Broadly, heritability is the proportion of variation (more strictly variance) in a phenotypic character in a population that is due to individual differences in genotype.

Narrowly, heritability is the proportion of variation (more strictly variance) in a phenotypic character in a population that is due to individual genetic differences that will be inherited by the offspring.

There are three possible ways to estimate the heritability of a real character:

• One method is to cross two pure lines. (This is mainly of interest in applied genetics, where the problem might be to breed a new variety of crops; it has little interest in evolutionary biology.)

• Another method is to measure the correlation between relatives.

• Finally, we can observe the response to artificial selection.

The geneticist Linda Partridge gives a definition of heritability.