New DNA evidence suggests "African Eve", the 150,000-year-old female ancestor of every person on Earth, may have lived in Tanzania or Ethiopia.
A genetic study has shown that the oldest known human DNA lineages are those of East Africans. The most ancient populations include the Sandawe, Burunge, Gorowaa and Datog people who live in Tanzania.
Fossil remains of A. afarensis ("Lucy"), a possible human ancestor, were found at Hadar, Ethiopia
Researchers found a very high amount of genetic variation, or diversity, between the mitochondrial DNA of different individuals in these populations.
Mitochondrial DNA is passed down exclusively through the maternal line. The longer a population has existed, the more variation accumulates in its DNA lineages.
"They are showing really deep, old lineages with lots of diversity. They appear to be the oldest lineages identified in Africa to date," said Dr Sarah Tishkoff, of the University of Maryland, US, who led the research.
The so-called African Eve represents the ancestral mitochondrial genome that gave rise to all the different types seen in people today.
Several of the ethnic groups sampled in the study also live in countries surrounding Tanzania.
"It's entirely consistent with what we expected," said Dr Spencer Wells, a geneticist and author. "All the evidence is pointing to East Africa as the cradle of humanity."
Dr Wells added that the data ties in well with archaeological evidence of a long occupation of East Africa by modern humans and hominids.
But Professor Ulf Gyllensten, a molecular biologist at the University of Uppsala, Sweden, was cautious about claims that the oldest DNA lineages were confined to East Africa.
"I wouldn't be surprised if Dr Tishkoff has found old lineages there, but I think we're just skimming the surface," he said.
"Too little research has been done in Africa to get a clear picture. I don't know why, because it's clear there is a great resource of genetic diversity there," added Professor Gyllensten.
Dr Tishkoff's team have collected mitochondrial DNA samples from 1,000 Tanzanians since they began their research in 2001.
Although the data comes from groups living in Tanzania, the Burunge and Gorowaa migrated to Tanzania from Ethiopia within the last 5,000 years.
Dr Tishkoff said Ethiopia was also a good candidate for the region where modern humans evolved.
One of the populations sampled in the study, the Sandawe, speak a "click" language like that of Khoisan people from southern Africa.
The Khoisan were previously thought to possess the oldest DNA lineages, but those of the Sandawe are older. This suggests southern Khoisan originated in East Africa, according to Dr Tishkoff.
"That is surprising, because it has been presumed that the oldest populations were in the south," said Professor Gyllensten. Some of the oldest modern human archaeological sites in Africa are in the south of the continent.
Dr Tishkoff said she planned to carry out further research to narrow down the most ancient East African lineages.