Key concepts evolutionary psychopathology, Darwinian medicine, pathogen, etiology, pathogenesis, trait variation, immune system, smoke detector principle, affective disorders, social competition hypothesis, schizophrenia, personality disorders

Life on Earth has existed in some form for well over three billion years. Given this lengthy period of evolutionary change, why is it that modern-day humans still suffer from colds, fever, morning sickness, personality disorders, anxiety and depression, and the most serious of psychiatric illnesses – schizophrenia? Surely natural selection has had time to rid us of such problems? One of the major contributions that evolutionary psychologists have made in the last decade lies in reconsidering the symptoms of mental and physical illnesses in one of three ways based on a knowledge of evolutionary theory. They suggest that symptoms may be adaptations, they may be due to constraints on evolutionary processes or they may be due to a mismatch between our evolutionary heritage and our current environment. Our susceptibility to infectious diseases, for example, is now seen as a pathogen/host arms race that, due to the vast asymmetry in life-cycle time and in sheer numbers, humans can never win. Darwinian medicine leads to the counterintuitive conclusion that perhaps sometimes unpleasant symptoms should be left to continue because they are good for you. It is in the field of psychiatry, however, that evolutionary psychology may have its greatest impact as, for the first time, psychologists are beginning to ask why the propensity for mental illness is so widespread in our species.