Bonobos uses a kind of syntax that was once thought to be unique to humans

Bonobos combines their calls in a complex way that forms different phrases, a sign that this type of syntax is more evolutionary old than previously thought.

Human language, often described as characteristic of our species, consists of many different buildings. A core block is syntax where meaningful devices are combined in length -sequences, such as words to sentence. This is made of possible through compositionality, where the meaning of the white derives from the meaning of the parts.

Compositionality in itself is not unique to humans. For example, chimpanzees combine calls to warn others about snakes. But so far, it is only “trivial composition” has been identified in non-human animals, whereby each unit adds the white meaning independently. For example, the term “blonde dances” has two independent units: a blonde person who is also a dancer. People were assumed to be unique in also having “non-trivial compositionality” where the words in a combination mean something other than what they mean individually. For example, the term “bad dancer” does not mean a bad person who also dances.

The problem was that biologists did not have tools to award a clear meaning to animal vocalizations, says Mélissa Berthet at the University of Zurich in Switzerland, so they could not be sure if a combination was trivial or non-trivial.

Berthet and her colleagues spent years learning and fine-tuning methods of linguistics to try to find unambiguous evidence of non-trivial composition in our closest living relatives. This first involved spending five months after 30 adult Bonobos in Kokolopori Bonobo Reserve in the Democratic Republic of Congo and recorded nearly 1,000 cases where a bonobo shouted. Of these utterances, about half were combinations where at least two different call types were paired in quick inheritance.

In a new step, the researchers noticed everything that happened at the time of the call and in the minutes after. The registered over 300 of these observations, including what the caller did at that time, what happened in the environment and call of the caller and the audience after the vocelization.

To reveal the importance of each call, they used a technique from linguistic science to create a cloud of types of utility and place vocalization that took place under similar circumstances closer together. “We established kind of this dictionary,” says Berthlet. “We have a vocalization and a meaning.”

Once they had this semantic cloud, they could see the individual calls in a combination had different meanings, and found that combinations were close to the devices made by Wow suggesting composition. Using this approach, the four composition calls identified, three of which were obviously non-trivial, with their meaning not directly overlapping with their pose. E.g. Combining “High-Hoot + Low-Hoot” The Calls that Seems to Mean “Be Aerting to Me” and “I’m excited” to say “Pay attention to me because I’m in need”, as Bonobos often used to demand support when another frightened them.

Almost all of Bonobos’ chatting was about coordinating the group, says Berthlet. Team Member Martin Surbeck at Harvard University believes this is because Bonobos has a fission-fusion group dynamic, where smaller breakout groups can do their own things.

“It is the first time in any animal species that there is clear evidence of non-trivial syntax, non-trivial compositionality, and then the game changes,” says Maël Leroux at the University of Rennes in France. “It’s revolutionary. It’s the cornerstone of the next decade with comparative linguistics, basic and evolutionary linguistics.”

This finding does not mean that Bonobos has language because language is the human communication system, says Berthet. “But we show that they have a very complex communication system that shares parallels with human language.”

Now we have evidence that both chimpanzees and Bonobos have syntax, it is inevitable that this capacity for compositionality was inherited from our last common tribal father, says Leroux. “They just showed unequivocally that this core building is evolutionary old and at least 7 million years old and maybe even older.”