Is IQ Genetic? How Much of Intelligence Is Inherited

Updated 15 October 2026. About 13 minutes to read.

Is intelligence genetic or learned?

Both. Scientists measure how much genes matter with a statistic called heritability: the share of the differences in a trait across a group of people that can be linked to genetic differences. For IQ, most large studies put heritability at around 50%, which means genes and environment both play major roles.

Heritability is easy to misunderstand, so three points are worth remembering:

• It describes groups, not individuals. A heritability of 50% does not mean half of your IQ came from your genes and half from your upbringing. It describes the causes of differences between people in a population.
• It can change. Heritability depends on the environment people live in. When everyone has similar access to good schools and nutrition, genetic differences explain more of what remains.
• High heritability does not mean unchangeable. Height is highly heritable too, yet average height has risen a lot over the last century thanks to better nutrition.

For a refresher on what IQ scores actually measure, see our guide to what an IQ test is.

How do we know IQ is partly genetic?

Researchers cannot run experiments on people’s genes, so they use natural experiments: comparing relatives who share different amounts of DNA and different environments.

Twin studies

Identical twins share almost all their DNA, while non-identical twins share about half, like ordinary siblings. If identical twins are more alike in IQ than non-identical twins, that points to a genetic influence. Across hundreds of studies, they are. A classic 1981 review by Thomas Bouchard and Matt McGue found IQ correlations of about 0.86 for identical twins raised together and about 0.60 for non-identical twins.

Twins raised apart

The Minnesota Study of Twins Reared Apart followed identical twins who were separated early in life and grew up in different families. Their IQs were still strongly similar, with a correlation of around 0.70, even though they shared no home environment.

Adoption studies

Adopted children’s IQs tend to resemble their biological parents more than their adoptive parents by adulthood. Yet adoption studies also show the power of environment. A 2015 Swedish study by Kenneth Kendler and colleagues found that brothers adopted into families with more educated parents scored about 4.4 points higher than their biological brothers raised at home.

How similar is IQ between relatives?

This table shows typical IQ correlations from family studies. A correlation of 1 would mean identical scores; 0 would mean no relationship at all.

The pattern is clear: the more DNA people share, the more similar their IQs. But notice that identical twins are not perfectly alike, and even the same person does not score identically twice. Environment, chance and measurement error all play a part.

Why IQ becomes more genetic with age

One of the most surprising findings in this field is that the heritability of IQ increases as we get older. A 2010 study by Claire Haworth and colleagues, using data from about 11,000 pairs of twins, found heritability rose from about 41% at age 9 to 55% at age 12 and 66% at age 17. Other research suggests it reaches around 80% in adulthood, a pattern sometimes called the Wilson effect.

The likely reason is that as children grow up, they increasingly choose their own environments. A child who loves reading seeks out books, friends and activities that build on that interest. Over time, small genetic differences in interests and abilities get amplified by the environments people choose. In early childhood, the family home has a bigger influence, but its effect on IQ fades by adulthood.

Is there an intelligence gene?

No. Intelligence is what geneticists call polygenic: it is influenced by thousands of genetic variants, each with a tiny effect. A 2018 study by Jeanne Savage and colleagues analysed the DNA of nearly 270,000 people and identified 205 regions of the genome linked to intelligence, involving more than 1,000 genes. Each one shifts IQ by only a fraction of a point.

Scientists can now combine these variants into a “polygenic score”. Today, such scores predict only around 10% of the differences in intelligence between people, far less than twin studies suggest genes explain overall. They cannot predict an individual’s IQ with any real accuracy, and you should be wary of any company claiming to test a person’s or an embryo’s intelligence from DNA.

Is intelligence inherited from the mother?

This claim went viral online and is still widely shared, but it is not supported by the evidence. The idea rests on the fact that some genes linked to brain development sit on the X chromosome. Mothers pass an X chromosome to all their children, while fathers pass theirs only to daughters.

Here is what that really means:

• Genes linked to intelligence are spread across all 23 pairs of chromosomes, not concentrated on the X chromosome.
• Children inherit half their DNA from each parent, so both parents contribute roughly equally to a child’s genetic potential for intelligence.
• Sons may get slightly more of their X-linked genes from their mother, but this is a small part of the overall picture.

Mothers often do have a big influence on children’s development, but mainly through upbringing, health in pregnancy and the home environment, which fathers can influence too.

Can two average parents have a gifted child?

Yes. Because intelligence depends on so many genes, each child receives a different random mix from their parents. Brothers and sisters can differ by 10 to 15 IQ points or more. Two parents of average intelligence can have a gifted child, and two very bright parents can have a child of average intelligence.

Statistically, children of parents with very high or very low IQs tend to score closer to the average than their parents, an effect called regression to the mean. It does not mean bright parents have less able children; it reflects the fact that an exceptional score usually involves some luck in both genes and circumstances, which does not repeat perfectly.

Does environment still matter?

Very much. Genes set a range of possibilities, and environment influences where within that range a person ends up. The strongest evidence comes from these findings:

• Education. A 2018 meta-analysis by Stuart Ritchie and Elliot Tucker-Drob found each extra year of education raises IQ by about 1 to 5 points.
• The Flynn effect. Average IQ scores rose by about 3 points per decade across many countries in the 20th century. Genes cannot change that quickly, so the rise must reflect better schooling, nutrition, health and more complex daily lives.
• Nutrition and health. Iodine deficiency, iron deficiency and childhood illness can lower IQ. Fixing these problems makes a measurable difference.
• Poverty and opportunity. A well-known 2003 study by Eric Turkheimer found that in poorer US families, genes explained much less of the variation in IQ, suggesting that a poor environment can hold back genetic potential. A 2016 meta-analysis found this pattern mainly in the United States rather than in Western Europe or Australia, where access to schooling and healthcare is more equal.

For practical, research-backed ways to make the most of your own ability, read our guide on how to increase your IQ.

Nature vs nurture: what the evidence really says

Frequently asked questions

IQScore guides are for education and information. Heritability figures describe averages across populations and cannot be applied to any individual or family.