The scientists' findings push back the origins of culturally transmitted behavior to 14 million years ago, when orangutans first evolved from their more primitive primate ancestors. Previous evidence for cultural transmission in chimpanzees suggested an origin of cultural traits 7 million years ago.
The researchers also warn that illegal logging and other habitat destruction in the forests of Sumatra and Borneo could not only threaten further research into the earliest origins of culture, but continue the dangerous decline in orangutan populations.
In an article in the Jan. 3, 2003, Science, the scientists presented evidence for cultural transmission of 24 behaviors. These include:
-- using leaves as protective gloves or napkins;
-- using sticks to poke into tree holes to obtain insects, to extract seeds from fruit or to scratch body parts;
-- using leafy branches to swat insects or gather water;
-- "snag-riding," the orangutan equivalent of a sport in which the animals ride falling dead trees, grabbing vegetation before the tree hits the ground;
-- emitting sounds such as "raspberries," or "kiss-squeaks," in which leaves or hands are used to amplify the sound;
-- building sun covers for nests or, during rain, bunk nests above the nests used for resting.
According to first author Carel van Schaik of Duke University, the impetus to look for cultural transmission among orangutans arose from earlier findings that orangutans use tools. In particular, van Schaik and his colleagues had discovered 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.