Discuss Biological Explanations of Anorexia Nervosa

There are three biological explanations of A.N; evolutionary, genetic and neurobiological. The evolutionary explanation focuses on the adapted to flee hypothesis. Guisinger (03) suggested that Anorexia served an adaptive purpose in the environment of evolutionary adaption. He explains that levels of restlessness, traits that characterise anorexia, would have been adaptive during times in which food supplies were exhausted, as hunter-gatherers had to find new sources of food. Therefore high levels of activity and denial of hunger would have promoted migration in response to famine.

Alternatively, a general evolutionary explanation would suggest that the behavioural component of Anorexia Nervosa could have been adaptive, particularly in females, as the ability to refrain from eating could have promoted the survival of one’s social group during times of famine. It is assumed that people evolved from hunter/gatherer societies, in which females would be responsible for gathering; the avoidance of eating would be a useful trait for the larger group as more food would be gathered rather than consumed. This would promote survival of the collective group, which would provide more safety for its individual members and so the trait would be passed onto further generations.

The Genetic explanation of Anorexia Nervosa suggests that anorexia is genetically transmitted through generations. Based upon research into the topic it appears that individuals that have a relative with anorexia have an increased risk of developing the disorder themselves, which would suggest that anorexia is not directly inherited as many physical attributes are but that a predisposition to Anorexia is inherited. The use of twin studies allows researches to establish the relative contribution of genetics and environmental factors, as MZ twins are genetically identical while DZ twins are only genetically similar. Given the fact that both twin sets share an environment it is assumed to mean that this is controlled with any differences in proneness to Anorexia Nervosa being attributed to genetics.

Lastly, the Neurobiological hypotheses, developed more recently suggests that abnormalities in CNS serotonin function may play a role in the development and persistence of the anorexia nervosa. Studies of long-term weight-recovered patients have revealed increased serotonin activity, such as elevated levels of serotonin metabolite 5-hydroxyindoleactic acid in the CFS and reduced binding potential of receptors, suggestive of higher levels of circulating CNS serotonin, in several brain regions (metabolites are by-products of metabolism that can be assessed infer neurotransmitter activity). Kaye et al. hypothesise that individual with anorexia nervosa may have a trait disturbance characterised by high levels of CNS serotoninergic activity leading to symptoms of anxiety that are relieved by dieting, which leads to a reduction in serotonin production.

Due to the fact the evolutionary explanation is speculative there is a complete lack of evidence to support it; it is near impossible to prove. It could be argued that if this trait were still an adaptive advantage and it was the sole explanation for anorexia then everyone should develop anorexia. As it stands, anorexia is not a hugely common disease. In addition, rates of anorexia have increased. The National Center for Biotechnology Information stated “An upward trend has been observed in the incidence of anorexia nervosa in the past century till the 1970s. The most substantial increase was among females aged 15-24 years, for whom a significant increase was observed from 1935 to 1999.” It could be argued that the evolutionary explanation cannot account for this increase in rates of anorexia. Due to the fact the evolutionary explanation of Anorexia cannot be supported by research this explanation therefore has no practical applications. Even if it could be proved, this explanation is revolved around evolution, a process over which humans can exert no real control. Therefore, there would be no obvious steps that could be taken to try and prevent these anorexic traits from being passed on.

Research into genetics and neurobiology are conventionally scientific as research is replicable and investigates working hypotheses with quantitative data. This can be contrasted with the evolutionary explanation, as this cannot provide research, which therefore cannot be replicated, and the hypothesis cannot be falsified. This means that the evolutionary explanation cannot be considered as scientific according to popper’s conceptualisation of science. However it should be considered that anorexia is clearly a complex disease that does not readily lend itself to investigations, which yield quantitative data.

There are studies to support the genetic explanation of anorexia nervosa. Holland et al offers strong support for the idea that a person may have a genetic predisposition for anorexia. The findings showed concordance rates of 55% in MZ twins and 7% in DZ twins. This demonstrated a dramatic increase in the chances of getting anorexia in twins with a higher percentage of shared genes. Yet, there are a number of problems with such research. Both MZ and DZ twins share experiences as well as genes so similarities, such as both having anorexia, are not necessarily exclusively genetic. Taking this idea further, MZ twins are likely to be treated more similarly than DZ twins due to their appearance. Therefore this could lead to results that are distorted due to self-fulfilling prophecy as MZ twins would live up to the expectation placed upon both of them. Focussing on Holland’s research specifically, the small sample size used would severely decrease its population validity.

Holland’s study introduces the idea that the biological explanations of anorexia nervosa are reductionist. With a concordance rate of only 55% with twins whose genes are identical it is clear there are other factors involved, else the concordance rate would be 100%. It is not just the genetic explanation of anorexia that takes a narrow explanatory focus. All three biological explanations focus solely on one casual factor and consequently overlook other potential important factors, which ultimately leads to an oversimplified account of anorexia. There is evidence to support the fact that there are other important factors involved with anorexia. Research by Button et al (96) supports the cognitive explanation, as those girls rated as having low self-esteem at 11/12 years were more likely to develop an eating disorder at 15/16 years. Button’s findings indicate that a person’s perceived worth/abilities, which are sometimes irrational, influence the probability of anorexia. Button’s research therefore supports the idea that the biological explanations are reductionist because they clearly all overlook other important factors such as cognition.