The role of the evolutionary approach in psychiatry
Authors: Riadh Abed, Martin Brüne, Daniel R. Wilson
Journal: World Psychiatry (2019)

Evolutionary psychiatry concerns the application of the principles of evolutionary biology to the understanding of mental health, psychological dysfunction, and mental disorder. It is neither a sub-specialty of psychiatry nor a separate field of clinical practice. However, as vulnerability to mental disorder has arisen through evolutionary processes, the whole of psychiatry (and medicine) benefits from being informed by evolutionary science. In one sense, therefore, all psychiatry is evolutionary, but some approaches are more explicitly so than others. Nevertheless, as the term has been in use for more than three decades, our WPA Section adopted it when it was set up in 2011. The aims of the WPA Section on Evolutionary Psychiatry include raising awareness of the importance of evolutionary biology to psychiatric theory and practice, and encouraging research into domains of psychiatry that can be meaningfully understood if viewed from an evolutionary perspective. These domains include, among the others, gene-environment interactions, ecological aspects, social interactions and nonverbal behaviour, and the interactions between the immune system, the microbiome, and the central nervous system. The Section also fosters cross-disciplinary networking with evolutionary scientists across a range of academic specialities as well as collaboration with national associations in the field existing around the world. Evolutionary psychiatrists call for the integration of the evolutionary perspective into psychiatric thinking, with the aim of supplementing and augmenting, rather than replacing, current mainstream psychiatric conceptualizations. To achieve this aim, our Section advocates for the inclusion of evolutionary biology as a basic science into both undergraduate medical education and psychiatric training curricula around the world. The evolutionary approach seeks to extend the concept of causation to incorporate phylogenetic (historical) as well as adaptational (functional) causes of mental disorders (referred to collectively as ultimate causes) alongside the proximate, mechanistic and developmental (ontogenetic) causes familiar to current mainstream psychiatry1. While the application of the principles of evolutionary biology to psychology and psychiatry was heralded by Bowlby's seminal work on attachment theory, this trend significantly gathered pace in recent years, evidenced by the publication of several textbooks in addition to numerous articles in peer-reviewed journals. A major insight of evolutionary thinking is the realization that selection shapes traits aimed primarily at reproductive success and not good health, happiness or longevity2. Hence, if negative emotions aided survival and reproductive success in the ancestral environment, they would have been selected for. It is safe to assume, for example, that humans in the ancestral environment who lacked the capacity for anxiety left either many fewer descendants or no descendants at all. The same logic may be applied to the capacity for low mood, although, compared to anxiety, the function of low mood remains less well-understood3. Hence, evolutionists would argue that any understanding of the human emotional system in both its functional and dysfunctional states will remain incomplete without asking crucial questions as to why most humans have the capacity for anxiety, low mood and psychic pain that can be activated under a range of predictable circumstances. The additional dimension of evolutionary or ultimate causation enables asking "why" questions alongside the "how" questions that are focused on proximate causes, and this enables the construction of more accurate and complete models of biological systems. The advantages of evolutionary science also include the fact that it offers a functional understanding of behaviour, provides a way to think clearly about developmental influences, proposes a functional approach to emotions and their regulation, and importantly provides a foundation for a scientific classification system2. Unlike existing classification systems that are either deliberately atheoretical or syndromal (ICD and DSM) or take a bottom-up biological approach (Research Domain Criteria), evolutionary approaches to classification tend to utilize high-level organizing principles derived from evolutionary insights regarding the adaptive significance of various brain systems, while remaining compatible with existing classification systems4. Importantly, an evolutionary approach to classification will prompt us to consider the functional significance of psychopathological signs and symptoms by comparing them with their evolved (adaptive) equivalents, alongside the current focus on symptomatology, candidate genes/biological markers and environmental risk factors5. We suggest that the neglect of evolution can result in equating distress with disorder, which runs the risk that some negative but functional emotional states be misclassified as pathological, with negative consequences for individual patients2, 6-8. Evolutionists strongly emphasize the importance of context, especially in mood and anxiety disorders. It may be argued that the reduced emphasis on context in current approaches to classification has been instrumental in the controversial removal of the bereavement exclusion in DSM-5, thus enabling a diagnosis of major depression disorder two weeks after a major loss. We are mindful, however, of the concerns that a greater emphasis on context can have a detrimental effect on inter-rater reliability of diagnostic categories. Aside from the various theoretical and research benefits of evolutionary science, we propose that there are also potential benefits to patients in applying evolutionary insights in clinical settings. We would argue that an understanding of the emotional functionality – why they exist, in addition to in-depth knowledge of signs and symptoms – can result in greater clinical efficacy. Examples of evolutionary models useful in clinical settings include the "smoke detector principle" in patients with anxiety disorders2 and the harm prevention model in patients with obsessive-compulsive disorder9. The WPA Section on Evolutionary Psychiatry has held a number of symposia at WPA conferences (Madrid, 2014; Cape Town, 2016), and some of its members have been involved in producing textbooks in both psychiatry and medicine as a whole, as well as publishing research and theoretical articles. The Section actively collaborates with the Evolutionary Psychiatry Special Interest Group of the UK Royal College of Psychiatrists.