Discussions of the implications of sexual reproduction have appeared throughout the history of evolutionary biology, from Darwin to Weismann, Fisher, Muller, Maynard Smith, and Williams. The latest of these appearances highlighted an evolutionary paradox that had previously been overlooked. In many animal and plant species reproduction is obligately sexual and also half the offspring are male, yet the males contribute nothing but genes to reproduction. If asexual mutants of such a species were to produce as many asexual offspring on average as sexual females in that species produce daughters and sons, the growth rate of their population would be twice as large. Whereas half the offspring of sexual females are noncontributory males, all the offspring of such an asexual mutant would contribute to growth rate. Nevertheless, sexual reproduction prevails in most species and is not lost evolutionarily.