Evolutionary psychiatry is the application of evolutionary theory to the study of mental illnesses. Evolutionary theory encompasses evolutionary biology, psychology and related disciplines. The principles of natural selection, sexual selection and group selection are used within these branches to explain how certain characteristics have developed in populations over time. Furthermore the unit of evolution is the gene which through mutation in successive generations codes for gene products with altered function. Typically it will be argued that when Gene X mutated, it conferred a certain advantage or fitness for the individual while at the same time resulting in an illness. Such is the advantage of the gene that it remains from one generation to the next despite the association with illness. Thus the explanations are of the form – this illness exists because of this mutation in Gene X which also results in Characteristic Y which is advantageous.
Where it starts to get even more interesting is in attempting to demarcate illness from health. One of the big questions that concerns psychiatrists drafting diagnostic manuals is where health ends and illness begins. Indeed there is also wider debate in society about this question which even emerges in health movements. One central arguments used against mental illness labels has focused on what is termed social constructivism in diagnostic formulation. In other words, some people critical of psychiatric diagnoses will argue that we choose diagnoses according to social convention. They will say that what we refer to in some cases is not an actual (biological) illness but rather it is a social construct – an agreement within society that certain behaviours or experiences are sufficiently different from those of the general population that with the use of an arbitrary threshold we can assign an illness label or else we can simply sanction certain behaviours altogether as illness behaviours.
In attempting to address these difficulties without being caught in the cycle of arguments about social conventions there is an interesting approach to investigating whether illness labels have a biological connection. This moves away from the approach discussed in the first paragraph and focuses instead on the languages of anthropology and primatology. I argue that these languages are better suited to answering these questions than the more constrained language used to describe the functions of genes at the molecular level whilst also holding validity. The areas of anthropology and primatology of relevance can be seen as extensions of evolutionary theory. In other words if we trace our ancestors back far enough we start to have common ancestors with living creatures. Our nearest living relative is the Chimpanzee although their ancestors diverged from ours some 8 million years ago (although the best estimates vary from time to time). However we need to accept the principles of selection in order to validate this understanding as well as to try to understand why we are now so different.
Having this tool allows us to look at our nearest relatives the Great Apes as well as the New and Old World Monkeys and ask what do we have in common? and what separates us? When we look at the question of what we have in common it enables a deeper understanding which can be absolutely relevant to the question of demarcating health and illness. If a critic questions an illness label, then they can use arguments along the lines of – the illness does not really exist and even though people manifest these behaviours then if we simply changed the description of the illness these people would no longer be ill. Statistical thresholds for experience or behaviour prevalence while helpful in forming an argument aren’t entirely convincing by themselves. Similarly the use of pharmacological explanations can be helpful but there might still be difficulties in linking neurotransmitter findings from research studies with phenomenology given the relative incompatibility of the descriptive languages.
However we may turn to our primate relatives and ask if certain behaviour are evident. Of course we do not readily have access to phenomenology but we do have the next reasonable alternative – observation of behaviours. If behaviours are frequently observed then they begin to take on a predictive quality and a language is developed as well as an implied understanding based on that language. We can then say do Chimpanzees have a well developed language or do they have a culture. Once we can begin to answer these questions with even a reasonable degree of success this inexorably leads to the next question of what happens when these functions are absent? It may be for instance that most of the Chimpanzees in a group engage in sharing of food in exchange for grooming for instance. Once such behaviours have been observed, research communities not have a language for describing altruism in these communities based on long term observations. Finally we can now see that if there are individuals that deviate from the general rules found within the community and where there are associated functional impairments do we have a basis for describing a mental illness? If such descriptions are on a firm foundation then we can then link this in with the bigger picture of how our primate relative relates to us in the evolutionary tree. We can start to meaningfully talk about evolutionary psychology – certain psychological functions which have been conserved over millions of years. We can then identify loss of these functions in individual humans and chimpanzees and argue more convincingly that we are looking not at a social construct but rather difficulties with a function which has been conserved over several million years.
There will no doubt be other benefits from the application of evolutionary psychiatry. What is evident is that the student of this approach can begin with an application to a specific question (has depression developed only in the Great Apes? and have the features of depression been observed in all of the Great Apes?) and utilise specific principles (e.g the principle of natural selection) in conjunction with empirical data (observations in the field) in attempting to answer that question. Many genomes have now been sequenced and they offer us the possibility of comparing small changes between genomes of humans and other living primates but also quite remarkably between modern humans and archaic humans. I have assembled here a number of resources on this blog related to the field of evolutionary psychiatry and will continue to add them as they become available.
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