Is Intelligence Genetic? What Heritability Really Means

By the IQ Revealed Team · Updated September 11, 2026

Partly — and the honest answer depends on a word most pages use incorrectly. Twin and family studies put the heritability of intelligence at about 20% in infancy, rising to perhaps 80% in later adulthood. But heritability measures where the differences between people come from in one population at one time. It is not the fraction of your own ability that came from your parents, and it is not a ceiling.

Quick answer

Intelligence is substantially heritable and not fixed. Genetic differences account for a large share of the variation in test scores between adults, the share grows with age rather than shrinking, and no single gene is responsible — thousands of variants each contribute a little. At the same time, each extra year of education adds roughly 1 to 5 points, average scores rose for most of the twentieth century, and in poor households the genetic share of variation falls close to zero. Both halves of that are mainstream findings, and a page that gives you only one of them is selling you something.

What heritability actually means

Almost every argument about this question is really an argument about one statistic that is routinely misread. Heritability is the proportion of the variation in a trait, within a particular population at a particular time, that tracks genetic differences among the people in it.

Three consequences follow, and they are the whole of the confusion:

It is a property of a population, not of a person. A heritability of 60% does not mean 60% of your intelligence is genetic and 40% is your upbringing. That sentence has no meaning for an individual.
It can change without any gene changing. Make schooling universal and the environmental differences between people shrink — so the genetic share of what remains goes up, even though nothing about anyone's DNA has moved.
High heritability does not mean unchangeable. Eyesight is highly heritable; spectacles work anyway.

The number rises with age, which surprises almost everyone

The intuition is that children start close to their genetic endowment and drift away from it as life happens to them. The data run the other way. Plomin and Deary list this first among their five special findings about intelligence: heritability increases from about 20% in infancy to perhaps 80% in later adulthood. Haworth and colleagues found the rise to be roughly linear from childhood to young adulthood across three continents.

Briley and Tucker-Drob asked why, meta-analysing longitudinal twin and sibling studies covering 11,500 pairs measured at least twice between six months and eighteen years. In early childhood, new genetic influences keep appearing; after about age eight that innovation largely stops and the existing genetic differences are progressively amplified. The usual reading is that as people gain control over their own lives, they increasingly select, shape and are selected into environments that suit their existing dispositions — so small early differences compound.

Poverty changes the answer

The high heritability figures come overwhelmingly from samples of reasonably comfortable families, and that turns out to matter more than any other caveat on this page.

Turkheimer and colleagues analysed Wechsler scores from 7-year-old twins in the National Collaborative Perinatal Project, a sample in which a substantial proportion of children were raised near or below the poverty line. Modelling socioeconomic status as a continuous variable, they found the proportions of IQ variance attributable to genes and to environment vary with it: in impoverished families, 60% of the variance was accounted for by the shared environment and the contribution of genes was close to zero; in affluent families the result was almost exactly the reverse.

The plain reading is uncomfortable for both of the usual positions. Where children have what they need, the differences left between them are largely genetic. Where they do not, deprivation dominates and genetic potential has little room to show up at all.

There is no “intelligence gene”

Headlines periodically announce one. None has survived. Intelligence is polygenic: influenced by thousands of genetic variants, each shifting scores by a vanishingly small amount.

Plomin and von Stumm put the current state of the search precisely: genome-wide association studies have identified inherited genome sequence differences that account for 20% of the 50% heritability of intelligence. That is a real advance and it is also a useful reality check — the best genetic prediction available explains a fraction of a fraction. The US National Library of Medicine's summary says the same thing in plainer words: studies have shown intelligence has a genetic component, but have not conclusively identified any single genes with major roles.

Is intelligence inherited from your mother?

This claim circulates every few years, usually in the form “the genes for intelligence are on the X chromosome, so you get your brains from your mother”. It does not hold up. The variants that genome-wide studies associate with cognitive ability are distributed across the genome rather than confined to one chromosome, and there are thousands of them.

There is a grain of real biology underneath the story — some genes behave differently depending on which parent they came from, and the X chromosome is inherited differently by sons and daughters — but nothing in that biology supports the popular version, in which one parent supplies the intelligence and the other does not.

Can two average parents have a gifted child?

Yes, and the reverse happens just as reliably. Each parent passes on a random half of their variants, environment and chance do the rest, and the result is that children's scores sit closer to the population average than their parents' scores do.

Francis Galton described this in 1886, measuring the heights of parents and their adult children, and named it regression toward mediocrity — what statistics now calls regression toward the mean. It is not a force pulling families back to average; it is what happens whenever a measurement combines something inherited with something variable. It applies to a high score exactly as much as to a low one, which is why exceptional parents usually have less exceptional children, and unexceptional parents sometimes have remarkable ones.

What actually raises scores

If genes explain so much of the difference between adults, can anything move a score? Two findings answer that directly, and both are large.

