Modern psychiatry appears to be at a standstill, wanting for better treatment and a substantive theoretical framework. Evolutionary theory has the potential to reinvigorate the field.
Why do psychiatric conditions exist?
This question is both unsatisfyingly unanswered and incredibly important. Here we will consider some features of the over-century-long failure of psychiatry to explain mental disorders, before reviewing a theoretical framework which promises to explain these conditions in a way which is not only scientifically sound, but emancipating. The framework in question is evolutionary psychiatry, and its principle thinking is simple: if we use evolutionary theory to explain biology, then we should be using evolutionary theory to explain psychiatric disorder. If evolution was given proper attention and integrated into mainstream psychiatry, we would usher in a new era of understanding and treatment of psychiatric conditions.
Psychiatry is a practice with more than a chequered past, perpetrating horrors even in living memory: Sprees of lobotomising adults and children; purposefully inducing comas in schizophrenics, producing thrashing, spasming and salivating so bad that one psychiatrist reported the scene on a ward as alike to artist Gustave Dore’s depictions of hell; and the widespread demonisation of homosexuality justifying the electrocution and injection of homosexuals with nauseating drugs during slideshows of sexually attractive individuals of the same sex, hoping to train them into being sick at their own sexuality.
Advances in treatment over the decades have come more from the dismissal of old and harmful practices than the inception of new ones. As electrocution and nauseation were slowly recognised as both immoral and ineffective, we are now left with psychotherapies and pharmaceuticals of unreliable and underwhelming efficacy. Tens of billions of dollars and several decades of research have led to few new discoveries. Many drug developers have now left psychiatry for more easily understood and chemically pliable conditions of the body rather than the mind. Leaders in national mental health research have expressed dismay that so little progress has been made. Some research suggests that the burden of psychiatric illness might even be worsening, not lessening.
Psychiatric therapies have never been atheoretical – psychiatrists have always justified their treatments with some school of thought: Freudian psychodynamic theories placed blame on early childhood and subconscious urges; behaviourism justified the application of pain to try and train people out of wrongthink; and more recently, chemical imbalance theories were used to advertise pharmaceuticals, despite the narrative of simple dopamine and serotonin dysfunctions having been long dismissed in academic circles. Recent advances in genetics and neuroscience have provided more evidence and complexity, but no promising new theories. Psychiatry today can be considered a discipline in crisis, surviving only because psychological and pharmaceutical treatments are effective for some people, some of the time, and so we still need them. The way is open for a new paradigm in psychiatric theorising.
In the conclusion of his first edition of Origin of Species in 1859, Charles Darwin prophesied: “In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation. Light will be thrown on the origin of man and his history.”
Darwin’s prophecy manifested itself in psychology around 100 years after his writing. Now, evolutionary psychology has become a common reference point for public discussion and academic research. Evolutionary psychiatry is a late follower, arising in the last years of the twentieth century alongside evolutionary medicine, its foundational work owing to Randolph Nesse, George Williams, John Price, and others.
Evolution by natural selection is the metatheory of biology, linking all species and all biological forms. The process of constant biological variation, reproduction and selection between forms leads to evolution of populations, explaining the form of our bodies and minds. Therefore, the logic of evolutionary medicine and psychiatry goes, evolutionary theory should also be referred to in explaining why our bodies and minds are vulnerable to disorder and disease. All biology is evolutionary, and psychiatry is biological, hence psychiatry should be understood in evolutionary terms. The lack of progress in understanding psychiatric disorders makes sense in this light, because mainstream psychiatry has been ignoring the key theory in biology.
Whilst the fundamental principles of evolutionary psychiatry have been defined, and important works published, there does not yet exist a dedicated evolutionary psychiatry university department or journal. In 2016, the first noteworthy institutional group dedicated to evolutionary psychiatry was formed, in the Evolutionary Psychiatry Special Interest Group (EPSIG) at the Royal College of Psychiatrists in the UK. This slow start and long build up does not dissuade evolutionary psychiatrists from believing that, in the ever-less-distant future, this theoretical paradigm will be recognised as the way to truly start explaining mental disorder.
