By Ann Gibbons
ScienceNOW Daily News
2 April 2009
CHICAGO, ILLINOIS--Paleoanthropologists working in Africa have
discovered stone blades more than a half-million years old. That
pushes the date of the earliest known blades back a remarkable 150,000
years and raises a question: What human ancestor made them?
Not long ago, researchers thought that blades were so hard to make
that they had to be the handiwork of modern humans, who had evolved
the mental wherewithal to systematically strike a cobble in the right
way to produce blades and not just crude stone flakes. First, they
were thought to be a hallmark of the late Stone Age, which began
40,000 years ago. Later, blades were thought to have emerged in the
Middle Stone Age, which began about 200,000 years ago when modern
humans arose in Africa and invented a new industry of more
sophisticated stone tools. But this view has been challenged in recent
years as researchers discovered blades that dated to 380,000 years in
the Middle East and to almost 300,000 years ago in Europe, where
Neandertals may have made them (ScienceNOW, 1 December 2008).
Now it appears that more than 500,000 years ago, human ancestors
living in the Baringo Basin of Kenya collected lava stone cobbles from
a riverbed and hammered them in just the right way to produce stone
blades. Paleoanthropologists Cara Roure Johnson and Sally McBrearty of
the University of Connecticut, Storrs, recently discovered the blades
at five sites in the region, including two that date to between
509,000 and 543,000 years ago. "This is the oldest known occurrence of
blades," Johnson reported Wednesday here at the annual meeting of the
Paleoanthropology Society.
Johnson and McBrearty found the stone blades in a basalt outcrop known
as the Kapthurin Formation, including four cores from which the blades
were struck. "These assemblages would have been made by a different
species of human," Johnson said. "Who were they?" The blades come from
the same part of the formation where researchers have found two lower
jaws that have been variously described as belonging to Homo
heidelbergensis or H. rhodesiensis, human ancestors in Europe and
Africa that predate the origin of our species, H. sapiens.
Regardless of the identity of the toolmakers, other researchers say
that the discovery of blades this early suggests that these toolmakers
were capable of more sophisticated behavior than previously thought,
perhaps as a result of the last dramatic expansion of brain size in
the human lineage about 600,000 years ago. "It's reflective of a major
shift in human cognition," says Alison Brooks, a paleoanthropologist
at George Washington University in Washington, D.C.
To convince most researchers that such a dramatic breakthrough really
took place so early in human evolution, however, anthropologists will
have to find more blades this ancient, says paleoanthropologist Rick
Potts of the Smithsonian Institution in Washington, D.C. Stay tuned:
The search is already under way for more African blade runners.
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