Heritability

Heritability is the measure of genetic contribution to phenotypic variance. Given phenotypic variance $V_P$ and genetic variance $V_G$, we have broad-sense heritability $H^2=\frac{V_G}{V_P}$. Genetic variance can be broken down between additive $V_A$, and non-additive (dominance $V_D$ and epistatic $V_I$). This allows to calculate narrow-sense heritability $h^2=\frac{V_A}{V_P}$.

Methods for estimating heritability include Twin studies and GWAS.

For example, twin studies put IQ heritability between 0.6 and 0.8 in adulthood¹².

Trait	Twin studies	GWAS
IQ	0.5 - 0.8	0.1 - 0.3
Big five traits	0.4 - 0.6	0.05-0.15
Height	0.7 - 0.9	0.5 0.7

Some traits, especially intelligence, show a great gap between heritability estimations from twin studies and GWAS. This is known as the Missing heritability problem.

However heritability is typically measured within group. Withing-group heritability does not automatically generalize to between-group heritability, see Lewontin’s separate soils.

Footnotes

1. Jacobs et al. (2001), Heritability estimates of intelligence in twins: effect of chorion type ↩

2. Wright et al. (2001), Genetics of cognition: outline of a collaborative twin study ↩