A unique advantage of evolutionary psychiatry is its ability to define disease and disorder upon an evolutionary concept of dysfunction. The current diagnostic and statistical manual of mental disorders (DSM), the handbook of the American Psychiatric Association (APA), defines mental disorder as dysfunction, but then fails to specify what that means. This allows transparently unscientific activities. Most famously, in 1973, after gay rights protestors had stormed an APA meeting, psychiatrists had donned anonymising hoods and professed their personal homosexuality to a group of their fellows, and national progressive values became a little too loud to ignore, the APA called a vote to reconsider homosexuality’s status as a mental disorder. By a 58% majority, it was struck off.
Voting to decide whether a condition is a disease is not the sign of a mature science, yet to this day consensus alone is the deciding factor of whether a mind is deemed disorderly. Commonly prescribed disorder labels in use today, such as Borderline Personality Disorder, included in the DSM-III because of the vote of a dozen or so psychiatrists, have criteria based primarily upon single review papers with poor empirical evidence from the 1970’s – even the authors of that paper expected it to be backed up with further evidence before becoming part of canon. In the most recent edition, the DSM-5, ‘internet gaming disorder’ was suggested, justified by comparing online (but specifically excluding offline) gaming to drug and gambling addictions. An international consortium has since voted clarifying its features. Evolutionary psychiatry can thankfully supersede this ambiguous line between order and disorder.
Unlike physics and chemistry, which describe things simply as they are, biological processes can be meaningfully considered to function or dysfunction. Biological traits evolved to increase reproductive success – that is their function. Eyes evolved to see, so eyes which cannot see are dysfunctional. Psychological and physical traits functioned to provide reproductive success to our ancestors, and where that function fails or is interrupted, there is dysfunction. Mental disorders can then be defined as harmful dysfunctions of the mind.
This analysis of function is inevitably historical (it concerns ancestral evolutionary function, not modern functioning) and so is difficult to ascertain in many cases, especially in psychology, and is complicated by the possibility of random processes of genetic drift. Nevertheless, this reference to evolutionary function is the only way to define function by an objective biological process rather than relying solely on subjective norms and cultural values – or indeed a vote.
This unique theoretical strength has been followed up by work in evolutionary medicine and psychiatry identifying six reasons why conditions we define as disorder or disease (of body or mind) persist in evolved creatures:
- Constraints on biological design, because evolution can only make alterations within a certain range.
- Pathogens evolve, so we cannot evolve perfect immunity against them.
- Design trade-offs and byproducts make perfection impossible.
- Evolved defenses against disease and danger often induce harmful symptoms.
- Selection is for reproductive success, not health, so we can evolve in ways which are debilitating if they allow us to reproduce more successfully.
- Mismatch between evolved systems and modern environments lead to novel, harmful, reactions.
Of these six reasons, it’s important to note that the last four are the modern result of functioning rather than dysfunctioning processes. The idea that natural selection would only encourage perfect health is mistaken. It’s entirely possible for evolution to lead our bodies and minds into states which we now diagnose and treat as disorders or diseases.
Work in evolutionary psychiatry has considered depression, anxiety, ADHD, OCD, eating disorders, substance use disorders, schizophrenia, psychopathy, and many more disorders through the evolutionary framework. Several can be explained as mental tendencies related to adaptations which were advantageous for our hunter-gatherer ancestors.
For instance, some are mismatched psychological systems which are exposed to over-stimulation in the modern environment, becoming the biggest causes of abuse, ruination and early death in developed countries. Alcoholism and drug abuse manipulate natural chemical pathways which exist for evolutionarily advantageous reasons; obesity by overeating is caused by natural desires for sweet and fatty foods; and gambling addiction is likely linked to a history of continuously searching for scarce high-calorie food and other risky but rewarding endeavours.
