NATURE . From Orphan to King . Orangutan Intelligence

It's a rainy evening on the Indonesian island of Borneo. High up in the forest canopy, a home builder is hurrying to put a cover over his head before the sun goes down. The builder is an orangutan, a great ape that is one of our closest relatives. Humans and these red apes share 95 percent of their genetic material.

But are orangutans intelligent? For years, the conventional wisdom was that they were not. This began to change in the 1960s when researchers observed chimpanzees using twigs to lure termites from their mounds, and using rocks to crack open fruits and nuts, skills long-believed to be uniquely human.

In the decades that followed, researchers observed that orangutans also used tools. For example, they used leaves and sticks to handle and open prickly fruit, and crafted leaves into rain hats. In some ways, such observations weren't a surprise. Zookeepers had long taught captive orangutans to hammer nails and to use keys or screwdrivers.

Orangutan holding a wooden tool

In the mid-1990s, a team led by biologist Carel van Schaik of Duke University watched Sumatran orangutans use specially prepared sticks to pry termites, ants, and other insects from colonies high up in trees. The apes also used the sticks to collect honey and then eat it as if it were on a lollipop.

Researchers, however, aren't ready to declare orangutans equal to humans. For one thing, orangutans don't craft a wide array of tools nor do all orangutans make them, perhaps because they don't really need them to survive.

Van Schaik and colleagues do argue that orangutans show evidence of "culture" -- that is, they can teach each other new skills, and pass them along from generation to generation. Different groups of orangutans can have different cultures.

The researchers laid out their case in the journal SCIENCE in 2003. The study shows "human culture didn't come out of nothing," says van Schaik. "It was built on a firm foundation. Early hominid maternal culture wasn't that different from what we see in apes today."

The study combined findings from 6 sites in Indonesia where researchers study orangutans. Overall, they identified 24 cultural "elements," each of which is common in at least one area and rare or absent in others. Some involve the use of tools, such as using leaves to scoop water out of a knothole. But other cultural elements involve nesting, such as building leafy roofs for protection from the rain or sun. Still others are ways of calling to one another, like the "kiss-squeak," the manner in which some orangs press their hands or leaves against their lips to make a loud sound.

Unfortunately, learning more about orangutans has become "a race against time," says van Schaik. Fires, hunting, and deforestation have been decimating wild populations for years. Experts estimate that as few as 20,000 orangutans exist today.