Separate chimpanzee societies develop their own traditions and customs, according to field researchers from seven sites in Africa
ON A GRASSY SLOPE above the shore of Lake Tanganyika in Tanzania, a female adult chimpanzee, followed closely by her two-year-old son, spots a mound of dirt and a busy train of driver ants scrambling toward the colony. The older female releases a rather joyous-sounding, short pant-a characteristic chimpanzee vocalization that may be translated as, "Mmm, a tasty meal."
She pauses beneath the light drizzle of an early morning rain and glances about for a proper utensil. The young male watches intently as his mother selects a long twig and strips away the leaves on its end. The female takes the stick and sits down beside the dirt mound. She dips the tool into the nest and watches patiently as the ants, alarmed by the invasion, swarm onto it. When the ants have covered the stick about half way up, she removes it, sweeps the ants into the palm of her free hand and pops them into her mouth. The little male, excited by his mother´s obvious satisfaction, grabs a flimsy reed and begins imitating her, poking clumsily and unproductively at the nest.
This scene and others like it are at the heart of a growing understanding among biologists that chimpanzees have something once thought to be uniquely human: cultural behavior. Just as humans employ forks or chopsticks, smiles or high fives, handshakes or kisses on the cheek, so do chimpanzees differ in their lifestyles. In this case, a youngster is observing its mother's method of catching and eating ants. Researchers have counted 39 separate regional chimp habits of dining, social grooming, attracting mates and using tools. Welcome then, chimpanzee, to the once exclusively human culture club.
Such conclusions come from studies at the seven longest ongoing chimp research field sites in Africa. Their data, amounting to 151 years of research, were recently pooled by Andrew Whiten of Scotland's University of St. Andrews, along with the field researchers, in a landmark article published last year in the journal Nature. "All in all, the evidence is overwhelming that chimpanzees have a remarkable ability to invent new customs and technologies, and that they pass these on socially rather than genetically," wrote anthropologist Frans B. M. de Waal, of Yerkes Regional Primate Center at Georgia's Emory University, in the same journal.
When primatologist Jane Goodall first observed chimpanzees "fishing" for ants and the larger, bulbousheaded red termites at Tanzania´s Gombe Stream National Park, she was astounded. Her now-famous observation of the chimp she named David Graybeard fishing for termites in 1960 was the first recorded use of tools by any creature other than a human. But Goodall did not realize at the time that she also was observing what could be considered a unique cultural behavior. Nor did she realize that her field notes, written beneath a gas lantern in her tent at night, would stir the curiosity of dozens of other primatologists worldwide and draw them to Africa to launch their own studies of chimpanzee life in the wild.
Forty years ago, no respected scientist would even consider the idea that chimpanzees might have personalities, reasoning or emotions. "That was all forbidden, and culture was totally out of the question," she now says. "I remember a few years later searching through all the definitions of culture and finally choosing one that says culture is behavior passed from one generation to the next through observation, imitation and practice."
That definition, which has guided Goodall throughout her years of chimpanzee research, also has been adopted by most of the scientists who have studied animal behavior over the past 40 years. A few staunch critics still argue that animals other than humans do not possess culture. For example, psychologist Bennett Galef of McMasters University in Ontario, Canada, and others contend that animals must have language before they can be said to have culture. But other scientists, including the team that authored the Nature article last year, point to a body of evidence other than language.
The first stirrings that animals might possess culture came from a study of Japanese macaques on the tiny island of Koshima. Japanese primatologist Kinji Imanishi startled the world in the early 1950s by suggesting the definition of culture later adopted by Goodall. Imanishi led the now historic study of Imo, a young female macaque that one day took sandy sweet potatoes to the water´s edge and washed off the grit before eating them. The behavior was eventually adopted by Imo´s colony, and their descendents continue to wash their potatoes today. Since then, especially in recent years, biologists have attributed cultural behavior to a wide variety of species, including whales, elephants, birds and even rodents.
The first evidence of cultural variation in chimps was found by comparing the way animals from different regions dine on ants. For example, across the continent from Gombe, in the Taï Forest of the Ivory Coast in western Africa, an adult male chimp has discovered the telltale mound of an ant colony. He too searches for a suitable tool, ignoring the longer sticks and selecting instead a short twig. He too begins dipping the tool into the nest entrance to fish for a meal. But unlike his cousin at Gombe, the Taï animal waits only until the soldier ants guarding the nest entrance climb about four inches up the stick and then sweeps his catch directly across his smacking lips. His method is less efficient than the one employed at Gombe, netting only a dozen or so ants at a time.
One of the main tenets of the primatologists´ definition of culture is that the behavior be imitated or passed on by learning. Humans do that all the time: Children imitate adults, and adults imitate other adults living in the same community. The result is that people who live together tend to develop similar customs.
Goodall remembers the first time she saw a clear example of observational learning by her study subjects at Gombe. Young chimps start, she says, by paying close attention to behaviors of other chimps. "With termite fishing they start imitating bits of the pattern when they are about two," she says. "But they aren´t any good at it until they are closer to four. At Gombe we were out filming and saw a very young female chimpanzee next to two adults that were termite fishing.
"What we saw was the infant using this tiny little inappropriate tool, which was very flimsy and not useful for fishing at all. But because it was the height of the termite season when the termites are all near the surface, she put her tool next to the nest entrance and came up with a big warrior termite clinging to the tool.
"There is an anxious, motionless moment when she doesn´t know what to do and then she reaches out to her mother who takes the termite off the tool and eats it. A moment later, the infant catches another one and this time puts in her mouth. But, she pushes her lips right back away from her gums and she´s terrified as she crunches it in her mouth. There was captured, in that moment, the infant learning to eat her first termite."
