Chimpanzee Culture

Chimps in the Wild Show Stirrings of Culture

Gretchen Vogel

T NATIONAL FOREST, CÔTE D'IVOIRE, WEST AFRICA--At the foot of a buttress tree, in the dappled sunlight of the rainforest floor, a young chimpanzee named Lefkas is working hard for his lunch. He holds a rock with both hands and a foot and slams it down with a sharp crack on a round coula nut, a bit smaller than a golf ball, which is balanced on a flat rock on the ground. After a few tries the nut cracks. The chimp pops the meat in his mouth and scampers off.

 The ground where Lefkas was sitting is strewn with coula nut shells, the leavings of other chimpanzees' meals. Indeed, from December through February, coula nut cracking is one of these chimps' main pastimes; primatologist Christophe Boesch, who has studied Lefkas's group at Taï for 20 years, says he watched another young chimp crack nuts nonstop for 5 hours.

 But chimps from just a few hundred kilometers away would probably stroll right past Lefkas's dining site. In a survey of chimps throughout Côte d'Ivoire, Boesch found no evidence for nutcracking anywhere east of a river called the Sassandra-N'Zo, even though both nuts and rocks are readily available throughout the forest. To Boesch, who is director of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, such differences in customs are akin to the use of chopsticks in Japan and forks in France: signs of distinct cultures, in which groups develop their own sets of behaviors based on social ties and shared history.

 Most people think of culture as encompassing such uniquely human skills as language, music, art, and clothing styles. But some biologists have a simpler definition: any behaviors common to a population that are learned from fellow group members rather than inherited through genes. By this generous definition, bird song dialects and the calls of whales might qualify as animal "culture" (Science, 27 November 1998, p. 1616).

 Most anthropologists stick to a narrower definition, requiring culture to include language and whole systems of behavior. But in the past decade, a growing number of primatologists and psychologists have sought to approach the question more rigorously, defining specific elements of culture that could potentially be observed in animals, then seeking these behaviors in the wild and in labs. They are turning up increasing evidence that nonhuman primates, in particular chimpanzees, may have a primitive type of culture that bridges the gap between the two definitions. Their argument rests on two main kinds of evidence: examples in which one chimp learns from another, and the results of such learning--the seemingly arbitrary differences in habits between chimpanzee groups at different sites. Although most examples of "culture" among animals involve just one or two behaviors, chimpanzees have dozens of learned behaviors involving tool use, social customs, and calls, says Andrew Whiten of the University of St. Andrews in Fife, Scotland.

 Of course, no primate society can build a mud hut or do any number of other tasks that are relatively easy for humans to master. Some researchers argue that that is because our primate cousins do not learn as we do, by imitation and instruction. And most agree that primates don't seem to be able to build on previous inventions, an ability that "is the hallmark of human culture" and that allows us to develop complex technologies and rituals, notes psychologist Bennett Galef of McMaster University in Hamilton, Ontario. Even so, Boesch and others argue that the nascent cultural stirrings of our primate cousins may help uncover the roots of human culture, showing that, for example, gregariousness--hunting and foraging together rather than alone --may have spurred cultural development. To see the beginnings of culture in other species, says Boesch, "helps us to see what is unique about humans."

Figure 1
How does mom do it? A mother chimpanzee in the Taï forest smashes open a coula nut; eventually her son Lefkas will catch on.


Multicultural chimps
Some of the best evidence for primate culture has come from field studies comparing the repertoire of chimpanzee skills and behaviors in groups around Africa. For example, in 1974 William McGrew of Miami University in Oxford, Ohio, detailed how chimps at Jane Goodall's Gombe site in Tanzania used sticks to fish driver ants out of their nests. A decade later at Taï, Boesch and his colleagues noticed a slightly different technique. At Gombe, chimps use 60-centimeter-long sticks to probe an ant nest. They wait for the insects to swarm halfway up the stick, then withdraw the tool and sweep ants off with their free hand, gathering a crunchy mouthful of hundreds of ants. At Taï, chimps use sticks about half as long, wait only a few seconds, then use their lips to sweep about a dozen ants directly into their mouth. The Taï method, analogous to eating soup with a tiny sugar spoon, collects only one-fourth as many ants per minute, but in 2 decades of observation, no animals at Taï have ever eaten ants Gombe-style, presumably because no chimp there ever discovered it. "A Gombe chimp would laugh at [the Taï chimps]" for their "primitive" method of ant fishing, says McGrew.

