sentences:  A proposed migration of proto-Chadic Afroasiatic speakers ~7,000 ya from the central Sahara into the Lake Chad Basin may have caused many western Nilo-Saharans to shift to Chadic languages (S99).Our data suggest that this shift was not accompanied by large amounts of Afroasiatic16 gene flow.Analyses of mtDNA provide evidence for divergence ~8,000 ya of a distinct mtDNA lineage present at high frequency in the Chadic populations and suggest an East African origin for most mtDNA lineages in these populations (S100)"."