by Whit Gibbons

October 6, 2003

Culture used to be a trait thought to be exclusive to humans, but apparently only because humans were the ones doing the reporting. Research on some of the great apes, which also include gorillas, orangutans, and gibbons, has provided evidence that chimpanzees pass cultural behavior down from one generation to the next. A recent study has shown that orangutans also have a cultural side.

Culture is the transmission of socially learned knowledge or tradition to succeeding generations, and not surprisingly, humans were once believed to be the only species in which cultural differences occurred between populations. Recently, variation in chimpanzee behavior in different geographic regions has been cited as evidence of culture. This past year Carel P. van Schaik of Duke University and colleagues documented that the behavior of orangutans also varies geographically.

Orangutans are large, some males reaching about 200 pounds, with extremely long, powerful arms. The big, intelligent apes have reddish hair that usually looks a bit shaggy. They were formerly native to Southeast Asia, where they are now extinct, presumably because of being hunted by humans. Today the last of the orangutans occur naturally only in the rainforests on the two large islands of Borneo and Sumatra. By one report, more than 300,000 orangutans were alive in the wild in 1900 compared to fewer than 20,000 today. If the report is true that more than 2,000 orangutans disappear from the wild each year, the species will be extinct before today's elementary school children reach college. Illegal removal of orangutans for the pet trade remains a problem for the species but, as is true for most wildlife, the greatest threat is habitat destruction.

The investigators examined wild orangutan populations at six sites, four in Borneo and two in Sumatra, to determine what forms of tool using and other specific behaviors were present in the different populations. The scientists considered evidence of culture to be situations in which most or all of the orangutans at one site exhibited a type of behavior that was not practiced by any orangutans at the other five sites. Orangutans anywhere were capable of the behavior, but only those who had learned it from their parents or members of their own population actually exhibited it. Such findings support the position that cultural evolution had occurred.

The investigators classified 19 behaviors as "very likely cultural variants," which included using leaves to wipe the face, using a branch as a swatter against bees and wasps, and using a leafy branch to scoop up water from a tree hole. Many of these were common behaviors in one population but were completely absent or rare in the other populations. For example, a customary habit throughout one of the populations from Sumatra was to poke into tree holes with a tool to obtain insects. But the orangutans in the Sumatra population were not more clever than other orangutans; using a stick as a tool is behavior learned from watching others, so now everyone at that site does it.

The scientists also noted that similarities in cultural traits among orangutan populations, as measured by behavioral repertoires, decreased with increasing geographic distance. That is, the closest population to another one was more likely to be similar in special behavioral traits than the population farthest away. An individual who moves from one population to another, and may bring a new skill or useful behavior that can be learned by others, is more likely to find its way to a nearby population than to a more distant one.

The scientists also found that some groups of orangutans had more social contact than other groups, in which individuals were more solitary. Not surprisingly, the former had a greater number of learned behavioral activities that would be more readily passed on as a result of greater social interaction. Such observations further support the idea that certain behaviors in orangutans have been passed on culturally. I feel certain that future studies with gibbons will show that they also are highly cultured great apes.

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