Orangutans Show Signs of Culture, Study Says
for National Geographic News
|January 3, 2003|
An international group of scientists pooling more than 30 years of data
has concluded that behavioral patterns among different orangutan
populations show evidence of culture.
The finding pushes the origins of culture among great apes back to 14 million years ago, when orangutans and African apes last had a common ancestor. Great apes include orangutans, found only in Asia, and Africa's gorillas and chimpanzees.
Earlier studies had shown evidence of cultural learning among chimpanzees, suggesting that great ape culture had been around for at least five to seven million years. Transmission of cultural knowledge in orangutans and other great apes has implications for understanding the evolution of human culture.
Culture, which can be defined as the presence of geographically distinct behavioral variants that are maintained and transmitted through social learning, was long considered to be a uniquely human trait.
"What this study shows is that the great apes have a solid foundation of their own culture, on which humans erected their own," said Carel van Schaik, a professor of biological anthropology and anatomy at Duke University.
"This study demonstrates the richness of orangutan behavior and how the study of orangutans is important for understanding human evolution," said Cheryl Knott, an anthropologist at Harvard University and a co-author of the study. "But our ability to study and learn from these fascinating creatures is vanishing as these forests rapidly disappear with the whirr of the chainsaw."
To be considered cultural elements, behaviors and practices must vary from region to region, be more common where there is more social contact within a group, and not depend on habitat.
Studying six populations of orangutans in Borneo and Sumatra, Indonesia, researchers identified 24 behaviors that show evidence of being culturally transmitted. Many of the behaviors involve tool useusing sticks to dig seeds out of fruit, to poke into tree holes to obtain insects, or to scratchor using leaves as napkins or as gloves to protect against spiny fruit.
The authors, writing in the January 3 issue of the journal Science, suggest that variations on these behaviors found among the different populations are cultural. For instance, some populations made sounds such as "raspberries" or "kiss-squeaks" using leaves to amplify the sound, others used flat hands, others balled their hands into trumpet-like fists. Among some populations the behavior was rare or absent.
Other traits that show evidence of cultural transmission include different forms of communication and play.
Many biological anthropologists would argue that culture is an evolved human adaptation, said Knott.
An alternative explanation to culturally transmitted learning would be that each individual just figures the behavior out for itself, or that the behavior is simply an adaptation to the environment in which it lives.
"This, however, cannot explain the occurrence of 'arbitrary' signals [like kiss-squeaks]," Knott said. "Social learning must be involved to explain the transmission of such behaviors."
Some behaviors, like using a stick to dig out seeds, are so advantageous to an animal that they'd never give it up voluntarily, said van Schaik.
"On the other end of the scale there are signal variants, like the kiss-squeak on a leaf or a hand that are not that different in functionality, and can go in and out of popularity within a group," he said.
Having cultural behaviors requires strong mother-infant bonds and close interaction within a group. Orangutan offspring stay with their mothers until they're seven or eight years old, but orangutans are on the lower end of the sociability scale among great apes.
"Infants and young learn most cultural knowledge from their mothers, but if that was the only way of learning you'd have as much individual variability as you have matrilineal lines," said van Schaik. "You wouldn't see this checkerboard pattern across populations that we're seeing."
The researchers found that sites closest to one another showed more behavioral similarities than with more distant sites.
"Also, we found the biggest behavioral repertoires within sites that showed the most social contact, thus giving the animals the greatest opportunity to learn from one another," said van Schaik.
Orangutans once ranged throughout Southeast Asia, and may have numbered in the hundreds of thousands. Today they are found only in Borneo and Sumatra, and are listed as critically endangered by the World Conservation Union. Increasing population pressure100 years ago 10 million people lived in Indonesia; today that number is close to 220 millionillegal logging, slash-and-burn agricultural practices, and civil unrest all pose threats to the orangutan.
Conservationists estimate there may be as few as 15,000 orangutans left living in the wild.
"We're losing the race against timejust as we discover how to study the roots of human culture, we're losing the tools," said van Schaik.
"At new sites we find new things; there is enormous cultural variation between populations, and we're losing it. You cannot protect one population and discover the whole cultural phenomenon," he said. "And even if somehow you could restore the forest and the animals, just as with human cultures, once a culture is gone, it's gone."
Editor's note: For more than 30 years two organizationsthe National Geographic Society and the Leakey Foundationhave supported long-term orangutan studies that contributed data to this recent finding.
|© 1996-2008 National Geographic Society. All rights reserved.|