Ancient humans started down the path of evolving into two separate species before merging back into a single population, a genetic study suggests. The genetic split in Africa resulted in distinct populations that lived in isolation for as much as 100,000 years, the scientists say. This could have been caused by arid conditions driving a wedge between humans in eastern and southern Africa.

It would be the longest period for which modern human populations have been isolated from one another. But other scientists said it was still too early to reconstruct a meaningful picture of humankind’s early history in Africa. They argue that other scenarios could also account for the data.

At the time of the split - some 150,000 years ago - our species, Homo sapiens, was still confined to the African continent.

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Human beings may have had a brush with extinction 70,000 years ago, an extensive genetic study suggests. The human population at that time was reduced to small isolated groups in Africa, apparently because of drought, according to an analysis released Thursday.

The report notes that a separate study by researchers at Stanford University estimated the number of early humans may have shrunk as low as 2,000 before numbers began to expand again in the early Stone Age.

“This study illustrates the extraordinary power of genetics to reveal insights into some of the key events in our species’ history,” Spencer Wells, National Geographic Society explorer in residence, said in a statement.

“Tiny bands of early humans, forced apart by harsh environmental conditions, coming back from the brink to reunite and populate the world. Truly an epic drama, written in our DNA.”

Previous studies using mitochondrial DNA — which is passed down through mothers — have traced modern humans to a single “mitochondrial Eve,” who lived in Africa about 200,000 years ago.

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