What motivates altruism? How essential is the phenomenon of altruism to the human experience? Is altruism readily accessible to the ordinary person? In The Altruistic Species, Flescher and Worthen explore these questions through the lenses of four disciplinary perspectives???biology, psychology, philosophy, and religion. In the course of their investigation, they make an extended argument for the existence of altruism against competing theories that construe all ostensible cases of benevolence as self-interest in disguise. The authors consider theories of egoism; the role of genetics and evolutionary biology; the psychological states that induce altruistic behavior; philosophical theories of altruism in normative ethics such as Kantian, utilitarian, and Aristotelian models of moral action; and accounts of love of the neighbor in Christianity and Buddhism. Additionally, they offer a new, comprehensive definition of altruism that is inclusive of the insights of each of these perspectives.