Culture, from a biological point of view, is behavior that is passed on through social contact. But what are the origins of culture? And what is it about humans that has allowed us to develop such rich and diverse cultures?

Our relatives might hold the answers.

Chimpanzees, our closest relatives, show a wide range of cultural behaviors, from tool use to signaling. That indicates that culture arose at least 7 million years ago, the point at which ancestors of chimps and humans diverged.

But work published in Science last week on a great ape unique to Asia suggests that primate culture has far older origins.

There are two closely related species of great ape in Asia, Pongo pygmaeus, the orangutan, and Homo sapiens, us. Carel van Schaik at Duke University in Durham, N.C., and a group of international scientists, have shown that wild orangutans exhibit true cultural traits. This pushes back the origin of culture to when the ancestors of chimps and orangutans diverged, around 14 million years ago.

Orangutans are only found on the islands of Sumatra and Borneo, where human activity (particularly the spread of palm oil tree plantations, but also illegal logging and gold mining) has resulted in their populations plummeting by 50 percent over the last 10 years. Eighty percent of orangutan habitat has disappeared in the last 20 years.

And despite decades of research, we have only just found that orangutans have culture.

The discovery comes not a moment too soon: the World Bank estimates that mechanized logging in the Kalimantan forest, Indonesian Borneo, will result in its total loss by 2010.

In Sumatra, orangutans are disappearing at a rate of 1,000 per year; in Borneo the rate is very likely higher.

The most optimistic predictions give the orangutans 10 years before they go extinct.

“Some people have asked us ‘Haven’t you learned enough by studying these animals for some 30 years?’ ” said van Schaik.

“And it is obvious from these findings that we haven’t. Some of the areas included in this study have already been lost to illegal logging. 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.”

In earlier work, van Schaik found that groups of orangutans in Sumatra use sticks to pry out fat-rich seeds from a fruit called neesia, thereby avoiding the stinging hairs that surround the seeds.

Significantly, such tool use was present only among certain groups, even when the habitat appeared to be the same. For example, orangutans on one side of a river used tools on the fruit, while those on the other, blocked by the river from social contact with the other group, did not. The observation suggested to van Schaik, a professor of biological anthropology and anatomy, that orangutan behaviors might be culturally transmitted.

To explore the possibility, van Schaik held a workshop where orangutan researchers from around the world, including primatologist Akira Suzuki of Kyoto University, also the author of the Science paper, met and pooled their data.

“It was an open-ended exercise, in which we looked at each other’s videos and other data from our own observation sites,” said van Schaik. “We looked for behaviors that were different among the different groups.

“While we were by no means certain that we would come up with any evidence for cultural variability, we ultimately identified 24 behaviors that likely represent cultural variants. Frankly, we were all rather giddy at the end, when we realized what had come out of our data.”

Newly identified orangutan cultural behaviors include making a spluttering “raspberry” or “kiss-squeak” sound; using leaves as protective gloves or napkins; and using sticks to poke into tree holes to obtain insects or to extract seeds from fruit.

Orangutans also have “snag-riding,” the apparent equivalent of a sport. The animals ride falling dead trees, grabbing hold of other vegetation before the tree hits the ground. And if that sounds like fun, what about this: sticks are also used by both sexes as “autoerotic tools” for sexual stimulation.

The researchers were worried that the behaviors they identified might be nothing more than the animals’ adaptation to varying habitats, without social transmission. In other words, that they wouldn’t demonstrate true culture.

“However, we saw that habitat did not have a significant impact on similarity of these behaviors,” said van Schaik. “And our confidence that we were seeing cultural transmission was increased by analyses showing that proximate sites showed more behavioral similarity than distant sites. This finding strongly suggested that we were observing a process of innovation and cultural diffusion. 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,” he said.

The findings shed light on the evolution of culture in humans.

“All these findings suggest that the first ancestral man-apes must have had a pretty solid evolutionary cultural foundation on which to build,” said van Schaik.

Van Schaik and his colleagues distinguish four kinds of culture — labels, signals, skills and symbols — of which all great apes show the first three. Human culture shows far more sophisticated development of all four. However, observations of chimpanzees and orangutans have revealed hints of symbol use, and further study might reveal clearer evidence of symbols, said van Schaik.

Van Schaik’s work is supported by that of a Japanese Ph.D student, Noko Kuze, who is based at the Tokyo Institute of Technology, but is currently working on orangutan behavior in the rain forest reserve at Sepilok in Malaysian Borneo. At Sepilok, orangutans that have been orphaned are rehabilitated and released into the reserve. Kuze’s field work suggests possible cultural behaviors.

“Rehabilitant orangutans can learn how and what they can eat in the forest without any assistance from humans,” Kuze told me when I met her in September last year. “Maybe they learn that from predecessors in the forest.” Predecessors are young and adult orangutans who have been released before.

Kuze also emphasized the precarious nature of the orangutan’s existence. “The most important thing we must do is conserve their natural habitat. At the same time, we need more research on the ecology of wild orangutans. Because now we don’t have enough information about their ecology for conservation,” she said.

And if we don’t act immediately, the orangutan (Malay for “man of the forest”) will be replaced by its relative, the plundering brute, the man of the city.

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