Orangutans' culture dictates their behavior

Feat in study was thought limited to chimps, humans

January 03, 2003|By Dennis O'Brien | Dennis O'Brien,SUN STAFF

Orangutans -- those tree-living apes with the flashy red manes -- have distinct cultures that dictate how they build their nests, use tools, eat, show off for each other and even how they say good night, according to a study being published today.

The study, in today's issue of Science, says that three decades of observations by some of the world's leading experts shows orangutans behave along cultural patterns, an intellectual achievement previously thought to be reserved to humans and chimpanzees.

The study says patterns of behavior demonstrated by orangutans scattered across Borneo and Sumatra show that they learn much of their lifestyle, right down to whether they sleep in a kind of bunk bed or under a thatched roof.

"All of them had unique elements to their behavior that were unique to their individual grouping," said Carel van Schaik, a biological anthropology professor at Duke University and the lead author of the report.

Learned behavior has been documented for decades in primates.

Jane Goodall first reported that chimpanzees used tools 30 years ago, and numerous studies have shown cultural traits among chimps, humans' closest genetic relative.

But the study is the first time that researchers have shown culturally transmitted behavior -- conduct learned from others and passed on to individuals -- among the orangutan, who are less social than chimps and live in smaller and more isolated groupings.

"What we're dealing with here is socially learned behavior. The big difference is whether you learn something on your own, or whether you learn it from others. If you learn it from others, it's culturally transmitted," said van Schaik.

Experts say the study shows that orangutans are on an intellectual par with chimpanzees.

"It shows that orangutans are more akin to ourselves than previously thought," said Gary Shapiro, a zoologist who has taught sign language to orangutans in Borneo and worked with them for 30 years.

Shapiro said there have been a number of studies documenting orangutans' ability to learn as individuals.

He has taught them up to 40 words and published reports on his work.

But today's study is the first to show how they have developed cultures that vary from one population to another.

"We've known they have an ability to learn, but now we're getting it put all together by researchers who studied the behaviors of the different populations," said Shapiro, who is vice president of the Los Angeles-based Orangutan Foundation International.

Isolated populations

Van Schaik said that thousands of hours of observations of two populations of orangutans in Sumatra and four in Borneo -- isolated from each other by rivers, mountains and woods -- showed 24 different types of culturally transmitted behaviors.

Up to 250 orangutans were observed over three decades, he said.

Cultural traits observed ranged from what the orangutans ate to how they said good night to each other, he said.

Some emitted raspberry-like sounds or a kissing-squeak noise before bedding down for the night. Van Schaik said he believes the noises are signals by the orangutans that they are going to bed for the night.

Some orangutans built two-story nests, or bunk beds, and slept in the lower berth to protect themselves from the rain. Others built one story with a thatched roof.

Some used sticks to fish insects out of tree holes and extracted seeds from a prickly fruit, known as a neesia, by poking it with a stick.

Others ate the seeds by breaking through the shell with their teeth, and still others didn't eat the fruit at all, he said.

Some also used leaves as gloves to protect their hands from the thorns of the fruit, while others didn't, he said.

"There is really no other way to explain those differences, other than cultural transmission," van Schaik said.

In some groups, orangutans climbed up the trunk of a dead tree and pulled it down to the ground in a show of strength to competitors.

"It makes a lot of noise and all the orangutans see it, and I guess they're impressed," he said.

Van Schaik, who first reported the orangutan's use of sticks as tools in 1994, said the study's eight authors agreed to compile the report at a meeting last February sponsored by the Leakey Foundation in San Anselmo, Calif.

Loss of habitat

He said the report is intended to highlight the importance of studying orangutans in the wild and to raise awareness about logging activities in Sumatra and Borneo that are killing off the habitat left for the world's 20,000 endangered orangutans.

"We're losing these cultures, and once the culture's gone, that's it, there's nothing left to study," he said.

Van Schaik said the findings suggest that culturally transmitted behavior among primates goes back 14 million years to when orangutans evolved from their more primitive primate ancestor and became a separate species of Asian apes.

Orangutans, chimpanzees and humans are believed to have shared a common ancestor until then.

Chimps evolved about 7 million years ago, which scientists previously thought was the beginning of cultural transmission among primates.

The ancestors of the chimpanzees branched off from human ancestors about 5 million years ago, Van Schaik said.

Studies have found that modern humans, Homo sapiens, emerged in Africa up to 500,000 years ago and began to migrate out of Africa about 100,000 years ago.

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