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Applying Evolutionary Theory to Psychiatry

Our emotions are the result of hundreds of thousands of years of evolutionary pressure and have been described as “Darwinian algorithms of the mind” by evolutionary scientists John Tooby and Leda Cosmides. Though emotions have likely evolved to serve specific adaptive purposes, there are currently several psychiatric diagnoses identifying what is presumed to be ‘pathological’ emotion states such as generalized anxiety disorder (GAD) in the case of excessive anxiety, or major depressive disorder (MDD) in the case of excessive sadness or apathy.

Rather than being pathological, these emotional states could in fact be somewhat adaptive if looked at through an evolutionary lens, as physician Randolph Nesse and evolutionary biologist George Williams argue in their book, “Why We Get Sick: The New Science of Darwinian Medicine.”

Let us take the case of anxiety. Anxiety has likely evolved to keep us away from dangerous situations, and to activate cognition and behaviors to help us escape from dangerous situations we find ourselves in. Nesse and Williams mention “the berry picker who does not flee a grizzly bear” and “the fisherman who sails off alone into a winter storm” (p. 212) to illustrate examples where anxiety is crucial to our survival.

It would then seem that high, constant levels of anxiety would lead to the greatest evolutionary fitness, as individuals always aware of and ready to flee from dangerous situations would have highest rates of survival. Though for the individual it may not be pleasant to constantly experience high levels of anxiety, as Nesse and Williams eloquently and bluntly phrase it, “natural selection cares only about our fitness, not our comfort” (p. 212).

The reason why all of us do not experience high levels of anxiety constantly is explained by its biological costs. The ‘fight or flight’ response associated with anxiety is calorically expensive, which in turn allows less energy expenditure for other processes. Furthermore, a large body of work has suggested negative effects of chronic stress on the body and on the mind. Thus, though perpetual high levels of anxiety would indeed help us guard ourselves from danger, the costs of doing so may be substantial enough as to negate the potential benefits.

The levels of anxiety that have been labeled as pathological have been designated as such by mental health professionals and not by evolutionary scientists, leading to potential differences in the ways physicians and evolutionary thinkers would classify pathological emotion. Large, empirical studies have not been conducted to determine whether individuals diagnosed with GAD actually have lower fitness as compared to individuals without a diagnosis.

Interestingly, looking on the other side of the anxiety spectrum, anecdotal evidence suggests that too little anxiety may jeopardize an individual’s fitness and survival. Such individuals are often unable to accurately assess potential dangers, and more frequently end up in socially and physically undesirable situations. However, there is currently no psychiatric diagnosis for this end of the anxiety spectrum, despite it being the end of the spectrum that may be ultimately more detrimental to the individual.

Throughout their chapter on mental disorders and throughout the rest of the book, Nesse and Williams stress the potential utility of evolutionary theory across a wide range of fields in medicine (see this previous AEPS post on Nesse’s contributions to cancer biology). Before jumping to disrupt a certain natural biological process or emotional/cognitive state, it is important to remain cognizant that such processes and states have been crafted to increase our genetic fitness, and that in some cases, we may perhaps be best off letting the “Darwinian algorithms of the mind” and body run their course.