Altruism, or selfless acts that benefit others, have long been a mystery of human behavior. The closest thing to conventional wisdom has been that selflessness is only an illusion of self-interest; we act altruistically because we expect reciprocation. But some anthropologists now argue that millions of years of evolution have hard-wired us for altruism, not self-interest. This theory is the subject of a new book "The Age of Empathy" by primatologist Frans de Waal. What de Waal is challenging is the very idea that our default is Thomas Hobbes's brutish "state of nature," or perhaps that the state of nature even really exists.