Are mental disorders diseases?

Do anxiety disorders, like many other diseases, result from novel stimuli not found in our ancestral environment? Not often. New dangers such as guns, drugs, radioactivity, and high-fat meals cause too little fear, not too much. In this sense we all have maladaptive hypophobias, but few of us seek psychiatric treatment to increase our fear. Some novel situations, especially flying and driving, do often cause phobias. In both cases, the fear has been prepared by eons of exposure to other dangers. Fear of flying has been prepared by the dangers associated with heights, dropping suddenly, loud noises, and being trapped in a small, enclosed place. The stimuli encountered in an automobile zooming along at sixty miles an hour are novel, but they too hark back to ancestral dangers associated with rapid movement, such as the rushing attack of a predator. Automobile accidents are so common and so dangerous that it is hard to say if fear of driving is beneficial or harmful.

The genetic contributions to anxiety disorders are substantial. Most people with panic disorders have a blood relative who has the same problem, and the search is on for the responsible genes. Will these genes turn out to result from mutant genes that have not been entirely selected out? Will they turn out to have other benefits? Or will we discover that genetic susceptibility to panic is simply one end of a normal distribution, like a tendency to develop a high fever with a cold or a tendency to vomit readily? When we find specific genes that predispose to panic and other anxiety disorders, we will still need to find out why those genes exist and persist.