The influence of cyclic fluctuations of Drosophila population density, which result from varying exploitation pressure and feeding conditions, on reorganization of the genotypic composition, evaluated for individual reproductive capacity, was studied. It was found that productivity, which was assessed in individual cultures by the number of adult offsprings, was higher for individuals that lived in low density conditions as compared to those in dense populations. These differences persisted in offsprings of compared individuals in two successive generations, thus testifying to their genetic determination. The genotypic composition of populations may change in one or two generations because of the selective pressure of density.