Bonobos often form friendly relationships with other bonobo s in separate social groups — the first time this has been seen in non-human primates (灵长类). This is in line with humans, but in contrast to chimpanzees, another primate, which frequently kill chimps in other groups. The findings challenge the idea that humans evolved (进化) from violent apes, says Surbeck at Harvard University. " This potential to form cooperative links between different groups is not uniquely human and it might have occurred earlier than we thought," he says.
Many animals cooperate, but they seem to do so only with those within their social circle, or in-group. Hostile (敌对的 ) interactions between groups are common among animals, including chimpanzees, so scientists have often assumed that hostility towards other social groups in humans is natural, says Samuni, also at Harvard. However, humans also often cooperate with people in different social circles, for example, by trading or teaching.
Bonobos are one of our closest living relatives. They are less studied than chimpanzees, but are known to be more peaceful, says Surbeck. To learn more about interactions between groups, Surbeck and Samuni observed 31 adult bonobo s from two social groups in Congo over a two-year period. The pair documented 95 encounters between the groups, which represented about 20% of their total observation time. Unlike chimpanzees observed in previous studies, they showed cooperation with out-group members. In fact,10% of all mutual grooming (梳毛) and 6% of all food sharing occurred among members of different social groups.
While bonobo s that groomed others usually got an immediate benefit, food sharing rarely resulted in a gift in return. This suggests that their actions were " not just motivated by selfish interests or immediate rewards" , Surbeck and Samuni report.
Otten, a researcher from the Netherlands, finds the study " exciting" , especially as it " challenges the idea of human exceptionalism" with regard to out-group cooperation. Otten says the bonobo s that were most cooperative within their groups were the same ones that cooperated more with out-group members. This agrees with findings from humans. " Scholars used to believe that in-group ‘love' goes together with out-group ‘hate' , but recent research suggests that often in-group cooperators are also out-group cooperators," he says.