Why Your Brain Hates Other People

As a kid, I saw the 1968 version of Planet of the Apes. As a future primatologist, I was mesmerized. Years later I discovered an anecdote about its filming: At lunchtime, the people playing chimps and those playing gorillas ate in separate groups.

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.

The core of Us/Them-ing is emotional and automatic.

Humans universally make Us/Them dichotomies along lines of race, ethnicity, gender, language group, religion, age, socioeconomic status, and so on. And it’s not a pretty picture. We do so with remarkable speed and neurobiological efficiency; have complex taxonomies and classifications of ways in which we denigrate Thems; do so with a versatility that ranges from the minutest of microaggression to bloodbaths of savagery; and regularly decide what is inferior about Them based on pure emotion, followed by primitive rationalizations that we mistake for rationality. Pretty depressing.

But crucially, there is room for optimism. Much of that is grounded in something definedly human, which is that we all carry multiple Us/Them divisions in our heads. A Them in one case can be an Us in another, and it can only take an instant for that identity to flip. Thus, there is hope that, with science’s help, clannishness and xenophobia can lessen, perhaps even so much so that Hollywood-extra chimps and gorillas can break bread together.

The Strength of Us Versus Them

Considerable evidence suggests that dividing the world into Us and Them is deeply hard-wired in our brains, with an ancient evolutionary legacy. For starters, we detect Us/Them differences with stunning speed. Stick someone in a “functional MRI”—a brain scanner that indicates activity in various brain regions under particular circumstances. Flash up pictures of faces for 50 milliseconds—a 20th of a second—barely at the level of detection. And remarkably, with even such minimal exposure, the brain processes faces of Thems differently than Us-es.

This has been studied extensively with the inflammatory Us/Them of race. Briefly flash up the face of someone of a different race (compared with a same-race face) and, on average, there is preferential activation of the amygdala, a brain region associated with fear, anxiety, and aggression. Moreover, other-race faces cause less activation than do same-race faces in the fusiform cortex, a region specializing in facial recognition; along with that comes less accuracy at remembering other-race faces. Watching a film of a hand being poked with a needle causes an “isomorphic reflex,” where the part of the motor cortex corresponding to your own hand activates, and your hand clenches—unless the hand is of another race, in which case less of this effect is produced.

The brain’s fault lines dividing Us from Them are also shown with the hormone oxytocin. It’s famed for its pro-social effects—oxytocin prompts people to be more trusting, cooperative, and generous. But, crucially, this is how oxytocin influences behavior toward members of your

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