 The idea that some characteristics of an organism are explained by its intrinsic nature, whilst others reflect the influence of the environment is an ancient one. It has even been argued that this distinction is itself part of the evolved psychology of the human species. The distinction played an important role in the history of philosophy as the locus of the dispute between Rationalism and Empiricism discussed in  another entry  in this encyclopedia. This entry focuses on accounts of the innate/acquired distinction from the mid 19th century to the present. These accounts have for the most part been inspired by the sciences of mind and behavior. Hence, Section 1 focuses on key scientific controversies about the innate/acquired distinction in the behavioral sciences since Darwin. We choose this starting point because the theory of evolution is the inevitable background to any modern discussion of innate behavior. Moreover, Darwin himself pioneered an approach to the study of innate behavior that remains influential even today.