Why do people fight wars? Following the devastation of the Second World War, this question became particularly pressing. Postwar scholars in the human sciences, from political science to anthropology, investigated the role of human nature in the causes of war even as they debated the very meaning of human nature itself. Among the wide-ranging efforts of postwar social and behavioral scientists to explain the causes of war, research on primate aggression became a compelling approach to studying the evolution of human warfare. In contrast, primatologist Frans de Waal's popular and scientific publications on primate reconciliation emphasized the naturalness of conflict resolution and peacemaking, thereby providing a counterpoint to the pessimism of aggression research while simultaneously shoring up the logic of simian analogy. De Waal's popular books heralded the "make love, not war" bonobo as humans' evolutionary next-of-kin and contributed to raising public interest in bonobos during the late twentieth century, although the apes' popular reputation subsequently exceeded the scientific discourse about them.