One child dies in a well, the world watches and weeps. But as the number of victims increases, our compassion tends to diminish. At the highest number of casualties—wars, tsunamis, acts of terror—the dead become faceless statistics. They call this compassion fade, but in reality, it’s our genetic inheritance—old adaptations from our ancestors persisting in our DNA. In the late-twentieth century, an anthropologist and evolutionary psychologist named Robin Dunbar proposed a theory that Homo sapiens can only care about, identify with, and maintain stable relationships with 150 people.
