Culture is what we learn from others and pass on to successive generations by practising it over and over. Scientists have found cultural traditions among humans as well as animals, the latter in the way they forage, socialise, use tools, care for themselves, and mate.
Among these traditions, the characteristic patterns of behaviour that involve communication are called dialects.
In new research published in the journal Cell, scientists with the Taï Chimpanzee Project in West Africa reported four dialects that male wild chimpanzees (Pan troglodytes verus) use in the Taï National Park to find mates to copulate with.
Unfortunately, after documenting the chimpanzees’ lives for more than a generation, the scientists also reported these apes are ‘forgetting’ parts of the dialect thanks to human influences.
“Cultural behaviours are crucial for survival,” Catherine Crockford, a scientist leading the project and researcher at the Max Planck Institute for Evolutionary Anthropology, Germany, and ISC Marc Jeannerod, France, said.
“Illegal hunting or logging may not only be killing individual chimpanzees but also destroying their cultures, which could threaten the survival of the remaining chimpanzees.” Chimpanzees are also poached for use as pets or for bushmeat.
‘Secretly ask females for sex’
Researchers once believed culture separated humans from other animals. But in the last seven decades, research has revealed cultural practices in many animals. Even so, community-specific dialects in non-human primates such as chimpanzees, orangutans, and bonobos have been rare.
The scientists with the Taï Chimpanzee Project reported four distinct types of dialects that male West Africa chimpanzees used to find mates: heel-kick, knuckle-knock, leaf-clip, and branch-shake.
In a heel-kick, the chimpanzees lifted their feet and kicked against a hard surface to make noise. The knuckle-knock involved repeatedly, but somewhat quietly, knocking their knuckles against hard surfaces.
Likewise, in the leaf-clip, chimpanzees bite a leaf and strip it into pieces without eating it, creating a ripping sound. The branch-shake is self-explanatory.
“It is amusing to watch how young subordinate males try to secretly ask females for sex without the dominant males knowing,” Crockford said. “This is the main function of these more subtle gestures”.
The team documented heel-kicks among the North, South, Northeast, and East chimpanzee communities; knuckle-knocking in the Northeast community; and leaf-clip and branch-shake among the North, South, and Northeast communities.
A dangerous demographic shift
The knuckle-knock gesture is restricted to the Northeast community. It was previously among adult males of the North community as well, but since 1999, it has suffered significant population loss.
The problem became so bad that between 2004 and 2011, the North group didn’t have two adult males existing at the same time. Put another way, any adult male didn’t have to compete with other adult males and thus had no use for the knuckle-knock dialect.
Researchers understand that demography plays a crucial role in shaping culture and keeping it alive across generations. A systematic data collection effort concluded in 2019 that no members of the North group had used knuckle-knocking in 20 years.
Significant changes in a population, in this case the near-complete loss of an entire demographic (adult males), can thus have a long-lasting impact on the preservation or loss of cultural traditions. Restoring them isn’t easy. For example, with the help of ecologists and the Côte d’Ivoire government, the North group has had four adult males since 2016 but the knuckle-knock gesture hasn’t reemerged among them.
“While establishing absence is challenging, our observations demonstrate a shift-away from knuckle-knock gesture usage,” the researchers wrote in their paper.
Learning their own language
To further understand the origins of the chimpanzees’ culture, the team compared mating solicitation gestures involving the use of tools between Taï chimpanzees and Sonso chimpanzees at the Budongo Forest Reserve in Uganda.
Whereas the Taї chimpanzees preferred the knuckle-knock, the Sonso chimpanzees used the object-slap: moving the arm from the shoulder to slap an object with an open palm.
Likewise, the Sonso chimpanzees frequently used leaf-clipping to express their interest in mating but the Taї chimpanzees didn’t.
Chimpanzees have genetically inherited certain gestures across subspecies but individuals have been known to express only a subset. But within a closed group, multiple individuals use the same set of gestures over time and can even differ from the gestures used in a neighbouring group.
The Budongo Forest Reserve is about 4,160 km from the habitat of the Taї chimpanzees of Côte d’Ivoire. “We can rule out that the different signals used in each community have a genetic origin. Given they live in a similar forest environment, we can also rule out environmental influences on culture,” Crockford said.
“This leaves us with the most likely option: that different signals in neighbouring communities arise through social learning.”
Bringing conservation to culture
“Cultures emerge over generations. Cultural behaviours — such as the use of specialised toolkits, nut-cracking with stone hammers or digging out underground bee nests with different-sized sticks — are crucial for survival,” Crockford said.
According to her, the preservation of animal culture is a relatively new concept. The International Union for the Conservation of Nature (IUCN) recently included it among the metrics it uses to prepare its ‘Red List of Endangered Species’. The message seems to be that chimpanzees should be protected as well as their cultures.
But the IUCN’s job isn’t done. In a November 2024 paper in Science, researchers reported that the deaths of a species’ elders are disproportionately more harmful than the deaths of other members. This is because the elders possess important cultural knowledge: where to find the best watering holes in particular weather, the ways to respond to different predators, caring for the young when the parents can’t, and so on.
One of the authors of this study wrote then that the “loss of old individuals is not yet recognised by the IUCN as a means of listing threatened species”.
Madhurima Pattanayak is a freelance science writer and journalist based in Kolkata.
Published – April 07, 2025 05:30 am IST
