How Do You Distinguish Between "Us" and "Them?"

The psychology of tribalism. From Scientific American:

Having an inbuilt facility to distinguish between Us and Them was a valuable resource, related to that essential ability to create artificial groupings from what, to a robot, would be entirely distinct objects. We take this talent for granted, but what would life be like if we lacked it: if we were like Funes, the cripple created by Jorge Luis Borges in his story Funes the Memorious--a man with mental recall so powerful that he could not stand back and objectify what he saw? Funes saw each dog, each leaf, each cloud as sui generis: his inability to form categories left him utterly unable to make sense of the world.