How did humans, a species of self-centered apes, come to care about others? Since Darwin, scientists have tried to answer this question using evolutionary theory. In The Kindness of Strangers, psychologist Michael McCullough shows why they have failed and offers a new explanation instead. From the moment nomadic humans first settled down until the aftermath of the Second World War, our species has confronted repeated crises that we could only survive by changing our behavior. As McCullough argues, these choices weren't enabled by an evolved moral sense, but with moral invention-driven not by evolution's dictates but by reason.