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Bonobos Exhibit Complex Communication Skills, Using Phrased Calls
Scientists have discovered that bonobos, our close primate relatives, utilize sophisticated vocal combinations to form distinct phrases, indicating that the capacity for syntax in communication may be more ancient in evolutionary terms than previously understood. This groundbreaking research sheds light on the complex communication systems of animals and provides new insights into the origins of language.
Understanding Compositionality in Animal Communication
Human language is characterized by several fundamental elements. A key component is syntax, the arrangement of meaningful units into extended sequences, like structuring words into sentences. This ability relies on compositionality, where the meaning of a complete expression is derived from the meanings of its individual parts.
Compositionality itself is not exclusive to humans. For instance, chimpanzees combine vocalizations to signal warnings about predators like snakes. However, previous research suggested that only “trivial compositionality” existed in non-human animals. Trivial compositionality implies each unit contributes independently to the overall meaning. For instance, “tall tree” consists of two independent units describing a tree and its height. Conversely, “non-trivial compositionality“, believed to be unique to humans until now, involves combinations where the meaning transcends the sum of individual parts. An example is “bitter lemon,” where “bitter” modifies “lemon” to indicate a specific flavor, not just a separate quality.
Research at Kokolopori Bonobo Reserve
A challenge in studying animal vocalizations has been the lack of tools to precisely interpret their meaning, explains Dr. Mélissa Berthet, a researcher at the University of Zurich. This ambiguity made it difficult to differentiate between trivial and non-trivial compositionality in animals.
Dr. Berthet and her team dedicated years to adapting linguistic methods to find clear evidence of non-trivial compositionality in bonobos, our closest living evolutionary kin. Their study involved an intensive five-month observation period of 30 adult bonobos at the Kokolopori Bonobo Reserve in the Democratic Republic of the Congo. During this time, they recorded nearly 1000 instances of bonobo vocalizations. Approximately half of these were combinations, where different call types were rapidly sequenced together.
In a crucial step, the researchers meticulously documented events occurring at the time of each vocalization and in the immediate aftermath. They compiled over 300 detailed observations, including the caller’s actions, environmental factors, and the behavioral responses of both the caller and other bonobos present.
Unveiling the Meaning of Bonobo Calls
To decipher the meaning of individual bonobo calls, the scientists employed a linguistic technique to create a “semantic cloud” of utterance types. Vocalizations produced in similar contexts were positioned closer together in this cloud. “We essentially established a dictionary,” Dr. Berthet elaborated. “Linking each specific vocalization with a specific meaning.”
With this semantic framework, they analyzed call combinations to determine if the individual calls retained distinct meanings within the combination. Their analysis indicated that the meaning of combinations was closely related to the meanings of the individual calls, suggesting compositionality. Using this approach, they identified four compositional calls, with three demonstrating clear non-trivial compositionality. This meant their combined meaning could not be directly predicted from the meanings of the separate calls. For example, the combination “high-hoot + low-hoot,” which appears to combine calls meaning “pay attention to me” and “I am excited,” actually conveyed “pay attention to me because I am in distress.” Bonobos frequently used this combination to solicit support when threatened by another individual.
Implications for Understanding Communication Evolution
Dr. Berthet notes that the majority of bonobo vocalizations serve to coordinate group activities. Dr. Martin Surbeck, a team member from Harvard University, suggests this emphasis on coordination stems from the bonobos’ “fission-fusion” social structure, where groups frequently divide into smaller units that operate independently.
Dr. Maël Leroux, from the University of Rennes in France, emphasizes the significance of these findings. “This is the first unambiguous evidence of non-trivial syntax in any animal species, non-trivial compositionality, and it fundamentally changes our understanding.” He adds, “It’s a revolutionary discovery. It’s the cornerstone for the next decade of research in comparative linguistics and evolutionary linguistics.”
While this discovery highlights the complexity of bonobo communication, Dr. Berthet clarifies that it doesn’t imply bonobos possess language in the human sense. “Language is specifically the human system of communication,” she explains. “But we are demonstrating that they have a highly complex communication system that shares parallels with human language.”
Dr. Leroux concludes that the evidence of syntax in both chimpanzees and bonobos strongly suggests that this capacity for compositionality was inherited from our shared ancestor. “They have shown, unequivocally, that this core building block is evolutionary ancient, at least 7 million years old, and potentially even older,” he states.