The peeps, hoots and grunts of wild bonobos, a species of great ape living in the African rainforest, can convey complex thoughts in a way that mirrors some elements of human language, a new study suggests.
The study says bonobos — humanity’s closest living genetic relative — can combine several types of calls to construct phrases in which one vocalization modifies the meaning of another. This is the first time such behavior has been documented clearly in an animal, the researchers behind the study said.
The research, published Thursday in the journal Science, challenges the prevailing thought that humans are the only species with that ability, which is called nontrivial compositionality and is considered a fundamental building block of human language.
“We would never say that bonobos have language because language is specific to humans. It’s our very special communication system,” said Simon Townsend, a professor at the University of Zurich who studies cognition and is an author of the study. But, “we’re showing that features of language seem to be present in the communication system of bonobos.”
Outside experts said the work was convincing. And because humans and bonobos share a common ancestor, the work could help explain how humans developed their ability to use language in the distant past.
“This is a terrifically novel and creative study,” said Robert Seyfarth, a professor emeritus at the University of Pennsylvania, who studied primates and cognition and was not involved in this study. “The evolutionary origins of language are kind of like the evolutionary origins of bipedalism, walking on hind feet. It doesn’t occur overnight. It occurs gradually and there are intermediate stages along the way. How do you get started and get on this evolutionary trajectory? This begins to help us be more precise in deciding the answers to these questions.”
It’s possible that other animals, like chimpanzees, could also have the ability to form phrases where words modify each other’s meaning.
“It could be that bonobos are exceeding chimpanzees in that capacity. It could be that they’re doing the same. It could be that many other species are doing this,” Townsend said. “Now, we’ve got the method to really test this.”
Eavesdropping
It took months of slogging through the rainforest and chasing after wild bonobos with microphones to pave the way for this discovery.
The study’s lead author, Mélissa Berthet, of the University of Zurich, spent about six months in the Democratic Republic of Congo following three groups of wild bonobos with colleagues at the Kokolopori Bonobo Reserve. Berthet and her colleagues took detailed notes about what was going on as the bonobos were making their vocalizations, recording about 400 hours of audio.
“I would have a list of about 300-something contextual parameters that I would use,” Berthet explained. “Was my caller feeding? Was it resting? Was it grooming?”
Bonobos have complicated, matriarchal social structures with lots of movement and activity, so Berthet took careful notes about group dynamics.
The researchers ultimately mapped more than 700 vocal calls, including combinations, and the circumstances of these vocalizations’ use. Then, they mapped the relationships between all the data points and found at least four instances in which the bonobos were combining different calls to create new meanings.
The researchers don’t have a precise understanding of what each bonobo call is intended to communicate, but they were able to make some assumptions about their purpose based on the context.
The researchers said some calls meant things like “I’m feeding,” “Let’s build a nest” or “Let’s keep traveling.”
The size of the groups often change as bonobos come and go.
“They mostly talk about things to coordinate the group,” Berthet said. “Just like humans, you know, they’re in the family, then they go to work, then they go with friends, then again with family and so on. They really need complex communication to coordinate that. And so it’s not surprising that most of the communication is about coordination, because this is actually a very important part of their social life.”
Origins of language
Bonobos and chimpanzees are the closest genetic relatives to humans. The research suggests that the last common ancestor of these species — which likely roamed the Earth between 7 million and 13 million years ago — could have had the capacity to communicate with the same fundamental building blocks of language bonobos are displaying.
The researchers behind this study said bonobos are almost akin to a time machine into humanity’s past.
And this research raises questions about what happened so long ago that pushed ancient humans to evolve and develop a more complex form of verbal communication.
“If bonobos and chimpanzees, in their natural communication systems, have a lot of these building blocks, it can help us understand what is that tipping point where humans jumped off into a language that is far more complex,” said Sara Skiba, a research scientist and director of communications for the Ape Initiative, a bonobo research facility in Des Moines, Iowa. Skiba was not involved in the new study.
Bonobos are difficult to study in the wild. They live in fragmented habitat in Congo, which has experienced human conflict in recent years.
The species is endangered and its population is likely less than 20,000, said Martin Surbeck, an assistant professor in the department of human evolutionary biology at Harvard University and an author of the study.
“Bonobos really have this unique opportunity to hold kind of a mirror to humankind,” Surbeck said. “I think they offer a unique opportunity, right, for us to really understand ourselves in ways that wouldn’t be possible without them, and I think losing them, I think we lose a lot of, a part of our heritage to a certain degree.”