Chimpanzee Culture Is Disappearing Because Of Us – Defector

9:27 AM EST on February 7, 2025For millennia, the western chimpanzees of Taï National Park in Ivory Coast have communicated with each other in a dialect of their own. They do not speak in words, but rather through gestures. In one gesture called leaf clip, a chimpanzee will take a leaf off a branch and rip it apart in their mouth, creating a ripping sound that might invite play. In another gesture called knuckle knock, males knock repeatedly on the trunk of a small tree; knuckle knock is an invitation meant to attract female chimpanzees, who may respond to the knocking gesture with a sexual display.Scientists have observed the four populations of chimps in the Taï forest—the North, Northeast, East, and South groups—since the 1970s, learning about each of their particular customs. Knuckle knock was a staple in the North group for generations; before 2004, every male in the group used knuckle knock to woo females. But in the ensuing eight years, the population never had more than one adult male. This eliminated the need for a male to distinguish himself among competitors, and also prevented any younger male chimps from seeing the gesture in use and learning it for the future. In 2008, the last adult male chimp in the North group, and perhaps the last of his population to use knuckle knock, was killed by a poacher.A new paper in the journal Current Biology finds that the North group has not used the gesture for the last 20 years—roughly a generation for the chimpanzees. Knuckle knock, which is not just a communication tool but a facet of the population’s unique culture, appears to be lost.The researchers tracked four “dialects” in the Taï’s four neighboring chimpanzee groups: leaf clip; knuckle knock; heel kick, in which a chimp taps their heel on a hard surface; and branch shake, in which a chimp shakes a branch at another individual. All of these gestures represent a way male chimps solicit attention from females in their quest to mate, and all fluctuate over time depending on the particular composition of a group of chimps. One 2018 paper described how an alpha male takeover in a group of wild chimpanzees brought back the leaf clipping gesture, which had vanished for nearly two years in that group.Trends wax and wane in any culture: chimp, human, or otherwise. These fluctuations are natural—the product of chimps existing in a society. Chimpanzees living in Taï in Ivory Coast are more likely to use knuckle knock to attract a female, whereas chimpanzees living in the Budongo Forest Reserve in Uganda with the same goal would slap an object. And while the Budongo chimps use leaf clip to solicit mates, Taï chimps reserve leaf clip for play or drumming. The chimpanzees live in similarly forested areas with similar leaves, similar trees, and other objects needed for such gestures, so these preferences are probably unrelated to the animals’ ecology, the authors explain.For generations, scientists have been trying to understand how great apes developed their gestures, and what insight they may hold into the evolution of human language. (This story by Carl Zimmer is a great primer on a new theory of ape gestures, which argues that apes’ flexibility in using gestures in their social lives leads to a broader flexibility in learning.) Scientists suspect that chimpanzees genetically inherit an array of gestures. But how they use them is dependent on the chimps around them. Chimps develop these dialects collectively, in their own communities. In other words, this is their culture.In the Taï forest, the outright loss of a gesture like knuckle knock is not the result of a natural fluctuation, but the result of human interference. “Since 1999, the North community lost many members including all adult males due to human pressure,” the researchers write. People are responsible for poaching many members of the North group and, by extension, preventing the chimpanzees from passing on their culture to new generations. In recent years, the North group has since gained four adult males. But these males appear to have no knowledge of knuckle-knock. Why would they? They have probably never seen it.It strikes me that the loss of chimpanzee gestures has some parallels to the death of human languages. With fewer people around to learn a language and fewer people around to speak it, populations start to lose proficiency. As a result, some of the singular facets of the language—intricacies of its grammar or the particular sounds of its phonemes—begin to disappear, blunting a brilliant-cut gemstone into something like a marble, if the marble even remains. It does not seem too much of an reach to suggest that when a community of chimpanzees loses a gesture like knuckle knock, they lose a channel of connection with each other. They lose a way of making meaning of the world.It is clear that people are depleting the chimpanzees’ resources and hindering their ability to learn from and teach each other, not just about gestures but also about tools, food resources, and ways of staying warm or cool. A 2019 paper in Science found that the behavioral diversity of chimpanzees living in areas with “high human impact” was reduced by 88 percent, compared to chimpanzees living in more remote areas. The authors argued that strategies for chimpanzee conservation should also encompass the preservation of their culture and, by extension, their capacity for cultural evolution. They suggested “chimpanzee cultural heritage sites,” which would explicitly protect populations with exceptional sets of behaviors. This concept could also be applied to other animal species with variable cultures, such as orangutans, whales, and sea otters.For now, knuckle knock survives in only one other population in Taï National Park. The researchers observed nine out of the 13 males in the Northeast group using the gesture (in this particular population, heel kicking is not so much in vogue.) Of course, these nine chimps do not know they are the last keepers of knuckle knock, nor do they know about the importance of its preservation. They only know it is a gesture that, for now, they share.If you liked this blog, please share it! 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