The aim of this chapter is to argue that evolutionary theory can and should serve as the general theoretical framework for explaining and treating mental disorders. As currently understood, mental illness has relatively little to do with the view that human mind and behavior are products of evolutionary processes and that some psychological and behavioral traits may be adaptive while others are not. Instead, psychiatry is deeply immersed in activities such as the description of signs and symptoms, the classification of disorders, the identification of pathogenetic mechanisms, and the development of new therapeutic strategies. It is not that these activities are unimportant; rather, there is a price to pay when they monopolize psychiatric research and clinical practice to the exclusion of a theory dealing with why people behave as they do (McGuire & Troisi, 1998).