Biological Explanation for Anorexia Nervosa Essay

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Biological Explanation for Anorexia Nervosa Evidence for a faulty gene.

AIMS:

to see if concordance rates for anorexia are higher in MZ twins compared to DZ twins. This would provide evidence for a faulty gene causing the disorder because if one MZ twin develops anorexia, there should be 100% concordance (agreement) with the second MZ twin also suffering from it, since they share the same genes. The rates for DZ twins should be much lower because they share only 50% same genes.

PROCEDURE:

· Natural experiment: because the IV (genetic relatedness) occurs naturally and cannot be changed by the investigator. Longitudonal
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Alternatively, a faulty gene may still be present in the non-sufferers, leaving them vulnerable to developing the disorder, but it does not develop unless some other factor triggers it eg. a stressful life event.

CRITICISMS:

· Environmental factors have been ignored. MZ twins share very similar environments (eg. same home, schools, treated similarly by parents etc) and this could explain the higher concordance compared to DZ twins who may not be treated so similarly. Since 100% concordance was not found, a faulty gene may make the person vulnerable but some kind of environmental factor is needed for the disorder to develop eg. stress.

· Over-simplistic and reductionist (using a simpler biological explanation to explain a complex behaviour). The fact that it is difficult to separate nurture (environmental factors) from nature (genes) shows that the evidence is not strong enough for a purely genetic explanation

· Natural experiments lack experimenter control over variables eg. the IV (genetic relatedness) could not be isolated from other (possibly confounding) uncontrolled variables eg. environmental experiences, socio-economic backgrounds (class factors). This means that internal validity was low (factors other than the IV may have caused anorexia). At best, that data has shown
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