In "South Pacific," they had Lt. Cable sing "you have to be carefully taught" prejudice.
That was consistent with the theory at the time that prejudice is learned, sometimes through the subtle behavior of our parents or other role models. We are literally taught to be wary of people of a different race, ethnicity, religion, or even politics.
But now there's evidence that prejudice is an evolutionary adaptation to living in groups.
Group living increases the odds of survival by making it easier to get resources like water, food, and shelter. It also makes it easier to find mates, to care for children, and to ward off predators.
But the group itself also needs to be protected. Outsiders can harm it by spreading disease, harming group members, or stealing resources. Those who developed ways to identify outsiders had a better chance of survival.
Over generations, this process of quickly evaluating others was so streamlined that it became the unconscious, automatic behavior we call prejudice.
Psychologists have known for a long time that prejudice operates at an unconscious level. There's even an online test for it. But now there's empirical evidence that prejudice is not unique to humans.
Several experiments with monkeys support the theory that prejudice is deeply rooted in our evolutionary past. That doesn't mean it can't be overcome. But it does suggest that we need a better approach than "other group appreciation."
We need to be more aware our automatic prejudices so we can correct them. And there's also evidence that when we take the perspective of an outsider, it reduces our automatic prejudice towards that person’s group.
It turns out, sadly, that no one needs to be taught prejudice; but we do need to be taught to guard against it.