This chapter introduces Bowen’s theory. Bowen’s theory of the family as a unit of natural selection involves a measure called “differentiation of self.” This chapter also describes how human beings habitually behave in the context of their early family life. It discusses the triangle hypothesis. It shows that the use of Bowen’s theory to the simplest and earliest life forms reveals what is most basic about social relationships in general; it simultaneously provides new ways to think about bacteria. This chapter also suggests that Bowen’s main idea helps explain extremes in survival and reproduction in social species.