The Levant versus the Horn of Africa: evidence for bidirectional corridors of human migrations

Abstract

Paleoanthropological evidence indicates that both the Levantine corridor and the Horn of Africa served, repeatedly, as migratory corridors between Africa and Eurasia. We have begun investigating the roles of these passageways in bidirectional migrations of anatomically modern humans, by analyzing 45 informative biallelic markers as well as 10 microsatellite loci on the nonrecombining region of the Y chromosome (NRY) in 121 and 147 extant males from Oman and northern Egypt, respectively. The present study uncovers three important points concerning these demic movements: (1) The E3b1-M78 and E3b3-M123 lineages, as well as the R1*-M173 lineages, mark gene flow between Egypt and the Levant during the Upper Paleolithic and Mesolithic. (2) In contrast, the Horn of Africa appears to be of minor importance in the human migratory movements between Africa and Eurasia represented by these chromosomes, an observation based on the frequency distributions of E3b*-M35 (no known downstream mutations) and M173. (3) The areal diffusion patterns of G-M201, J-12f2, the derivative M173 haplogroups, and M2 suggest more recent genetic associations between the Middle East and Africa, involving the Levantine corridor and/or Arab slave routes. Affinities to African groups were also evaluated by determining the NRY haplogroup composition in 434 samples from seven sub-Saharan African populations. Oman and Egypt's NRY frequency distributions appear to be much more similar to those of the Middle East than to any sub-Saharan African population, suggesting a much larger Eurasian genetic component. Finally, the overall phylogeographic profile reveals several clinal patterns and genetic partitions that may indicate source, direction, and relative timing of different waves of dispersals and expansions involving these nine populations.

Figure 1

Maximum-parsimony hierarchy and frequency table. A total of 44 binary markers and 36 haplogroups are represented; 31 of these haplogroups are detected in 702 African and Omani males. Markers not typed are shown in italics. Om = Oman, Eg = Egypt, SC = southern Cameroon, Kn = Kenya, Tn = Tanzania, Bn = Benin, Rw = Rwanda.

Figure 2

Geographic frequency distribution of binary markers in eight African populations and one Omani population

Figure 3

ML radial phylogeny based on Y-haplogroup frequencies of 25 populations (24 African and 1 Omani). The nodal values represent the number of bootstrap replicates out of 1,000 that share the corresponding bifurcations. “PS*” denotes the present study.

Figure 4

CA based on the Y-SNP haplotype frequency data of 25 populations (24 African and 1 Omani). Percent of total inertia is shown for each axis. “PS*” denotes the present study.