a, The maximum-likelihood phylogeny of individuals used in this study based on whole-genome transversion differences, rooted using the American black bear outgroup. b, Measures of clade differentiation based on D statistic tests inconsistent with the species tree. The tested topologies are shown on the left, with points showing the calculated clade differentiation (D values) for all possible combinations of the sampled individuals. This measure of clade differentiation scales between 0 (indicating a phylogenetic trifurcation) and 1 (indicating complete lineage sorting and absence of post-divergence gene flow). Measures of differentiation for the brown bear clade relative to polar bears, and for the polar bear clade relative to brown bears, are shown for comparison with values obtained for cave bears.