Wednesday, December 28, 2005

Mental Disorder, Creativity and Evolutionary Trade-offs: Just-So Story or Testable Hypothesis?

The circumstantial evidence begins to mount that what we call mental illness is in fact "too much of a good thing." In other words there is a fine line between physiological attributes of mental disorders that lead to behaviors we consider dysfunctional, and behavioral attributes that we generally define as "good" (i.e. "inventive," creative," or "perceptive"), but originate in the same physiological processes that are connected with mental illness. Below are quotes from reports on three recent studies that lead to this conclusion. Taken together these quotes are tempting to an evolutionary psychologist but I will argue that the temptation should be resisted. We should not completely dismiss speculation about these matters but we should keep clear the line between speculation, hypothesis, and theory.

Researchers at the Stanford University School of Medicine have shown for the first time that a sample of children who either have or are at high risk for bipolar disorder score higher on a creativity index than healthy children. The findings add to existing evidence that a link exists between mood disorders and creativity.
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Many scientists believe that a relationship exists between creativity and bipolar disorder, which was formerly called manic-depressive illness and is marked by dramatic shifts in a person's mood, energy and ability to function. Numerous studies have examined this link; several have shown that artists and writers may have two to three times more incidences of psychosis, mood disorders or suicide when compared with people in less creative professions. Children of bipolar parents score higher on creativity test


The more creative a person is, the more sexual partners they are likely to have...
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The lead author of the study, Dr Daniel Nettle (pictured), lecturer in psychology with Newcastle University’s School of Biology, suggested two key reasons for the findings. He said: “Creative people are often considered to be very attractive and get lots of attention as a result. They tend to be charismatic and produce art and poetry that grabs people’s interest.The lead author of the study, Dr Daniel Nettle (pictured), lecturer in psychology with Newcastle University’s School of Biology, suggested two key reasons for the findings. He said: “Creative people are often considered to be very attractive and get lots of attention as a result. They tend to be charismatic and produce art and poetry that grabs people’s interest.
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Dr Nettle added that the results suggested an evolutionary reason for why certain personality traits that serious artists and poets were found to share with schizophrenic patients perpetuated in society.
He added: “These personality traits can manifest themselves in negative ways, in that a person with them is likely to be prone to the shadows of full-blown mental illness such as depression and suicidal thoughts. This research shows there are positive reasons, such as their role in mate attraction and species survival, for why these characteristics are still around.”
Yet although some 'schizotypal' traits are linked with high numbers of partners, schizophrenic patients do not experience this level of sexual activity. These people tend to suffer from acute social withdrawal and emotional flatness - characteristics that the researchers found were linked with a reduced number of sexual partners.Creativity determines sexual success


(Also see the article in Nature - Write poems, get lucky - They may be badly paid, but artists have more sexual success by Tom Simonite.)


Surprisingly, people with mild depression are actually more tuned into the feelings of others than those who aren’t depressed, a team of Queen’s psychologists has discovered.

“This was quite unexpected because we tend to think that the opposite is true,” says lead researcher Kate Harkness. “For example, people with depression are more likely to have problems in a number of social areas.”

The researchers were so taken aback by the findings, they decided to replicate the study with another group of participants. The second study produced the same results: People with mild symptoms of depression pay more attention to details of their social environment than those who are not depressed.


The basic speculation among evolutionary psychologists is that "mental illness" is an evolutionary trade-off. The best example of an evolutionary trade-off is the sickle cell gene. Inheriting a sickle cell gene from a single parent promotes resistance to malaria. Inheriting a sickle cell gene from both parents causes anemia and death. In geographical regions of heavy malaria there is a trade off between resistance to malaria provided by the sickle cell gene and the possibility of death from sickle cell anemia - more people sexually reproduce if they have one sickle cell gene and they are able to resist malaria than if they have two sickle cell genes and die of anemia or no sickle cell genes and are not able to resist malaria. (For full explanations see the following links: The Mosquito and the Bottle. The Loom: -Carl Zimmer ; An Immune Basis for Malaria Protection by the Sickle Cell Trait; Malaria and the Human Genome - PDF.

Similarly, there are aspects of brain physiology that lead to creativity or the ability to perceive the world "realistically", or to perceive the social environment more empathetically, etc. These same aspects of brain physiology also are traits that are associated with various kinds of mental "illness," such as "manic-ness" and depression. If pushed beyond a tipping point these same aspects of brain physiology lead to dysfunctional mental breakdowns. The reproductive success and sexual attractiveness that rebounds to the person who is very creative or socially perceptive is offset by the possibility of dysfunctional (or non-functional) mental illness.

The problem with this line of reasoning is that it is a good story but as a story but it is as yet not a testable hypothesis. We can test the correlation between creativity and bipolar mental disorder in various ways, ranging from statistical studies to studies of the physiology of the brain. But I have yet to see a research program to test the hypothesis of evolutionary trade-offs in relation to mental illness. The hypothesis is a good beginning but too broad. I am very skeptical that an evolutionary theory of mental illness can be developed by focusing on human beings at the level of behavior. I think that the level where such hypotheses can be tested is at the physiological level or perhaps at the "modular" level of a mental system.

To illustrate the problem of the appropriate level of study it is only necessary to observe why we know so much about sickle cell anemia. We know the genes that must be inherited in order to produce sickle cell anemia and the shape of a human blood cell when the genes are inherited from both parents. Further, we know the shape of the cell when the gene for sickle cell is inherited from only one parent. We know the geographical spread of sickle cell anemia and we can calculate the differential between resistance to malaria provided by one gene and the possibility of inheriting two genes with the result of early death. In other words we have a good way of estimating the differential of reproductive success between a sickle cell population and a non-sickle cell population in geographical regions rife with malaria. We can trace this back to the physiological and genetic level.

The problem with this line of reasoning about mental disorders is that for the most part we are only beginning to learn what mental disorders are and how they exhibit themselves in behavior. The basic descriptive problems of defining mental illness are well known. But the descriptive problems in defining such vague notions as "creativity" or "inventiveness" are even greater. We know creativity when we see it, but that is about all. I am not saying that an evolutionary explanation of mental disorder is impossible only that at this point we must content ourselves with good hints and interesting stories. Turning a just-so story into a testable hypothesis is the hardest part of any scientific project.


New York City
2 December 2005

Selected by
See Tangled Bank #43 @ Rural Rambles


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