COURTESY DUKE NEWS SERVICE

For humans, the sputtering sound known as a raspberry is commonly considered a contemptuous gesture. But among some orangutans, the expression seems to simply signify that the utterer is turning in for the night. Not all orangutan groups mark the end of the day this way, however. In fact, according to a report published today in the journal Science, a raspberry before bed is one of 24 socially transmitted behaviors that scientists say may represent cultural variation in the great apes. If the findings are confirmed by additional field observations, they could push the origin of culture back nearly seven million years to the last common ancestor of orangutans and the African apes.

Man's closest living relative, the chimpanzee, provides the best evidence for the existence of nonhuman culture: scientists have identified 39 behavior patterns that vary culturally among the animals. To investigate whether similar conduct exists in orangutan groups, Carel P. van Schaik of Duke University and his colleagues assessed previously collected data on six different wild populations in Borneo and Sumatra. "Culture requires more than just a mother-infant bond, but also extensive social contact, and orangutans are at the low end of the sociability spectrum," van Schaik says. Nevertheless, the team identified two dozen behaviors that fall into three of the four categories of cultural elements: labels, signals and skills (The fourth category is symbols, which only humans employ). Van Schaik notes that the group 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." Examples of culturally-based behaviors that the scientists distinguished include using leaves as napkins, using leafy branches to ward off attacking insects and riding "snag" (dead trees that are falling toward the ground) for sport.