 Equation (1) simply says that the phenotypic variance is the variance due to genes plus the variance due to the organisms’ environment. Behavioral geneticists and psychologists introduce heritability in the following way: Heritability is the proportion of phenotypic variance that is attributable to genotypic variance: heritability \(= \bfrac{V_G}{V_P}\) (Biologists will also sometimes talk of “environmentability”, which is \(\bfrac{V_E}{V_P}\).)