Venn diagrams illustrate the counts of polymorphisms segregating within each continental group for one example replicate. Sizes of circles and areas of overlap are approximately proportional to number of sites in those categories. Fixed differences between populations are not shown here. (A) Full data sets for the empirical data and the three simulated data sets. (B) 1,000-marker subsets of the empirical data set and the simulated data sets. Three demographic conditions were analyzed: (a) No migration; (b) low taurine–indicine gene flow; and (c) low taurine–indicine gene flow, plus higher recent indicine to Africa gene flow. In addition, three types of ascertainment sampling scheme were applied: (I) SNPs were based on random samples of loci (no bias); (II) sampled loci were selected from those that were polymorphic within Europe; and (III) sampled loci were selected from loci that were polymorphic in two or more subpopulations. Figure made using EulerAPE . Counts of polymorphisms in all groups are shown in Additional file 1: Table S2.