Positive selection of lactase persistence among people of Southern Arabia.

OBJECTIVE: Frequency patterns of the lactase persistence (LP)-associated -13,915 G allele and archaeological records pointing to substantial role played by southern regions in the peopling and domestication processes that involved the Arabian Peninsula suggest that Southern Arabia plausibly represented the center of diffusion of such adaptive variant. Nevertheless, a well-defined scenario for evolution of Arabian LP is still to be elucidated and the burgeoning archaeological picture of complex human migrations occurred through the peninsula is not matched by an equivalent high-resolution description of genetic variation underlying this adaptive trait. To fill this gap, we investigated diversity at a wide genomic interval surrounding the LCT gene in different Southern Arabian populations. METHODS: 40 SNPs were genotyped to characterize LCT profiles of 630 Omani and Yemeni individuals to perform population structure, linkage disequilibrium, population differentiation-based and haplotype-based analyses. RESULTS: Typical Arabian LP-related variation was found in Dhofaris and Yemenis, being characterized by private haplotypes carrying the -13,915 G allele, unusual differentiation with respect to northern groups and conserved homozygous haplotype-blocks, suggesting that the adaptive allele was likely introduced in the Arabian gene pool in southern populations and was then subjected to prolonged selective pressure. CONCLUSION: By pointing to Yemen as one of the best candidate centers of diffusion of the Arabian-specific adaptive variant, obtained results indicate the spread of indigenous groups as the main process underlying dispersal of LP along the Arabian Peninsula, supporting a refugia model for Arabian demic movements occurred during the Terminal Pleistocene and Early Holocene.

Pleistocene-Holocene boundary in Southern Arabia from the perspective of human mtDNA variation.

It is now known that several population movements have taken place at different times throughout southern Arabian prehistory. One of the principal questions under debate is if the Early Holocene peopling of southern Arabia was mainly due to input from the Levant during the Pre-Pottery Neolithic B, to the expansion of an autochthonous population, or some combination of these demographic processes. Since previous genetic studies have not been able to include all parts of southern Arabia, we have helped fill this lacuna by collecting new population datasets from Oman (Dhofar) and Yemen (Al-Mahra and Bab el-Mandab). We identified several new haplotypes belonging to haplogroup R2 and generated its whole genome mtDNA tree with age estimates undertaken by different methods. R2, together with other considerably frequent southern Arabian mtDNA haplogroups (R0a, HV1, summing up more than 20% of the South Arabian gene pool) were used to infer the past effective population size through Bayesian skyline plots. These data indicate that the southern Arabian population underwent a large expansion already some 12 ka. A founder analysis of these haplogroups shows that this expansion is largely attributed to demographic input from the Near East. These results support thus the spread of a population coming from the north, but at a significantly earlier date than presently considered by archaeologists. Our data suggest that some of the mtDNA lineages found in southern Arabia have persisted in the region since the end of the Last Ice Age.

The Nubian Complex of Dhofar, Oman: an African middle stone age industry in Southern Arabia.

Despite the numerous studies proposing early human population expansions from Africa into Arabia during the Late Pleistocene, no archaeological sites have yet been discovered in Arabia that resemble a specific African industry, which would indicate demographic exchange across the Red Sea. Here we report the discovery of a buried site and more than 100 new surface scatters in the Dhofar region of Oman belonging to a regionally-specific African lithic industry--the late Nubian Complex--known previously only from the northeast and Horn of Africa during Marine Isotope Stage 5, ∼128,000 to 74,000 years ago. Two optically stimulated luminescence age estimates from the open-air site of Aybut Al Auwal in Oman place the Arabian Nubian Complex at ∼106,000 years ago, providing archaeological evidence for the presence of a distinct northeast African Middle Stone Age technocomplex in southern Arabia sometime in the first half of Marine Isotope Stage 5.