When chimpanzees encounter humans, it’s usually bad news for the chimps. Logging, hunting, and epidemics have helped push chimpanzee populations to the brink across their range in West and Central Africa. Now, a new study suggests human activity may also rob chimp populations of their cultures.
Chimpanzees perform distinct behaviors, such as using tools to crack nuts or collect termites, that are passed on from one generation to the next, like human culture. These behaviors include adaptations that can be crucial for the animals’ survival—but chimp groups living near people have fewer such behaviors, according to the study. The authors say “chimpanzee cultural heritage sites” may be needed to protect key behaviors. “A lot of conservation effort is focused on species diversity and genetic diversity, but we need to look at cultural diversity as well,” says Hjalmar Kühl, a primatologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who helped lead the study.
Nearly 2 decades ago, primatologist Carel van Schaik, an emeritus professor at the University of Zurich in Switzerland, proposed that human impacts like habitat destruction and poaching could wipe out key behaviors in great apes. (Van Schaik studied cultural behaviors in orangutans.) For example, a population may lose important traditions when a key resource it involved—like kola nuts—becomes scarce, or when fewer experienced group members are alive to pass on the behavior. But it has been hard to collect enough data to test the hypothesis.
A huge effort to catalog behaviors in 144 chimpanzee communities now suggests Van Schaik’s hypothesis is right. Kühl and Ammie Kalan, another primatologist at the Max Planck Institute, worked with more than 70 co-authors to collect data on chimpanzee behaviors from 46 populations that hadn’t previously been studied, part of a larger project to study cultural behaviors in chimpanzees. They combined those data with published observations from 106 additional chimpanzee groups. (Their “gargantuan efforts” produced a sample size that was “unimaginable just a few years ago,” says Van Schaik, who was not involved in the new study.)
All in all, the researchers tallied 31 behaviors that could be called cultural. “In one national park, chimps are known for fishing algae. In another they crack nuts or have certain hunting methods or fish for termites,” Kühl says.
But the closer chimps lived to human influence, the less likely they were to exhibit diverse behaviors, the researchers report online today in Science. For groups living in areas with high human impact, the probability of any given behavior occurring dropped by an average of 88%. Groups far from human influence might exhibit 15 or even 20 behaviors, Kalan says, whereas groups strongly affected by humans had only two or three.
Humans have myriad ways of extinguishing chimp behavior, Van Schaik notes, from decreasing their numbers—which limits the animals’ social contacts and opportunities to share skills—to isolating populations, which restricts encounters with other groups. However, he cautions that there are no long-term data from chimp populations living far from human influence, “so the conclusion remains tentative.”
Kühl, who also works at the German Centre for Integrative Biodiversity Research in Leipzig, notes that some chimp traditions wax and wane depending on natural cycles like tree nut production. Those behaviors can be especially vulnerable, he says. In years where nuts are scarce, young chimpanzees don’t learn how to crack and eat them. If a group then loses key older members, the behavior is lost for the entire group.
The study adds support, Kalan says, to recent calls that cultural traits and groups should be recognized and included in plans to help conserve endangered animal populations—whether great apes, whales and dolphins, elephants, or migratory birds. “We need to pay attention to the social and cultural knowledge that these species use to survive” when trying to protect them, she says. For many species, culture is not “some kind of nice luxury, but an intrinsic and essential part of their local adaptation,” Van Schaik adds. “In cultural species, the extinction vortex may be swirling faster.”