Nature-nurture debate

• A strength of research into the nature-nurture debate is the use of adoption studies. Adoption studies are useful because they separate the competing influences of nature and nurture. If adopted children are found to be more similar to their adoptive parents, this suggests the environment is the bigger influence. Whereas, if adopted children are more similar to their biological parents then genetic factors are presumed to dominate. A meta-analysis of adoption studies by Rhee and Waldman found that genetic influences accounted for 41% of the variance in aggression.
• However, research suggests that nature and nurture are not two entities that can simply be pulled apart. According to Plomin people create their own ‘nurture’ by actively selecting environments that are appropriate for their ‘nature’. Thus, a naturally aggressive child is likely to feel more comfortable with children who show similar behaviours and will ‘choose’ their environment accordingly. Then, their chosen companions further influence their development. Plomin refers to this as niche-picking. This suggests that it does not make sense to look at evidence of either nature or nurture.
• A strength is support for epigenetics. An example of how environmental effects can span generations presumably through epigenetic effects comes from events of WW2. Nazis blocked the distribution of food to the Dutch and 22,000 died in the Dutch Hunger Winter. Susser and Lin report that women who became pregnant during this went on to have low birth weight babies. What is more interesting is that these babies were twice as likely to develop schizophrenia later on compared to more typical population rates. This shows life experiences of previous generations can leave ‘epigenetic markers’
• A strength of the debate is that it has real-world application. Research suggests OCD is a highly heritable mental disorder. Such understanding can inform genetic counselling because it is important to understand that the individual will go on to develop the disorder. This means that people who have a high genetic risk of OCD because of their family background can receive advice about the likelihood of developing the disorder and how they might prevent this. This shows the debate is not just a theoretical one but that it is important to understand the interaction between nature and nurture.
• The nature-nurture debate seeks to answer the question of whether our behaviour is more influenced by nature or nurture. It is not really a ‘debate’ about one or the other because any behaviour arises from a combination of both.
• For example, Bowlby claimed that a baby’s attachment type is determined by the warmth and continuity of parental love (an environmental influence). Kagan proposed that a baby’s innate personality (temperament) also affects the attachment relationship. Thus, nature (the child’s temperament), in a real sense, creates nurture (the parents response), so environment and hereditary interact.
• Psychologists are now more likely to ask what the relative contribution of each influence is. Therefore the nature-nurture debate is really about discussing how nature and nurture interact - an interactionist approach.
• The diathesis-stress model suggests behaviour is caused by a biological or environmental vulnerability (diathesis) which is only expressed when coupled with a biological or environmental ‘trigger‘ (stressor). For example, a person who inherits a genetic vulnerability for OCD may not develop the disorder. But combined with a psychological trigger (e.g. a traumatic experience) this may result in the disorder appearing.
• Epigenetics refers to a change in our genetic activity without changing the genes themselves. It is a process that happens throughout life and is caused by interaction with the environment. Aspects of our lifestyle or events we encounter leave ‘marks on our DNA (genes), which switch genes on or off. This explains why factors such as smoking have a lifelong influence even after you actually stop -they have changed the way your genes will be expressed.
• Even more remarkably these epigenetic changes may go on and influence the genetic codes of our children, as well as their children. Epigenetics therefore introduces a third element into the nature-nurture debate - the life experience of previous generations.
• Nature refers to inherited influences, or hereditary. Early nativists such as Descartes argued that all human characteristics are innate. Psychological characteristics like intelligence or personality are determined by biological factors (genes), just as physical characteristics like eye colour or height are.
• Nurture refers to the influence of experience and the environment. Empiricists including John Locke argued that the mind is a blank slate at birth, which is then shaped by the environment. This view later became an important feature of the behaviourist approach.
• Lerner has identified different levels of the environment. This includes prenatal factors, such as how physical influences (smoking) or psychological influences (music) affect a foetus. More generally development is influenced postnatally in terms, for example, of the social conditions a child grows up in.
• The degree to which two people are similar in a particular trait can be represented by a correlation coefficient and is called concordance. Such concordance provides an estimate about the extent to which a trait is inherited - called heritability.
• Heritability is the proportion of differences between individuals in a population, with regards to a particular trait, this is due to genetic variation.
• A figure of .01 (1%) means genes contribute almost nothing to individual differences and 1.0 (100%) means genes are the only reason for individual differences. The general figure for heritability in IQ is about .5 across multiple studies in varying populations (Plomin). This means that about half of a person’s intelligence is determined by genetic factors and the other half must be environmental.