August 9, 2011
Chimps Can Be Generous After All
Scientists, wondering for years how long ago our so-called prosocial behavior evolved, have recently found that chimpanzees also have a significant favoritism for prosocial behavior, which is in contrast to previous studies that positioned chimps as reluctant altruists that led to the widely held belief that human altruism evolved in the last six million years only after humans split from apes.
In a new paper published this week in the Proceedings of the National Academy of Sciences (PNAS), researchers at Emory University's Yerkes National Primate Research Center in Atlanta, Georgia conclude that chimpanzees are indeed willing to do favors for others, leading them to believe our prosocial behavior may date back further than previously thought.
The scientists tested seven female chimpanzees to see if observations of the species' generous behavior in the field matched their decisions in a lab.
When given a choice of two colored tokens -- one which guaranteed a banana treat for two and the other which gave a reward for the chooser only -- the chimps tended to pick the social option, the researchers note in their published work.
The team of scientists also found that chimps most often acted generously when the waiting partner reminded the chooser gently of her presence but did not act up or bully her into picking a treat for two.
"We were excited to find female after female chose the option that gave both her and her partner food," said lead author Victoria 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."
The researchers decided to undertake the study because of a contradiction in the scientific literature. Lab experiments on chimps in the past failed to show a willingness to help. However, primatologists who had observed chimps in the wild saw many examples of what looked like helping.
"They're sharing food, they're helping each other in fights "” there was a huge mismatch between what was going on in the field and in the lab," Horner told the New York Times.
Horner and her colleagues think chimpanzees may not have shown prosocial behaviors in past studies because of design issues, such as complexity of the apparatus used to deliver rewards and the distance between the animals.
"I have always been skeptical of the previous negative findings and their over-interpretation," said Frans de Waal, one of the study authors. "This study confirms the prosocial nature of chimpanzees with a different test, better adapted to the species,"
The authors say this study should put to rest the longstanding mystery 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 results in the new study confirm chimpanzee altruism in a well-controlled experiment, suggesting human altruism is less of an anomaly than previously thought.
"These new results suggest chimpanzees may help others proactively simply because they understand they need help," Brian Hare, an anthropologist at Duke University, told the New York Times.
Several other experts also gave Horner and her colleagues high marks.
"They have been able for the first time to duplicate what field researchers already knew was a natural ability of chimpanzees," Christophe Boesch, a primatologist at the Max Planck Institute for Evolutionary Anthropology in Germany, told Times reporter Carl Zimmer.
But one primatologist, Michael Tomasello, also from the Max Planck Institute, found the study poorly designed.
"The results are un-interpretable," he said. He noted that the Emory researchers ran their control sessions after the experimental sessions. "Maybe the chimpanzees were just tired of choosing the two-pieces-of-food option by the time the control conditions were run."
Tomasello and his colleagues have published their own experiments on prosocial behavior in chimps, most recently in July in the journal Nature.
His research leads to a somewhat different conclusion than Horner's study. "Chimps help others, but what they do not do is give up food themselves so others can have it," he said. "So they are prosocial when it is not costly, but when it is, not so much."
The Emory scientists said they believe their study was more appropriately designed to judge chimps' behavior than in any previous study because it placed the waiting partner in view of the chooser and included a treat that was wrapped in a noisy package.
The study authors next plan to determine whether the altruistic tendency of the chimpanzees towards their partners is related to social interactions within the group, such as reciprocal exchanges of food or social support.
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