THE NATURE v NURTURE DEBATE
THE NATURE v NURTURE DEBATE
Nurture: Different Types of Environmental Influence
Environment is thought as: external to the individual; post-natal and acting on a passive individual
Levels of the environment:
discusses different levels of the environment, pointing out particularly that the environment can be internal and pre-natal as well external and post-natal and that the influence of the environment can be narrow or more general.
Inner biological level:
the mothers physical state during pregnancy (eg) Foetal Alcohol Syndrome (FAS) characterised by being smaller than average; having smaller than average brains; heart defects and low IQ scores
Individual psychological level:
mother's psychological state during pregnancy
Physical environmental level:
where and when the child is born; currents state of scientific knowledge; educational and healthcare policies.
Interaction of Heredity and Environment
refers to a change in our genetic activity without changing our genetic code. It's a process that happens throughout life and is caused by interaction with the environment.
Aspects of our lifestyle, and the events we encounter - from smoking and diet to pollution and war - leave epigenetic 'marks' on our DNA. These marks-like highlighted text, or bookmarks - tell our bodies which genes to ignore and which to use, and in turn, may go on and influence the genetic codes of our children, as well as their children. Epigenetics therefore introduced the third element into the nature-nurture debate: the life experience of previous generations.
Brian Dias and Kerry Ressler (2014)
gave male lab mice electric shocks everytime they were exposed to the smell of acetophenone, a chemical used in perfume. As any behaviourist would predict, the mice showed a fear reaction as soon as the scent was presented. Surprisingly, the rats' children also feared the smell - event hough they hadn't been exposed to acetophenone before or receive.
The truth is that behaviour is the result of a complex interaction between both. The Diathesis-Stress model of schizophrenia suggests that although people may inherit a predisposition to schizophrenia, some sort of environmental stressor is required in order to develop the disease. The explains why schizophrenia happens in the late teens of early adulthood, times of considerable upheaval and stress in people's lives.
Phenylketonuria - Implications for Dietary Choices
PKU is a genetically inherited disorder in which individuals are unable
Psychologists don't adopt an extreme position of either heredity (nature) or environment (nurture) as an explanation of behaviour, because heredity is expressed within an environment.
Both nature and nurture are essential for any behaviour - it cannot be said that a particular behaviour is genetic and another is environmental.
Nor can it be said that a particular behaviour is due to a specified percentage of nature and nurture as the influences don't operate in a separate and additive way but interact in a complex manner. Furthermore, genes may be largely responsible for one person behaving in a particular way but the environment could be more important for another person who displays exactly the same behaviour.
What we can say is that the difference between two people's behaviour is mostly due to heredity or mostly due to environmental factors.
Evaluation of Twin and Adoption Studies
Adoption and twin studies don't show 100% concordance for characteristics such as depression. This indicates environmental factors still have an impact and therefore an interactionist approach may be preferable.
Adoptive environments are often remarkably similar to one another because of the demographics of adoptive parents.
It's difficult to recruit large groups of adopted children and twins, particularly when one twin is depressed, so sample sizes can be extremely small.
Twin and adoption studies are forms of natural experiments as genetic relatedness and environmental conditions aren't controlled by the experimenter.
Nativism is the philosophical idea that certain human characteristics and even aspects of knowledge are innate (nature)
Empiricism is the philosophical idea that behaviour results from learning and experience (nurture). John Locke believed that at birth the human mind is a blank slate (tabula rasa) which is filled by learning from the environment.
Today, few psychologists adopt an extreme 'nature' or 'nurture' stance. This is due to an increasing recognition of the complex relationship between the two. A person's genes (i.e their genotype) clearly influence their observable characteristics, such as height and eye colour (i.e their phenotype). However, the issue gets more complex; a person's genes can interact with their environment. The environment, as well as genes, can influence phenotypes - nature and nurture can interact.
Nature v Nurture
Concerned with how genes influence behaviour. Genes are passed to offspring from the parents. For example, depression may be the result of inheriting a particular combination of genes
useful applications (e.g drug therapy)
Neglects the role of the environment in behaviour
Concerned with the role of the environment and experience in shaping all of a person's personality and behaviours. For example, substance abuse may be the result of observing such behaviour in those around you, imitating the behaviour and being rewarded for doing so.
Useful applications (e.g behaviour therapy)
Neglects the impact of biological factors on behaviour
MZ twins share 100% genes and DZ share 50%. So if MZ twins are more likely to share a characteristic than DZ twins, it implies a genetic influence. This is shown by concordance rates. For example
Holland et al (1988)
found a 56% MZ concordance for anorexia compared to only a 5% concordance in DZ twins. This suggests that genes influence the development of anorexia. However, if a trait was completely genetic then MZ concordance would be 100%, so their behaviour must also be influenced by environment. For example, people might treat MZ twins more similarly than DZ twins. As such, it's much more useful to do research on twin who haven't been brought up together.
If family members share a trait more frequently than unrelated people do, then this could imply a genetic influence for that behaviour. For example,
Solyom et al (1974)
showed that phobias can run in families. However, similarities between family members may actually be the result of their shared environment - relatives might learn the behaviour from each other through observational learning.
Implications of the Debate
If genes are found to be largely influential in terms of intelligence, then this raises the question of whether it's worth spending time and resources in developing educational enrichment programmes for children.
If nurture or the environment is implicated in schizophrenia, this could lay the burden of blame on the family (but could also lead to effective family-based interventions).
Shared and Unshared Environments
As we have seen, if trait or behaviour was completely genetic, then concordance rates between MZ twins should be 100%, as MZ twins share the same genes.However, twin studies don't yield 100% concordance rates, meaning that environmental factors must be influential. It doesn't follow that individuals living in the same home necessarily have the same environment - we have to distinguish between shared and unshared environments.