Dialects In Chimpanzees

Human influence has led to loss of chimpanzee culture and calls for conservation strategies to include preserving cultural distinctiveness

A new study, conducted on wild chimpanzees (Pan troglodytes verus) in Taï National Park, Côte d'Ivoire, provides evidence that the gestures used by male chimpanzees from four neighbouring communities during copulation requests may reflect different dialects. One gesture, used predominantly in one community, disappeared from the repertoire 20 years ago after a poaching incident and did not return. This incident documents a cultural loss associated with human-induced population decline, a phenomenon rarely documented in animals.

Much like people from different regions speak with different accents or use unique expressions, many animals have their own 'dialects'. Songbirds such as sparrows and finches, or even whales, learn their songs from others, resulting in variations that are as unique to a region as local accents in humans. However, in primates, which are phylogenetically closer to humans, evidence for community-specific dialects remains surprisingly scarce, presenting an intriguing area for further scientific investigation.

Researchers from the Taï Chimpanzee Project observed members of the four neighbouring communities of wild chimpanzees every day from the time they left their nests in the morning until they went to sleep at night. "We identified four types of communicative gestures, 'heel kick', 'knuckle knock', 'leaf clip' and 'branch shake', used by male chimpanzees to attract females to mate with them," explains first author Mathieu Malherbe of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and the Institute of Cognitive Sciences at the University Claude Bernard in Lyon, France. "Between 2013 and 2024, we found differences in the frequency of use of these communicative gestures between neighbouring chimpanzee communities, but also between populations across Africa," Malherbe adds.

Long-term data collected over 45 years

Using long-term data from 45 years of research in the Taï Chimpanzee Project, the researchers also revealed variations in gesture use over time. These findings highlight the ability of humans' closest living relatives to produce cultural differences in communicative signals. "The consistent use of the same mating request signal forms within communities, but different signal forms between neighbouring communities that experience regular gene flow through female migration, suggests socially learned dialects in chimpanzees, evidence that has rarely been demonstrated before," says Catherine Crockford of the Institute of Cognitive Sciences and the Max Planck Institute for Evolutionary Anthropology, one of the study's senior authors.

"These days, males in the North group, one of the four communities, have not been observed to use the 'knuckle knock' for 20 years, although all males in the North group used this gesture before 2004," describes Liran Samuni of the Cooperative Evolution Lab at the German Primate Center in Göttingen, another senior author of the study. Following a series of human-induced events leading to demographic loss, the last adult male of the North group was killed by a poacher, resulting in several years without an adult male.

The loss of competition between adult males for females or the loss of all role models could be responsible for the cultural loss of this specific copulation request gesture in this community. "This finding provides evidence that human illegal activities have altered the cultural behaviour of chimpanzees," says Roman Wittig of the Institute of Cognitive Sciences and the Max Planck Institute for Evolutionary Anthropology, another senior author of the study. He adds: "There is an urgent need to integrate the preservation of chimpanzee culture into conservation strategies." Mathieu Malherbe concludes: "This initiative is crucial not only for the survival of the species, but also for understanding our own evolutionary history".