The crisis of psychiatry — insights and prospects from evolutionary theory

Darwin’s emphasis on natural selection has had a transformative influence on how biological and medical sciences are conceptualized and conducted. However, the relevance of his ideas for the understanding of psychiatric conditions is still under-appreciated. Modern understanding of disease has required appreciation of the dialectical give and take between environmental influences, life history theory imperatives, human behavioral ecology, and characteristics of adaptive processes at all levels of the individual. This has enabled a better comprehension of metabolic disturbances, cancers, auto-immune disease, inherited anemias, and vulnerability to infectious disease 1. Here we propose that a contemporary and scientifically satisfying understanding of psychiatric conditions requires adopting a similar logic of inquiry, by taking into consideration the influence of environmental contingencies and natural selection in sculpting not just brain based mechanisms and processes germane to clinical neurosciences, but also diverse characteristics of behavior. One approach to understand psychiatric disorders in an evolutionary perspective builds upon Nobel laureate Nikolaas Tinbergen’s ideas, suggesting that, for a full understanding of any given phenotypic trait, one needs to detect the development and nature of its mechanisms, construed as the “proximate causes”, and, in addition, its evolutionary (or phylogenetic) history and adaptive value 2. Studying the proximate mechanisms is standard in psychiatry and the clinical neurosciences, but the questions pertaining to the phylogeny of traits have largely been ignored. Admittedly, placing dysfunctional cognitive, emotional and behavioral processes in the context of possible adaptation is not straightforward at first sight. The clinical directive requires that “disorder” represent the appropriate focus. However, a “disorder” – by definition – is counter-intuitive in the context of adaptation. By adaptation we mean a genetically-mediated structural or behavioral trait, which when possessed, increased survival and reproductive success in the environment in which the trait evolved. Were psychiatry’s focus be placed on “traits” (i.e., cognitive processes, emotions, and behaviors), problems which are clinically relevant could more satisfactorily be understood as distorted expression of mechanisms that in earlier environments provided answers to problems of adaptive significance, but which currently interfere in light of prevailing environmental contingencies 3. Important to the understanding of a particular phenotype is the evolutionary concept of variation. Without variation, no evolution by natural selection could take place. Mainstream psychiatry has largely ignored the fact that variation is the rule, not the exception, and this creates conceptual tensions. Psychiatry conceptualizes “disorder” as a statistical deviation from a normative statistical mean, yet handles it as a category. In other words, both “normalcy” as well as “disorder” with regard to psychological or behavioral functioning are burdened with the connotation of low variation. Phenotypic variation is the result of a complex interplay of genotype and environment, including epigenetic mechanisms that are decisively shaped by experience over the individual lifespan. These issues translate to providing a clinician with a rationale for explaining why, how, and when adaptive behavior is compromised and constrained; that is, when social, cultural, or ecological conditions and circumstances pose hindrances or risks which interfere with achievement of best solutions to socio-biological problems, and which may require a modification of a strategy of coping, selection of an alternative strategy, and/or the setting of more realistic biological goals. This integrative view of psychopathology, we believe, can have profound effects on how psychiatry conceptualizes disorders, which shall be illustrated briefly in three examples.