An evolutionary perspective on psychiatry

Recent progress in the evolutionary understanding of behavior may greatly assist psychiatry. Although explanations of psychopathology have traditionally emphasized proximate causes of individual differences, consideration of the evolutionary functions of human behavior is essential for psychiatry, just as biology, ethology, and medicine routinely consider both proximate and evoluGonary explanations for a variety of phenomena. The methods and data for testing evolutionary hypotheses are reviewed, and the ways in which evoluGonary principles can help to explain maladaptive behaviors are considered. Some psychiatric symptoms that seem maladaptive may, in fact, serve specific survival functions. Hypotheses are proposed about the possible evoluGonary significance of overeating, anorexia nervosa, panic attacks, and sexual disorders, and tests of these hypotheses are considered. By incorporating an evolutionary perspective on psychopathology, psychiatry may share the foundation that evolution provides for the rest of natural science. I N THE PAST ten years, evolutionary theory has gained substantial new power to explain behaviors and social structures.’ Unanswered problems from Darwin’s time have finally been solved, and a whole class of new hypotheses is being generated and tested. Milestones for this progress include Hamilton’s 1968 formulation of the principle of inclusive fitness, and the 1975 publication of Wilson’s Sociobiology.z-3 The exponential growth since 1975 of publications in this area, attests to the impact of these new ideas. The evolutionary study of behaviors and social structures is quickly becoming an independent discipline. This new power of evolutionary theory to explain human behavior has not been widely appreciated or utilized by psychiatry. Yet, the application of evolutionary principles to psychiatric phenomena makes new questions possible and provides a framework for integrating the seemingly diverse levels of the biopsychosocial model. The territory of evolutionary psychobiology is large, so this presentation must be limited to an outline of the logic of evolutionary explanations in psychiatry, and some examples that illustrate the benefits and problems of testing evolutionary hypotheses about specific psychiatric conditions. For every biological phenomenon, two different kinds of causes must be understood. Proximate (immediate) causes are those that explain a structure or event in an individual organism. Ultimate (evolutionary) causes are those that explain the existence of a structure or capacity in all members of a species.4 Why does the firefly glow? The proximate causes are the environmental precipitants, and the sensory, neural, and chemical mechanisms that result in the flash of light. The question of ultimate cause may be answered only by explaining the evolutionary function of the capacity to glow, and the way that this capacity has increased survival or reproduction in the face of specific forces of natural selection.5 Psychiatry has been preoccupied with proximate explanations, and only rarely has considered ultimate explanations .69 “Why do people experience anxiety?’ The