Disordered doctors or rational rats? Testing adaptationist and disorder hypotheses for melancholic depression and their relevance for clinical psychology.

Most clinicians view depression as a painful disorder in which motivation to pursue adaptive goals is lacking and cognition is impaired. An alternative hypothesis-grounded in a common evolutionary approach-suggests that depression is inherently motivational and evolved to motivate avoidant learning of harmful situations. Testing these hypotheses requires a clear definition of "disorder". Wakefield's harmful dysfunction evolution-based definition proposes that all unambiguous cases of disorder involve a malfunctioning adaptation. These hypotheses-functional adaptation and malfunctioning adaptation-are mutually exclusive and require a common research strategy. One must identify and map out the relevant adaptation-characterized by a high degree of non-random organization and coordination for promoting a function-which will eventually result in a conceptual blueprint of where and how the adaptation can malfunction. Using inescapable shock in rats and physicians' emotional responses to medical errors to provide context, we show how the symptoms of melancholic depression exhibit signs of adaptation for motivating a time-consuming, attentionally-demanding, energetically-expensive avoidant learning style after experiencing a harmful event. We discuss how this adaptationist approach may provide insight into spontaneous remission and the effects of psychotherapies and antidepressant medications.