Testing support for the northern and southern dispersal routes out of Africa: an analysis of Levantine and southern Arabian populations.

Objectives: The Northern Dispersal Route (NDR) and Southern Dispersal Route (SDR) are hypothesized to have been used by modern humans in the dispersal out of Africa. The NDR follows the Nile into Northeast Africa and crosses the Red Sea into the Levant. The SDR emerges from the Horn of Africa and crosses the Bab el-Mandeb into southern Arabia. In this study, we analyze genetic data from populations living along the NDR and SDR to test support for each dispersal route.
Materials and Methods: We genotyped 90 Yemeni samples on the Affymetrix Human Origins array. We analyzed these data with published data from Levantine and other southern Arabian populations as well as 157 comparative populations for a total sample size of >550,000 genetic variants from >2,000 individuals in >160 populations. We calculated outgroup f ₃ statistics to test how Levantine and southern Arabian populations relate to African populations living along the NDR and SDR and to other non-African populations.
Results: We find that Levantine and southern Arabian populations bear similar genetic relationships to both African and non-African populations, thus providing no support for the use of one dispersal route over the other.
Discussion: Our results are consistent with a history of gene flow between the Levant and southern Arabia. Consideration of genetic, archaeological, and paleoclimate data provide a slight edge for the SDR but, ultimately, more data are needed to definitively identify which dispersal route out of Africa was used.
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