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      WASHINGTON (AP) - The worldwide spread of ancient humans has
long been depicted as flowing out of Africa, but tantalizing new
evidence suggests it may have been a two-way street.


      A long-studied archaeological site in a mountainous region
between Europe and Asia was occupied by early humans as long as
1.85 million years ago, much earlier than the previous estimate of
1.7 million years ago, researchers report in Tuesday's edition of
Proceedings of the National Academy of Sciences.


      Early human Homo erectus is known to have occupied the site at
Dmanisi later. Discovering stone tools and materials from a much
earlier date raises the possibility that Homo erectus evolved in
Eurasia and might have migrated back to Africa, the researchers
said - though much study is needed to confirm that idea.


      "The accumulating evidence from Eurasia is demonstrating
increasingly old and primitive populations," said Reid Ferring of
the University of North Texas. Dmanisi is located in the Republic
of Georgia.


      "The recently discovered data show that Dmanisi was occupied at
the same time as, if not before, the first appearance of Homo
erectus in east Africa," the team led by Ferring and David
Lordkipanidze of the Georgia National Museum reported. They
uncovered more than 100 stone artifacts in deep layers at the site.
Previously, fossil bones from a later period had been found at the
site.


      The new discovery shows that the Caucasus region was inhabited
by a sustained population, not just transitory colonists. "We do
not know as yet what the first occupants looked like, but the
implication is that they were similar to, or possibly even more
primitive than those represented by Dmanisi's fossils," Ferring
explained.


      The occupants of Dmanisi "are the first representatives of our
own genus outside Africa, and they represent the most primitive
population of the species Homo erectus known to date," added
Lordkipanidze. The geographic origins of H. erectus are still
unknown.


      The early humans at Dmanisi "might be ancestral to all later H.
erectus populations, which would suggest a Eurasian origin of H.
erectus," said Lordkipanidze. However, there's another theory as
well: H. erectus originated in Africa, and the Dmanisi group might
represent its first migration out of Africa.


      Wil Roebroeks, a professor of archaeology at Leiden University
in the Netherlands, said the new findings suggest a sustained
regional population which had successfully adapted to the temperate
environment of the southern Caucasus at about 1.8 million years
ago.


      He called it "an important observation for our views on the
earliest colonization of Eurasia."


      Roebroeks had suggested in a 2005 paper that Asia might have
been a core area where Homo erectus emerged, evolving from an
earlier, thus far unknown, pre-human.


      But he stressed that's a hypothesis which will be tested in
future studies. "Possible does not equate with observable, but the
Dmanisi evidence has forced us to have a good fresh look at some of
our basic assumptions," said Roebroeks.


      Homo erectus, heavier, or more robust, than modern humans, and
with characteristic brow ridges, is generally listed as having
existed from about 1.8 million to 0.3 million years ago. It has
some overlap with the earlier Homo habilis and was the first of the
species to spread widely outside of Africa.


      Not so sure of Ferring and Lordkipanidze's theory is Richard
Potts, director of the human origins program at the Smithsonian's
National Museum of Natural History.


      "The new evidence at Dmanisi consists of stone tools, not
fossil bones. So we don't really know who the toolmaker was in the
time range of 1.85 to 1.77 million" years ago, he said. "(We)
cannot know this for sure until fossils come from this older
level."


      Michael D. Petraglia, co-director of the Centre for Asian
Archaeology, Art & Culture at England's University of Oxford, said
the findings do show that early humans were present in Eurasia
between 1.85 million and 1.78 million years ago.


      "The stone tool evidence represents the oldest and best
documented case for the presence of early humans in Asia. This
means that early forms of humans probably migrated out of Africa at
or before 1.85 million years ago, or before, colonizing new regions
of the world for the first time," he said.


      But Petraglia added, that he thinks the authors "are on less
solid ground" with their suggestion that this early group may have
migrated back to Africa.
    

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The worldwide spread of ancient humans has been depicted as flowing out of Africa, but new evidence suggests it may have been a two-way street.

Were ancient human migrations two-way streets?

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