Sexual selection is designated as variance in the number of mates.
Because females are the limiting sex, and females invest more in offspring than males, males tend to be competing for females. Thus, males tend to develop ornaments for attracting females or engaging other males in contests. These are referred to as sexual dimorphisms. For example, in pipefish, a form of sea horse, males are limiting because they brood the offspring in a pouch. In this case females compete for mates, and in some pipefish species, females are more brightly colored than males.