Origin of Ethiopian genetic heterogeneity

In agreement with previous research, a new study observes the intermediate position of Ethiopians between Sub-Saharan Africans (Negroids) and Western Eurasians (Caucasoids); genetic heterogeneity of Ethiopians is found to be the result of admixture:

However, the reduction in Tn diversity does suggest that a population bottleneck occurred in Ethiopia, associated with a major out of Africa expansion(s), which parallels the conclusion made by Tishkoff et al. (1996) from analysis of the CD4 locus. Certainly our data are not incompatible with the argument from Tishkoff et al. (1996) that an element of the contemporary Ethiopian population may be descendants of the ancestral population that spawned the migration out of Africa. We also argue, however, that in addition to this early bottleneck event, later periods of admixture have played a major role in shaping the gene pool of Ethiopia, and its populations display both Eurasian and Sub-Saharan genetic influences.

These results confirms what I have stated on several occasions in the past, about the three major elements in the East African population, e.g.,:

Thus, it appears that a large fraction of present-day East African mitochondrial ancestry is derived from different populations than the ones that spawned non-Africans. This element is probably responsible for the introduction of the Negroid type in the region, which now forms a major element in the population, together with the pre-Negroid East Africans and more recent Caucasoid arrivals from across the Red Sea.

Annals of Human Genetics (OnlineEarly)

Ethiopia: between Sub-Saharan Africa and Western Eurasia

A. Lovell et al.

Summary

Ethiopia is central to population genetic studies investigating the out of Africa expansion of modern humans, as shown by Y chromosome and mtDNA studies. To address the level of genetic differentiation within Ethiopia, and its relationship to Sub-Saharan Africa and Eurasia, we studied an 8kb segment of the X-chromosome from 72 chromosomes from the Amhara, Oromo and Ethiopian Jews, and compared these results with 804 chromosomes from Middle Eastern, African, Asian and European populations, and 22 newly typed Saharawi. Within Ethiopia the two largest ethnic groups, the Amhara and Oromo, were not found to be statistically distinct, based on an exact test of haplotype frequencies. The Ethiopian Jews appear as an admixed population, possibly of Jewish origin, though the data remain equivocal. There is evidence of a close relationship between Ethiopian and Yemenite Jews, likely a result of indirect gene flow. Within an African and Eurasian context, the distribution of alleles of a variable T_n repeat, and the spread of haplotypes containing Africa-specific alleles, provide evidence of a genetic continuity from Sub-Saharan Africa to the Near East, and furthermore suggest that a bottleneck occurred in Ethiopia associated with an out of Africa expansion. Ethiopian genetic heterogeneity, as evidenced by principal component analysis of haplotype frequencies, most likely resulted from periods of subsequent admixture. While these results are from the analysis of one locus, we feel that in association with data from other marker systems they add a complementary perspective on the history of Ethiopia.

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