ST. LOUIS, MISSOURI--Gorillas deserve to join the club of "cultured apes." That's the conclusion of the first large-scale study of multiple behaviors in zoo gorillas, reported here yesterday at the annual meeting of the American Association for the Advancement of Science (which publishes ScienceNOW).
Culture is defined as a range of behaviors learned from others that varies with the group one belongs to. For example, chimpanzees belonging to one population in Mahale, Tanzania, groom each other with one hand while clasping their free hands together. Another group in the same region has a slightly different tradition: grooming partners touch their free wrists. Yet despite growing evidence for culture in chimpanzees, bonobos, and orangutans, not much is known about gorilla culture or whether it exists at all. The elusive nature of most gorilla species makes it difficult to gather behavioral data in the wild.
So a team led by primatologist and conservationist Tara Stoinski of Zoo Atlanta in Georgia decided to monitor the behavior of captive gorillas in 17 American zoos. Earlier observations by her group had shown that gorillas could copy their group members. When one gorilla used sticks to pry apart electric wires around trees to get at the bark, for example, others in the group followed suit. But in order for this behavior to be considered culture, other populations of gorillas would need to react differently.
By asking zoo officials to fill out a survey of their gorillas' behaviors, Stoinski and colleagues discovered that gorillas in fact do vary widely in how they deal with the same situations. For example, while members of some zoo groups regularly used sticks to retrieve peanut butter or baby food, other groups didn't use tools at all. In addition, gorillas in some zoos clapped their hands to invite others to play, while those in other zoos did not. That matches the definition of culture, Stoinski concluded.
The findings make the first strong case for the existence of culture in gorillas, says Andrew Whiten, an evolutionary and developmental psychologist at the University of St. Andrews in the United Kingdom, who studies social learning and culture in chimpanzees. He notes that Stoinski's data from captive populations is "more robust" than his own field data because all zoo environments are fairly similar, allowing her to control for the complex effects environment may have on social behavior.