After decades of observation, an international collaborative of primatologists has gleaned evidence indicating that orangutans show behaviors that are culturally based.
The scientists' findings push back the origins of culturally transmitted behavior to fourteen 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 seven 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 also continue the dangerous decline in orangutan populations. In an article in Science, they presented evidence for cultural transmission of twenty-four 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 researcher Carel van Schaik, professor of biological anthropology and anatomy at Duke, 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.
Significantly, such tool use was present only among some groups, even when the habitat appeared to be the same, the researchers found. For instance, they discovered that, while orangutans on one side of a barrier river used tools on the fruit, those on the other did not. Nevertheless, says van Schaik, the popular perception of orangutans did not suggest that they would show cultural transmission.
" 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," says van Schaik. To explore the possibility of culture in orangutans, The Leakey Foundation sponsored in February 2002 a gathering of orangutan researchers from throughout the world to correlate their data.
" It was an open-ended exercise, in which we looked at each other's videos and other data from our own observation sites," says van Schaik. "We looked for behaviors that were different among the different groups.
" While we were by no means certain that we would come up with any evidence for cultural variability, we ultimately identified twenty-four behaviors that likely represent cultural variants. Frankly, we were all rather giddy at the end, when we realized what had come out of our data."
According to van Schaik, the researchers are acutely aware that such differences might be nothing more than the animals' adaptation to varying habitats, without social transmission. "However, we saw that habitat did not have a significant impact on similarity of these behaviors," he says. "And our confidence that we were seeing cultural transmission was increased by analyses showing that proximate sites showed more behavioral similarity than distant sites. This finding strongly suggested that we were observing a process of innovation and cultural diffusion. Also, we 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."
According to van Schaik, the discovery of cultural transmission in orangutans has implications for understanding the process in humans. "First of all, this finding emphasizes that human culture didn't just arise de novo, but reaches far back in evolutionary time," he says. "The findings in chimpanzees meant that culture originated at least seven million years ago, and the discovery in orangutans pushes its origins back to about fourteen million years."
" All these findings suggest that the first ancestral man-apes must have had a pretty solid evolutionary cultural foundation on which to build," says van Schaik. He and his colleagues distinguish four kinds of culture: labels, signals, skills, and symbols. The Great Apes have shown the first three. Human culture is distinguished by far more sophisticated development of all four, he says. However, observations of chimpanzees and orangutans have revealed hints of symbol use, and further study might reveal clearer evidence of symbols.
Van Schaik warns that political unrest and destruction of orangutan habitat could prevent such studies. "Some people have asked us, 'Haven't you learned enough by studying these animals for some thirty years?' And it is obvious from these findings that we haven't. Some of the areas included in this study have already been lost to illegal logging. And even if somehow you could restore the forest and the animals, just as with human cultures, once a culture is gone, it's gone."
Of the Science article's nine co-authors, three are from Duke. In addition to van Schaik, they are graduate students Gwendolyn Borgen and Michelle Merrill.