This book demonstrates the generality of inclusive fitness theory, with particular emphasis on its fundamental evolutionary logic. It presents the basic mathematical theory of natural selection and shows how inclusive fitness theory deals with more complicated social scenarios. Topics include the Price equation, Hamilton's rule, nonadditive interactions, conditional behaviors, heritability, and maximization of inclusive fitness. This chapter provides a brief historical introduction to the problem of apparent design in biology, evolutionary explanations of this, and in particular, evolutionary explanations of individual behaviors that appear designed to benefit not the individual themselves, but other members of their species. It examines how social behaviors can be shaped by natural selection and discusses the problem of providing an evolutionary explanation of self-sacrifice by individuals, altruism in group selection, and multilevel selection theory.