Threads from the past : a genetic study of African ethnic groups and human origins : a thesis presented in partial filfulment of the requirements for the degree of Doctor of Philosophy in Biological Science, Biological Anthropology at Massey University

Abstract

Mitochondrial DNA (mtDNA) provides an efficient tool for investigating human pre-history and evolution. In this thesis Hypervariable I sequences from 241 individuals representing nine diverse African ethnic groups arc presented, and analysed together with published sequences. Each ethnic group studied represents a different combination of geography (East and West Africa), linguistic phylum (Niger-Kordofanian, Nilo-Saharan, and Afroasiatic), and subsistence mode (agricultural and pastoral). The African mtDNA dataset is expanded considerably by the addition of these samples. Questions concerning human evolution and human pre-history are readdressed. These samples demonstrate a higher diversity in Africa than previously reported. An ethnic group such as the Turkana has a higher mitochondrial diversity than the rest of the world combined. There is some evidence of regionalism, in that some of the clusters are specific to West or East Africa; however, there is also sharing of lineages across Africa suggesting substantial migration and admixture both in the past and more recent times. In Africa, the !Kung being the exception, the mtDNA from one ethnic group does not show a common unique ancestor, rather the ethnic groups are composites of several mtDNA types, with distinct origins and population histories. Combined analysis with Median networks and pairwise distance methods, demonstrate that within Africa approximately 60,000 years ago, there was a phenomenal expansion of one cluster, which was associated with the people who subsequently moved out of Africa. Almost all non-African populations are derived from this cluster. The Out of Africa hypothesis is supported, but there may have been more than one expansion of modern humans out of Africa. Further sampling in Asia and Australia is crucial to conclude the Multiregional-Out of Africa debate.