Frozen Evolution. Or, that’s not the way it is, Mr. Darwin. A Farewell to Selfish Gene.

If an advantageous mutation occurs in an individual whose genome carries a disadvantageous mutation, an advantageous mutation cannot be fixed in asexually reproducing organisms or it becomes fixed together with the disadvantageous mutation. In contrast, in sexually reproducing species, an advantageous mutation sooner or later during genetic recombination gets rid of its unpleasant neighbourhood and “moves” to a chromosome without a disadvantageous mutation (Fisher 1958). This model is currently considered to be extremely important, as it is capable of explaining the advantageousness of sexual reproduction in a wide range of ecological and genetic parameters in organisms with very diverse reproductive systems (Crow 1994). Experiments with cultures of the yeast S. cerevisiae have demonstrated that sexuality increases the average fitness of individuals especially under stable conditions, to which the yeast is adapted, but not under altered or changing conditions. This indicates that sexuality is apparently of fundamental importance for elimination of detrimental mutations from the genome, but not for fixation of new adaptive mutations required for adaptation to changing conditions (Zeyl & Bell 1997).