The fact that almost all psychological disorders exist on spectrums blending with normality is problematic for simple dysfunction explanations. Different etiologies within a single disorder label add complexity, which evolutionary psychiatry allows us to parse out. Take autism spectrum disorder (ASD) as an example, a topic of much public and academic conflict. Neurodiversity advocates argue that autism should be treated as a difference rather than a disease, conspiracy theorists blame vaccinations for sharp autism prevalence increases, and pseudoscientific doctors prescribe ‘cures’ involving the ingestion of heavy metals or bleach. Parents of autistic children are left confused and susceptible to misinformation, which can be linked to the vast width of the autism spectrum and lack of scientific consensus on autism’s explanation. Approaching autism from a systematic, evidence-based, evolutionary perspective could help bring an end to these controversies.
A diagnosis of ASD requires two co-occurring criteria: deficits in social communication and social interaction concurrent with restricted, repetitive patterns of behaviour, interests, or activities. However, these are loosely defined. Social deficits range from being entirely non-verbal to not being able to interpret facial expressions or understand sarcasm. Restricted behaviour could range from a special interest in trains in one individual, to another who persistently, uncontrollably bangs their head against walls and hard objects when upset. These wide individual differences have resulted in a mantra amongst the autistic community: “if you’ve met one person with autism, you’ve met one person with autism”. Nevertheless, evolutionary psychiatry can sort these differences into groups by either dysfunction or mismatched function and begin to make sense of the spectrum.
Investigating the most severely disabled autistic individuals you almost always discover damaging genetic mutations or early life trauma, such as foetal alcohol syndrome. These are clear cases of biological dysfunction. On the other hand, the less severely disabled individuals (who would once have been called Asperger’s or “high-functioning”) show none of those biological signs of dysfunction, instead showing evidence we expect from functional adaptations: the associated genes are common and complex, brain differences are subtle, the characteristics appear early in life when they are guaranteed to affect reproduction, and the prevalence is high enough that at least one person per Dunbar-sized hunter-gatherer social group of one hundred and fifty would show the same traits – in which case, every one of our ancestors would have known an autistic person. These biological signs are those we expect to see from adaptations, not dysfunction. The question we are led to ask is what autism’s function could have been.
Psychologically, autistics often show unusual abilities in intelligence, memory, and perception, especially in their areas of special interest or obsession. An anthropologist once stumbled upon a reindeer herder in Siberia who camped alone, ate alone and chose to keep away from the rest of their small nomadic group, but who could list the names, medical history, parentage and more of a group of 2,600 reindeer. Researchers have identified this as a possible case of an autistic mind playing a crucial role in a group’s survival. Technologies which played crucial roles in human civilisation’s birth such as oil lamps, multi-component tools, star maps, grinding stones and fire hearths have also all been suggested as the sorts of things which autistic people gravitate towards. Social oddities could be forgiven when your mind is spectacularly useful, so this ability profile explains why these cases of autism evolved. Autistic minds sacrificed social nuance as trade-offs in becoming the object and system specialists amongst our hunter-gatherer ancestors. Those same individuals can excel in technological and scientific endeavours in the modern world.
Notably, this story of function, only conceivable through an evolutionary perspective, is also supported by the biological evidence which shows all the physical signs of adaptation as opposed to dysfunction. This is not merely a matter of consensus or opinion – it is a matter of drawing inferences from the evidence we find in the physical world. Prominent autism researchers already remark that the breadth of the spectrum contains conditions which classify as diseases alongside those which classify as differences. Evolutionary psychiatry allows the introduction of evidence-based systematic methods to make these ideas more precise, and the reasoning more clear.
