Parents and their children, or people who know each other well, often share some expressions that are unique to them. Phrases and gestures that started by chance, but gradually acquired a meaning known only to them.
The same is true for Beryl, a chimpanzee who lives in Uganda's Kibale National Park, and her young daughter, Lindsay. When Lindsay wants to climb onto her mother's back and travel, she puts one hand over Beryl's eyes. This is a gesture that no other chimpanzee is known to make. It is their own private signature.
Bas van Boekholt, a primatologist at the University of Zurich in Switzerland, said: “It happens very often to us humans, and now we know it's also happening in the wild, in chimpanzees.”
Dr van Bokholt first noticed the gesture during his second field season in Kibale's chimpanzee community, called Ngogo, in 2022. Scientists have been working with them since the early 1990s. Chimpanzees are now so tame that researchers accompany them for hours at a time, often observing them from several yards away and recording their lives in great detail.
Of particular interest to Dr. Van Boekholt is chimpanzee communication, especially gestures. Chimps has a rich repertoire, and while it may not technically qualify as a language, we use it in language-like ways. More than 80 gestures have been translated, including the palm up arm request for food. Big long scratches inviting grooming. And a two-foot stomp that means “Please stop!”
When Dr. Van Boekholt saw Lindsay putting her hand on Beryl's eyes, “it was obvious she was doing this for the trip,” he said. “That piqued my interest.” Such a gesture had not been previously documented.
Dr. Van Bockholt and his colleagues reviewed recordings made before arriving in Kibale. Recordings showed that Lindsay began making eye-hand signals when she was about 35 years old. At first, the gesture did not serve as a request to leave on the mother's back. It started happening at about 4 and a half years old.
Several other young chimpanzees in their community were also seen making the movements, but none did so with any regularity or with the same intent.
Researchers don't know how Lindsay and Beryl's unusual exchange came about, but they have a theory. Like any dexterous toddler, Lindsay would have been moving her hands while riding on her mother's back, but Beryl has lost her eyes. (Scientists don't know the backstory; when Beryl joined the Ngogo community in 2012, the eye was already missing.) When Lindsay inevitably covers a good one, she doesn't know what to do to elicit a reaction. I was bound by
Perhaps this prompted Beryl to repeat the action. It gradually took over meaning as interactions occurred over and over again. What started as a way to tease mom while riding has become a symbol of riding.
In a study published in the journal Animal Cognition, Dr. Van Borkholt and his colleagues put the story of Chimps into context within the ongoing debate about the nature of chimpanzee gestures and perhaps the roots of human language. did.
Some researchers suggest that the gesture of other great apes – chimpanzees, bonobos, orangutans, gorillas, primate families that include humans – is a fixed part of the species' biological inheritance. If so, gestures are a relatively limited and inflexible mode of communication, bearing no resemblance to language or human gestures. And since all chimpanzees are based on the same inheritance, there are no instances of what protologists call “idiosyncratic” gestures used only by one or two individuals.
Other scientists argue that social learning is paramount. This may involve watching and imitating the gestures of other chimpanzees. It also involves the emergence of a shared understanding of movements that were not originally communicative through the informal back-and-forth negotiations that occur when two individuals interact.
It is certainly a more flexible, language-like system, and unique and idiosyncratic gestures are expected to occur within it. Lindsay and Beryl's eye-shake gesture seems to fit that bill. “We see that not everything is rigid,” said Simone Pica, a co-author of the new study and an ethologist at the University of Osnabrück in Germany. “They're creating new signals.”
“There's only a 1% difference in DNA between us and chimpanzees, right?” Dr. Pica added. “So why are we always making up these huge gaps instead of saying, 'What do we share?' And we share gestures. ”
Kat Horvatier, a primatologist at the University of St. Andrews in Scotland, who was not involved in the study, cautioned that the eye-carrying gesture may not qualify as technically unique. Perhaps it's just unusual. But it was clearly “shaped into a particular look between mother and daughter,” Dr. Hawfighter said.
For Dr. Hawfighter, the nature/nursing dichotomy that characterized the discussion of chimpanzee gestures has evolved into a more nuanced appreciation of the importance of both influences. Dr. Pica agreed.
Of course, Beryl and Lindsay's story is just one data point. As scientists collect more examples, the pair's private cell phone code continues to serve as a poignant reminder of how much chimpanzees resemble their closest living relatives.
“I can't help but notice how human this interaction is,” Dr. Van Borkholt added Lindsay. Mother's back. ”
