Abstract In many species the sexes may differ in their contribution to the production and care of offspring. Previous theory and observations have shown that the sex which contributes least will also be the sex with the highest variance in mating success. I show that this phenomenon can result from random mating. Bateman's (1948) experiment showed that male Drosophila melanogaster were more variable in their mating success than were females. This additional variability is usually attributed to intra-male competition and female choice but I show that this phenomenon can result from random mating.