(a) How much nature (genetic factors) and nurture (environmental factors) contribute to a person's physical, cognitive and…

(a) Contribution of nature and nurture Development is an interaction: genes set a range of potential and the environment decides where within it a person ends up.

• Physical: height is highly heritable within stable populations, yet malnutrition, infection and deprivation reduce adult stature. Pubertal timing is genetic but is shifted by nutrition and stress. Epigenetic changes show the environment altering gene expression without changing the DNA sequence.
• Cognitive: twin and adoption studies (for example, the Minnesota study and TEDS) put IQ heritability near 0.5 in childhood, rising to 0.7–0.8 in adulthood. Equal-environment assumptions and sample limits call for caution. The Flynn effect, rising IQ scores across generations too fast for genetic change, and the effects of schooling and home environment show strong environmental influence.
• Socio-emotional: temperament has heritability of about 0.4–0.6, but attachment security depends on responsive caregiving.

Gene–environment correlation complicates the picture (Scarr and McCartney). It is passive when parents supply both genes and home, evocative when a child's temperament draws particular responses, and active when individuals choose matching environments. The same genotype can also produce different outcomes in different environments (gene–environment interaction). Heritability is a population statistic for a given environment, not an individual's fixed destiny.

(b) Principles of classical conditioning and applications Pavlov's principles:

• A neutral stimulus (bell) paired repeatedly with an unconditioned stimulus (food) becomes a conditioned stimulus that elicits a conditioned response (salivation); this is acquisition.
• Extinction: the CR weakens when the CS is presented without the US. Spontaneous recovery: the CR reappears after rest.
• Generalisation: similar stimuli evoke the CR. Discrimination: response only to the specific CS.
• Timing and contiguity matter, and the CS should predict the US.

Applications:

• Watson's Little Albert experiment showed how fear (a phobia) can be learned. It is an ethical caution as well as an illustration.
• Systematic desensitisation (Wolpe) pairs the feared stimulus with relaxation (counterconditioning) to treat phobias.
• Aversion therapy pairs alcohol with an unpleasant response.
• Advertising pairs products with attractive people or music.
• Taste aversion: a child who falls ill after a food often rejects it later.

(c) Cognitive neuropsychology and socio-cultural perspective Cognitive neuropsychology links mental functions to brain mechanisms. Cases such as Phineas Gage (executive control), patient HM (memory systems) and split-brain patients (hemispheric specialisation) show how damage reveals structure. fMRI and PET allow study of the living brain, supporting both localisation and plasticity. It helps in diagnosis and rehabilitation after stroke and injury.

The socio-cultural perspective holds that cognition develops through social interaction and culture. Vygotsky's zone of proximal development, scaffolding and the more knowledgeable other show how learning is guided. Bronfenbrenner's ecological systems place the person within micro-, meso-, exo- and macrosystems. Cross-cultural work shows that behaviour and meaning vary with context; in India, family structure, shared language and community norms shape cognition, roles and identity.

The two perspectives complement each other: one explains the neural basis of behaviour, the other explains how culture shapes how those capacities are used.