December 17, 2004 EST

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Earliest Human
Ancestors Found

AFP

Our Earliest
Relatives

June 11, 2003 — Scientists
believe they have found our oldest immediate ancestors, a finding
that sheds fresh light on the rise of Homo sapiens rise out
of Africa.

The skulls of two adults and a child, found in 1997 in the Middle
Awash area of central Ethiopia, have been carbon-dated to between
154,000 and 160,000 years old, around 50,000 years earlier than the
previous oldest finds of Homo sapiens.

That provides solid proof for the "Out of Africa" theory and
confirms that the enigmatic hominids known as Neanderthals were not
our distant ancestors, the authors said.

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The fossils "provide crucial evidence on the location, timing and
contextual circumstances of the emergence of Homo sapiens,"
they reported on Thursday in the journal Nature. "They ...
represent the probably immediate ancestors of anatomically modern
humans. Their anatomy and antiquity constitute strong evidence of
modern-human emergence in Africa."

Pieced together from fossilized fragments in an agonizingly long
game of 3-D jigsaw puzzles, the skulls have deep faces and long,
rugged cases that enclosed large brains.

They resemble modern crania in the face, top of the skull and
brain capacity, which at around 1,450 cubic centimeters compares
with anatomically modern man's average today of between 1,350 and
1,400 cc.

Those similarities, but also subtle differences in skull
characteristics, mean that the fossils are a member of Homo
sapiens yet, like us, they are also a subspecies of it.

The finds have been dubbed Homo sapiens idaltu ("idaltu"
meaning "elder" in the Afar language of Ethiopia).

Anatomically modern humans, a subspecies called Homo sapiens
sapiens, gradually emerged from Homo sapiens idaltu,
bodies shaped by diet and other evolutionary forces, the authors
suggested.

The earliest remains of Homo sapiens sapiens, found in
South Africa, Ethiopia and the Middle East, have been dated to
around 100,000 years ago.

Competing Theories
The study's leaders were Tim White
and Clark Howell, who are professors of anthropology at the
University of California at Berkeley, and Giday WoldeGabriel, a
geologist at Los Alamos National Laboratory, N.M.

They argue that the discovery is a much-wanted chunk of evidence
in a heated 25-year debate. Molecular studies, based on the
evolutionary changes in DNA over a long period, have suggested that
modern humans appeared on the scene around 150,000 years ago in
eastern Africa.

They then migrated to other regions, starting with the Middle
East and then heading northwards and westwards into Europe and
eastwards into Asia, eventually crossing into the Americas via
Alaska.

Critics laughed at the idea that a tiny population of humans
living on a subsistence diet could migrate and survive such
distances, and questioned assumptions about the gene flow and
mutation rate. They especially targeted the theory's biggest
weakness -- the lack of good fossil evidence to support it.

Their alternative was a "multiregional" model, in which modern
humans arose in different parts of Africa and Europe at roughly the
same time, emerging from the local population of hominids.

In the case of Europe, that would have meant that Homo
sapiens sprung out of the Neanderthals, who showed up around
400,000 years ago but then mysteriously disappeared around 30,000
years ago.

Did the Neanderthals disappear because they had evolved into or
interbred with modern humans, as some have suggested? Not if the
Idaltu fossils are any indication.

"They show that near humans had evolved in Africa long before the
European Neanderthals disappeared," said Howell. "They thereby
demonstrate conclusively that there was never a 'Neanderthal' stage
in human evolution."

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Picture(s): Courtesy of Tim White |

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