Observing animal species with exaggerated ornaments and weapons that do not seem of importance in the animal’s struggle for survival, Darwin created the concept of sexual selection to account for the evolution of these traits. A result of the interactions between individuals of the same sex, opposite sexes or both, sexual selection essentially occurs when individuals compete for access to gametes of the opposite sex. As typically it is the male sex that produces abundant sperm and the female that generates less numerous eggs, a competition among males ensue to ensure their sperm locates and fertilizes the eggs. This generates male-male competition, driving intrasexual selection.Females tend to be the ones who choose with whom to mate – a phenomenon that has led to the evolution of elaborate male traits. More specifically, Fisher’s hypothesis accounts for the evolution of traits such as the extreme tail lengths in widow birds. The idea proposed by Fisher was that females preferred initially a trait that indicates something about the male’s quality. The advantage of this trait was then passed to the female’s sons which are found more attractive by females and have higher reproductive success, eventually leading to the establishment of the preference for longer tails. This leads to a positive feedback between preference and the development of the traits.
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