It's a reassuring thought: What separates man from beast is culture. Except chimpanzees appear to have what anthropologists define as culture -- the ability to invent seemingly arbitrary new behaviors and pass them along to others. And this week, a team working in Southeast Asia reports in Science magazine that another ape -- the orangutan -- has culture, too.
As NPR's Christopher Joyce reports, the finding appears to whittle away a little more of the divide between humans and their ape ancestors.
Duke University anthropologist Carel van Schaik studies orangutans, and in a Sumatran swamp, he noticed something odd about one particular group. They liked a fruit that was protected by needle-like spines, and to get to the edible seeds inside, the apes used a tool. With a sharp stick, they pried open the fruit to extract the seeds.
When Van Schaik's team crossed a major river to watch a separate group of orangutans, they found the same fruit, but no tools. "We had found a cultural boundary," says Van Schaik.
The orangutans on the far side of the river had plenty of sticks available, but they didn't use them on fruit. Most ignored the fruit. Others smashed it to get the seeds. The stick trick seemed to be an invention created by one group that was passed along, up to a point.
"If culture is innovation followed by social transmission, the innovation happens at a particular place, then you get this spread over space until it hits a barrier," says Van Schaik. "We found that pattern suggesting that, yep, we're really looking at culture."
Van Schaik took his case to a major orangutan conference in San Francisco. It turned out that some of his fellow scientists had also seen unusual behaviors in some orangutan populations.
For example, Duke University's Michelle Merrill recorded the "kiss-squeak," a signal of annoyance.
When the primatologists compared notes, they found that different orangutan groups created variations on the kiss-squeak.
"In some areas they kiss on an object, it probably makes the kiss louder, and that could be their hand but it could also be leaves," says Van Schaik. "In Sumatra nobody ever kisses on leaves, whereas in Borneo several populations kiss on leaves. It seems arbitrary but that's exactly the kind of indicator that tells us culture is happening."
The discovery could mean that primate cultural behavior is 14 million years old. That's when orangutans split off from the primate line that led to chimps and humans. Researchers presume orangutans behave now the same way they did then.
"One of the big things this tells us," says Harvard University primatologist Richard Wrangham, "is that there's a lot of different behaviors that may turn out to be similarly socially transmitted in other animals that haven't been examined in a similar way."
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