Ape cousins use same gestures to communicate

Primate sign language may be ‘biologically inherited’, scientists believe.
Primate sign language may be ‘biologically inherited’, scientists believe. Primate sign language may be ‘biologically inherited’, scientists believe.

Two closely-related ape species employ the same sign language, scientists have learned.

If a chimpanzee and a bonobo met face to face for the first time they would probably be able to communicate.

The discovery is surprising given that the two ape cousins separated from a common ancestor between one and two million years ago.

It suggests that primate gestures with shared meanings are biologically inherited and may even extend to humans.

Lead researcher Dr Kirsty Graham, from the University of York, said: “The overlap in gesture meanings between bonobos and chimpanzees is quite substantial .. in future we hope to learn more about how gestures develop through the apes’ lifetimes.

“We are also starting to examine whether humans share any of these great ape gestures and understand the gesture meanings, so watch this space.”

While chimpanzee gestures have been well studied less is known about those of bonobos.

Scientists knew that the apes used many of the same gestures, but whether or not they shared similar meanings was much less clear.

Bonobos, an endangered species from central Africa, closely resemble the chimpanzees but are more slightly built.

They are famous for their ability to display positive “human” traits such as compassion, empathy and altruism, the high status they give to females, and the importance of sex in their society.

For the new study, the researchers systematically defined the meanings of 33 bonobo gestures and compared them to those of chimpanzees.

Each gesture meaning was ascertained by observing the reaction it produced and whether the bonobo making the gesture was satisfied with the response.

For instance, an arm extended in front of another bonobo translated as “climb on me”. In this case, the second ape responded by climbing on the first, which then stopped gesturing, indicating satisfaction.

Other gesture meanings included “acquire object/food”, “contact”, “follow me”, “initiate grooming”, “move away” and “stop behaviour”.

The “initiate grooming” signal, a loud scratching of an ape’s own arm, was almost universally recognised by both species, as was the “acquire object” gesture, a mouth stroke.

Standing on two legs, on the other hand, was only an invitation to have sex among bonobos.

Many gestures had more than one meaning, the scientists found.

The team wrote in the journal Public Library of Science Biology: “We find that the similarity between the two species is much greater than would be expected by chance.

“Bonobos and chimpanzees share not only the physical form of the gestures but also many gesture meanings.”