The mismatched adaptation theory of autism coincidentally aligns with socially important goals associated with the neurodiversity movement, which seeks autism and other common disorders to be seen as mere differences, defined by strengths rather than weaknesses. In the evolutionary theory, this can become not just socially appealing but scientifically correct: the collection of cognitive differences we diagnose as autism may have provided some kind of ability to our ancestors. Any deficits were worthwhile costs of these different cognitive profiles: the strengths literally caused autism, and so should be considered the defining feature of these cases.
Theoretical clarity does not necessarily make for treatment improvements, but one way in which explanations from evolutionary psychiatry could instantly improve lives, essentially free of financial cost, is through the alteration of stigma. The causal explanation of a disorder affects its stigmatisation. People believing chemical imbalance theories of depression feel more hopeless when diagnosed as depressed; people believing in genetic and neurological causes of psychosis are more stigmatising of psychotic individuals than people who believe psychosis results from stress. In turn, an evolutionary explanation of a disorder inevitably changes that disorder’s perception. The full effects of this shift in perception are yet to be seen, and will of course depend on the condition and specific explanation. Psychopathy, for example, may not be destigmatised by an explanation as a cheating strategy which is game theoretically optimal for some portion of a group.
A non-dysfunctional explanation of a disorder doesn’t imply that treatment isn’t required. Psychiatry has been defining disorder based on debilitation, meaning treatment is justified, even if the disorder is not biologically dysfunctional. The contraceptive pill and painkillers are some of modernity’s greatest medicines, notwithstanding the fact that ovulation and pain are naturally evolved functions. The introduction of evolutionary psychiatry doesn’t seek to deprive individuals of life improving drugs, and won’t change our values around who should be helped, but it will inevitably affect our perspective on how to help – examples include encouraging diagnosed individuals to make use of their experience to support others who are struggling, and adopting a drug-centred rather than disease-centred model of pharmaceuticals.
What does evolutionary psychiatry mean for the direction of research? For the last thirty or so years the great hope (and funding) of mental health research has been in neuroscience and genetics. Disease was assumed to be present, and the mission was to discover its underlying cause, just as we discover the virus causing the infection or the insulin deficiency causing the diabetes. This reflects an over-concentration on what evolutionarily minded researchers distinguish as proximate rather than ultimate causes.
Neuroscience can find brain differences associated with a disorder, but once a proximate brain difference is discovered, its existence still needs to be explained: that requires reference to the ultimate cause of evolution. Genetic research discovers genes that cause a propensity to mental disorder, yet the existence of those genes need to be explained in turn. These proximate causes are important, and can be used to furnish our evolutionary theories, but are never explanatory in themselves. Recognising the necessity of thinking through the lens of evolution, these fields can shift focus away from dead-end disease seeking. Neuroscientists can work specifically on identifying signs of true evolutionary dysfunction and geneticists can work on analytical techniques to discern trait selection histories. The theories which guide research on new treatments can begin without assuming there’s a specific dysfunction which needs to be targeted. Progress will be slow and steady, but will finally have turned to march in the right direction.
The fact that evolutionary psychiatry rests on the simple principle that if evolution explains biology, evolution can explain psychiatry, gives all believers in evolutionary psychiatry hope for the future. Evolutionary biologists have spent decades developing a theoretical basis which can now be used to explain mental disorder. Researchers in epidemiology, neuroscience and genetics have been gathering evidence which can now start to make sense. Thomas Kuhn noted that a scientific revolution takes place when the current paradigm is in crisis and a new, superior paradigm is proposed. Current psychiatry is that paradigm in crisis, and evolutionary psychiatry seems like the only suitable replacement. Theory in psychiatry can become coherent with theory in biology, and diagnostic handbooks can be written and rewritten because of new evidence, as opposed to changing consensus. Unlike any scientific paradigm shift before, this will have an immediate and tangible effect on human wellbeing. Decades of degrading mental health and fruitless theorising can be halted. In time, the money saved will be in the trillions and the people helped will be in the billions. If evolutionary psychiatry is given the attention it deserves, we could be tantalisingly close to that reality.