combinations. For example, the phrase “tall cook” is straightforward: a cook who is tall. But “good cook” is more complex—it doesn’t mean a cook who is generally good at everything, but rather someone skilled specifically in cooking. This ability to produce nontrivial combinations is a core feature of human communication.
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To find out if bonobos can do something similar, Mélissa Berthet, a researcher at the University of Zürich (UZH), spent eight months studying wild bonobo groups in the Kokolopori Bonobo Reserve in the Democratic Republic of the Congo. Beginning her days before sunrise, Berthet followed bonobos through their forest habitat, recording their vocalizations and meticulously noting the context of each call—from who made it and what they were doing, to how others responded and what the weather was like. Each call could be linked to over 300 contextual details.
Over time, Berthet began to recognize patterns. “You see a vocalization and then everybody moves… and it’s very satisfying to be like, ‘Ah, I think I’m starting to get it,’” she says.
She recorded around 700 unique vocalizations, including many combinations of two distinct calls—like “whistle and peep” or “high hoot and low hoot.” To test whether these pairings carried unique meanings, the team applied a statistical method commonly used in human language research, analyzing how often different calls appeared in similar contexts.
Three call combinations stood out as likely nontrivial, meaning they conveyed more than just the combined meanings of each individual call. One example was the pairing of “high hoot” and “low hoot.” While “low hoot” typically signals excitement—something like “I’m excited”—and “high hoot” functions more as a call for attention, their combination wasn’t just “I’m excited, pay attention to me.” Instead, it was used when another bonobo was putting on an aggressive display, suggesting a more subtle message—perhaps an attempt to stop the display or alert others to the situation.
This finding points to what study coauthor Simon Townsend, also at UZH, describes as a “precursor” to the complex compositionality found in human language. It’s possible, he says, that both bonobos and humans inherited this capacity from a common ancestor that lived roughly 7 million years ago.
Beyond the results themselves, the study’s methodology drew praise from experts. Leroux and others highlighted the team’s novel approach to interpreting vocal meanings by systematically analyzing their specific contexts. “It’s revolutionary,” says Gal Badihi, an animal communication researcher at the University of St. Andrews. “This method has incredible potential for future studies on communication in other species.”
Cedric Boeckx, an evolutionary linguist at the Catalan Institution for Research and Advanced Studies, agrees. He notes that much research on great ape communication has focused on gestures, but this study reveals the richness of bonobos’ vocal calls. He adds that similar studies could be extended to chimpanzees, gibbons, and marmosets, potentially revealing new layers of complexity in their communication as well.
The findings suggest that while human language may be unique in its complexity, its roots could lie deeper in the primate lineage than previously thought.
Nebitno
