An evolutionary approach to mental illness

16 December 2020

Towards the start of Good Reasons for Bad Feelings, Randolph M. Nesse cites a Science article from 2010 regarding the future of psychiatric research. The article’s authors – themselves eminent psychiatric researchers – assert (with some regret) that ‘there have been no major breakthroughs in the treatment of schizophrenia in the last 50 years and no major breakthroughs in the treatment of depression in the last 20 years’. While the claim might be up for debate, it is perhaps true to say that mental health research has not produced the seismic breakthroughs that might have been hoped for over the past few decades.

It is in this context that Nesse – co-author of Why We Get Sick, renowned professor of Psychiatry and Psychology, and founder of Evolutionary Medicine – poses a new sort of question: Why has evolution left humans so vulnerable to mental illness? At first glance, we might think it seems strange that human evolution would select for diseases such as schizophrenia or bipolar. To reason in this way, however, would be to commit an error which Nesse calls Viewing Diseases As Adaptations (VDAA). Indeed, it is not diseases themselves that are evolutionary adaptations, but the features of human beings that leave us vulnerable to such diseases. Such a realisation served as the launch pad for Nesse’s research.

For Nesse, the way in which we have traditionally viewed mental disorders is fundamentally flawed. In the realm of mental health – in contrast to that of physical health – we have a tendency to classify symptoms such as low mood and anxiety as disorders in themselves, regardless of the surrounding context that might be causing them. This error Nesse calls Viewing Symptoms as Diseases (VSAD). Indeed, far from disorders in themselves, such negative emotions are better viewed as responses that have been beneficial for the transmission of our genes.

The so-called Smoke Detector Principle provides one lens through which Nesse explains the evolutionary utility of suffering. According to this principle, our body’s ‘emergency response system’ is activated at any sign of potential danger. In evolutionary terms, a sensitive emergency response system was advantageous, enabling our ancestors to escape from hungry lions on the savannah. The cost of ‘false-alarms’ was clearly worth bearing at a time when one misplaced step might spell the end. Today, our environments tend to be rather different. And yet, modern-day anxiety disorders, characterised by ‘fight or flight’, are rooted in this same emergency response system.

In the case of depression, low mood conserves calories and circumvents risk, whereas high mood is costly and potentially dangerous. In the harsh and unpredictable world inhabited by our ancestors, the inhibiting effects of low mood could quite literally save your life – and your genes.

This book contains more questions than answers, and its novel approach to mental illness is one that warrants our attention as psychologists. Nesse’s warning against viewing symptoms as diseases shines a spotlight on the inherent pitfalls in the classification of mental disorders, whilst his onus on the utility of ‘negative’ feelings reminds us of the trade-offs that have been necessary to ensure our survival. It is hoped that, with such an evolutionary backdrop in place, we might begin to view mental illness through a broader, more all-encompassing lens.

- Reviewed by Ben Wethered, Trainee Psychological Wellbeing Practitioner, Westminster Talking Therapies