Develops a general model for the effects of variation in reproductive success on gene-frequency change and phenotypic evolution. The approach is based on distinguishing among individual, genotypic and population-level reproductive success and on relating these 3 levels through correlations. The authors use these correlations to show the simple relationship among earlier models of selection on the variance of reproductive success, of temporal variation in selection, of spatial variation in selection, and of variation in behavioral traits. This approach also applies to diploid individuals by regarding diploidy as a way to induce correlations in reproductive success between pairs of alleles. The method is applied to patterns of developmental homeostasis, evolution of iteroparity, and the effects of variability in resource acquisition under nonlinear gains. -from Authors