For centuries, the egoism-altruism debate has echoed through Western thought. Egoism says that the motivation for everything we do, including our seemingly selfless acts of care for others, is to gain one or another self-benefit. Altruism, while not denying the force of self-interest, says that under certain circumstances we can care for others for their sakes, not our own. Over the past half-century, social psychologists have turned to laboratory...