From the age of Darwin to the present day, biologists have been grappling with the origins of our moral sense. Why, if the human instinct to survive and reproduce is "selfish," do people engage in self-sacrifice, and even develop ideas like virtue and shame to justify that altruism? Many theories have been put forth, some emphasizing the role of nepotism, others emphasizing the advantages of reciprocation or group selection effects. But evolutionary anthropologist Christopher Boehm finds existing explanations lacking, and in Moral Origins, he offers an elegant new theory.