ATLANTA, Aug. 9 (UPI) -- U.S. researchers say chimpanzees have shown a significant bias toward prosocial, or altruistic, behavior among themselves, contradicting some earlier studies.
Scientists as Emory University said their study is in contrast to previous studies that had characterized chimpanzees as reluctant altruists and led to the widely held belief that human altruism evolved only after humans split from apes, a university release said Tuesday.
In the study, primate researcher Victoria Horner and colleagues offered seven adult female chimpanzees a choice between two similar actions involving food, one that rewarded both the female chimp and a partner, and another that rewarded only the female chimp herself.
The test animals could make a choice between responses that resulted in food treats for both members of the pair -- pro-social -- or a treat for just the chooser -- selfish.
"We were excited to find female after female chose the option that gave both her and her partner food," Horner said.
Choosers behaved especially altruistically toward partners that either patiently waited or gently reminded the choosers they were there by drawing attention to themselves, while the chimpanzees making the choices were less likely to reward partners who made a fuss, begged persistently or spat water at them, demonstrating their altruism was spontaneous and not subject to intimidation, the researchers said.