It appears that bonobos ‘speak’ much like humans

How ancient is language? A recent investigation by scholars from the University of Zurich and Harvard University indicates that bonobos, our nearest living relatives alongside chimpanzees, utilize equivalents of word compounds and phrases, implying that the origins of language predate humanity.

Communication has always encompassed more than mere words, assert the researchers, Assistant Professor Martin Surbeck of Harvard’s Department of Human Evolutionary Biology, and Professor Simon William Townsend along with postdoctoral researcher Melissa Berthet, both from the University of Zurich. The manner in which we combine words to construct phrases and sentences—and subsequently link these elements into coherent statements—defines language and our capacity to communicate with one another.

This ability — termed “compositionality” — enables us to generate new words and phrases. For instance, a “bad dancer” isn’t inherently “bad” in a strict sense. That qualifier merges with “dancer” to formulate an easily comprehensible neologism. Such constructions can effectively relay complex social scenarios.

“There’s been a long-held evolutionary link between vocal intricacy and social intricacy,” noted Townsend. Humans exemplify this. “It can be argued that humans possess the most intricate social organization, and we also have the most elaborate communication system with the most sophisticated forms of ‘combinatory’ reality.”

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The study outlines the researchers’ analyses of the vocal conduct of wild bonobos, a pivotal species for deciphering human evolution, in the Kokolopori reserve in the Democratic Republic of Congo. Utilizing innovative methodologies adapted from human linguistics, the team demonstrated for the first time that bonobo vocal communication heavily relies on compositionality.

Similar to humans, bonobos share complex social connections. For instance, their social group may occasionally split into smaller factions before reuniting. “The social organization may indeed hinge on this advanced communication,” remarked Berthet, the primary author of the study.

The data gathering process, conducted over eight months, was meticulous. Researchers started with a compilation of approximately 300 contextual characteristics to check off when a bonobo emitted a sound categorized as a peep, yelp, or whistle, and “what they were doing or what was occurring.” These assumptions relied on the notion that a call could issue a command — like, “Run!” — announce an impending action (“I will travel”), convey an internal state (“I am fearful”), or refer to an external occurrence (“There is a predator”). The team chronicled what ensued for two minutes following each vocalization to determine how that vocalization influenced the group.

Not only did different vocalizations correspond with distinct actions or events, but sequences of vocalizations unveiled their own meanings, enabling the team to establish “a kind of dictionary,” said Berthet. This glossary illustrated how many of the call combinations exhibited the compositionality recognized in human languages. “This dictionary signifies a crucial progression in grasping animal communication, marking the first instance in which researchers have systematically defined the meaning of all the calls of an animal,” Berthet noted.

“The advantage of this approach is that we suddenly have a means to quantify these aspects of the vocal repertoire across various species,” stated Surbeck. “It ushers in a novel understanding of animal communication.”

This structured language is not exclusive to humans and bonobos: Similar configurations have been documented in chimpanzees. However, prior research has often concentrated on single-call combinations, while this latest study examined an entire vocal repertoire.

“It appears that at least in chimpanzees and now bonobos, these species characterized by quite complex social systems and long-lasting social connections between individuals indeed begin to exhibit levels of combinatorial complexity that may not be present in species with less complex social frameworks,” noted Townsend. This suggests that species “develop elaborate communication systems to maintain social bonds and relationships over distances.”

Since humans and bonobos have a common ancestor from around 7 to 13 million years ago, Surbeck stated, they inherit numerous traits through descent. “It appears that compositionality is likely one of these shared traits.”