Evolution: Psychiatric nosology's missing biological foundation

The new system of diagnostic criteria for emotional disorders has brought much needed reliability, but it neglects the most fundamental distinction in medical diagnosis, that between symptoms and the diseases that cause them. As a result, psychiatric diagnosis for emotional disorders remains where medical diagnosis was two centuries ago, classifying constellations of protective responses as if they were diseases. The result is emphasis on individual differences in tendencies to negative emotions, and neglect of other emotional disorders and the life situations that give rise to emotions. An evolutionary perspective can advance the diagnosis of emotional disorders in several ways. First, it emphasizes that disorders of both excess and deficiency are possible for every emotion, thus calling attention to neglected disorders with deficits of negative emotion or excesses of positive emotion. Second, it confirms that the normality of an emotion depends unavoidably on the context. Third, it notes that variations in brain mechanisms that make a person susceptible to anxiety or depression are only sometimes diseases; they may have the same causal significance as variations in brain mechanisms that make a person especially prone to cough or fever during a cold. Fourth, it notes that biologically normal responses may be aversive and even harmful to individuals. Finally, it suggests the importance of a detailed and evolutionarily informed analysis of the motivational structure of every patient's life. This understanding is the foundation for all treatment.