Independent evidence about variant age comes from the length of the shared haplotypes on which they are found. We find, as expected, a negative correlation between variant frequency and the median length of shared haplotypes, such that chromosomes carrying variants at 1% frequency share haplotypes of 100-150 kb (typically 0.08-0.13 cM; Figs. 3b and S7a), although the distribution is highly skewed and 2-5% of haplotypes around the rarest SNPs extend over 1 Mb (Figs. S7b,c). Haplotype phasing and genotype calling errors will limit the ability to detect long shared haplotypes and the observed lengths are a factor of 2-3 shorter than predicted by models that allow for recent explosive growth6 (Fig. S7a). Nevertheless, the haplotype length for variants shared within and between populations is informative about relative allele age. Within populations and between populations where there is recent shared ancestry (e.g., through admixture and within continents) f2 variants typically lie on long shared haplotypes (median within ancestry group 103 kb, Fig. S8). In contrast, between populations with no recent shared ancestry, f2 variants are present on very short haplotypes, for
