Final answer:
Sexual dimorphism varies among species, resulting in differences in reproductive success between males and females. Males often have elaborate traits and ornaments to attract females, while females tend to choose more desirable males.
Step-by-step explanation:
Sexual dimorphism varies widely among species, and some species are even sex-role reversed. In such cases, females tend to have a greater variance in their reproductive success than males and are correspondingly selected for the bigger body size and elaborate traits usually characteristic of males.
Males and females of certain species are often quite different from one another in ways beyond the reproductive organs. Males are often larger, and display many elaborate colors and adornments, while females tend to be smaller and duller in decoration. Such differences are known as sexual dimorphisms, which arise from the fact that in many populations, particularly animal populations, there is more variance in the reproductive success of the males than there is of the females.
This variation in reproductive success generates a strong selection pressure among males to get those matings, resulting in the evolution of bigger body size and elaborate ornaments to get the females' attention. Females, on the other hand, tend to get a handful of selected matings; therefore, they are more likely to select more desirable males.