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What is heritability?
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Inheritance

What is heritability?

Heritability is a statistical concept that measures how much of the variation in a specific trait within a population is due to genetic differences.

Understanding Heritability

Heritability (represented as h²) describes how well differences in people’s genes account for differences in their traits, such as height, eye color, intelligence, or disorders like schizophrenia and autism spectrum disorder. An estimate of heritability is specific to one population in one environment and can change over time.

Interpreting the Scale

Heritability estimates range from zero to one:

  • Close to zero: Indicates that almost all variability is due to environmental factors. Traits like religion or language spoken have a heritability of zero because they are not under genetic control.
  • Close to one: Indicates that almost all variability comes from genetic differences. Disorders caused by variants in single genes, such as phenylketonuria (PKU), have high heritability.
  • In the middle: Most complex traits and multifactorial diseases result from a combination of genetic and environmental factors.

Common Misconceptions

  • Not a proportion of a trait: A heritability of 0.7 does not mean a trait is 70% caused by genes; it means 70% of the variability in that population is due to genetic differences.
  • No information on specific genes: It does not identify which genes or environmental influences are involved.
  • Heritable vs. Familial: A trait is "familial" if shared by family members, but this can be due to shared environment or lifestyle rather than genetics.
  • Changeability: High heritability does not mean a trait is difficult to change (e.g., hair color is highly heritable but easily changed with dye).

Why Researchers Study It

Researchers use heritability to understand complex traits. By comparing traits in identical twins (who share almost all DNA) versus fraternal twins (who share about 50%), scientists can gain initial clues about the relative influence of "nature" (genetics) and "nurture" (environment).

Frequently Asked Questions

Researchers compare identical (monozygotic) twins, who share 100 percent of their DNA, with fraternal (dizygotic) twins, who share about 50 percent of their DNA. If identical twins show a significantly higher rate of sharing a disorder than fraternal twins when raised in the same household, the excess similarity is attributed to genetics. Adoption studies complement this by comparing adopted children to both their biological parents (shared genes, separate environments) and adoptive parents (shared environment, separate genes).
hereditary disease refers to a medical condition directly passed from parent to child through specific genetic variants, such as Huntington disease. In contrast, heritability is a broader statistical metric used in research to evaluate how much the overall differences among individuals in a group are tied to their genetic differences. A trait can be biologically hereditary without researchers having a clean heritability estimate, and complex traits like height or blood pressure have high heritability without being caused by a single hereditary gene.
No. Heritability describes the proportion of variation among people in a population, not the inevitability of a trait in a single person. Even traits or diseases with high heritability can be influenced significantly by environmental interventions. For example, phenylketonuria (PKU) is a genetic disorder with nearly 100 percent heritability, yet strictly removing phenylalanine from an infant's diet completely prevents the severe intellectual disability the gene variant would otherwise cause.
Because heritability is a population-specific ratio that depends on both genetic variation and environmental variation in that specific group at that specific time. If a population lives in a very uniform environment with identical diets, healthcare access, and living conditions, environmental differences diminish, causing the genetic proportion of variance (heritability) to rise. Conversely, in a population with wide disparities in environment, environmental variance increases, driving the heritability estimate down.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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