1 Psychology and human development1.5 Intelligence
1.5.7 Genetic and environmental influences on intelligence
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Written by Resident Doctor Committee · Published
New in the 2027 syllabus
The College added this topic for exams from January 2027.
What heritability means
Heritability is the proportion of variation in a trait that is linked to genetic variation, in a specified population and environment.
Narrow-sense heritability covers only additive genetic variance, which comes from the summed effects of individual gene variants.
Broad-sense heritability also includes other genetic contributions.
A heritability estimate describes differences between people. It is not the genetic percentage of one person's intelligence. It can change with age and with the environment.
Genes and experience together
Genes and environment do not act separately.
Process | What it means | Example |
|---|---|---|
Gene-environment interaction | The effect of the environment differs by genotype | A genetic influence varies with educational opportunities |
Passive correlation | Parents provide both inherited variation and the environment | Family traits relate to learning opportunities |
Evocative correlation | A person's characteristics draw out responses from others | Interests attract teaching or encouragement |
Active correlation | A person chooses their own environments | Choosing mentally demanding activities |
Epigenetic mechanisms change how genes are regulated without changing the deoxyribonucleic acid (DNA) sequence. Finding an epigenetic association does not show what caused it, or whether it can be reversed.
Environmental influences include nutrition, schooling, illness, toxins and access to learning. High heritability does not mean that intervention cannot change outcomes.
Heritability measured within one group cannot explain why average scores differ between groups. The groups may differ in their environments and in how they were tested.
Worked example: calculating heritability
Quantity | Variance units |
|---|---|
Additive genetic variance | 40 |
Total observed variance | 100 |
Narrow-sense heritability is additive genetic variance divided by total variance: 40 / 100 = 0.40.
Express this as 40% of variation in this hypothetical population.
It does not mean that 40% of one person's score is inherited, or that the remaining variation can all be changed.