Heritability

Heritability is the proportion of the variation in a trait within a population that is due to genetic differences between individuals. It is a statistic about a group in a particular environment, not a measure of how much of a person's trait is "genetic."

Broad-sense heritability (H²) is the share of total variation in a phenotype caused by all genetic variation. Narrow-sense heritability (h²) counts only the additive effects of alleles, which are the part that parents pass predictably to offspring. The concepts were worked out by Ronald Fisher and Sewall Wright, and they are central to quantitative genetics.

Heritability is estimated by comparing relatives: the resemblance of parents and offspring, of identical and fraternal twins, or of animals with known pedigrees. Modern studies also use differences in the genome among unrelated individuals. Human height has a heritability of around 80 percent in well-nourished populations, while many behavioral and disease traits are lower.

A high heritability does not mean a trait is fixed or immune to the environment: the value changes if the environmental variation changes, as when better nutrition raises height. It also says nothing about the causes of differences between groups. Heritability determines how fast a trait can respond to natural selection, as expressed in the breeder's equation.

• Phenotype — the trait being studied
• Breeder's Equation — how heritability predicts response to selection
• Population Genetics — the field where it is used