Science is now learning what makes us both noble and terrible. Primatologist Frans de Waal saw at the Arnhem Zoo how apes vigorously enforced group norms.

If the entire human species were a single individual, that person would long ago have been declared mad. The insanity would not lie in the anger and darkness of the human mind—though it can be a black and raging place indeed. And it certainly wouldn’t lie in the transcendent…