Realized Heritability. The proportion of the variation in reflectance peak wavelength that is caused by additive genetic variation in our laboratory pop- ulation is called the realized heritability (43). This measure of heritability was estimated from two quantities: the response to selection and the cumulative selection differential. The response to selection (y axis in Fig. 2B)tracksthe change in mean reflectance peak wavelength for all individuals in a generation over the course of the selection experiment. The cumulative selection differential (x axis in Fig. 2B) is a cumulative measure of the selection pressure applied in