Why do some birds have long tails, others have bright plumage or patterns and others possess beautifully complicated songs. Many animal behaviourists have agreed that all these characteristics are developed as a result of female sexual selection, but that is where the agreement stops. The many theories on the evolution of secondary sexual characters, are an evolution in their own right. The purpose of this paper is to analyse the evolution of the research and hypotheses on this subject.
Sexual selection is a corollary of natural selection and the two processes work in the same manner.
Sexual selection occurs when the members of one sex mate disproportionately with members of the opposite sex on the basis of secondary traits, i.e. behaviours or structures other than reproductive organs or gametes. There are three main hypothesis that run through the whole subject of sexual selection, within which are many more hypothesis. Darwin suggested that many apparently deleterious secondary sexual characters in males such as bright colours, elaborate ornaments and conspicuous displays, evolved as a result of female choice. Darwin never tried to explain the crucial agent of selection, that females have preferences for exaggerated male traits. Fisher Fisher's basic idea was that a novel but essentially arbitrary male trait such as a long tail might appear in a population and enjoy, for whatever reason, a slight advantage.