From the data of an experiment of selection for increased longevity, a
realized heritability of longevity was calculated. The low value of t
his heritability (3.4%) was very close to values observed in other exp
eriments concerning Drosophila melanogaster wild strains. The error va
riance of the heritability estimator was calculated through the use of
orthogonal contrasts. In this way, it was possible to calculate the c
onfidence interval of the realized heritability. The amplitude of this
interval was wide although the size of the sample was large. This sho
ws the difficulty of estimating with precision the heritability of lon
gevity from data obtained in selection experiments.