Given the obvious benefits of having access to more territory in which to gather and hunt, outsiders – particularly those who bear characteristics that mark them as genetically distant – were treated as foes. In this sense, the notion of “us versus them” has been fundamental to human evolution, and it continues to shape our interactions.
人类从灵长类进化而来。灵长类组成一起工作从而实现存活的社区。进入更多狩猎采集领地的好处显而易见，因此外来者——特别是那些具备表现出基因不同的特征的外来者——被视为危害。从这角度讲，“我们和他们”是人类进化的根本，并一直在左右我们的互动。