The notion that culture is strictly a human characteristic has been dealt another blow. An international team of researchers has found that orangutans exhibit behaviors that can also be called culture.
As evening descends in Borneo's Kinabatangan Forest, a careful listener can hear a loud spluttering sound. This sound indicates that a local orangutan is going to sleep for the night. Almost every orangutan in the region calls the same way, while elsewhere on the island, orangutans make their nests more quietly.
Duke University primate specialist Carel van Schaik says the difference is a sign that orangutans have some characteristics of what we call culture; behaviors that are transmitted socially.
"You should find that more distant places are also more distant culturally and vice versa," he said. "Indeed, we found that correlation, which is boosting our confidence in the cultural interpretation."
Mr. Van Schaik and colleagues from several U.S., Asian, and European institutions studied six orangutan populations in Borneo and Sumatra and found that the Asian primates exhibit a collective total of 24 behaviors that are present in some groups and absent in others. As the researchers report in the journal Science, the behaviors include using leaves as napkins or gloves, employing sticks to extract seeds from fruit or insects from trees, and building covers over nests as rain or sun shields. Orangutans also display varieties of signals, such as a squeaky kiss to indicate annoyance or distress.
According to Mr. Van Schaik, some orangutans kiss on the hand, others kiss on the lips, while still others kiss a leaf. "As far as we can tell, the meaning remains the same but it's clearly different in different places," he said. "We are fairly confident it's cultural because when animals kiss on a hand, everybody in a population does it, when they kiss on the leaf, everybody does it, and they don't do the other variants."
Culture was once thought unique to humans, but evidence has been mounting for socially learned traditions elsewhere in the animal kingdom: song learning in birds and whales, for instance. The best evidence came in 1999 from chimpanzees in Africa. Researchers documented 39 behaviors specific to particular groups of chimps. Activities that did not seem to be determined by the environment.
Carel van Schaik says such observations not only provide insights into animal behavior, but might also help shed light on how human culture evolved.
"We have taken culture to a completely unprecedented level in the animal kingdom," he explained. "It has always been an interesting question for scientists where that came from. What we see now is that the human lineage was building our own unique culture on a very solid foundation where skills and signals were already culturally transmitted."
The accumulating research on animal culture lessens the distinction between human and animal and between culture and nature. Primate specialist Frans de Waal of Emory University in Atlanta, Georgia says this troubles many, particularly social scientists, who avoid calling behaviors culture unless they are based on language.
"They say it is very important how culture is transmitted, [that] we humans do it with teaching and imitation," he said. "And if you cannot demonstrate that in an orangutan or some other animal, you shouldn't call it culture."
But Mr. de Waal points out that biologists do not hold such a narrow view of the mechanisms of cultural transmission. He compares notions of culture to those of locomotion, which is not defined by how it occurs. "So we don't care whether an animal flies or swims or walks. We all call it locomotion. The same thing we do with culture," he said. "We give it a broad, sweeping definition, and how exactly it is accomplished is a secondary question."
As the debate continues, scientists warn that research to illuminate orangutan behavior is threatened by loss of habitat because of human encroachment, pushing the animals toward extinction. Ninety percent of the ape population in Asia has disappeared in 50 years.