Group stereotypes. Ethnic prejudices. Wars. These are substantial social problems, and they attract the attention of many social scientists, including psychologists who study social cognition and behavior. That’s good. But in order to grapple intelligently and realistically with these problems, it is important to consider not just the insights of the social sciences but the biological sciences as well. The roots of modern prejudices and intergroup conflicts can be found in the ecological circumstances within which our species evolved and in the psychological processes that emerged as adaptations to those circumstances. Inquiry into these evolved psychological processes helps us understand intergroup stereotypes and prejudices, and how these contribute to various forms of discrimination as well as to full-blown intergroup conflict. An evolutionary analysis also yields novel insights into the circumstances under which these prejudices may be exaggerated or inhibited. These insights may prove useful in the development of interventions that might actually help alleviate intergroup discrimination and conflict in the modern world.