Darwinian medicine and mental disorders

Darwinian medicine applies the principles of evolutionary biology to the problems of medicine. It asks, for each disease, "Why has natural selection left the body vulnerable to this disease?" There are six possible kinds of answers: (1) novel environments, (2) co-evolution with pathogens, (3) constraints on what natural selection can do, (4) design trade-offs, (5) traits that increase reproduction at the expense of health and (6) defenses that are useful even though they are costly and aversive. These principles prove even more useful for understanding mental disorders than they do for understanding physical disorders. In particular, they offer psychiatry a diagnostic framework that distinguishes defenses from defects in the same way the rest of medicine does. It also calls attention to the utility of emotions, especially negative emotions. This knowledge will become increasingly essential as we gain new powers to use drugs to influence cognition and emotion. It can also help psychiatry to finally become recognized as a medical specialty just like any other.