Yes, intelligence is substantially heritable. In adults, genetic differences account for roughly 60% of the variation in IQ scores across a population, with some estimates reaching as high as 80% by late adolescence and early adulthood. But that number is more nuanced than it first appears, and understanding what “heritable” actually means in this context changes the picture considerably.
What Heritability Actually Means
Heritability is a population-level statistic. It describes how much of the variation between people in a given trait can be traced to genetic differences versus environmental ones. A heritability of 0.60 for intelligence does not mean 60% of your IQ was “caused” by your genes. It means that, within a particular population living in a particular set of circumstances, 60% of the reason people differ from one another in cognitive ability comes down to genetic variation.
This distinction matters because heritability estimates can shift when environments change. In a population where everyone has access to similar nutrition, schooling, and stability, most of the remaining differences between people will be genetic, pushing heritability higher. In a population with wide disparities in living conditions, the environment explains more of the gap, and heritability drops. The number is always a snapshot of one group in one context, not a fixed property of intelligence itself.
Genetic Influence Grows With Age
One of the most consistent findings in behavioral genetics is that the heritability of intelligence increases as people get older. In infancy, genes account for only about 20% of IQ variation. By adolescence, that figure climbs to around 40%. In adulthood, it reaches roughly 60%, and some evidence places it as high as 80% by the late teens and into middle age. After about age 80, it appears to drop back to around 60%.
This pattern, known as the Wilson effect, initially seems counterintuitive. You might expect life experience to accumulate and push environmental influence higher over time. Instead, the opposite happens. One explanation is that as people gain more freedom to choose their own environments (selecting hobbies, careers, social circles, and learning opportunities that match their natural inclinations), their genetic predispositions get amplified rather than diluted. A child’s environment is largely chosen for them; an adult’s environment increasingly reflects who they already are.
At the same time, the influence of the shared family environment (the home you grew up in, your parents’ income, the neighborhood) shrinks to roughly 10% by age 18 and stays low into adulthood. The childhood home matters enormously in the short term, but its measurable effect on IQ variation fades as people build their own lives.
Twin Studies: The Classic Evidence
Much of what we know about intelligence and genetics comes from twin research. Identical twins share virtually all their DNA; fraternal twins share about half. By comparing how similar each type of twin pair is on IQ tests, researchers can estimate genetic influence.
The most striking data comes from identical twins raised in separate families. These individuals grew up in different homes, sometimes in different countries, yet their IQ scores correlate at about 0.75, meaning they track each other closely. Identical twins raised together correlate even higher. Fraternal twins, whether raised together or apart, are far less similar. That gap between identical and fraternal correlations is the core evidence for a strong genetic component.
Recent reanalysis of twins raised apart has added an interesting wrinkle: differences in how much schooling each twin received significantly affect how similar their IQ scores end up being. Twin pairs with similar education differed by only about 6 IQ points on average (correlation of 0.87), while pairs with large educational differences diverged by roughly 15 points (correlation of 0.56). Genes set a strong baseline, but education clearly pulls scores apart or pushes them together.
What DNA Studies Have Found So Far
Twin studies estimate heritability indirectly. Genome-wide association studies take a more direct approach, scanning hundreds of thousands of people’s DNA to find specific genetic variants linked to cognitive performance. The largest of these studies have identified hundreds of genomic regions associated with intelligence, implicating around 350 candidate genes. No single gene has a large effect. Each variant nudges cognitive ability by a tiny amount, and intelligence appears to be influenced by thousands of genetic variants working together.
Researchers can combine these small effects into a single number called a polygenic score, essentially a genetic prediction of where someone might fall on the IQ spectrum. Current polygenic scores for intelligence explain only about 5% to 7% of the actual variation in people’s test scores. Interestingly, polygenic scores built from education data (years of schooling completed) predict IQ somewhat better, accounting for roughly 10% of the variance. That is partly because education studies have much larger sample sizes, giving the statistics more power.
There is a large gap between the 60% to 80% heritability estimated from twin studies and the 5% to 7% that DNA-based scores can currently predict. This “missing heritability” likely reflects the sheer number of genetic variants involved (many too small to detect individually), rare variants not captured by current methods, and complex interactions between genes that are difficult to model.
How Poverty Changes the Equation
One landmark study examined how socioeconomic status reshapes the balance between genes and environment. Among children growing up in affluent families, the pattern matched the standard story: genetic differences explained most of the IQ variation, and the shared home environment contributed relatively little. But in impoverished families, the results flipped almost entirely. Roughly 60% of IQ variation was explained by the shared environment, and the genetic contribution dropped close to zero.
This does not mean genes stop working in poverty. It means that when children face severe material deprivation, environmental constraints become so powerful that they suppress the expression of genetic potential. Think of it like growing different seed varieties in poor soil: you will not see much difference between the plants because the soil is limiting all of them. Plant those same seeds in rich soil, and the genetic differences between varieties become obvious. For intelligence, the “soil” includes nutrition, cognitive stimulation, stress levels, exposure to toxins, and access to education.
This finding is a strong argument that heritability is not destiny. A high heritability estimate in one population says nothing about whether improving environments could raise scores across the board. It simply describes the current sources of variation among people who share roughly similar conditions.
The Brain Connection
Part of the genetic influence on intelligence appears to operate through brain structure. Total brain volume correlates with IQ, and twin research shows this overlap is driven almost entirely by shared genetic factors rather than shared environmental ones. The genetic correlation between brain volume and performance-based IQ measures (tasks involving spatial reasoning and pattern recognition) is particularly strong, ranging from 0.58 to 0.82 depending on the brain region measured. Processing speed shows a similarly high genetic link with total brain volume and white matter volume.
This suggests that some of the same genes influencing brain development, particularly how much neural tissue you build and how efficiently it connects, also influence cognitive performance. But brain volume is far from the whole story. It is one of many biological pathways, alongside neural efficiency, synaptic pruning, and neurotransmitter function, through which genetic variation translates into measurable differences in thinking ability.
Genes and Environment Work Together
Framing intelligence as “nature versus nurture” misses the real picture. Genes and environments are not independent forces that add up to 100%. They interact constantly. A child with a genetic predisposition toward curiosity may seek out books, ask more questions, and end up in advanced classes, all of which further develop their cognitive ability. This gene-environment correlation means that what looks like a purely genetic effect often includes a chain of environmental responses triggered by genetic tendencies.
Intelligence is heritable in the statistical sense: genetic variation is the largest single source of cognitive differences between people, especially in adulthood and in populations with relatively equal access to resources. But heritability is not fixedness. IQ scores have risen dramatically across generations (a phenomenon called the Flynn effect) in response to better nutrition, education, and living standards, gains far too fast to reflect genetic change. The genes that influence intelligence have not changed in a century, but the environments those genes operate in have changed enormously, and scores moved with them.