Partly. Twin and adoption studies consistently estimate the heritability of IQ at somewhere between 50% and 80% in adults, meaning that share of the variation between people is statistically associated with genetic differences. That is not the same as saying any given person's IQ is "caused by" their genes.

Why does heritability rise with age?

One leading interpretation is gene-environment correlation: as people grow up, they increasingly choose environments that match their inclinations, amplifying small early genetic tendencies. Parents' shared home environment plays a stronger role in childhood and fades in adulthood.

Does high heritability mean environment doesn't matter?

No. Heritability is a population-level statistic under existing conditions. Severe malnutrition, lead exposure, or long institutional neglect can lower IQ substantially, and better schooling and nutrition have historically raised it – see the Flynn effect.

BackgroundPublished July 19, 20265 min read

Nature vs Nurture: What Really Determines Your IQ?

Twin studies suggest that 50–80% of the variation in adult IQ is explained by genetics – but the rest is far from trivial. Here's how genes and environment actually interact.

Is intelligence something you're born with, or something you build? The question is old but the research has become remarkably specific: roughly half to four-fifths of the variation in adult IQ between people is statistically explained by genetic differences, with the rest attributed to environment and chance. The number sounds more decisive than it really is.

What twin studies show

Identical twins share 100% of their DNA, fraternal twins about 50%. Comparing how similar their IQ scores are lets researchers estimate the genetic share of variation. Meta-analyses land on a heritability of 50–60% in childhood, rising to 70–80% in adulthood – a paradoxical pattern where genes seem to matter more as you get older.

Which environments matter

High heritability does not mean environment is irrelevant. Adoption studies show that an enriched home can lift IQ by several points, while severe malnutrition, lead exposure and prolonged institutional neglect lower it substantially. Length of schooling is one of the most robust single environmental factors: each extra year is associated on average with a couple of IQ points, independent of family background. See our guide on whether you can improve your IQ.

How genes and environment interact

Modern behavioural genetics emphasises interplay. A child with a slight genetic tilt toward pattern reasoning gravitates towards puzzles, mathematics and logic problems, and becomes even better at them. Environment and genes reinforce each other in a positive spiral (or the reverse). In practice, "nature or nurture" is the wrong framing; it is always both, and the balance shifts by age and population.

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FAQ

Is IQ inherited?: Partly. Twin and adoption studies consistently estimate the heritability of IQ at somewhere between 50% and 80% in adults, meaning that share of the variation between people is statistically associated with genetic differences. That is not the same as saying any given person's IQ is "caused by" their genes.
Why does heritability rise with age?: One leading interpretation is gene-environment correlation: as people grow up, they increasingly choose environments that match their inclinations, amplifying small early genetic tendencies. Parents' shared home environment plays a stronger role in childhood and fades in adulthood.
Does high heritability mean environment doesn't matter?: No. Heritability is a population-level statistic under existing conditions. Severe malnutrition, lead exposure, or long institutional neglect can lower IQ substantially, and better schooling and nutrition have historically raised it – see the Flynn effect.