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, Andrew Michael Flescher and Daniel L. Worthen explore these questions through the lenses of four disciplinary perspectives—biology, psychology, philosophy, and religion. In 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 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 includes the insights of each of these perspectives. The Altruistic Species reinvigorates the debate over the prevalence of selfless motivation in human behavior—whether it is a rare or ubiquitous phenomenon—something considered exceptional or a capacity that members of any community could potentially develop. This noteworthy interdisciplinary examination of altruism balances science, virtue theory, and theology. It is ideal for ethics, human behavior, and evolutionary biology courses as an educational resource for other multidisciplinary studies and interested lay readers.