Specification: The nature-nurture debate: the relative importance of heredity and environment in determining behaviour; the interactionist approach.
The nature versus nurture debate is one of the oldest debates in psychology. It centres on the relative contributions of genetic inheritance and environmental factors to human development and behaviour.
The influence of ‘nature’
Nature is the view that behaviour is the product of innate biological or genetic factors. For a long time, psychologists have known that certain physical characteristics, such as eye colour and skin pigmentation, and certain diseases (e.g. Huntingdon’s) are biologically determined and the result of heredity (or genetic inheritance). Heredity is the process in which traits are passed down from one generation to the next. Furthermore, characteristics like height, weight, hair loss, life expectancy and vulnerability to specific illnesses are positively correlated with genetic relatedness. This has led psychologists to investigate whether psychological characteristics are also “wired in” before we are born.
This is known as the nativist position, and the underlying assumption is that the characteristics of the human species are a product of evolution and that individual differences are the result of each person’s unique genetic code.
For example, family, twin and adoption studies show that the closer the relatedness of two people, the more likely it is that they will show the same behaviours. For example, the risk of being diagnosed with schizophrenia is approximately 1% of the general population. However, Gottesman and Shields (1991) pooled the results of around 40 family studies and found that the risk increases to 46% for those with two parents who have schizophrenia. Also, Joseph (2004) pooled the data for schizophrenia studies conducted before 2001 and found an average concordance rate of 40.4% for MZ twins and 7.4% for DZ twins, highlighting a significant genetic component.
Characteristics and differences that are not observable at birth, but which emerge later in life, are regarded by nativists as the product of maturation, as we have a ‘biological clock’ which switches certain behaviours ‘on’ or ‘off’ in a pre-programmed way. For example, Huntingdon’s disease is a genetically transmitted disorder that usually emerges between the ages of 30 and 50. However, it can appear at any time, since the genetic cause is innately present.
Evolutionary explanations also emphasise the importance of nature, as they assume that behaviours or characteristics that increase our chances of survival and reproduction will be naturally selected; the genes for these characteristics or behaviours will be passed on, as they provide an adaptive advantage. For example, Bowlby proposed that children come into the world biologically programmed to form attachments because this will help them to survive. This suggests attachment behaviours are naturally selected and passed on as a result of genetic inheritance (heredity mechanisms).
The influence of ‘nurture’
Nurture is the view that behaviour is the product of environmental influences. The environment is seen as everything outside the body, which can include people, events and the physical world. Environmentalists (also known as empiricists) hold the assumption that the human mind is a tabula rasa (a blank slate) and that this is gradually ‘filled’ as a result of experience. This view was first proposed by John Locke in the 17th Century and was later taken up by behavioural psychologists. For example, John Watson (1913) famously wrote:
“Give me a dozen healthy infants, well-formed, and my own specified world to bring them up and I’ll guarantee to take any one at random and train him to become any type of specialist I might select–doctor, lawyer, merchant-chief, and yes, even beggarman and thief, regardless of his talents, penchants, tendencies, abilities, vocations, and race of his ancestors.”
According to environmentalists, psychological characteristics and behavioural differences that emerge through infancy and childhood are the result of learning.
For example, behavioural psychologists explain attachment in terms of classical conditioning, where food (unconditioned stimulus) is associated with the mother (neutral stimulus). Through many repeated pairings, the mother becomes a conditioned stimulus who elicits a conditioned response in the child. Therefore, the child forms an attachment-based on the pleasure experienced as a result of being fed.
Bandura argued that aggression is learned through observation, vicarious reinforcement and imitation, and is therefore explained by social learning theory. However, he did acknowledge that the urge to behave aggressively might be biological, which suggests a more interactionist approach.
Environmental explanations can also partly explain the occurrence of schizophrenia. Batson et al. (1956) proposed the double bind theory, which suggests that schizophrenia is the result of disordered communication within the family. This is where one instruction is given overtly to a child (e.g. a mother says ‘come to me’) while another instruction is given covertly (e.g. the mother’s manner and tone of voice are rejecting). Prolonged exposure to such interactions prevents the development of a coherent construction of reality, and in the long run, this manifests itself as schizophrenic symptoms.
Evaluation
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 how 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, 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 the reported cases of schizophrenia occurred in families rated as ‘disturbed’. When the family environment was assessed 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 the hippocampus on each side of the brain (and especially the right hippocampus) was larger in taxi drivers in comparison to non-taxi drivers. Consequently, Maguire concluded that driving a taxi (nurture) influenced 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.
In passive gene-environment interaction, parents pass on genes and 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.
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.
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.
Critical thinking
Why is it impossible to accurately answer questions regarding how much behaviour is due to nature and how much due to nurture? If a study is conducted the biological children of parents with schizophrenia that suggests (like Gottesman & Shields) a large positive correlation between the parents and the children for schizophrenia, this is just at one moment in time and is also an average, with variations in home circumstances (see the Finnish adoption study) also bearing some responsibility. As Plomin et al. demonstrate, nurture can act to increase the effect of nature, though parental and peer actions and through niche-picking, all of which can increase the genetic influences over time. So genetic influence becomes time and context sensitive.
What is meant by the phrase ‘nature via nurture’? This is the title of a book by geneticist Matt Ridley where he states “No longer is it nature versus nurture, but nature via nurture. Genes are designed to take their cues from nurture.” What do you think he means?
Possible exam questions
Explain what is meant by an interactionist approach in relation to the nature-nurture debate. (4 marks)
“Research suggests that depression runs in the family. However, many depressed people also have other issues, including social problems, or problems with drink or drugs. Despite these challenges, many depressed people overcome their depression and find ways to resolve their issues.” With reference to the item above, identify one influence of nature on our behaviour and one influence of nurture on our behaviour. (4 marks)
Discuss the relative importance of heredity (nature) in determining behaviour. (8 marks)
Discuss the nature-nurture debate in psychology. Refer to at least two topics you have studied in your answer. (16 marks)
