An illustration of the possible mutations available to an RNA molecule. The blue lines represent mutations that will not change its function (phenotype), the grey are mutations to an alternative phenotype with slightly higher fitness and the red are the ‘fittest’ mutations. As there are so few possible mutations resulting in the fittest phenotype in red, the odds of this mutation are a mere 0.15%. The odds for the slightly fitter mutation in grey are 6.7% and so this is far more likely to fix, and thus to be found and survive, even though it is much less fit than the red phenotype.,,,
By modelling populations over long timescales, the study showed that the ‘fitness’ of their traits was not the most important determinant of success. Instead, the most genetically available mutations dominated the changes in traits. The researchers found that the ‘fittest’ simply did not have time to be found, or to fix in the population over evolutionary timescales.