Issues & Debates: Evaluating the Nature-Nurture Debate - Interactionist Approach

Recently psychologists have begun to question whether human behaviour is due to heredity factors (nature) or the environment (nurture). It is now widely accepted that heredity and the environment do not act independently and both nature and nurture are essential for almost all behaviour. Therefore, instead of defending extreme nativist or environmentalist views, most researchers are now interested in investigating the ways in which nature and nurture interact. The interactionist approach is the view that both nature and nurture work together to shape human behaviour.

The interactionist approach is best illustrated by the genetic disorder PKU (phenylketonuria). PKU is caused by the inheritance of two recessive genes, one from each parent. People with PKU are unable to break down the amino acid phenylalanine which builds up in the blood and brain causing mental retardation. However, if the child is diagnosed early, they are placed on a low protein diet for the first 12 years, which helps to avert this potentially lifelong disorder. Therefore, the disorder PKU (nature) is not expressed, because of an altered environment (low protein diet – nurture).

In psychopathology, many psychologists argue that both a genetic predisposition and an appropriate environmental trigger are required for a psychological disorder to develop; this is set out in the diathesis-stress model. The diathesis is the biological vulnerability such as being born with a gene that predisposes you to develop a disorder. However, the disorder will only develop if there is an environmental ‘stressor’ to trigger it. Evidence to support the diathesis-stress model comes from the Finnish Adoption Study w which compared 155 adopted children whose biological mothers had schizophrenia, with a matched group of children with no family history of schizophrenia. The researchers also assessed the quality of parenting through questionnaires and interviews. They found that the group with schizophrenic mothers had a 10% rate of schizophrenia, but they also discovered that all of the reported cases of schizophrenia occurred in families rated as ‘disturbed’. When the family environment was rated as ‘healthy’, even in the high-risk sample (mother with Schizophrenia), the occurrence of schizophrenia was well below the general population rates. However, the environment was not the sole cause, as the low-risk children from ‘disturbed’ families did not develop Schizophrenia – so the environment alone was not enough to trigger the disorder. This research provides strong evidence that schizophrenia is best explained by looking at an interaction between genetic inheritance and environmental triggers, in this case, family environment.

Neural plasticity is another example of how nature and nurture interact. The brain can reorganise itself by forming new neural connections throughout life. Neuroplasticity is a term which describes the changes in the structure of the brain (nature), as a result of life experience (nurture). For example, Maguire et al. (2000) investigated the hippocampi volume of London taxi drivers’ brains. She found that this region of the brain was larger in taxi drivers in comparison to non-taxi drivers. Consequently, Maguire concluded that driving a taxi (nurture) actually had an effect on the size of the hippocampi (nature).

Nature and nurture can interact in a variety of ways, and three separate types of gene-environment interactions have been described by Plomin et al. (1977): passive, evocative/reactive, and active.

1. In passive gene-environment interaction, parents pass on genes and also provide an environment, both of which influence the child’s development. For example, highly intelligent parents are likely to pass on genes for intelligence to their children. They are also more likely to provide high levels of cognitive stimulation and a good education. These correlated genetic and environmental influences both increase the likelihood that their child will be highly intelligent.
2. In evocative gene-environment interaction, heritable traits influence the reaction of others and hence the environment provided by others. For example, a shy child (partly genetically influenced) may be less fun to other children, making other children less likely to want to spend time with him or her. This environment may result in the child becoming even more socially withdrawn.
3. In active gene-environment interaction, a child’s heritable traits influence his or her choice of environment. For example, an aggressive child may choose to watch violent films and engage in contact sports. This is known as ‘niche-picking’ and is one reason research has shown that the influence of genes increases as children get older.

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