Gottesman and Shields carried out an experiment to investigate the relationship between genetic make-up and schizophrenia. They used both identical and fraternal twins where at least one of the twin pair had been hospitalised and diagnosed with schizophrenia. The rate of schizophrenia in fraternal twins of schizophrenics was lower than for identical twins, but was still higher than in the general public. Therefore, the results suggest that there is a genetic component in the cause of schizophrenia.
A weakness of this study would be that it is likely that the shared environmental settings between the twins might have affected their behaviour. However, this kind of research has lead to the production of very successful treatments that can help control the symptoms.
Twins have also been used to investigate whether genes have an effect on behaviour. Psychologists compare the concordance rates between identical twins. The concordance rates are than compared between Monozygotic and Dizygotic twins. It is possible to see if there is a genetic cause because MZ twins share more genes in common than DZ twins. However, both set of twins share the same environment, so there is a possibility that similarities in behaviour may be due to environmental factors and not genes. Psychologists would often use twins separated at birth/ childhood in order to separate the nature and nurture effects on behaviour.
However, even twins separated at birth would have shared the same pre-natal environment in the womb for duration of 9 months. This could account for some similarities in behaviour. Also, the number of twins reared apart is minimal, so sample sizes are small and it may be difficult to generalise the results and participants are usually volunteers and they be very different to those who would not volunteer.
Surgery has also been used to disable parts of the brain to see how this affects behaviour, which is known as lesion studies. Modern studies can now and try to ensure that any damage to the brain is not permanent.
Animals have been used a lot in lesion studies, where damage to the brain to the brain caused and the resulting change in behaviour is measured. Damage to the brain is could be done by surgically cutting or burning away a part of the brain, or by using drugs and other techniques to shut off parts of the brain temporarily. The animals with damaged brains will then be compared with a control group containing animals with fully-functioning brains.
Advantages of using animals are: they are easier to monitor during research than humans; large samples can usually be bred in a short period and animals are more likely to be naïve participants which results in a higher validity as there will be less chance of demand characteristics. However, disadvantages of using animals are that they might be more expensive as only the highest level of care is acceptable, whereas humans can go home and look after themselves. Also, human have different brains to animals, so any change in behaviour in animals might not necessarily mean that humans will behave in the same way.