Christopher Boesch of the MaxPlanck Institute for Evolutionary Anthropology in Germany was among the first to observe a behavior common to the Taï chimpanzees but never observed in 40 years of study at Gombe. Somewhere in their cultural past, the Taï chimps developed a fondness for Coula nuts. Both the Gombe and Taï groups have access to nuts and to the tools, a "hammer" and "anvil," needed to crack them open. A hammer is anything hard enough to crack open a nut. The anvil is a hard surface, such as a rock or piece of wood upon which the nut is placed.
Gombe chimps don´t even open up the nuts. The Taï chimps, however, place a nut in a depression on the anvil, usually a rock. They then grasp the hammer, another rock or hard wooden club and smack it against the hard shell to get at the prize within. Here too, Boesch found evidence of learning by young chimps from adults. While the adults expertly open nuts with their hammers and anvils, the young chimps pick up pieces of fruit, crumbling pieces of termite mounds or rotten branches and go about pounding on nuts.
Another cultural behavior commonly observed in five of the seven study sites, but with various purposes, is the socalled "leafclip." It was first seen in chimpanzees of the Mahale Mountains in eastern Africa, about 100 miles from Gombe, and in another region called Bossou in Guinea. Researchers have only seen the Gombe chimps engage in leaf clipping on two rare occasions.
To leaf clip, a chimpanzee gathers one to five stiff leaves and bites little bits off with its front teeth without eating the leaves. The biting produces a distinctive ripping sound, which appears to be the goal. At Mahale Mountains National Park, young male chimpanzees and adult female chimpanzees that are ready to mate make the clipping sounds to attract each other´s attention. The sound might be translated as meaning, "I would like to mate."
At Taï, leaf clipping appears to be reserved only for males as part of their drumming display behavior, which is common to most chimpanzee groups. Males drum on trees and make noise by leaf clipping as means of asserting themselves. But in Bossou, the same leafïclipping behavior is interpreted by researchers as a sign of anxiety or nervousness. When primatologists first began observing chimpanzees at Bossou, they noticed that startled chimpanzees would start shredding leaves. But after the chimps became accustomed to the observers, they stopped. Youngsters engage in leaf clipping simply while playingapparently because they like the sound.
But Galef and the handful of remaining critics of animal culture argue that these behaviors are due to environmental pressures. After all, such pressures lie at the heart of natural selection. But because of the different meanings of leaf clipping among the groups at Taï, Mahale and Bossou, Boesch and others who have observed the behavior in the field conclude that an ecological explanation is unlikely and that the behavior is cultural.
Ruling out environmental causes of differences was, in fact, key to the inclusion of any of the behaviors in the Nature paper. For example, in some areas chimpanzees make nests on or near the ground, and in other areas they build nests by weaving together the terminal ends of branches high in the trees. The difference was found not to fit a cultural interpretation. Chimpanzees simply won´t sleep near the ground in areas where leopards or lions are likely to pay a nocturnal visit. The authors also were careful to exclude examples of activity unique to a single chimpanzee. To be included, a behavior had to be one adopted by most members of a group.
The "knuckleknock," for example, is practiced by most lowranking males at Taï. Their aim is to attract females without acting like the dominant males, which attract the opposite sex by shaking tree branches and creating a loud fuss. The lowerranking males, averse to being savagely beaten up by their dominant colleagues, stand aside and rap their knuckles against tree trunks.
Like pop culture that arises suddenly and spreads quickly through a group of teens, new behaviors also appear in chimpanzees. In the mid1990s Gombe chimps suddenly began using leaves to squish bugs called ectoparasites, which they pull from each other´s coats while grooming. Maybe the practice arose because one chimp didn´t like getting its hands messy, or maybe a chimp discovered that the leaves made it easier to kill the hardshelled bugs. Taï chimps, on the other hand, remove the parasites from a partner, place them on a forearm, smack them with their hand and then eat them. Boesch writes, "Here again, we have two different solutions to the same problem."
Grooming, which strengthens social bonds, provides some of the richest examples of chimp cultural behavior. Take, for example, the "handclasp," first observed among chimps in the Mahale Mountains. Recalls primatologist William McGrew of Miami University in Oxford, Ohio, "Each of the participants simultaneously extended an arm overhead and then either or both grasped the other´s wrist or hand, or each grasped the other´s hand. Meanwhile, the opposite hand was used to groom the other individual´s underarm area revealed by the upraised limb."
Only adults and adolescents perform the behavior, and the pairs usually are male and female. They perform the grooming handclasp more often, every 2.4 hours on average, than any other type of behavior including foodsharing, toolusing and sexual and aggressive displays.
At nearby Gombe, scientists have taken special interest in the fact that the chimps there use a similar but significantly different technique. There, chimpanzees raise their arms overhead and sometimes grasp an overhead limb for support. Since the sites are only about 100 miles apart, the differences cannot be due to genetic isolation.
More recently, the Mahale chimpanzees have adopted a new grooming technique called the "socialscratch," which has caught on like another pop culture phenomenon. Here, the grooming chimpanzee rakes the hand up and down his subject´s back at the end of a grooming session. The social scratch is not used at Gombe, nor has it been observed at any other site.
Commenting in the journal Science, McGrew wrote, "We have enough data in enough populations that we can start doing the sorts of comparisons that cultural anthropologists do across human populations." And already there is enough evidence of behavioral differences among chimp communities that anthropologist Frans de Waal can boldly conclude, "Biologically speaking, humans have never been alone; now the same can be said of culture."
USA Today science writer Tim Friend is writing a book on animal communication.