Parent-offspring conflict is the “flip side” of altruism. Instead of accounting for the evolution of traits for helping relatives at the expense of the actor, the theory of parent-offspring conflict attempts to account for the evolution of traits in the offspring for hurting close relatives. Robert Trivers presented a model of parent-offspring conflict based on the concepts of inclusive fitness and coefficients of relationship. With respect to parent-offspring conflict, the mathematical models remove the theoretical objections raised by Alexander, and indicate that parent-offspring conflict of the type envisioned by Trivers could exist in nature. The history of the study of antagonistic behavior between animals is long and encompasses many types of interactions. Several different approaches have been made to modeling parent-offspring conflict. The subject of parent-offspring conflict was raised ten years after W. D. Hamilton’s discussion of altruism, so it is natural that there should be less empirical evidence for the former theory.