 Social interactions vary among groups, too. For example, McGrew, primatologist Linda Marchant, and their colleagues have recently documented a new behavior they call "social scratch," in which one chimp rakes its hand up and down another's back after grooming. The behavior is common at Mahale in Tanzania but never seen elsewhere. Like some human fads and fashions, the behavior isn't utilitarian, but a part of social etiquette that apparently caught on simply because it feels good. "It's unlikely to be related to functional significance of grooming," McGrew says, but rather helps to reinforce the social hierarchy. In preliminary studies, higher ranking chimpanzees received more social scratches per grooming session.

 Such examples add up to an impressive list. In last week's issue of Nature, researchers from the seven longest established chimpanzee field studies combined observations and listed 39 behaviors, from tool design to grooming to mating displays, that are distinct to particular groups and not readily explained by ecological differences. "We now have, in a sense, an ethnographic record" of chimp populations, McGrew says. "We have enough data in enough populations that we can start doing the sorts of comparisons that cultural anthropologists do across human populations."

 Such geographical differences suggest that a chimpanzee's specific behavior and skills are shaped by where it is raised. That idea "is the most exciting finding" in chimpanzee field research this decade, says primatologist Tetsuro Matsuzawa of the Primate Research Institute at Kyoto University in Japan. Yet simply noting these geographical differences begs the question of how they develop and how they are maintained.


Figure 2

Twist, then pull. An "artificial fruit" that opens several different ways allows researchers to test whether chimpanzees imitate specific actions.


Do apes ape?

A chimpanzee pant-hoot sounds like nothing else in the forest: who-ho-who-ho-who AH AH AH AH.
Another voice usually responds, and soon the din drowns out even the copulation cries of monkeys and the screech of the hyrax. "Chimps are the loudest animals in the forest, except for humans," Boesch notes, when the din dies down. Researchers are now analyzing these hair-raising hoots for another proof of culture, one that helps explain the origin of geographical customs: that chimps learn from one another.

 In 1992, primatologist John Mitani of the University of Michigan, Ann Arbor, reported that different chimpanzee groups had distinct pant-hoot patterns and pitch, suggesting the possibility of learned chimpanzee "dialects." But earlier this year he noted that those differences correlate with factors such as average body size and so might be genetic rather than "cultural" in origin. To find out, anthropologist Richard Wrangham of Harvard University and his colleagues studied calls in two captive groups where chimps from a mix of wild populations live together. In spite of the mixture of genetic backgrounds, each colony had a characteristic style of pant-hoot. "This is some of the best evidence for learning" of vocalizations, says Wrangham. "It's very difficult to think of an alternative hypothesis here."

 Evidence that chimp behaviors can spread from one group to another would also strengthen the case that they are learned. Successful human practices tend to spread when people travel, and Matsuzawa has shown that in at least one case, a chimp skill spread the same way. He studies a community near the village of Bossou, Guinea, where the chimps are skilled tool users and frequently use rock hammers and anvils to crack the hard shells of oil palm nuts to get at the fatty meat inside; coula nuts do not grow here, although they are found on nearby Mount Nimba.

 In a 1996 experiment, Matsuzawa and his colleagues left rocks, oil palm nuts, and the unfamiliar coula nuts in a clearing, then hid behind a grass screen and videotaped the chimps. Several chimps picked up the unfamiliar nuts, but only an adult female named Yo cracked and ate them. Although other adults ignored Yo's nutcracking, a few young chimps watched her intently and later picked up and cracked nuts themselves. Matsuzawa suspects that Yo, who joined the group as an adolescent and may have been raised in the coula-rich Mount Nimba area, remembered the skill from her childhood. The fact that she passed it on to other young chimps shows, he says, that chimpanzee behaviors can spread from one group to another throughout a region, just as human cultural behaviors do.

 But the field is divided over whether monkeys and apes learn from one another the same way humans do, and researchers interpret the same experimental results in very different ways. For example, in the very first evidence of possible primate culture, reported in 1958, primatologists Shunzo Kawamura and Masao Kawai of Kyoto University observed as a young female macaque living on the small island of Koshima discovered how to wash sandy sweet potatoes (provided by the researchers) in a nearby stream. Eventually most of her group was doing it too. Kawamura suggested that this was a "precultural" behavior, and the observations were touted in textbooks for decades as evidence for culture among animals.

