How does sexual dimorphism commonly arise in a species?

Sexual dimorphism, the distinct difference in size or appearance between the sexes of a species, commonly arises from sexual selection and competition. This evolutionary process occurs when individuals of one sex (typically females) choose mates based on certain desirable traits, or when individuals of one sex (typically males) compete with one another for access to mates.

Traits that are favored by sexual selection, such as larger size, more vibrant colors, or elaborate display behaviors, can lead to pronounced differences between males and females over generations. For example, in many bird species, males may develop bright plumage to attract females, while females remain more cryptic in color for better camouflage against predators. This difference in traits is directly influenced by reproductive success, as those individuals that possess traits favored by the opposite sex or that can successfully compete for mates will be more likely to reproduce and pass those traits on to future generations.

This mechanism highlights the role of sexual selection in driving the evolution of distinct morphological and behavioral characteristics between sexes, ultimately leading to the phenomenon of sexual dimorphism.