One method involves looking at so-called microsatellites - short, repetitive segments of DNA that differ between populations.
These microsatellites have a high mutation, or error, rate as they are passed from generation to generation, making them a useful tool to study when two populations diverged.
Researchers from Stanford University, US, and the Russian Academy of Sciences compared 377 microsatellite markers in DNA collected from 52 regions around the world.
Analysis revealed a close genetic kinship between two hunter-gatherer populations in sub-Saharan Africa - the Mbuti pygmies of the Congo Basin and the Khosian bushmen of Botswana.
The researchers believe that they are "the oldest branch of modern humans studied here".
The data also reveals that the separation between the hunter-gatherer populations and farmers in Africa occurred between 70,000 and 140,000 years ago. Modern man's migration out of Africa would have occurred after this.
David Whitehouse BBC News/Science 9 June, 2003Activists from Pygmy communities in the Democratic Republic of Congo want the United Nations to set up a tribunal to try government and rebel fighters accused of slaughtering and eating Pygmies during fighting in the north-east of the country.
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Independent UK May 23 May 2003
