Ethiopia and East Africa is one of the most interesting places to conduct research projects in human population genetics and anthropological genetics. First, East Africa is the place of origin and human lived there for a long time. Second, there have been constant gene flows or interactions between Africans and Eurasians through this area. Third, all four major African language groups are found in East Africa.
Kivisild and his colleagues analyzed mtDNA HVRI sequences as well as some RFLP and sequences of HVRII and coding region of Afro-Asiatic speakers and the Yemenis to understand the interactions between Africans and Eurasians. Through their analyses, they demonstrated that there were bidirectional gene flows between East Africa and Middle East at different points of time, supporting previous mtDNA studies and Y chromosome studies.
As for Salas et al. (2002), the major part of the analyses is phylogeographic analysis using Network. I believe both Salas and Kivisild worked closely with Bandelt, who developed the Network phylogenetic program. Using this method, they defined new East African specific sub-clades of sub-Saharan L3, showing great genetic diversity observed among the Ethiopians. They also defined a new clade, L6, which is common among the Yemenis, but rare among the Ethiopians and has not been found in other parts of Africa. They suggest this is an evidence of out-of-African event.
However, the most interesting finding is their haplogroup frequencies. Only about half of the mtDNA haplogroups found among the Ethiopians were sub-Saharan African specific and other haplogroups were North Africans and Eurasians. Sub-Saharan genetic contribution to the Yemenis is high and sub-Saharan haplogroups were common among the Yemenis. Multidimonsional scaling analysis support this observation. Ethiopians and Yemenis were plotted between Africans and Eurasians on the Multidimensional scaling plot.
Unfortunately, at the time of publication, there was not much comparative data from East Africa to characterize the mtDNA variation in East Africa. Even today, there is only limited data available from Kenya and Somalia. If we consider the cultural, linguistic, and genetic diversity exists in East Africa, there should be a lot more genetic research projects in East Africa.