Figure 3.

Dynamics of reversion for a codon model where the focal amino acid has scaled selection coefficient S over all other amino acids and mutations occur at rate 1 at each site with an equal probability of producing each of the alternative nucleotides. The top row shows the probability of having reverted by time t and the bottom row shows the reversion rate, $h\left(t\right),$ where each of the 20 curves corresponds to a different choice of one of the 20 amino acids as the focal amino acid. Under moderate selection for the focal amino acid ($S=5$), the time evolution of the fraction of populations that have already reverted shows a pronounced knee.