Thursday, August 11, 2011
ScienceDaily (Aug. 9, 2011) — Researchers at the Yerkes National Primate Research Center have shown chimpanzees have a significant bias for prosocial behavior. This, the study authors report, is in contrast to previous studies that positioned chimpanzees as reluctant altruists and led to the widely held belief that human altruism evolved in the last six million years only after humans split from apes.
According to Yerkes researchers Victoria Horner, PhD, Frans de Waal, PhD, and their colleagues, chimpanzees may not have shown prosocial behaviors in other studies because of design issues, such as the complexity of the apparatus used to deliver rewards and the distance between the animals.
In each trial, the chooser, which was always tested with her partner in sight, selected between differently colored tokens from a bin. One colored token could be exchanged with an experimenter for treats for both members of the pair (prosocial); the other colored token would result in a treat only for the chooser (selfish). All seven chimpanzees showed an overwhelming preference for the prosocial choice. The study also showed the choosers behaved altruistically especially towards partners who either patiently waited or gently reminded them that they were there by drawing attention to themselves. The chimpanzees making the choices were less likely to reward partners who made a fuss, begged persistently or spat water at them, thus showing their altruism was spontaneous and not subject to intimidation.
"We were excited to find female after female chose the option that gave both her and her partner food," says Dr. Horner. "It was also interesting to me that being overly persistent did not go down well with the choosers. It was far more productive for partners to be calm and remind the choosers they were there from time to time," she continues.
The authors say this study puts to rest a longstanding puzzle surrounding chimpanzee altruism. It is well-known these apes help each other in the wild and show various forms of empathy, such as reassurance of distressed parties. The negative findings of previous studies did not fit this image. These results, however, confirm chimpanzee altruism in a well-controlled experiment, suggesting human altruism is less of an anomaly than previously thought.