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DNA from 4,500-year-old Ethiopian reveals surprise about ancestry of Africans
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[QUOTE]Originally posted by the lioness,: [QB] http://www.ncbi.nlm.nih.gov/pubmed/22726845 [IMG]http://picturestack.com/270/981/8RaPicture5ACm.png[/IMG] [IMG]http://picturestack.com/270/981/JAWPicture6IVW.png[/IMG] Introduction Much of the key fossil evidence for human origins and evolution is found in modern-day Ethiopia. Early putative hominin fossils such as Ardipithicus kadabba (5.2–5.8 million years ago [mya]) 1 and Ardipithecus ramidus (4.4 mya; e.g., “Ardi”), 2 as well as the earliest indisputable hominin species, Australopithecus anamensis (3.9–4.2 mya) and the better-known Australopithecus afarensis (3.0–3.9 mya; e.g., “Lucy”), 3 have all been found there. It is also the homeland of the earliest known anatomically modern human remains: Omo 1 (195 thousand years ago [kya]) 4 and Homo sapiens idaltu (154–160 kya). 5 Perhaps for these reasons and because of Ethiopia's geographical position between Africa and Eurasia, its capital, Addis Ababa, is often used in genetic studies as a proxy embarkation point for modern human range expansions. 6 and 7 However, such studies have seldom included Ethiopians; they are absent from widely used collections, such as the Human Genome Diversity Project (HGDP), 8 HapMap, 9 and 1000 Genomes 10 sets. In practice, our understanding of genome-wide patterns of diversity in Africa has been limited to populations from central and western Africa. Indeed, with a few exceptions, 11 and 12 studies of African genetic diversity that have included Ethiopians have been restricted to mtDNA 13, 14, 15 and 16 and the Y chromosome. 14 and 17 This deficiency has led to an incomplete picture of African genetic diversity that has implications for the study of our origins as a species, including the route followed during the dispersal(s) out of Africa and more recent demographic events involving East Africa. In linking present-day genetic diversity to the Middle and Late Stone Age populations of Africa, it is important to consider the possibility of long-term population discontinuity in the region and the sparseness of information relating to Ethiopia over the past 200 thousand years (ky). Although archaeological studies focusing on the past few millennia document indigenous Ethiopian developments, including the early cultivation of local species such as teff (Eragrostis tef, a cereal), enset (Musa ensete), and coffee (Coffea arabica), 18 they also reveal some cultural influences from outside, such as the cultivation of wheat and barley, which originated in the Fertile Crescent and reached Ethiopia presumably through Egypt during the first documented trade links, around 5 kya. 19 and 20 External contacts with the Ethiopian region are also evident in the historical record from the first millennium BCE onward, wherein Sudanese, Egyptian, South Arabic, and Mediterranean influences are documented. 19 and 21 Another line of evidence for the variegated history of the Ethiopian people comes from linguistic studies. The spread of the two major language families spoken in Ethiopia today—Afro-Asiatic and Nilotic—is considered to be the outcome of cultural and demographic events over the past 10 ky. 22 The presence of three diverse Afro-Asiatic branches (Omotic, Semitic, and Cushitic) makes the Horn of Africa one potential source of this family, although the Ethio-Semitic branch is likely to have originated at a later stage in the Middle East. 23 The Nilotic languages, represented in Ethiopia by the East Sudanic, Kunama, and Koman branches, are more widespread in Sudan, and their presence in Ethiopia is probably the result of recent demographic processes. 24 Similarly, genetic studies indicate that a major component of recent Ethiopian ancestry originates outside Africa: for example, half of the mtDNA haplotypes 16 and more than one-fifth of Y haplotypes 17 found in Ethiopia belong to lineages that, on the basis of phylogeographic criteria, have been attributed to a non-African rather than a sub-Saharan African origin. These historical admixture events are themselves of interest to historians, anthropologists, and linguists, as well as to geneticists. Our current study is motivated by four questions. First, where do the Ethiopians stand in the African genetic landscape? Second, what is the extent of recent gene flow from outside Africa into Ethiopia, when did it occur, and is there evidence of selection effects? Third, do genomic data support a route for out-of-Africa migration of modern humans across the mouth of the Red Sea? Fourth, assuming temporal stability of current populations, what are the estimated ages of Ethiopian populations relative to other African groups? In order to address these questions, we generated genome-wide SNP genotypes from Ethiopian individuals. [URL=http://www.ephotobay.com/share/picture-5-25.html] [IMG]http://www.ephotobay.com/image/picture-5-25.png[/IMG][/URL] [/QB][/QUOTE]
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