Female chimpanzees like to spontaneously help others rather than act selfishly, suggesting altruism may not be a uniquely human trait, US researchers said on Monday. Scientists at the Yerkes National Primate Research Center in the southeastern state of Georgia tested seven female chimpanzees to see if observations of the species\' generous behavior in the field matched their decisions in a lab. 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, said the study in the Proceedings of the National Academy of Sciences. Previous studies have suggested that chimps tend to act selfishly in so-called pro-social tests. The researchers 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,\" she said. Researchers said they believe this study was more appropriately designed to judge chimps\' behavior than previous studies because it placed the waiting partner in view of the chooser and included a treat that was wrapped in a noisy package. \"I have always been skeptical of the previous negative findings and their over-interpretation,\" said co-author Frans de Waal. \"This study confirms the pro-social nature of chimpanzees with a different test, better adapted to the species,\" he said.