Figure 3
Cultural divide. The six longest running chimp field studies in Africa have revealed distinct behavior patterns in each group.

But in the early 1990s McMaster's Galef and other animal behaviorists pointed out that the skill took several years to spread through the group and suggested that troop members, once they paid attention to the potatoes, discovered on their own how to wash them--essentially reinventing the wheel. In contrast, humans learning a new skill tend to carefully mimic the exact movements they see in an expert and are often deliberately taught by another person. Although reinvention might work for learning to crack nuts or fish for ants, says psychologist Celia Heyes of University College London, it wouldn't work for passing on more sophisticated cultural behaviors such as chipping arrowheads or weaving baskets.

 Such critiques sparked a flurry of new work in both the field and lab to discern whether great apes do in fact imitate. St. Andrews's Whiten and his colleagues developed "artificial fruits," which required several steps to open, and found in 1996 that chimpanzees tended to complete the steps in the same order as the demonstrator. Primatologists such as McGrew say that the experiments have "nailed down" the point: "In the right sorts of circumstances, chimps imitate." The observations of the different ant-dipping methods offer an example in the wild, adds Whiten. "It's difficult to see how such consistent behaviors could come about with anything but imitation," he says.

Figure 3
Let's do lunch. Social orangutans use tools more frequently than their solitary cousins.


But the animal behaviorists aren't so sure. Following the order of simple actions is not the same as humans' imitation of fine motor movements such as dance steps, says Heyes. And Matsuzawa cautions that chimp imitation is rare in the wild. "Imitation is much more difficult than we expected," he says. "Yes, there is imitation, but it is very, very difficult for the chimpanzee." He and others also note that active, deliberate teaching, which some claim is a prerequisite for culture, is also rare among chimpanzees. Boesch has described two instances of mothers helping their offspring with the fine details of nutcracking, but as Galef points out, only two clear examples in 20 years of observation suggests that teaching is very rare. "The primatologists are pushing very hard for a rich interpretation of the data that are available," he says. "Given that imitation is rare in nonhuman primates and teaching is essentially nonexistent, it's hard to see how you're going to get the cumulative culture which is the hallmark of our culture."

The benefits of tolerance
Whether you call primate behaviors "culture" or not, researchers say that primate traditions may offer insight into the origins of human culture. Take orangutans, which love to eat the high-fat seeds of the neesia fruit. "It's like chocolate; they eat it for hours," says Duke University biological anthropologist Carel van Schaik. Most orangs won't touch the fruit after it ripens, however, because the seeds are then surrounded by stinging hairs. But one population, in Sumatra, uses sticks to scrape out the hairs and get at the seeds. "The whole population knows the trick," van Schaik says. "It's very similar to what we see in some chimp populations." And it's the only case in which orangs--skilled tool users in captivity --have been spotted using tools in the wild.

 Orangs that avoid ripe neesia have the same sticks available for tools, so lack of materials can't explain why their behavior differs, van Schaik says. The key difference, he and his colleagues found, is that whereas most orangs are solitary, the Sumatran tool-using animals travel and feed close together, perhaps because there is plenty of food to go around. In most environments, food is thinly distributed and the animals "can't afford" to forage together, says van Schaik. The extra interaction in Sumatra allows an invention by one animal to spread when its compatriots observe it, he adds.

 The pattern also holds for chimpanzees, as van Schaik and his colleagues report in this month's issue of the Journal of Human Evolution. In a survey of the behaviors reported at the five longest running chimp field studies, the researchers found that those with higher "social tolerance" (measured by the amount of meat sharing, female-female grooming, and similar indicators) have more varied tool use. The theory could help to explain why captive primates are better at using tools than wild ones, as animals in captivity have more chances to observe one another and have plenty of food, van Schaik says.

 The correlation might help explain the rise of human tool use as well. The earliest tool-using hominids "didn't have a much bigger brain yet, so we shouldn't look for major cognitive advances," van Schaik says. "I hypothesize that there was a social change that made them tolerate each other," which led to increased opportunities to learn and build on each other's inventions.

 The fossil record might support such a theory, says anthropologist John Fleagle of the State University of New York, Stony Brook. Ancient humans have small canine teeth and lots of tools compared to other apes, he notes, and "when you look at the fossil record, you see reduction of canines early and tools later." He thinks smaller teeth might be a sign of increased tolerance, as canines are often used in fighting among group members. "And once you have tolerance, you have bigger tool kits."

