Chapter 29 covers how a field of scientific research is often transformed by the influence of ideas or modes of thought from a quite different field. Though this can often be highly beneficial, it can also have negative effects, involving an inappropriate attempted expansion of the domain of the intervening science, something the author of this chapter has referred to in the past as “scientific imperialism.” This chapter explores the application of evolutionary ideas to psychiatry and diagnoses this as an example of such undesirable imperialism. At least in the neo-Darwinian guise in which evolutionary ideas have been applied to psychiatry, they suffer the fatal defect of treating psychiatric conditions as genetically determined responses to the environment. It is argued in this chapter that they should rather be seen as outcomes of a complex and multifactorial developmental process to which evolved genetic factors have very limited relevance.