Education. Ritchie and Tucker-Drob meta-analysed 142 effect sizes from 42 datasets involving over 600,000 participants, using three separate quasi-experimental designs — controlling for earlier intelligence, exploiting compulsory-schooling policy changes, and comparing children either side of a school-entry age cutoff. All three converged on roughly 1 to 5 IQ points for each additional year of education, persisting across the life span and appearing on every broad category of ability studied. Their conclusion is blunt: education is the most consistent, robust and durable method yet identified for raising intelligence.

The Flynn effect. Average scores rose across generations for most of the twentieth century. Trahan and colleagues meta-analysed 285 studies since 1951 and put the rise at 2.31 standard-score points per decade overall, and 2.93 points per decade on modern Stanford-Binet and Wechsler tests. Gene pools do not move that fast; environments do. There is more on what that means for score comparisons on our page about the average IQ.

Those two facts sit alongside high heritability rather than contradicting it — which is the point. Heritability tells you where today's differences come from. It does not tell you what would happen if you changed the conditions, and when we have changed them, scores moved.

Why heritability says nothing about groups

Because it is the question people arrive with, it is worth answering plainly: a heritability estimate is calculated within a population and carries no information about why two populations differ on average. A trait can be highly heritable inside each of two groups while the entire gap between them is environmental. This is a limitation of what the statistic measures, not a political position, and it means heritability figures cannot be used to draw conclusions about national, ethnic or social groups. Anyone using them that way has misunderstood the number, whatever conclusion they reach with it.

How this relates to a test score

A score on any cognitive test is a measurement of how someone performs today, on a particular sample of reasoning tasks. It is not a readout of inherited potential, and no test can separate what a person was born with from what they have learned. If you want to know what a score does and does not represent, our guide to how IQ tests work covers the mechanics, and types of intelligence covers what a single number leaves out.

Two working conclusions follow from everything above, and they are deliberately modest. A score is informative about the present and unreliable as a prophecy. And a person's worth, character and prospects are not contained in it — heritability is a statement about variance in a population, never about the value of anybody in it.

IQ Revealed does not offer genetic testing and does not analyse DNA. Our assessment estimates reasoning ability from your answers on the day you take it. Nothing on this page is a medical, diagnostic or genetic service, and no test can tell you what you inherited. Stanford-Binet and Wechsler are the intellectual property of their respective publishers, Riverside Insights and Pearson; they are named here for reference only, and IQ Revealed is not affiliated with, endorsed by or connected to either company.

Frequently asked questions

Is intelligence genetic or environmental?＋

Both, and the proportions are not fixed. Twin and family studies put the heritability of intelligence at roughly 20% in infancy, rising to perhaps 80% in later adulthood (Plomin & Deary, Molecular Psychiatry, 2015). But heritability describes how much of the variation between people in one population, at one time, tracks genetic differences — it is not the share of any one person's ability that came from their genes, and it changes with circumstances.

Is IQ 80% genetic?＋

That figure is the top of a range, not a general fact. Heritability estimates for intelligence rise with age: about 20% in infancy, around 40–50% in childhood, and up to roughly 80% in later adulthood. Quoting the adult figure as though it applied to a child is the single most common error in this area. Estimates also fall sharply in poorer households — see the section on socioeconomic status below.

Is intelligence inherited from your mother or your father?＋

From both. The popular claim that intelligence comes only from the mother rests on the idea that the relevant genes sit on the X chromosome. Genome-wide studies do not support it: the variants associated with cognitive ability are spread across the genome, and there are thousands of them, each with a very small effect (Plomin & von Stumm, Nature Reviews Genetics, 2018). No single "intelligence gene" has been identified, from either parent.

Can two parents with average scores have a child with a high IQ?＋

Yes, and it is common. Because a child's score depends on which half of each parent's variants they happen to receive, plus environment and chance, children's scores cluster nearer the population average than their parents' do. Francis Galton described this pattern in 1886 and called it regression toward the mean. It runs in both directions: the children of very high-scoring parents also tend to score closer to average than their parents did.

Does heritability mean intelligence cannot be changed?＋

No, and this is the most important thing to understand about the word. Heritability is a description of where variation currently comes from, not a limit on what is possible. A meta-analysis of 142 effect sizes from 42 datasets covering more than 600,000 people found that each additional year of education raises intelligence-test scores by roughly 1 to 5 points, with effects that persist across the life span (Ritchie & Tucker-Drob, Psychological Science, 2018).

Have scientists found the genes for intelligence?＋

Not in the sense most people mean. Genome-wide association studies have identified inherited sequence differences that account for about 20% of the roughly 50% heritability of intelligence — a substantial research achievement, and still a long way from a readable genetic prediction of anyone's ability. The trait is polygenic: thousands of variants, each contributing a tiny amount.

Does a high heritability explain differences between groups?＋

No. Heritability is calculated within a population and says nothing about why two populations differ on average. A trait can be highly heritable inside each of two groups while the gap between those groups is caused entirely by their different environments. This is a point of basic statistics rather than a matter of opinion, and it is why heritability figures cannot be used to draw conclusions about national, ethnic or social groups.