The genetic data appear to be consistent with the archaeological and linguistic data indicative of extensive population interactions between North African and Middle Eastern populations. A recent NRY study explores the distribution of haplogroups in a sample of African, Middle Eastern, and European males (Semino et al., 2004). Whereas a subclade of haplogroup E (M35) appears to have arisen in eastern Africa over 20 kya and subsequently spread to the Middle East and Europe, haplogroup J (M267) appears to have arisen in the Middle East over 20 kya and subsequently spread into northern Africa (Semino et al., 2004). A recent study of genome-wide autosomal microsatellite markers reports that Middle Eastern and African samples share the highest number of alleles that are also absent in other non-African samples, consistent with bidirectional gene flow (Tishkoff et al., 2009). In addition, a recent study of domestic goat mtDNA and NRY variation reports similar findings as well as evidence of trade along the Strait of Gibraltar (Pereira et al., 2009). The combined archaeological, linguistic, and genetic data, therefore, suggest bidirectional migration of peoples between northern Africa and the Levant for at least the past ~14 ky.
There is increasing archaeological, linguistic, and genetic evidence that the Sahel has been an important region for bidirectional migration between western and eastern Africa (Bereir et al., 2007; Cerny et al., 2007; Hassan et al., 2008; Tishkoff et al., 2009). Linguistic evidence indicates population interactions for ~20–10 kya between the Nilo-Saharan and Afroasiatic speakers in this region (Cavalli-Sforza et al., 1994). The combined linguistic and archaeological data support a model in which the Nilo-Saharan language family arose in eastern Sudan >10 kya and Nilo-Saharan speakers subsequently migrated westward to Lake Chad and southward into southern Sudan (Ehret, 1983; Tishkoff et al., 2009). Linguistic data also suggest that ~7 kya, proto-Chadic Afroasiatic speakers migrated from the Sahara into the Lake Chad Basin (Newman, 1997). This possibility is supported by an analysis of NRY variation that finds that the pattern and distribution of haplogroup R (V88) are consistent with the emergence of proto-Chadic ~7 kya and subsequent expansion of this linguistic group into the Lake Chad Basin (Cruciani et al., 2010). Whereas the inferred migration route is not consistent between NRY and mtDNA analyses, perhaps due to sex-biased migration, studies of mtDNA corroborate a model in which Sahel is a corridor for bidirectional migration between eastern and western Africa and, on the basis of the distribution of haplogroup L3f3, the proto-Chadic speakers expanded from eastern Africa into the Lake Chad Basin (Cerny et al., 2007, 2009).