The definition of disorder as a harmful dysfunction (J. C. Wakefield, 1999) is a useful concept, anchored in the recognition that the evolved human architecture consists of a collection of functional mechanisms that may potentially be impaired and whose impairment may be harmful. Because natural selection organized each mechanism to solve a distinct adaptive problem under ancestral conditions, the criteria for whether a mechanism is dysfunctional are supplied by whether the mechanism has become impaired in performing its ancestral function. Because evolutionary function and dysfunction diverge markedly from normal human standards of value, many dysfunctions are beneficial, whereas various mechanisms that are performing their evolved function may cause disturbing outcomes. For this reason, many conditions in addition to disorders may require treatment, and the authors attempt to sketch an evolutionary taxonomy of treatable conditions.