Darwin used the phrase ‘survival of the fittest’ for natural selection. But the article points out that natural selection is not necessarily survival selection. Survival is only important as it is part of the reproduction process. Darwin made some observations that didn’t seem to be about survival, for example, brilliant plumage of a bird that could not have been advantageous for survival. He also noticed that males and females of the bird were different (the males were gaudy and the females were drab) yet faced the same survival challenges. Because of these anomalies, Darwin put forward a second evolutionary process which he called sexual selection which basically said that characteristics that give an organism advantage for competition for mates can evolve. He defined two processes in this evolutionary process. One is intrasexual with same-sex competing for a mate so that whatever characteristics the mate favours will evolve. The second is intersexual in which the quality is determined by the mate as desirable. Then those with that quality will have a preferential advantage. Characteristics evolve for reproductive advantage acquired through successful mate competition. The theory explained a lot of Darwin’s anomalies but still was not widely accepted in Biology when he put it forward in 1871.Darwin’s theory did not explain the origin of mate choice. The next major development came in 1930 with the publication of R.A. Fisher’s book The Genetical Theory of Natural Selection. Fisher proposed the theory of ‘runaway selection’. He described evolution as a two-step process. First, there is genetic variation in a trait, for example, tail length in some animals. Males with longer tails will survive more. Secondly, the female has a genetic variation for their choice of the tail- they prefer long tails. Therefore females will select long-tail males and bear sons with longer tails. Over generations, the genes for long tails will survive and the genes for female preference for long-tailed males will survive.