Evolutionary Theory and Anorexia Nervosa

Anorexia nervosa (AN) is a difficult disease to explain, and therefore one difficult to treat. Increasingly, evolutionary theory is being used to attempt to explain phenomena that are inadequately explained through other frameworks. Nicholas Gatward, in his 2007 article “Anorexia Nervosa: An Evolutionary Puzzle,” outlines evolutionary explanations for the behavior that is archetypical of the disorder.

Typically, when biological/genetic causes are discovered for a behavior, we have reason to believe there is some evolutionary reason for that variation persisting, regardless of its current expression (adaptive vs. maladaptive) in an individual. AN seems to be strictly maladaptive in any context, but Gatward argues for mechanisms that could be adaptive that play a role in the development of this disease. He proposes three different explanations for the development and maintenance of AN: (1) Threat of Exclusion, (2) Threat of Starvation, and (3) Threat of Eating.

The threat of exclusion has roots in the importance of social relationships in our species. Throughout the majority of our evolutionary history, these relationships greatly improved the survival of those involved. If you were not able to cultivate and maintain bonds within your group, you could be shunned and you were much less likely to survive or reproduce. Competing for social resources with the same people you must be accepted by involves complicated assessment of the social climate in order to maintain balance. Social comparison  was, therefore, adaptive throughout much of our history. As social groups grew larger and hierarchies became more pronounced (early human groups were largely egalitarian), social comparisons revealed larger gaps and created greater dissonance within individuals. In our current cultural climate, thinness is seen as a sign of higher status, so restriction (and subsequent weight loss) allows individuals control over their perceived status.

The threat of starvation  provides an explanation for how individuals who begin dietary restriction can continue for such long periods of time when there should be evolutionary mechanisms driving the search for food instead of abstinence. The prevailing theory is that the mechanism that allows people suffering from AN to resist eating is the same mechanism that helped out ancestors deal with famine. Behaviors exhibited by people with AN such as “over activity, denial of starvation, and refusal to eat what limited food is available” are all components of adapted behaviors meant to get people to seek places with more food instead of conserving energy in a place of famine. Regardless of the original reason for restricting, the results activate this famine response and make long term starvation possible.

The threat of eating is another explanation for how starvation can be maintained and treatment attempts are largely unsuccessful. There are a couple different explanations within this category, but they both recognize AN behavior as a submissive response to social competition. First, it is believed that women of higher status use their influence to perpetuate the idea that thinness is desirable, resulting in the development of AN behavior in lower status individuals, therefore removing them from social competition. Second, AN could be a way for individuals to remove themselves from competition by suppressing reproduction, resulting in the removal of stress associated with competition. With this view, it is easy to see how recovery can seem unappealing if it means re-entering competition that individuals view as a losing battle.

These three explanations have their strengths and weaknesses. I find that the threat of exclusion and threat of starvation (adapted to flee famine) explanations are the most persuasive. They reflect current social climates and adequately explain how once adaptive mechanisms can be influenced by environmental factors to become maladaptive to the degree exhibited in those with AN. I especially like the “adapted to flee famine” example, because it exhibits how the ability to endure long periods of starvation is adaptive, contrary to how we normally think of evolutionary adaptations.

I think the threat of eating framework is a little harder to justify and therefore is his weakest argument. His examples are pulled from several different directions and I don’t feel that they are adequately synthesized. Particularly, the argument that AN is a result of higher status individuals perpetuation of thin-ideal in order to eliminate low status competition doesn’t really make sense to me. My own observations have seen AN as a “high class” disorder. Maybe I’m misunderstanding this argument, but I think Gatward’s lack of elaboration on this point is indicative that he doesn’t put as much stock in this explanation as the others.

Gatward does a good job of pointing readers in the direction of how these evolutionary explanations could be translated into individual causation of this disorder. I don’t think he quite hits the mark, but he does make a point of distinguishing ultimate and proximate explanations of behavioral phenomena. That is, evolutionary explanations are ultimate, meant to explain how AN behaviors were once adaptive. Proximate explanations, or those on an individual level, are best explained through other frameworks. I think we can understand proximate explanations better in the context of evolutionary theory, but we should not rely on solely on evolutionary theory when considering how to deal with this behavior individually.

Overall, I thought this article was informative and successful in getting me to think about AN outside of the psychological framework. It is easy to say that these disorders are a product of their environment, but stopping with that explanation is not very helpful when helping patients recover.

All information for this summary/review from:
Gatward, N. (2007). Anorexia Nervosa: An Evolutionary Puzzle.
European Eating Disorders Review, 15, 1-12.

One thought on “Evolutionary Theory and Anorexia Nervosa”

  1. Interesting article. I have read other articles on the idea that current disorders, or at least aspects of disorders, may have been at one time adaptive. I agree with you that the most persuasive argument presented is the threat of starvation. It definitely would have been adaptive to be able to resist eating in times of famine. I have also read articles suggesting that body image ideals of the elite are often copied, or sought to be copied, among lower socioeconomic groups, for example in Brazil, the girl from Ipanema body type.

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