Surprising Chimpanzee Signal Reveals Secrets of Ape Communication
A rare and deliberate signal between a mother chimpanzee and her daughter raises new questions about ape communication, culture and the meaning of sharing a language
A mother chimpanzee, Beryl, sits by her infant, Lindsay, in a remote forest in Uganda.
On one such morning in 2019, a few researchers spotted something curious: Lindsay, a chimpanzee around two years old, reached forward from her mother Beryl’s back to cover the older chimp’s only eye. At first, it seemed like a fleeting moment of play. But the scientists would later learn that Beryl, who moved attentively through the undergrowth with occasional pauses, responded the same way each time—by stepping forward. Within a few years, the gesture had clearly become an intentional “let’s get moving!” signal. Again and again, she would lay her fingers over Beryl’s eye; each time, her mother would move forward.
Chimpanzee Beryl and her infant, Lindsay, perform their “hand-on-eye” gesture.
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What may have started as Lindsay’s simple, spontaneous attempt to get her mother’s attention—by blocking Beryl’s already limited vision—became a ritualized and regularly used signal, a form of shared meaning akin to a secret handshake or inside joke. Among the Ngogo chimpanzees, researchers are coming to realize that such behaviors aren’t random quirks but part of a growing picture of how apes develop and transmit culture.
Lindsay covers Beryl’s eye.
To investigate further, researchers from various field seasons conducted a collaborative quantitative analysis of 179 videos of Lindsay and Beryl that included 21 instances in which Lindsay used the gesture. Young chimps are known to be playful while riding on their mother’s back, so the scientists scrutinized Lindsay’s behavior for markers of intentionality. Was she simply brushing her mother’s eye by accident? The data suggested otherwise.
Van Boekholt’s team also reviewed more than 1,020 video clips of 12 other mother-child pairs within the Ngogo community and found no evidence of the gesture occurring among them—except for three isolated instances in which other chimps performed it just once, without the same intentionality markers present in Lindsay and Beryl’s interactions.
“Infants do play around on their mothers’ backs and sometimes touch their mothers’ eyes, but it’s different; there’s no clear intent or consistent outcome,” van Boekholt says. “Maybe if we analyzed another 1,200 clips, we’d find more cases, but at this point, we feel confident in saying this is an idiosyncratic gesture.”
Chimpanzees Lindsay and her mother, Beryl, in 2019.
Clark, who specializes in social behavior development in juvenile and adolescent chimpanzees, says that chimps exhibit foundational elements of symbolic communication—humans’ ability to create limitless symbols for different meanings—and that gestures like Lindsay’s could be the building blocks of eventual humanlike communication.
“There are multiple theories on how gestures develop in primates, particularly great apes,” van Boekholt says. “Tracking their development over a lifetime offers clues about the evolution of language and communication.”
For instance, the long-recognized and well-documented gesture of leaf clipping—in which a chimpanzee tears a leaf with its teeth—varies in meaning across chimp communities. In some groups, leaf clipping’s distinctive sound serves as a mating call, while in others, it signals frustration or an alpha male’s display of dominance.
Ape communication researchers have long debated whether gestures and signals such as these are innate or learned through social context and experience. Many scientists now recognize that while gestures may have biological roots, their meanings are shaped by social and environmental dynamics.
Beryl and Lindsay on the move.
The development of Lindsay’s gesture, Hobaiter explains, suggests that apes—like humans—have the capacity to form particular shared uses of a signal. “It doesn’t necessarily mean that it was created by them from scratch,” she says. For instance, a baby chimp could see a gesture in another context and adapt it to have a new meaning.
Hobaiter cautions against overemphasizing uniqueness at the expense of a broader insight: the more we observe, the more depth we see in ape cultures. Chimpanzees and bonobos share nearly 99 percent of their DNA with humans. And their traditions, social learning and communication reveal a continuum rather than a sharp divide between us and other great apes.
Lindsay covers Beryl’s eye.
Avery Schuyler Nunn is an avid surfer, free diver and environmental science journalist based in California. She earned her Master of Science degree from Columbia University in 2021 and has used her notebook and camera as tools for exploration, both above and beneath the surface, ever since. She is a freelance contributor to Scientific American, National Geographic, Smithsonian Magazine, Grist, and more. Follow her work on Instagram and X (formerly Twitter) @earthyave and at www.averyschuylernunn.com.
Source: www.scientificamerican.com