Figure 3 .

D-statistics provide formal tests for whether an unrooted phylogenetic tree applies to the data, assuming that the analyzed SNPs are ascertained as polymorphic in a population that is an outgroup to both populations (Y, Z) that make up one of the clades. (A) A simple unrooted phylogeny, (B) phylogenies in which (Y, Z) and (W, X) are clades that diverge from a common root, (C) phylogenies in which (Y, Z) are a clade and W and X are increasingly distant outgroups, and (D) a phylogeny to test if human Eurasian populations (A, B) form a clade with respect to sub-Saharan Africans (Yoruba).