ATLANTA - Primatologists at the Yerkes Primate Center of Emory University have found new evidence that capuchin monkeys (a small but large-brained South American primate) cooperate to obtain food and share the rewards of their efforts. The study, conducted by Frans de Waal, Ph.D., director of Yerkes' Living Links Center, and Michelle Berger, senior laboratory assistant, has implications for understanding the evolutionary basis of reciprocity, a fundamental feature of human society. Dr. de Waal's research appears in the April 6 issue of Nature.
In his three-year study, Dr. de Waal and his colleagues at the Living Links Center modeled the natural hunting behavior of capuchin monkeys. In the wild, these primates pursue a prey as a group, but only one actually makes the capture. That individual ultimately shares the meat with the rest of the group.
Dr. de Waal examined how same-sex pairs of brown capuchins in a test chamber cooperatively work for food when separated by a mesh partition. Two transparent food bowls, one containing apple slices, were positioned in front of the monkeys on a weighted tray. An individual monkey could not pull the tray within reach on its own, but the monkeys could accomplish the task cooperatively. When successful in the effort, the monkey that secured the food consistently shared it with the helper.
"It was remarkable that the second monkey helped to pull the tray even though there was no guaranteed reward of food for him," explained Dr. de Waal. "His willingness to cooperate in the pull was enhanced if he received payment for his work."
Compared to tests of solitary effort in which an individual monkey could pull a tray of food on his own, the researchers found that food obtained through joint effort was shared substantially more than individually obtained rewards. The scientists also determined that the helping capuchin was two or three times more willing to assist again
Contact: Poul Olson
Emory University Health Sciences Center