 But the researchers attempting to learn the roots of culture by studying wild primates worry that they are running out of time. Habitat loss and increased hunting are pushing many great ape populations to the brink of extinction. Illegal loggers are threatening the Sumatran orangutans that van Schaik studies. And on a recent market day at the village of Taï, just outside the park where Boesch works, three chimpanzee heads were stashed in the game warden's office, confiscated from poachers. If Boesch and his colleagues are correct, says Whiten, such sights mean "we're not just losing chimpanzees; we're losing lots of different chimpanzee cultures." That, he says, would be a major loss for humans. "If we want to understand how humans came to have the minds we have and the cultures we have, then we're only going to learn about that by looking for similar characteristics in our close relatives"--close relatives who are fast disappearing.
Volume 284, Number 5423 Issue of 25 Jun 1999, pp. 2070 - 2073 
©1999 by The American Association for the Advancement of Science.

Chimpanzee Medicine
Source:  Sears, C. "The Chimpanzee's Medicine Chest" New Scientist. Aug 4, 1990 pp 42-44.

Medicinal Plant Use by Chimpanzees in the Wild Because chimpanzees are so like us they are often used in laboratory experiments to find cures for many human diseases. Chimpanzees are now also teaching us about how they cure some of their own diseases in the wild. Extensive field and laboratory studies in progress at Mahale Mountains National Park show us how chimpanzees infected with nematodes [a parasite] use plants which help keep their infections under control. It now appears that some of these plants have a chemical effect (e.g. Vernonia amygdalina) while others have a physical purging effect (e.g. Aspilia mossambicensis). The strongyle nematode species Oesophagosotmum stephanostomum is largely responsible for the observed cases of illness recorded at Mahale during the rainy season, when these medicinal plants are most frequently used by chimpanzees.

Bitter-pith chewing : Vernonia amygdalina Chimpanzees carefully remove the leaves and outer bark from young shoots and chew on the exposed pith, sucking out the extremely bitter juice. In a few well-documented cases, chimpanzees have been shown to recover their appetites, regain strength, lower parasite loads, and recover from constipation or diarrhoea within 24 hours after using this plant. Interestingly, this species is also used widely across Africa as medicine by many traditional human societies. Chemical investigations of compounds which are effective against illness caused by bacterial infection, bilharzia, cancer, and malaria.

Whole leaf-swallowing : Aspilia mossambicensis Chimpanzees use their lips to carefully remove one leaf from the plant at a time and pull it into the mouth with the tongue. This causes these rough,hairy leaves to fold up accordion-style. Each folded leaf is then swallowed whole without being chewed. Leaves are evacuated whole and undigested in their feces. It has recently been demonstrated that leaves swallowed in this manner physically remove adult worms that were previously attached to the wall of the large intestine. As many as 21 worms have been found trapped within the folds and attached to the surface of these leaves. Leaves are now known to be swallowed whole by chimpanzees, bonobos, and lowland gorillas across Africa. The hairy, rough texture of the leaf is a characteristic common to 19 species now known to be used in this way.

Chimpanzee Archaeology
Original URL:

Scientists Use Archaeological Methods To Investigate Chimp Camp

Wild Chimpanzee Foundation

Munich - May 23, 2002
West African chimpanzees use stones and branches as hammers to crack open different types of nuts. Some of these hammers are very heavy, and chimpanzees have been observed using them for up to 2 hours per day during the 4 months that the nut season lasts. How old is this behavior? Have nut-cracking techniques changed over time?
To answer these questions Christophe Boesch of the Max Planck Institute For Evolutionary Anthropology in Leipzig, Germany, Julio Mercader, a specialist in rainforest archaeology at the George Washington University, and Melissa Panger, who studies primate tool use, also at George Washington University, launched the first archaeological excavation of a chimpanzee nut-cracking site in September 2001. The results of these investigations are presented in the 24th May issue of Science.

Since 1979, Christophe and Hedwige Boesch have been following the chimpanzees of the Tai National Park, in the rainforest of the Ivory Coast and have shown that juveniles take several years to become proficient at nut-cracking. Mothers share nuts with their offspring while they are learning the behavior.

