Why search for evolutionary explanations for mental disorder?

"Nothing in biology makes sense except in the light of evolution".

(Theodosius Dobzhansky, 1973).

"Most of medical & psychiatric research explore the proximate explanation for why human biology goes wrong ... on the anatomical, physiological, biochemical & genetic levels. These explanations explain "what" & "how" questions about origins & functions. Most research seeks proximate explanations about how some part of the body works or how a disease disrupts this function. The questions as to what things are for & how they got there has been neglected in medicine. An evolutionary explanation is about why the DNA specifies the trait in the first place & why we have DNA that encodes for one kind of structure & not some other. An evolutionary approach to illness & disease studies not the evolution of the disease but the design characteristics that make us susceptible to the disease. The apparent flaws in the body's design, like everything else in nature, can only be understood with evolutionary as well as proximate explanations. Evolutionary hypotheses predict what to expect in proximate mechanisms. Trying to determine the evolutionary origins of illness & disease is more than a fascinating intellectual pursuit; it is a vital yet underused tool in our quest to understand, prevent & treat illness."

(Nesse & Williams, 1996).

"As Tinbergen pointed out so clearly, a complete biological explanation has four components: (1) mechanism, (2) development, (3) function, and (4) phylogeny. Together, mechanism and development offer a complete proximate explanation, but they cannot explain why a trait or mechanism is in the way it is. That requires an evolutionary explanation. A complete evolutionary explanation is as elusive as a complete proximate explanation because it would require knowing (1) the precursor trait, (2) its minor variations, (3) the genes responsible for those variations, (4) how those variations increased or decreased fitness in response to the selective forces of earlier environments, and (5) the random effects of drift and other chance factors. A partial explanation is usually possible, however, based on what we know about ancestral traits, comparative data, and about the selection forces that are likely to have shaped the observed trait. Testing these explanations requires methods different from those used for proximate studies; so misunderstanding is easy. Probably the most common and serious misunderstanding, however, is the failure to recognize that both evolutionary and proximate explanations are needed, and that they are not competitors, but two halves of a whole."

(Nesse RM, 1999)

"... an evolutionary view already offers an extraordinarily useful guide for understanding our patients. Even our crude state of knowledge takes us a giant leap from the idiosyncratic theories without biological foundation that have characterized much of the history of psychology. Furthermore, the age-old problem of “normality” makes much more sense in an evolutionary perspective. From a perspective of reproductive success, many emotions, cognitions, and behaviors patterns that have been thought of as pathological can be recognized as adaptive, even if often distressing or socially prohibited. And for some of these, like anxiety, it is clinically useful to explain their functions to patients. When people who experience panic attacks learn that their symptoms are the normal fight-flight response that is going off at the wrong time, this often helps them give up their fears that the symptoms are caused by heart or brain disease. These principles are likely to have early application as a foundation for a revised perspective on psychiatric diagnosis. The successive Diagnostic and Statistical manuals published by the American Psychiatric Association have been essential in allowing researchers to study comparable groups, but they have also been widely criticized because they lack a foundation in theory and they encourage simplistic thinking of psychiatric syndromes as discrete diseases (Kendell, 1984). An evolutionary view, by contrast, requires us to use what we know about the emotions and their regulation and thus to distinguish several categories of mental disorders. First, there are conditions that are painful and perhaps undesirable, but normal and evolutionarily useful, like much jealousy, anxiety and sadness. Second, there are conditions that arise from an initially normal brain that has been exposed to learning or trauma that leads to emotional pathology or maladaptive behavior. Third, there are conditions, like most depression and panic disorder, that arise from dysregulation caused by genetic vulnerability interacting with environmental factors. Fourth, there are conditions that arise from primary abnormalities of brain tissue, like obsessive-compulsive disorder, schizophrenia, and Alzheimer’s disease. In contrast to current diagnostic systems that encourage separation of a patient’s difficulties into many “co-morbid” conditions, an evolutionary approach fosters exploration of all the factors that interact to account for a person’s emotional and behavioral difficulties. Finally, the greatest current value of a Darwinian perspective on psychiatry is its heuristic utility. Without an evolutionary perspective, Daly and Wilson never would have asked about the frequency of child abuse in families with a step-parent present. Without an evolutionary perspective, it is far harder to even imagine the possible benefits of anxiety, sadness, and grief. Without an evolutionary perspective, it is hard to ask the right questions about the functional significance of various aspects of human nature, adaptive and maladaptive."

(Nesse R, 1999)

What Evolutionary Psychiatry searches for:

A theory of behaviour & motivations & function

…explaining why people behave as they do in ordered & disordered states

A theory of environment-behaviour-gene interactions

A theory of traits & capacities & their uses

Causal hypotheses

Integration of prevailing causal models

A framework

improved classification system

The meaning of life...

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Citation suggestion: Dr Gary Galambos, Why, Evolutionary Psychiatry Interest Group Sydney Australia (http://www.ep.org.au/why.htm) [date accessed]

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