When we want to know more about abnormal behaviour, we can focus on its causes. Abnormal behaviour is construed from a number of different perspectives. I will tell you more about different aspects of a multi-faceted group of mental disorders in the following models. Biological and genetic models assert that mental disorders are diseases, and symptoms of mental disorders are caused by factors such as brain defects (abnormalities in the structures of the brain), biochemical imbalances (complex dysregulation processes involving various neurotransmitters) and genetic predispositions (risk for psychopathology carried via our genetic material). By and large, the evidence for brain defects and biochemical imbalances as causes of mental disorders is correlational, which means that, although we know that such biological problems occur among people with mental disorders, we don’t know whether they actually cause the disorder. Because the brain is a fairly malleable organ, our behaviour and experiences can also affect our brain functioning, suggesting that the association between biology and abnormal behaviour may be reciprocal rather than unidirectional. Genetic models of mental disorder suggest that psychopathology is inherited from parents, and there is certainly evidence for the familial transmission of many disorders. For example, monozygotic (identical) twins should be more likely than dizygotic (fraternal) twins to have the same disorder because they share 100 per cent of their genetic material, whereas dizygotic twins share only 50 per cent. For many disorders, this is exactly what research shows. But given that monozygotic twins share 100 per cent of their genetic material, you might expect them to have the same disorders 100 per cent of the time. But in fact they have the same disorders only about 50 per cent of the time. These findings have led researchers to conclude that, rather than being deterministic, genetics contributes about 50 per cent of the risk for...