Hermaphrodite. 1. The proportion of total phenotypic variation in a trait attributable to genetic variation; determines the potential for evolutionary change in a trait. 2. Heritability is the amount of variability within a group, raised in the same environment, that is due to genetics.It does not apply to between-group differences.. The proportion of total phenotypic variation in a trait attributable to genetic variation; determines the potential for evolutionary change in a trait. 2. Heritability is the amount of variability within a group, raised in the same environment, that is due to genetics. It does not apply to between-group differences.