Relationship between population size N and genetic diversity at varying intensities of selection. Nucleotide diversity represents mean pairwise proportion of sequence differences between random individuals in the population. Diversity estimates are taken from 105 generations across 3 replicate simulations. Neutral dynamics are shown as a dashed line. Selective dynamics are shown as solid lines. In each case, 1% of mutations are selectively advantageous, with a selective advantage s of 0.001, 0.01 or 0.1.