FIG. 4.—

The magnitude of divergence rate elevation scales with effective population size. For a set of sites with selection coefficient s, the long-term evolutionary rate is given by 2π₁(s). Using the distribution of negative s, gamma(0.23, 0.187), we integrate 2π₁(s) times this distribution function to obtain the asymptotic rate across a set of sites whose fitness effects are distributed as assumed. Denote this rate r_a. Using r_a, we plot the rates obtained in figure 3 as a multiple of r_a on the y axis. To be precise, the quantity on the y axis is n where r = nr_a. On the x axis, we plot the number of generations as a multiple of population size N. Hence, the quantity on the x axis is l where the number of generations equals lN. The figure was calculated using N = 500, but for other values of N considered (up to 5,000), the figure superimposes. For the other distributions of s considered in this paper, the results are similar.