Adoption studies compare the biological parents and the adoptive parents to the child for example to test for schizophrenia or bipolar.
Another cause for mental disorders according to the biological model is biochemistry. This is when there is a chemical imbalance in the brain. An example of this is low levels of serotonin can cause depression.
The third cause is brain damage. This can be either through disease or accident. An example is Alzheimer’s disease which is a form of dementia caused by the malformation and loss of cells in a number of areas of the nervous system.
The last cause of mental disorders according to the biological approach is infection. Bacteria or viruses can cause mental illnesses as well as physical illnesses. Infections can cause physical illnesses which have mental illnesses as symptoms. For example, liver disease can cause hallucinations.
The biological approach can be criticised for having a stigma attached to mental illnesses. Some people do not know how to interact with someone who has a mental illness as so they try to stay away from them as they think the person is dangerous or unpredictable. According to this approach, people with mental disorders are patients who are not in control of their disorder and therefore are not responsible for their own recovery. They are not responsible for their abnormal behaviour and so it is not their fault. They are more likely to be treated sympathetically by others and be in need of help rather than punishment. The biological approach is reductionist. It attempts to break things down to their most basic level. However, it is much more likely that psychological disorders are caused by the interaction of many factors.
Another approach which looks at the causes of abnormality in a different way to the biological approach is the behavioural approach. According to this approach all behaviour, normal or abnormal, is learnt. The process in which behaviour is learnt is known as conditioning. There are two main types of conditioning which are known as classical conditioning and operant conditioning.
Classical conditioning is learning through association. This is when we learn to associate an unconditioned stimulus with a conditioned stimulus. Phobias, such as going to the dentist, can develop in this way. The unconditioned stimulus would be the drill hitting the nerve which results in an unconditioned response of pair or fear. We would then associate the unconditioned stimulus with the condition stimulus which would be the sound of the drill. In the end, we would associate the sound of the drill with pain or fear.
Operant conditioning is learning through consequence. We learn through consequences of our behaviour by positive reinforcements where rewards are received for good behaviour and negative reinforcements where punishment is received for bad behaviour. Lack of positive reinforcement or an excess of negative reinforcement can explain an eating disorder like anorexia. A bully taunting someone about his or her weight is a punishment which could result in the person loosing weight. The positive reinforcement is the praise that person receives for loosing the weight and then they could end up wanting to loose even more weight but instead develop an eating disorder.
The social learning theory is learning by observing others. Someone could develop a phobia by learning from watching their own parents deal with a phobia they might suffer from and copy them.
The behavioural approach can be criticised by saying it is too simplistic as it only takes into account what can be observed and measured. It also ignores the underlying causes of a mental disorder as it only looks at what you can see. However, the behavioural approach is scientific because all the causes of mental disorders can be scientifically tested.
In the nature versus nurture debate the biological approach is nature and the behavioural approach is nurture. So therefore it is unlikely that abnormality is just due to one cause in isolation.