“It’s been said, ‘There are two kinds of people in the world: those who divide the world into two kinds of people and those who don’t.’ In reality, there’s lots more of the former. And it can be vastly consequential when people are divided into Us and Them, ingroup and outgroup, ‘the people’ (i.e., our kind) and the Others.” A primatologist tries to explain why your brain hates other people. (In fairness to your brain, other people sort of had it coming…)