Sex ratio affects both the growth rates and the evolutionary trajectories of wild populations. The sex ratio of the population affects, and is affected by, birth, death, immigration, and emigration rates. It is measured as the ratio of the number of individuals of one sex to that of the other sex, or the ratio of allocation in each. The production of males and females in a ratio of 1:1 is generally the most common evolutionary stable strategy (ESS), led by frequency-dependent natural selection due to competition for mates among individuals of the same sex. Natural selection often appears to determine the differences within and among populations and species in sex ratio. The optimum sex ratio for a given individual in a given population depends on both the existing sex ratio of the population and...