We send money to help famine victims halfway around the world. We campaign to save whales and oceans. We stay up all night to comfort a friend with a broken relationship. People will at times risk -- even lose -- their lives for others, including strangers. Why do we do these things? What motivates such behavior?

Altruism in Humans takes a hard-science look at the possibility that we humans have the capacity to care for others for their sakes rather than simply for our own. Based on...