Definition
Heritability is a statistic that estimates what fraction of the variation in a trait, across a particular population in a particular environment, can be attributed to genetic variation among its members. It is a property of a population, not of a person.
Sapolsky flags heritability as one of the most misunderstood numbers in science. A heritability of 0.6 does not mean a trait is 60 percent genetic in any individual. It means that, in the studied group and setting, roughly 60 percent of the differences between people tracked with genetic differences.
Why it matters
How it works
Heritability is usually estimated by comparing the similarity of relatives who share known proportions of genes — identical versus fraternal twins, adopted versus biological relatives. If genetically closer pairs resemble each other more on a trait, that resemblance is read as a genetic contribution to variance. Crucially, the estimate is anchored to the specific environments those people lived in; it does not travel cleanly to other populations or settings.