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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 — not genes — would become the dominant factor, reducing heritability.
