For decades, researchers have been crouching in the bushes, peering from behind trees and creeping through the underbrush to catch glimpses of how chimpanzees, man's closest living relatives, live in the wilds of Africa.
Primatologists have gathered voluminous records of the habits of these complex creatures, noting their mating rituals, eating habits, tool use and myriad other behaviors.
Now, researchers have performed the most systematic analysis of these copious journal entries and have concluded that individual groups of chimpanzees, like humans, have distinctive behavioral patterns that are passed down through generations to create what are in essence their own unique versions of "culture."
"What's not been previously appreciated is how many of these behaviors are culturally transmitted," said Richard Wrangham, a professor of anthropology at Harvard University who helped conduct the analysis. "A lot of the chimpanzee behavior is transmitted by learning from one generation to the next, and that's a conclusion that we haven't been able to be very secure about until now."
Since humans are so closely related to chimps, the findings provide insight into the evolution of our own culture, he said.
"Chimpanzees are similar to the kind of species we evolved from. We can imagine the increase in the importance of cultural transmissions in the ancestor of our species," Wrangham said. "It is in many ways the defining mark of humanity."
Many animals have complex social systems and distinctive behaviors that are passed down through generations. Songbirds, for example, learn local versions of their species' songs from their parents. Some groups of dolphins feed on sponges while others do not. But no other creature, aside from humans, has been shown to have as much diversity as the chimpanzee, he said.
To document this, Andrew Whiten of the University of St. Andrews in Scotland circulated among the leaders of seven major chimpanzee research groups a list of behaviors reported over the equivalent of 151 years of collective chimpanzee observation. The researchers, including renowned British primatologist Jane Goodall, then added to or subtracted from the list. The final list was analyzed to determine which behaviors could be explained by differences in their surroundings, such as the absence of certain foods or types of rocks or plants. In the end, the researchers identified 39 distinct behaviors that are unique among certain populations of chimpanzees and seem to be the result of their individual culture and not their environment or genes.
"I think it's exciting," said Anne Pusey, a professor in the department of ecology, evolution and behavior at the University of Minnesota. "It tells us that chimps are inventive and do pass on certain habits, presumably socially. Chimps must learn from the example of others rather than anything that's in their genes."
For example, chimps in Kibale, Uganda, and Gombe, Tanzania, have developed a custom known as "leaf grooming." It's a way for one chimp to signal that he or she is willing to groom another animal.
"As they sit around, they pick up a leaf and run their fingers over it as if they were running their fingers over an individual," Wrangham said. "It's a system of grabbing the attention of a neighbor."
But chimps in nearby Budongo, Uganda, do not do this.
"This means the behavior is not genetic. It's not hard-wired. Some individual invented the signal in a particular population, and it spread through the population and has been adopted by cultural transmission, passed by generation to generation," Wrangham said.
The chimps in Kibale also have a unique behavior that involves treating wounds. The Kibale chimps will dab wounds with leaves to help stop the bleeding. No other chimps do this.
Researchers have also discovered wide variations in how chimps eat ants. Chimps in the Tai Forest in the Ivory Coast dip a short stick into an ant hole to retrieve just a few ants at a time. Chimps in Gombe, in contrast, use long sticks to sweep dozens of ants into their mouths all at once. Chimps in Kibale don't eat ants at all, even though they are plentiful there as well.
"Even more important than ants is the use of nuts. Nuts in some areas are smashed by use of a stone or log hammer and provide very important food. In other areas there is not smashing--they seem to just not have thought of it, and they are missing out on an opportunity," Wrangham said.
The contrast is most dramatic in the Ivory Coast, where chimps in the Tai Forest on the west side of the Sassandra River smash nuts while chimps on the east side of the river do not.
The researchers also noted that while members of four of the chimp groups do a ritual dance when it begins to rain, seemingly to welcome the water, chimps in two other populations only sometimes do a rain dance and those in the last one never do. Based on these differences, the researchers concluded that chimps have what could be called individual "cultures," even though anthropologists typically require the use of language for the existence of culture.
"The question of whether animals have culture is a bit like asking whether chickens can fly," writes Frans B.M. de Waal in an article accompanying Whiten's paper in last week's issue of the journal Nature. "Compared with an albatross or a falcon, perhaps not, but chickens do have wings, they do flap them, and they can get up in the trees. Similarly, viewed from the cultural heights achieved by humans in art, cuisine, science and politics, other animals seem to be nowhere in sight."
But "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," de Waal wrote.
"The 'culture' label befits any species, such as the chimpanzee, in which one community can readily be distinguished from another by its unique suite of behavioral characteristics," he wrote. "Biologically speaking, humans have never been alone--now the same can be said of culture." In addition to expanding the definition of "culture," the finding offers another reason to protect chimps in the wild, where they are threatened by hunting, logging and farming, Wrangham said.
"The threat of extinction of chimpanzees is all the more poignant when we recognize that each population has its own culture," Wrangham said.
Chimpanzees have their own version of "culture," according to a new analysis that compared the behaviors of seven well-studied groups of chimps in Africa, including the practice by some chimps of "fishing" for ants with sticks.