A plot of the first two eigenvectors (Fig. 2a) highlights the major historical influences on population structure in southern Morocco. PC1 separates just a dozen individuals, and we inferred that this axis represents a sub-Saharan African contribution, consistent with expected levels of admixture in Morocco, by performing an analysis including 21 Yoruban individuals (Supplementary Fig. 1b online). PC2 is highly correlated with both location and self-reported ethnicity, so is inferred to capture the major component of Arab-Amazigh ancestry.
