Evolution and Mental Disorders

Report from a Workshop led by

Martin Brüne, Professor of Psychiatry, University of Bochum, Germany

Alfonso Troisi, Professor of Psychopathology, University of Rome Tor Vergata

Workshop summary by rapporteur Daniel Stein, University of Capetown

One of five workshops in a conference on
Evolution and Diseases of Modern Environments
Organized by Randolph Nesse, at the Berlin Charité,  October 13-14, 2009
In conjunction with The World Health Summit
Sponsored by the Volkswagen Foundation

Participants in our group on mental disorders had a broad range of academic backgrounds, including psychiatry, psychology, medicine, evolutionary theory, genetics, epidemiology, economics, and philosophy.

The group aimed to follow a number of rules of engagement outlined at the start;  we were not merely nice about one another’s theories, nor were we simply oppositional, and we asked all to participants to contribute in roughly equal measure.

We attempted to address 6 questions:

–          Why is early environment so important in mental illness?

–          What better explains the relevance of gene-environment interactions/correlations for the etiology of mental illness:  Vulnerability or plasticity?

–          Has there been a genuine increase in prevalence rates of mental disorders, and if so, why?

–          There are large age and sex-related differences in prevalence of psychiatric disorders.  Are there evolutionary explanations?

–          What directions can evolutionary medicine suggest for psychiatric treatment?

–          What methodological changes can evolutionary medicine suggest for psychiatric research?

The first question, then, is why is early environment so important?

This question, however, raises additional questions eg “what is early?”, and “what is mental illness?”.  Michael Ruse called this later question “the elephant in the room”.  A key issue is that reproductive success (R/S) (a crucial outcome for evolutionary theory) is not the same as health.  We spent a good deal of time on the question of whether evolutionary theory could help define mental illness, and were unable to reach full consensus.  On the one hand, many argued that by helping to define the science of emotions and their dysregulation, evolutionary medicine could contribute to such a decision.  However, there was also a significant emphasis in the room that judgments of mental illness also entail social values that are a step removed from the concerns of evolutionary science.

In tackling the question of why early environment is so important, we noted that homo sapiens is characterized by a unique life history;  we have a particularly long developmental period, and this then creates many possibilities for dysfunction.  At the same time, our particular environment creates significant constraints, and we develop in an optimal way to cope optimally with these constraints.  Indeed, we also noted, in a way that is somewhat skeptical of conventional approaches to understanding pathology, that we should not simply think of humans as susceptible, like machines, to environmental stressors which cause breakdown.  In particular, there is tremendous resilience;  humans are typically able to respond to whatever environments we are in, in adaptive ways.

This immediately leads to the question of gene-enviroment interactions.  There have been significant advances in understanding the ways in which particular genes and particular environments interact to lead to subsequent psychopathology.  At the same time, there is much to learn;  multiple genes may have small effects, and not all data on G x E interactions have been replicated.  We noted that alleles can be risky vs healthy in different environments (eg, in an adaptive way) and that alleles are expressed differently in novel environments (eg, in a non-adaptive way).  Methodological problems include how to assess the extent of allele variation, and how to measure outcomes.  We agreed that where there are common genes and common disorders, then we must look a great deal to environments to help explain susceptibility to mental disorders.

From a skeptical point of view, the question was raised of to what extent research on gene-environment explanations of mental disorders was really part of evolutionary medicine.  One argument was put forward that all such work on genetic variation ultimately should be conceptualized as part of evolutionary medicine, insofar as it emphasized individual variation and its consequent trade-offs.  However, a counter-argument was made by some that in order for particular work to be a central component of evolutionary medicine one necessarily needed data on reproductive success, and this was typically not available in psychiatry.

We agreed that there was not a great deal of data on changes in prevalence of psychiatric disorders over time (eg we have little data on psychopathology in hunter-gatherer or other early populations).  Perhaps there has been an increase in the prevalence of autism, and there is certainly evidence for changes in the pattern of substance use over time.   Arguably anorexia is one disorder of modernity, having increased markedly in recent times in countries with western values and perceptions of beauty.  Internet disorders may be another disease of modernity.  The problem of determining whether there has been a change in prevalence of psychiatric disorders over time is compounded by the difficulty in defining boundaries of disorder.  While epidemiological data does not necessarily lead to a conclusion that psychiatric disorders are disorders of modernity, the universality of phenomena such as anxiety and depression are consistent with a perspective that highlights their adaptive value.

We noted gender and age differences in the prevalence of psychiatric disorders.  It seems clear that evolutionary explanations are important in understanding such differences (consider, for example, the different nature of sexual disorders in males – where so-called sexual addiction is more common, and in females – where anorgasmia is more common).    However, there are a range of different evolutionary theories about gender and age differences in psychiatric disorders, and deciding between them will require further work.  Also, we also acknowledged that more knowledge of proximal factors to explain gender and age differences, both biological and cultural, is needed.

There was again some disagreement on the question of what evolutionary medicine could offer in the way of psychiatric treatments.  There was clear agreement that evolutionary medicine offers a theoretical basis for understanding the role of emotions, of motivational structure, and of human cooperation and conflict.  There was also clear agreement that psychotherapy could be improved by a more integrative approach to understanding the doctor-patient relationship, behavioral ecology of symptoms (eg bereavement), functional analysis of behavior, goals/strategies of treatment.  It was also argued that an evolutionary medicine approach is useful in normalizing symptoms, and in enhancing empathy for patients.

However, there was disagreement about the extent to which a therapy was simply “evolutionary”.  For example, all good psychotherapies might draw on evolutionary principles (eg emphasizing the importance of the doctor-patient relationship).  In terms of medication, the argument was put forwards that evolutionary medicine could be particularly important in analyzing the trade-offs of treatment (eg pluses/minuses of SSRIs for depression).  However, a counter-argument is that treatments must be judged simply on the basis of the extent to which they are efficacious.  For DSM-V, it is not wholly clear how evolutionary medicine can contribute, although clearly DSM-V needs improvement.

In terms of future research informed by evolutionary medicine, several ideas were put forwards.  For example, we need to better research adaptive phenomena, defective phenomena, and their interaction.  We reviewed Nesse’s work on depressive symptoms, Badcock’s work on imprinting in autism/schizophrenia, Troisi and Brune’s work on non-verbal behavior, and their implications for future research in these areas.  We discussed recent work by Rook and colleagues, who have put forwards several ideas for future investigation of psychiatry-immune presentations.  Evolutionary medicine can help refine particular hypotheses in a range of different psychiatric areas.  Importantly, it provides, we thought, an integrative and rigorous framework for approaching problems – emphasizing the adaptive value of human variation, the complexity of interactions between people and their environments, and the pros and cons (trade-offs) of negative emotions.  Epidemiological studies need to include more sophisticated dimensional measures, and to perhaps to include intermediate functional behaviors.