Bonobo evidence suggests ancient origin of the 'common enemy effect'

In the face of threats from other groups, humans, chimpanzees, and a selection of other species get closer to their own. Now an international team led by Kyoto University has shown that even our more peaceful cousins, bonobos—who have never been observed to kill outsiders—show a moderated version of this effect, hinting that this behavior may have emerged several million years ago, before our lineages went their separate ways.