Recent theorists have suggested that human altruism toward non-family members evolved because of the tremendous benefits of reciprocity. Developing further the notion that evolutionary theory can help to explain moral sentiments, Howard Kahane proposes that a sense of fair play is essential to ethics and argues that moral obligation, too narrowly construed, prevents us from living rationally. He brings his account of fair play to bear on the ethics of various domains of social life including friendship, taxes, civil rights, and nation states.