Fig. 1.
Age distribution of ascertained selected alleles. Each point represents the number of variants dated to a single 10-generation bin. Fitted curves are the number of ascertained variants predicted by Eq. 2 under a constant population size and constant s̄ = 0.022 for YRI and s̄ = 0.034 for CEU. The distribution drops to zero approaching the present, because all alleles have frequencies >22% today. The 2,965 (YRI) and 2,246 (CEU) selection ages shown have had 509 alleles removed that are likely examples of ongoing balanced selection (SI Appendix). Including these alleles in the analysis does not change the overall conclusion of acceleration of selection.