The Out of Africa theory has long been established as the leading contender for human origins: our most recent common ancestors, including such people as Mitochondrial Eve and Y Chromosome Adam, probably lived in Africa between 100 000 and 200 000 years ago; and some time later, perhaps 50 000 to 70 000 years ago, some of them moved out of Africa and into the rest of the world. These were the first of our modern subspecies, Homo sapiens sapiens, and replaced all more primitive Homo sapiens throughout the world.

Recent genetic and linguistic research has suggested that the place of origin can be narrowed down to East Africa. Now East Africa has long been the major source of fossils of earlier hominid and australopithecine species, but this new research would mean that it has continued to be the driving habitat of our line for several million years.

The Out of Africa theory is supported by studies over the last decade or so making a family tree of mitochondrial DNA, using samples from ethnic groups all over the world's continents. The African branches were the most diverse, and those on other continents derived from a single African sub-branch.

The most recent study looks more closely at African populations and finds that the greatest diversity is found in a number of groups in Tanzania. They include the Sandawe, Datog, Gorowaa and Burunge peoples. The latter two moved to Tanzania from Ethiopia within the last 5000 years.

The team led by Dr Sarah Tishkoff of the University of Maryland had previously announced that work in linguistics correlated with the findings from genetics. The Sandawe people speak a click language, very distantly related to the Khoisan group of click languages of southern Africa. But the immense divergence in mitochondrial DNA mutations between the Sandawe and the Khoisan seemed to rule out the possibility that they were connected by more recent migration from one place to the other, in either direction: their shared use of clicks must date back to the very beginning of the H. sapiens sapiens lineage.

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