Are altruism and aggression polar opposites, or are they two sides of the same coin? In this review, the authors examine the evolved biological roots of these behaviors and focus on the psychology of kinship and how it can serve to bridge both behaviors. Drawing on inclusive fitness theory (Hamilton, 1964), the kinship, acceptance, and rejection model of altruism and aggression (KARMAA; Webster, 2008), and a sociofunctional threat-based approach to prejudice (Cottrell & Neuberg, 2005), the authors propose that altruism and aggression can be viewed as two sides of the same coin depending on context and perspective. For example, a mother bear protecting her cubs by attacking a predator may be simultaneously exhibiting an act of altruism and aggression. After offering some empirical support for their view, the authors discuss the theoretical and practical implications of viewing altruism and aggression as related constructs at the intrapersonal, interpersonal, and intergroup levels.