Heritability
The share of trait differences in a population traceable to genetic differences.
What it means
Heritability is a statistic estimating the proportion of the variation in a trait across a population that can be attributed to genetic differences among individuals, typically derived from twin, family, and adoption studies or molecular methods. Most personality traits, intelligence, and well-being show moderate to substantial heritability (often 40–60%). Crucially, heritability is widely misunderstood: it is a population-level statistic, not a statement about how 'genetic' a trait is in any individual; it says nothing about immutability (highly heritable traits can be changed by environment); and its value depends on the population and environment studied. The remaining variance reflects environment, much of it the 'non-shared' environment unique to each person. It matters because nearly every individual-difference construct in behavioral science carries a genetic component, and misreading heritability fuels fatalism and flawed nature-versus-nurture conclusions.
Examples
Saying a trait is '50% heritable' means half the differences among people in a given population trace to genes — not that half of any one person's trait is genetic.
Height is highly heritable, yet Dutch adults grew markedly taller across the twentieth century — genes explain who is tallest within a generation, not why the whole generation shifted.
If every child had identical schooling, the differences left in reading would trace more to genes and heritability would rise — the number describes the environment as much as the genes.
First described in Quantitative behavior genetics; Fisher, Falconer; modern twin studies.