4.3.1 - The nature–nurture debate

What the debate asks

The nature-nurture debate asks how far behaviour is shaped by heredity and how far it is shaped by the environment. AQA's wording is precise: the issue is the relative importance of heredity and environment in determining behaviour, plus the interactionist approach. In other words, exam answers should not sound like a simple vote for genes or experience. A useful answer explains what each kind of evidence supports and how the influences may combine; no conclusion wins simply by using the word interactionism.

The classic nativist position argues that important abilities and characteristics are innate. Philosophers such as Rene Descartes are often used as historical examples of nativist thinking. The classic empiricist position argues that knowledge and behaviour come from experience. John Locke's phrase tabula rasa, or "blank slate", is the usual AQA shorthand for this view.

A biological feature is not automatically evidence of an inherited cause: brain structure and hormone activity can also change with experience. In this debate, a nature explanation emphasises inherited or innate influences, while a nurture explanation emphasises experience.

Psychologists estimate genetic contributions to population differences using heritability.

This definition has an important trap. Heritability is about variation in a population, not the cause of one person's behaviour. If a trait has high heritability, it does not mean the trait is fixed, inevitable or impossible to change. Heritability can also differ between ages and environments. For example, behavioural genetics research suggests intelligence has genetic influence, but the size of that influence varies across development and across populations.

For a hypothetical trait, a heritability estimate of 0.60 concerns differences between people in that studied population. It does not mean that 60% of one person's trait is genetic. If access to nutrition or education changes, the estimate may change too. High heritability therefore provides no shortcut from a population statistic to an individual prediction.

The useful question is: what do heredity and environment each contribute under these conditions, and how do they combine?

Evidence across Psychology

The nature-nurture debate appears across the whole A-level course. Different explanations tend to lean towards different sides of the debate, although few are purely one-sided.

Genetic evidence often comes from twin and adoption studies. If monozygotic (MZ) twins are more similar than dizygotic (DZ) twins for a trait, this suggests genetic influence because MZ twins share more DNA. Concordance measures agreement in the presence of a trait within twin pairs. Pairwise concordance is the proportion of pairs with at least one affected twin in which both are affected. Probandwise concordance estimates the chance that a co-twin is affected when one twin is affected. Published rates must use comparable counting rules before they can be compared. If MZ concordance is below 100%, identical inherited DNA is not sufficient to account for the outcome; environmental and developmental differences may also contribute. This is why twin studies usually support nature and nurture, not nature alone.

Evolutionary explanations also sit on the nature side. For example, Bowlby argued that attachment behaviours are adaptive because they help infants keep caregivers close, increasing survival chances. This treats attachment as partly rooted in evolved biology.

On the nurture side, behaviourism explains behaviour through learning. A behaviourist account of phobias, for instance, would focus on classical conditioning and reinforcement rather than inherited fear. Social learning theory is also strongly environmental because it explains behaviour through observation, imitation and vicarious reinforcement. However, Bandura-style explanations can still allow for biological capacities; the environment shapes how those capacities are expressed.

AO2 scenario: Leila has shown a cautious temperament from early childhood. When she starts secondary school, she avoids busy clubs and spends break times with one quiet friend. Over time, she becomes even more anxious in large groups because she has less chance to practise social confidence. A nature explanation might propose an inherited contribution to temperament, but early appearance alone does not prove inheritance. A nurture explanation would examine her learning and school experiences. A combined explanation proposes a feedback loop: temperament affects the environments she chooses, and those environments may maintain her anxiety. This is a testable possibility, not a diagnosis established by the scenario.

For a hypothetical disorder, suppose concordance is 60% for MZ twins and 25% for DZ twins. The higher MZ rate is consistent with genetic influence, provided environmental similarity and other confounds are considered. The MZ rate below 100% challenges genetic sufficiency. These figures do not mean that 60% of an individual's disorder is genetic, and they do not isolate the precise environmental cause. More similar treatment of MZ twins could contribute to their similarity.

The interactionist approach

Interactionism explains how inherited vulnerabilities and environmental experiences can change each other’s effects.

Interaction can happen in several ways. Genes may affect how sensitive someone is to an environmental stressor. Environments may affect whether genes are expressed. Genetically influenced traits may also affect the environments a person selects or creates.

A vulnerability can be genetic, psychological or developmental; it need not be one identifiable gene. These models usually concern changes in probability, not a guarantee that stress produces a disorder.

The diathesis-stress model is one of the clearest AQA examples of interactionism. A person may inherit a vulnerability to a disorder, but that vulnerability may not lead to symptoms unless it is triggered by stress, trauma, family dysfunction or another environmental factor. Equally, someone may experience stress but not develop the disorder if they do not have the vulnerability or if protective factors are present.

Tienari et al. (2004) provide evidence from the Finnish Adoption Study. The researchers compared adopted-away children at high genetic risk of schizophrenia-spectrum disorder with low-risk adoptees. In the sample with family ratings available, 145 adoptees were classified as high genetic risk because their biological mothers had schizophrenia-spectrum diagnoses, while 158 were low genetic risk. Adoptive family functioning was assessed using the Oulu Family Rating Scale, and adoptees were followed up over many years.