Previously, a belief was widely held that human altruism evolved only after humans split from their ape cousins about 6 million years ago. In recent years, however, research has revealed just how much chimpanzees have in common with us. They can hunt with spears, play with dolls and mourn their partners’ death.

　　"Most of the earlier studies had presented the apes with a complex implement that helped them deliver food to themselves or others, often so complicated that the experiments tested tool skills rather than social tendencies," De Waal told Live Science. "Ours is the first study that uses no such implement at all."

　　In addition to using complex food-delivery systems, past experiments often placed the chimpanzees so far apart that they might not have realized how their actions benefited others. In these new, simplified experiments, two apes were housed next to each other with a screen through which they could see each other. Then, one chimpanzee had to choose between two differently colored tokens (币) from a bin, one of which represented a pro-social (亲社会的) option, the other a selfish option. The pro-social option would cause both chimpanzees to receive a piece of banana wrapped in paper. The selfish option only rewarded the ape who made the choice.

　　In a study with seven adult female chimps placed into various pairs, the scientists found all the apes showed a definite preference for the pro-social option. "For me, the most important finding is that like us, chimpanzees take into account the needs and wishes of others," researcher Victoria Horner, said.

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