Given the opportunity to spread random acts of kindness, chimps would just as soon pass, finds a new UCLA-led study.
The study, published in the Oct. 27 issue of the journal Nature, suggests at least one way in which humans differ from their closest living relatives in the animal kingdom.
"Because chimps participate in collective activities such as cooperative hunting and food sharing and they console injured group members and human caregivers, their capacity for empathy and altruism has been an object of considerable curiosity," said UCLA anthropologist Joan Silk, the study's lead author. "This is the first experiment to show that chimps don't share the same concern for the welfare of others as do humans, who routinely donate blood, tithe, volunteer for military duty and perform other acts that benefit perfect strangers."
Silk led a team of researchers from Emory University, the University of Texas and the University of Louisiana as they conducted experiments with two separate groups of chimps.
They first studied seven adult chimps in captivity in Louisiana. Although the chimps were not related, they were quite familiar with each other, having lived together for 12 years.
The chimpanzees were brought into a small testing room with a window in it. Behind the window was a feeding device attached to two trays of food. When the chimp pulled a handle, one of the trays moved toward him and the other tray moved toward another chimp in a room on the opposite side of the window.
The chimps with access to the handle faced two choices: They could continue delivering food to both themselves and the other chimp or they could pull a handle that delivered food only to themselves. Each of the chimps had the chance to dispense rewards to each of the other chimpanzees in the group. As a control, all of the dispensers of rewards were offered the same choice without a chimp in the other room.
At another site in Texas, the researcher tested 11 other adult chimps. The animals had rich social experiences and were members of stable social groups, but they had not participated in cognitive testing before. They worked with a slightly different apparatus, but confronted the same sets of choices.
The results from both these sites were similar: The presence of a potential recipient of the food had no impact on the chimpanzees' choice. The chimps in Louisiana chose this option about 56 percent of the time when another chimp was present and about 58 percent when another chimp was absent. The chimps in Texas chose the option that provided rewards to the other chimp 48 percent of the time, exactly the same percentage of time that they delivered rewards to an empty enclosure.
"It is possible that the chimpanzees in our experiments understood how to obtain food for themselves, but did not understand that they were responsible for delivering rewards to the chimpanzee in the adjoining enclosure," Silk and her colleagues wrote in the Nature paper. "Yet, potential recipients sometimes displayed begging gestures, suggesting that at least they had some understanding of the other's role in delivering rewards to them. Nevertheless, chimpanzees were clearly motivated to obtain rewards for themselves, but not to provide rewards for other group members."
The findings add mystery to the origins of human altruism, a popular research topic among economists and anthropologists.
"Had the chimps shown signs of altruism, researchers looking to explain the origins of altruistic behavior in humans would have known to look at other species with whom we share a common ancestor," Silk said. "This study suggests that concern for the welfare of unrelated group members and strangers may be a trait that has emerged in humans, but not in other closely related species, like great apes. Alternatively, perhaps a better place to look for prosocial preferences would be in species that rely more heavily on cooperation, such as cooperatively breeding mammals."
The research received support from the MacArthur Foundation Preferences Network, James S. McDonnell Foundation and the National Institutes of Health.
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