Just like humans, chimpanzees have local traditions. Neighboring chimp communities in Uganda, for instance, rely on different tools to extract honey from fallen logs; some use sticks, while others use chewed-up leaves to sop up the sweet stuff. Scientists have observed a slew of other behaviors that they believe to be “cultural,” meaning that these behaviors are population-specific and acquired through social learning: nut cracking, using tools to fish for algae or termites, loudly ripping leaves from branches, throwing stones at predators or intruders. But as Michael Marshall reports for New Scientist, a recent study has found that in the face of human encroachment, chimp culture is disappearing.
For their sobering investigation, researchers tracked 31 chimpanzee behaviors in 144 distinct communities, according to their study published in Science. The bulk of the data was pulled from existing literature, but 46 communities were observed by the Pan African Programme, which studies behavioral diversity in chimpanzee populations. To avoid disturbing the animals, researchers followed them from afar—via cameras, by searching for tools during “reconnaissance” surveys and by searching the chimps’ poop for traces of foods that can only be obtained through tool use. The team also measured human influences, like infrastructure, population density and forest cover reduction.
The results of the study were striking. The researcher found that chimps living in areas with a “high degree of human impact” were 88 percent less likely to display any of the 31 behaviors than chimps residing in regions with the lowest degree of human impact. “However we divided up the data, we got the same very obvious pattern,” Ammie Kalan, study co-author and primatologist at the Max Planck Institute for Evolutionary Anthropology, tells Ed Yong of the the Atlantic.
This in turn suggests that human-inflicted disruptions that affect chimps and their habitats—factors like poaching, logging, mining and road building—are also interfering with chimps’ social learning. In their study, the researchers outline a number of reasons why this might be the case. For one, humans are causing great ape populations to decline at a rate of two to six percent each year, and in some communities, there may not be enough individuals left to pass on cultural traditions. It is also possible that chimps deliberately suppress certain behaviors to avoid detection as humans get closer.
Climate change could also be playing a role; since weather fluctuations are impacting the availability of nuts, for instance, researchers may be less likely to observe chimps in engaging in nut cracking. But “[m]ost likely,” the researchers write, “a combination of these mechanisms interacts with environmental stability, demography and population connectedness, to create the overall loss of chimpanzee behavioral diversity associated with human impact.”
On an immediate level, it matters that chimps are losing their culture because certain cultural behaviors—like nut cracking and termite fishing—help the animals get food.
Then there are the more mysterious traditions, which are poorly understood but seem to be important to chimp socialization. In 2016, for instance, Kalan and her colleagues revealed that some chimps in West Africa repeatedly throw rocks at the same trees. It’s not clear why they do this, but researchers posit that they might be marking territorial boundaries in a “symbolic ritual.”
“We’re still investigating it,” Kalan tells Yong. “And we might be running out of time.”
To protect chimps and better understand their complex societies, a “more integrative approach to conservation is needed,” the study authors write. The researchers recommend designating “chimpanzee cultural heritage sites,” or protected areas that are connected to specific behaviors. And this approach could benefit other animals, like whales and orangutans, which have their own sets of cultural practices. In other words, Kalan tells Inverse’s Sarah Sloat, conservationists need to think not only about preserving species’ numbers and genetic diversity, but also their unique cultures—before it’s too late.