The foraging assay: fruit flies are eating the yeast that ferments fruits. In an experiment, yeast was mixed with water and spread on a well on a glass plate. A rover and a sitter were placed on the glass plate: the rover moved over a much longer distance than the sitter. This shows the phenotype: green fluorescent protein was used through genetic crosses to make rovers and sitters that would either glow or not glow, in the experiment, vials were filled with 32 larvae. Natural selection: natural selection does not necessarily lead to an absolute optimum in a particular trait. Instead, natural selection favours a competitive optimum: as good or better then alternatives. Evolution as a controversy: evolution can be a controversy to people who have religious beliefs. Charles robert darwin (1809 1882): he was born in shrewsbury england to a wealthy family, he was always interested in nature.