The nuts they crack are actually available throughout tropical Africa, yet nut-cracking behavior has been documented only among chimpanzees from Western Ivory Coast Liberia and Southern Guinea-Conakry. Therefore, nut-cracking is a cultural behavior , which, like human culture, can help distinguish one population from another.

The African rainforest has been a place traditionally avoided by archaeologists because of, among other reasons, the cumbersome logistics of transportation, survey, and isolation.

Today, we know that many of our typical assumptions about tropical forest archaeology and the role of rainforests in human evolution and cultural complexity will have to be changed as scientists continue to unveil archaeological evidence from these regions.

The excavation of a chimpanzee stone tool site in the Ivory Coast is a good example that discoveries relevant to human ancestry may indeed come from unexpected places.

For the chimpanzee archaeology project, the first decision was where to dig. Based on the detailed records of chimpanzee nut-cracking sites, a site was selected where chimpanzees had been seen over the course of many years using stone hammers to crack the very hard nuts of Panda oleosa.

Early on in the project it was apparent that having an archaeologist working with primatologists would be beneficial. Christophe Boesch had previously noticed large pieces of stone breaking off hammers.

After looking at a chimpanzee hammer, Julio Mercader was quick to point out to Christophe Boesch and Melissa Panger the existence of flake scars. The scars were produced by the removal of stone pieces detached during the cracking of nuts and are as small as a few centimeters.

Using archaeological methods on a non-human species, for the first time the excavations revealed new facets of chimpanzee tool behavior. Especially interesting was the excavation of Panda 100, a large tree where Hedwige and Christophe Boesch have observed for many years chimpanzees cracking nuts with different stones they transported over hundreds of meters from other Panda trees.

Due to the low visibility across the rainforest floor chimpanzees have to mentally calculate all of these movements keeping transport costs to a minimum. The archaeological data show that chimpanzees collect rocks from various sources across the landscape and bring them to nut-cracking sites.

This project has confirmed for the first time that archaeology can be successfully applied to the study of past chimpanzee behavior. The distribution of remains is not random, presenting very clear concentrations of nut shells and stone remains at nut-cracking areas.

The distribution of these clusters, with well defined edges, closely resemble what archaeologists understand as "activity areas". The unearthed materials include more than 4 kilograms of stone pieces and almost 40 kilos of nut-shell, and demonstrate that, like human sites, it is the repeated occupation of the same spot and the creation of large refuse accumulations that creates what archaeologists call a "site".

Because the site of Panda 100 is most likely older than 100 years, this discovery indicates that nut-cracking behavior has been present in this region for many generations.

The stone remains retrieved were unintentionally produced by chimpanzees as they hit rock hammers against wooden anvils. In all, 479 stones pieces were excavated, some from a depth of as deep as 21 cm.

A fascinating aspect of this discovery is that the size of the stones, the shape of flakes, and the many small pieces of debris left by chimpanzees are similar to the stones left behind by some of our early ancestors in East Africa during a period called the "Oldowan".

Moreover the number of stone pieces per m2, and the size of the stone clusters themselves mimic some assemblages from this period.

Thus we see that chimpanzees produced a visible record of their tool using activities. Archaeology has proven a reliable, efficient, and feasible method to uncover past chimpanzee activities in the rainforest. This type of archaeological application is useful in reconstructing past primate behavior both human and non-human.

The results open a new territory for many disciplines, including primatology, archaeology, and paleoanthropology, and indicate the possibility that some of the technologically simplest Oldowan sites could be re-interpreted as nut-cracking sites and more generally that some subsets of artifacts from the more sophisticated Oldowan assemblages could be seen as material proof that early hominids were able to eat nuts contained in hard shells.

The archaeologists will continue the excavation of chimpanzee sites in the African forest and explore the implications of this work in East Africa. "The data highlight how much more we still need to learn about our closest living relative, the chimpanzee, to understand humanity's uniqueness. Every day chimpanzees are being killed in the wild and their forest habitat is being destroyed. All of us have a responsibility to care for other species," says Boesch.

Acknowledgements This project was primarily supported by the Max-Planck Institute for Evolutionary Anthropology in Germany. Additional funding was received from the National Geographic Society, George Washington University, and the National Science Foundation. We thank the Ivorian authorities for their constant support of the Tai Chimpanzee Project, and specially the authorities of the Tai National Park, and the Swiss Research Center.