London, April 25 : A genetic study has suggested that ancient humans had diverged into two separate species for 100,000 years before merging back into a single population.
According to a report by BBC News, this genetic split happened in Africa, which resulted in distinct populations that lived in isolation for as much as 100,000 years.
At the time of the split - some 150,000 years ago - our species, Homo sapiens, was still confined to the African continent.
The results have come from the Genographic Project, a major effort to track human migrations through DNA.
The latest conclusions are based on analysis of mitochondrial DNA in present-day African populations. This type of DNA is the genetic material stored in mitochondria - the "powerhouses" of cells.
It is passed down from a mother to her offspring, providing a unique record of maternal inheritance.
"We don't know how long it takes for hominids to fission off into separate species, but clearly they were separated for a very long time," said Dr Spencer Wells, director of the Genographic Project. "They came back together again during the Late Stone Age - driven by population expansion," he added.
Although present-day people carry a signature of the ancient split in their DNA, today's Africans are part of a single population. The researchers compiled a "family tree" of different mitochondrial DNA groupings found in Africa. They found that a major split occurred near the root of the tree as early as 150,000 years ago.
While on one side of this divide are the mitochondrial lineages now found predominantly in East and West Africa, and all maternal lineages found outside Africa, on the other side of the divide are lineages predominantly found in the Khoi and San (Khoisan) hunter-gatherer people of southern Africa.
Many African populations today harbour a mixture of both.
According to scientists, the most likely scenario is that two populations went their separate ways early in our evolutionary history, which in turn gave rise to separate human communities localised to eastern and southern Africa that evolved in isolation for between 50,000 and 100,000 years.
This divergence could have been related to climate change as recent studies of ancient climate data suggest that eastern Africa went through a series of massive droughts between 135,000-90,000 years ago.
"It is possible the harsh environment and changing climate made populations migrate to other places in order to have a better chance of survival," said lead author Doron Behar.
"Once this population reached southern Africa, it was cut off from the eastern African population by these drought events which were on the route between them," Dr Wells told BBC News.