Could mental illnesses be caused by the mismatch between our present environment and the one for which we are adapted?

Evolutionary psychologists argue that to understand the brain properly, we must understand the environment in which the brain evolved and was shaped. They believe memory, perception, and language all are the products of natural selection.

Psychiatrists who subscribe to this view also have developed the field of evolutionary psychopathology — a new take on abnormal psychology from the perspective of evolution.

J. Anderson Thomson Jr., M.D., of the University of Virginia has found this approach helpful in treating depression. He believes that, though it appears to be all cost and no benefit, major depressive disorder might be “a psychological adaptation engineered by natural selection to help individuals resolve complex, socially-imposed stresses that could affect long-term fitness.” It does so by “signaling need and compelling help from reluctant others,” he said. Drug monotherapy may not be enough. Instead, Thomson recommends that physicians ask about the patient’s social conflicts and “become tenacious advocates for their resolution.”

Professor Randolph M. Nesse of the University of Michigan agrees. A pioneer of the movement, he currently is investigating how and when mood disorders provide an advantage. In his opinion, some cases of depression are an extreme version of a system that adapted to “disengage motivation when an organism is engaging in efforts that will not pay off.”

Such situations may well be much more common for humans nowadays than they were in ancestral times, because many of us pursue large goals with uncertain payoffs. For Professor Nesse, therapy would include going over the patient’s life goals in order to find out if an unreachable goal is the root of his or her depression.

Edward H. Hagen of Humboldt University in Berlin also is a proponent of evolutionary psychology, although he concedes that it is not without major problems. For example, researchers cannot directly study complex neural circuits, so it is hard to “unveil the workings of the brain.” A clear idea of the environment which evolutionary psychologists believe we are adapted for does not exist. And such adaptations would have to be shown in humans around the globe to be confirmed.

Nevertheless, Hagen argues that the theory may explain depression, suicide attempts and deliberate self-harm as rational bargaining tactics to gain assistance from others.