The truth about intelligence: How genetics shape it — but don’t define it
Understanding heritability and why it fails to explain IQ differences between groups
If intelligence has a genetic basis, does that mean some groups are inherently smarter than others? This question, sometimes asked out of curiosity, other times to promote false and harmful narratives about racial differences in intelligence, can be answered with an understanding of two key scientific concepts: heritability and gene-environment interaction.
Heritability is often misunderstood
Heritability measures the proportion of variation in a trait (like IQ) within a specific population that can be attributed to genetic differences under stable environmental conditions. This means heritability estimates apply only within populations with similar conditions and cannot be used to explain IQ differences between groups exposed to different environments.
Consider height: In well-nourished populations, genetic differences explain about 80% of height variation. But in a country suffering widespread malnutrition, nutrition would become the dominant factor.
The same principle applies to intelligence, and IQ which serves as a limited and much debated proxy for intelligence. In societies with equal access to education, genetics explain a larger proportion of IQ variation among individuals. But between groups experiencing vastly different environments due to disparities in education, income, or discrimination, environmental factors overshadow genetic influences.
This is key when comparing intelligence between groups. If two groups have different average IQ scores but also have vastly different social, economic, and educational conditions, heritability estimates within each group cannot be used to explain the difference between them because these environmental disparities overshadow any genetic effects. As a result, heritability within groups does not translate into genetic explanations for IQ differences between groups.
A flawed comparison: Why height is different from intelligence
Proponents of genetically determined differences in intelligence often use height as an analogy, saying things like, “If genetics explain why people from Group 1 are taller than Group 2, why not intelligence?”
This analogy fails because intelligence is shaped by far more complex environmental factors than height, such as education, social interaction, and economic conditions. Unlike height, which is largely determined once basic nutrition is met, intelligence remains highly malleable throughout life.
A better analogy is athletic performance. Genes influence muscle composition, but athletes succeed due to training, nutrition, and coaching. Likewise, genetic potential for intelligence exists, but life circumstances determine how it develops.
Genes matter, but environments shape outcomes
Consider two children with the same genetic potential for intelligence. One is raised by caring parents in a home full of books and engaging conversations, and also benefits from a quality school education. The other has parents who neglect or abuse them and attends an underfunded school where they are bullied. Despite their genetic similarities, their IQ scores as adults are likely to be quite different.
This is gene-environment interaction in action. Genetic potential is not a fixed upper limit, it is an evolving interaction with the environment. Just as plants of the same species grow differently based on soil quality, intelligence develops in response to life conditions. Likewise, any apparent IQ differences between our socially constructed racial groups are best explained by environmental disparities.
Environmental factors best explain group level IQ differences
While genetic differences contribute significantly to IQ variation between individuals within a given population, the same does not hold at the group level, and yet some wrongly claim IQ disparities between racial or ethnic groups are rooted in genetics. This is scientifically unfounded because:
- IQ disparities shrink when the environment improves. Throughout the 20th century, global IQ scores increased by about three points per decade due to better nutrition, education, and healthcare — a trend known as the Flynn Effect. This contradicts the idea that intelligence is primarily genetic and highlights the dominant role of the environment. If IQ were fixed by genes we wouldn’t see such large and rapid increases over generations. And we see the same pattern across racial groups — when barriers to learning and healthy development disappear, so do IQ disparities.
- Genetic potential for intelligence is evenly distributed across human populations. Large-scale genetic studies show that while thousands of genes influence intelligence, each gene variant only contributes an incredibly small effect. This complex, polygenic nature of genetic influence on intelligence is why studies have consistently found no evidence of genetic differences in intelligence between ‘races’.
This second point makes sense when you consider the fact that genetic variation is greater within the so-called racial groups than between them. The reality is our racial categories are social constructs that have no scientific or genetic basis. Because human populations have mixed throughout history, the genetic factors influencing intelligence are widely distributed and do not cluster into racial categories in a way that meaningfully impacts group-level differences in intelligence.
The danger of genetic determinism
The idea that genes alone determine intelligence is not only wrong but weaponised pseudoscience historically misused to promote racist ideologies and justify eugenics, racial discrimination, and educational neglect. In reality, intelligence is a malleable trait.
Past claims of genetic racial IQ differences have been debunked due to their flawed methodologies, especially the failure to account for socioeconomic and educational factors. When these variables are accounted for, racial IQ differences shrink significantly or disappear altogether.
Intelligence is heritable, but it is not genetically determined. That distinction makes all the difference, as does the environment — studies show interventions such as early childhood education and enriched environments can significantly influence cognitive ability.
Intelligence is complex — don’t let anyone oversimplify it
Whenever someone claims intelligence gaps between racial groups are genetic, ask them: Why do IQ scores increase over generations regardless of racial groupings when barriers to learning and healthy childhood development are removed? Why haven’t genetic studies found intelligence genes unique to any one so-called racial group?
The answer is simple: there is no genetic evidence supporting racial intelligence differences.
Apparent intelligence differences between racial groups result from environmental disparities. The thousands of genes associated with intelligence do not cluster along our socially constructed racial divides, meaning on average human beings all have the same genetic potential for intelligence — it is just that our shared genetic potential for intelligence can yield vastly different outcomes depending on life circumstances. That’s why when opportunities to learn and develop improve, so does intelligence across all groups.
Genes influence intelligence, but they do not determine it. Genetic potential for intelligence is the same across all racial groups because racial groups are socially constructed rather than genetically demarcated — what differs is access to opportunities. Recognising this and working toward equality of opportunity is the key to ensuring everyone reaches their full potential.
Jonathan Meddings is an author and advocate from Melbourne, Australia.
