Heritability
The proportion of variation in a trait across a population that is due to genetic differences, rather than environmental factors.
The percentage of variation in a trait within a population attributable to genetic differences between individuals, rather than environmental influences. Measured through twin studies, family studies, and adoption research, heritability ranges from 0% (entirely environmental) to 100% (entirely genetic). A trait's heritability in one population does not predict its heritability in another with different environmental conditions.
What this means in real life
If a condition has 60% heritability, it means genetic differences explain about 60% of why some people develop it and others don't in a given population—but the remaining 40% comes from environment, lifestyle, or chance.
What it isn’t
Heritability does not mean a trait is unchangeable or 'genetic destiny.' High heritability only describes variation in a specific population; it says nothing about whether interventions, therapy, or environmental changes can reduce the trait's expression.
Commonly misused online
People often treat heritability as proof that a condition is 'hardwired' or untreatable. In reality, highly heritable traits (like height) are still shaped by nutrition; heritability is a population statistic, not a guarantee about individual outcomes.