The Nature-Nurture Debate

The nature-nurture debate asks whether behaviour is primarily the result of biological inheritance (nature) or environmental influences (nurture). This is one of the most enduring debates in psychology. Modern psychology has largely moved beyond the either/or dichotomy towards an interactionist position, recognising that nature and nurture work together.

Key Definition: Nature refers to the influence of genes, evolution, and biological factors on behaviour and psychological characteristics.

Key Definition: Nurture refers to the influence of experience, learning, socialisation, and culture on behaviour and psychological characteristics.

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The Nature Position

Biological Factors

The nature position holds that behaviour is determined by inherited biological factors:

• Genes: Our DNA provides the blueprint for physical development and influences psychological characteristics. Behavioural genetics uses twin and adoption studies to estimate heritability.
• Evolution: Evolutionary psychology argues that behaviours that promoted survival and reproduction were naturally selected over thousands of generations (e.g., attachment behaviours, aggression, mate preferences).
• Neurochemistry and hormones: Brain chemistry (e.g., serotonin, dopamine) and hormones (e.g., testosterone, cortisol) influence mood, behaviour, and mental health.

Twin Studies and Concordance Rates

Twin studies compare monozygotic (MZ) twins (genetically identical) with dizygotic (DZ) twins (sharing ~50% of genes) to estimate the genetic contribution to a trait.

Gottesman & Shields (1966):

• Studied concordance rates for schizophrenia in twin pairs.
• MZ twin concordance: ~48%
• DZ twin concordance: ~17%
• The higher concordance in MZ twins suggests a genetic component, but the fact that it is not 100% demonstrates that environmental factors also play a role.

Adoption Studies

Adoption studies compare adopted children with their biological and adoptive parents. If the child's behaviour more closely resembles their biological parents, this supports a genetic influence; if it more closely resembles their adoptive parents, this supports environmental influence.

Heston (1966) found that children adopted away from schizophrenic mothers had a significantly higher rate of schizophrenia than adopted children from non-schizophrenic mothers, supporting a genetic contribution.

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The Nurture Position

Environmental Factors

The nurture position holds that behaviour is shaped by experience:

• Classical conditioning: Pavlov, Watson — learning through association.
• Operant conditioning: Skinner — learning through reinforcement and punishment.
• Social learning: Bandura — learning through observation and imitation.
• Socialisation: The process by which individuals learn the norms, values, and behaviours of their culture.
• Cultural influences: Cultural norms shape behaviour, as demonstrated by cross-cultural research on conformity, attachment, and definitions of abnormality.

Behaviourism

Watson (1924) famously declared: "Give me a dozen healthy infants... and I'll guarantee to take any one at random and train him to become any type of specialist I might select — doctor, lawyer, artist, merchant-chief, and yes, even beggar-man and thief."

This extreme nurture position assumes that individuals are born as "blank slates" (tabula rasa) and that all behaviour is the product of learning.

Evaluation (AO3):

• Behaviourism produced effective therapies (e.g., systematic desensitisation, token economies) — demonstrating that behaviour can be shaped by environment.
• However, it ignores biological influences entirely, which is inconsistent with evidence from twin and adoption studies.

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Heritability

Key Definition: Heritability is a statistical estimate of the proportion of variation in a trait within a population that can be attributed to genetic differences between individuals. It does not tell us the extent to which genes determine a trait in any individual.

Key Points about Heritability

• Heritability estimates vary depending on the trait. For example, intelligence has a heritability estimate of approximately 50%, meaning that about half the variation in IQ scores within a population is attributable to genetic differences.
• A heritability estimate of 50% does not mean that 50% of your intelligence is genetic — it refers to variation at the population level.
• Heritability is population-specific — it can differ across cultures and time periods.

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The Interactionist Approach

Modern psychology recognises that the nature-nurture debate is a false dichotomy — behaviour is almost always the product of both biological and environmental factors interacting together.

The Diathesis-Stress Model