Role of Genetic & Environmental Factors in Determining Human Behaviour
Behaviour is best understood as a dynamic product of biology (genes, brain, hormones) and context (family, culture, learning, stressors). This module builds a clear, exam-ready picture using models, diagrams, and crisp conceptual linkages for fast revision.
Key exam idea: most traits show both genetic influence and environmental shaping—often through Gene × Environment interplay across development.
1) Core Concept: Why it’s “Nature + Nurture + Interaction”
The older “nature vs nurture” debate is now framed as multiple layers operating together: genes provide biological potentials and constraints, while environments supply experiences that strengthen, suppress, or redirect those potentials. Importantly, people also select and modify environments (for example, a curious child seeks books; an impulsive child invites stricter monitoring), creating feedback loops over time.
What genetics mainly contribute
- Temperament tendencies (reactivity, sociability, effortful control)
- Neurobiological sensitivity (reward, threat detection, arousal patterns)
- Limits and baseline capacities (e.g., sensory thresholds, learning speed)
- Risk propensities (vulnerability to certain behavioural difficulties)
What environment mainly contributes
- Learning histories (reinforcement, modelling, conditioning)
- Culture and norms (values, scripts, role expectations)
- Stressors and resources (poverty, trauma, support systems)
- Developmental inputs (nutrition, schooling, parenting, peers)
2) Key Genetic Ideas for Behaviour: From DNA to Disposition
Genes influence behaviour through the biological systems they help build and regulate—especially the brain, neurotransmitters, and endocrine systems. Genes do not encode “behaviours” directly; instead, they bias processing styles (attention, emotional reactivity, impulse control) and affect how strongly a person responds to environmental inputs.
3) Heritability: What it Means—and What it Does NOT Mean
Heritability refers to the proportion of observed variation in a trait within a population (at a given time, in a given environment) that is associated with genetic differences. It is not a statement about how “genetic” a trait is in an individual.
Heritability tells you
- How much population variation relates to genetic differences
- Why people differ in the same setting
- Which traits tend to show family resemblance
Heritability does NOT tell you
- Whether a trait is unchangeable
- Whether genes matter more than environment overall
- Whether a policy/intervention can work
4) Environmental Influence: How Context “Writes” on Behaviour
Environmental factors influence behaviour by shaping what is learned, what is valued, what is rewarded, and what is feared or avoided. Environment includes not only dramatic events (trauma, deprivation) but also everyday patterns—parenting style, peer norms, teacher expectations, media exposure, and cultural scripts.
5) Gene × Environment Interaction: Same Genes, Different Outcomes
Gene × Environment (G×E) interaction means that the effect of an environment depends on a person’s genotype, or the effect of a genotype depends on the environment. Practically, this explains why the same stressor does not affect everyone equally, and why the same genetic tendency can express as very different behaviours across settings.
Classic interaction logic
A biologically sensitive person may show stronger emotional reactions. In a harsh environment, this may increase risk for anxiety or aggression; in a supportive environment, the same sensitivity may translate into empathy, creativity, or high responsiveness to learning.
“Diathesis–Stress” framing
A genetic vulnerability (diathesis) increases the chance of difficulties primarily when environmental stress is high; when stress is low, the vulnerability may remain “silent.”
flowchart TB A["Genetic Sensitivity / Vulnerability
(Diathesis)"] --> B["Environmental Conditions"] B --> C["Low Stress / Supportive Context"] B --> D["High Stress / Adversity"] C --> E["Adaptive Outcomes
better self-regulation, learning, well-being"] D --> F["Risk Outcomes
anxiety, impulsivity, behavioural problems"] G["Differential Susceptibility Idea"] --> H["Some individuals are more affected by BOTH
good & bad environments"] H --> E H --> F
6) Gene–Environment Correlation: How People “Choose” Their Environments
Genetic influence can also appear indirectly because genes shape the likelihood of encountering particular environments. This is called Gene–Environment Correlation (rGE). It explains why environments are not always “random exposures”—people often evoke, select, or inherit them.
| Type of rGE | Meaning (in simple terms) | Behavioural implication |
|---|---|---|
| Passive | Child receives genes and an associated environment from parents | Home climate may align with inherited dispositions |
| Evocative | Child’s traits evoke certain responses from others | Temperament can bring harsher discipline or more support |
| Active | Person selects environments that fit their traits | Interests lead to niche-picking (friends, hobbies, careers) |
7) Epigenetics: How Experience Can Regulate Gene Expression
Epigenetics refers to chemical changes “around” DNA that influence whether certain genes are turned on/off—without changing the DNA sequence. From a behavioural perspective, epigenetic processes help explain how early-life stress, nurturing, toxins, nutrition, sleep, and chronic adversity can produce long-lasting changes in stress reactivity, emotion regulation, and cognitive functioning.
8) Developmental View: Timing Matters (Sensitive Periods & Plasticity)
The impact of genes and environments changes across the life span. Early development features high neural plasticity, so environments can have strong, sometimes enduring effects. However, plasticity does not vanish—learning and intervention can still alter trajectories later, especially when contexts become safer and more supportive.
flowchart TB A["Prenatal & Early Childhood
high plasticity"] --> B["Middle Childhood
skill building + schooling"] B --> C["Adolescence
identity + peer influence + reward sensitivity"] C --> D["Adulthood
roles + habits + cumulative exposure"] A --> E["Environment has strong shaping power
nutrition, caregiving, stress"] C --> F["Environment reorganises social behaviour
peer norms, risk context"] D --> G["Genes may influence stability of traits
via temperament + self-selection"]
Smart Summary: Fast Revision Grid
| Concept | One-line meaning | Why it matters for behaviour |
|---|---|---|
| Genetic influence | Biological predispositions via brain/hormone systems | Explains stable tendencies & sensitivity differences |
| Environment | Learning + culture + stressors + resources | Shapes habits, skills, values, coping styles |
| Heritability | Population-level genetic contribution to variation | Not destiny; depends on context |
| G×E interaction | Gene effects depend on environment and vice versa | Explains different outcomes under same conditions |
| rGE | Genes influence exposure to environments | People evoke/select environments that reinforce traits |
| Epigenetics | Experience can regulate gene expression | Bridge between biology and lived reality |
| Developmental timing | Effects shift across life stages | Plasticity + sensitive periods shape trajectories |
