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.
             Fisher (1930) (Fisher in Krebs 1981) first suggested that females selected males with an enhanced feature as it indicated something about the male. Maybe they were better at flying and collecting food. It may also indicate something about male quality. Longer tails for example could simply be easier to detect and a point for species recognition. Longer tailed males may pass on an advantage to the females sons, hence the 'sexy son hypothesis'. The off-spring would both possess the genes that grow long tails (males) and those that choose them (females). Eventually the co-evolving genes for enlarged features would become so large that it would endanger the species, so the species would be checked by natural selection. (Howlett 1993). This is what Fisher called the 'Runaway' hypothesis (R.A. Fisher in Krebs & Davies 1993)Fisher then simplified his h
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