free will and determinism

• A problem with both genetic and environmental determinism is that neither can be the sole determining factor in behaviour. studies that compare identical twins find about 80% similarity on intelligence or about 40% for depression. In other words, if one twin has a high IQ, there is only an 80% chance that the other twin will be the same. Therefore genes do not entirely determine behaviour. But equally the environment doesn't entirely determine behaviour.This means that an interactionist rather than a determinist approach better represents reality.
• Argued that there is no such thing as total determinism. Very small changes in initial conditions can result in major changes, sometimes called 'the butterfly effect. The conclusion is that causal relationships are probabilistic rather than determinist. Determinist explanations tend to oversimplify human behaviour. They may be appropriate for non-human animals but human behaviour is less rigid and influenced by many factors, including cognitive factors as well as biological impulses. This means finding a simple determinist formula from psychological research is unrealistic.
• There have been attempts for criminals to claim their behaviour was determined and therefore they should not be punished. Determinism is also an issue in the treatment of mental disorder. If we take the view that disorders such as schizophrenia and depression are determined then it follows that treatment should target their genes or neurotransmitters. However, this may ignore other reasons and so other treatments that might be beneficial, like CBT. Therefore, a determinist position allows individuals to 'excuse' their behaviour and also restrict options for the treatment of mental disorders 
• Being able to decide between different courses of action is not free will, but it may give us the illusion of having free will. Skinner argued this and said a person might 'choose' to buy a car or see a film, but these choices are determined by previous reinforcement experiences. Furthermore, the idea of self-determination may be a culturally relative concept, appropriate for individualist societies only. Collectivist cultures place greater value on behaviour determined by group needs.This suggests that free will is a product of socialisation and not something 'real!
• Separating nature and nurture is not possible. It was argued this was the same as asking whether the length or width of a rectangle was more important when working out the area of a rectangle. Both contribute. Such as a disorder that prevents amino acid being metabolised, resulting in brain damage. If the condition is detected at birth, an infant can be given a diet which averts the brain damage. If prevention can be achieved through environmental manipulation, is this condition due to nature or nurture?This highlights the importance of an interactionist approach.
• The diathesis-stress model offers a way to understand nature and nurture.This is often used to explain mental disorders such as phobia or schizophrenia. A diathesis is a biological vulnerability. However, research has shown that not everyone with those genes does develop the disorder. Expression of the gene or genes depends on experience in the form of a 'stressor which triggers the condition. Thus a person's nature is only expressed under certain conditions of nurture.This again emphasises the importance of taking an interactionist approach.
• Genes may have an indirect effect. A child who is genetically more aggressive might provoke an aggressive response in others. This response becomes part of the child's environment and affects the child's development. This is called reactive gene environment interaction because the child is reacting to genetically influenced behaviour. This highlights how nature can indirectly actually affect nurture in different ways.
• neural plasticity has taught you how life experiences shape your biology- that is, how nurture affects nature.For example, Maguire et al!'s (2000) study of London taxi drivers showed that the region of their brains associated with spatial memory was bigger than in controls. The taxi drivers were not born this way; rather, their hippocampi had responded to increased use. This example give a clear demonstration of how nurture can affect nature.