Why is sexual selection considered a theory?

Sexual selection is regarded as a theory because it provides a robust framework for understanding the evolution of certain traits that do not necessarily enhance an individual's survival but instead increase their chances of reproductive success. A clear example of this is the extravagant plumage of the peacock, which can actually hinder its survival due to increased visibility to predators. However, the peacock's impressive tail is an adaptation that attracts peahens and enhances the male's reproductive success, illustrating how sexual selection drives the evolution of traits that might seem counterintuitive in terms of survival.

This concept goes beyond simple survival of the fittest, which encompasses all aspects of fitness, including those traits that contribute to survival rather than reproduction. Sexual selection also extends to a variety of contexts beyond just specific animal behaviors or mate competition strategies, encompassing diverse forms of sexual traits and preferences across many species. Therefore, understanding sexual selection as a theory involves recognizing its broad application and the unique role it plays in influencing evolutionary trajectories.