Humans are often thought of as the only truly altruistic species. We help others out — by giving blood, donating to the poor, or committing to recycling — for no immediate payoff, and often at a cost to ourselves. But evidence is gathering that we might not be alone. Felix Warneken and colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, have shown that chimpanzees will do favours for unrelated chimps – even when they do not get rewarded for it. Previous studies have refuted the idea that chimps are so giving. In 2005, anthropologist Joan Silk of the University of California, Los Angeles, found that when she presented chimps with the choice of getting food just for themselves, or for their entire group, they showed no preference for feeding their pals as well.
But other work has shown that chimps can have a non-selfish streak. In a study published in Science last year, a Leipzig team reported that chimps would help their human keepers retrieve a pen that they had dropped — an action with no direct benefit for the chimp. That study involved chimps helping out human carers whom they were familiar with — and who had on other occasions provided the chimps with food. To get rid of these complications, the Leipzig team replicated the pen-dropping experiment with unfamiliar humans. As they now report in PLoS Biology, the chimps still chose to help out.