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What is the Biological Model?

  • Definitions of abnormality are concerned with identifying what behaviours or symptoms are considered abnormal. This looks at how different approaches can help to explain abnormality.
  • The most widely respected model due to it's emphasis on scientific investigation and understanding. The Biological model suggests that mental illness is caused by underlying biological or physical factors including: structural abnormalities, bio-chemical imbalances and genetic predispositions. 


  • Similar to a disease, a physical cause: abnormal behaviour may be compared to a disease. It is assumed that all mental illnesses have a physiological cause related to the psysical structure and/or functioning of the brain. Organic disorders involve obvious physical brain damage and/or disease eg. a brain tumor. Functional disorders don't have an obvious physical cause, eg. depression.
  • Symptoms: in medicine, physical illnesses have clear-cut symptoms. Similar to doctors, psychiatrists use diagnostic manuals for mental illness and compare symptoms with classifications of illness. Brain scans can also be used to help with diagnosis, particularly with organic disorders.
  • Genetic inheritance: it is assumed that genes have a major effect on the likelihood of a person developing a mental illness. Twin and family resemblance studies have shown that some mental illnesses 'run in the family'. Kendler et al found that relatives of schizophrenics were 18 times more likely to develop the illnesses than a matched control group. Gurling et al performed a genetic linkage analysis in 13 large multiply affected families, to test the hypothesis that there is an exstensive genetic inheritence for schizophrenia. The 13 families contained multiple affected cases in three or more generations. DNA samples were taken from these families. They found strong evidence that certain chromosomes were linked to schizophrenia and that these are passed on through the generations.
  • Biochemistry: chemical imbalances in the brain may be involved in certain metal illnesses. Neurotransmitters are important in behaviour; an excess of dopamine has been detected in the brains of schizophrenics. These findings are correlations and don't prove cause and effect, eg. it might by the schizophrenia causing the dopamine rather than the other way round.
  • Infection: this is a common cause of physical illness, but has also been found with some mental illnesses. Barr et al found increased levels of schizophrenia among children of mothers who had suffered from flu while they were pregnant, suggesting a possible link with the disorder. 

Twin studies. 

  • Mcguffin - study based on 200 pairs of twins and found that when an identical twin (monozygetic) had depression, 46% concordance for the other twin, only 20% in non-identical (dizigetic) group. This supports the biological model because the monozygetic group was higher.
  • HOWEVER: twins are reared in the same environments so how do we know how much of concordance rates are down to biology and how much is down to environmental factors? Also, if it's just biological, then identical concordance should be 100%.

Evaluation points.

  • Inconclusive evidence - there is no evidence that mental disorders are purely caused by biology. Concordance rates


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