fixation without the interference of the second mutant. For small positive $\Delta t$, we observe a decrease of $T_{1}$. The decrease occurs for those $\Delta t$ for which the two beneficial mutants coexist for several generations in the population. Fixation of mutant 1 in this regime occurs only when mutant 1 reaches fixation so quickly that mutant 2 has not had time to build up momentum. Otherwise, most likely mutant 1 will be displaced by mutant 2 before reaching fixation. For mutant 2, the time to fixation $T_2$ is shorter for negative $\Delta t$ than for positive $\Delta t$. For positive $\Delta t$, in a fraction of cases mutant 2 has to go to fixation in a background of mutant 1, rather than in a background of wild type. In the background of mutant 1, the selective advantage of mutant 2 is smaller than in a wild-type population, which explains the increased time to fixation. Interestingly, before $T_2$ starts to rise for increasing positive $\Delta t$, it quickly spikes at $\Delta t\approx 30$. This spike has the following explanation: If mutant 1 is introduced right before mutant 2 has reached fixation, then the time to fixation of mutant 2 is 