By Andrea Thompson, Senior Writer
posted: 11 March 2009 02:02 pm ET
Pics at cite
1/Homo erectus skull
Homo erectus fossil from Zhoukoudian caves. Credit: Copyright Russell
L. Ciochon, Univ. of Iowa
2/Western Wall of the Zhoukoudian cave sites
The Western Wall of the Zhoukoudian cave sites where the Homo
erectus fossils were found. Credit: Guanjun Shen, Nanjing Normal
University
3/Map of Homo erectus fossils
This map show the sites of Homo erectus fossils and artifacts in
northern China and Java. Credit Russell L. Ciochon, University of Iowa
The famous fossils of an early relative of modern humans commonly
called Peking Man may be 200,000 years older than previously thought,
a new study finds.
The revised date could change the timeline and number of migrations of
the Homo erectus species out of Africa and into Asia. It also suggests
that Peking Man endured glacial climates.
Previous studies estimated that H. erectus fossils found nearly a
century ago in China were from about 500,000 years ago. The authors of
the new study sought to re-date the fossils using a relatively new
method that looks at the radioactive decay of aluminum and beryllium
in quartz exposed to cosmic radiation. With this method, they pinned
the date closer to 780,000 years ago.
Understanding the history of H. erectus is of interest to scientists
because the populations of the species that lived in Africa are
"implicated in the ancestry of modern humans," said
paleoanthropologist Russell L. Ciochon of the University of Iowa in
Iowa City, who was not involved in the new study.
Fossils found
H. erectus was a type of hominin, the group to which early and modern
humans belong. H. erectus walked upright, had a thick skull with a
brain a little smaller than our own and used stone tools.
The first fossils of the species were found on Java, Indonesia, in
1892 by Eugène Dubois.
Nearly 30 years later, more H. erectus fossils were found thousands of
miles away during excavations of the Zhoukoudian cave system just
outside of Beijing.
These caves turned out to be "one of the most important Paleolithic
sites in the world," the authors of the new study wrote. After the
first fossil was found, anthropologists eventually turned up skulls
and bones representing at least 40 H. erectus individuals, other
mammal fossils and tens of thousands of stone artifacts.
The latest research on the fossils, funded by the National Natural
Science Foundation of China and the Wenner-Gren Foundation, is
detailed in the March 12 issue of the journal Nature. Guanjun Shen at
Nanjing Normal University, China, headed up the study.
Glacial dwellers
Pushing back the date of the Zhoukoudian fossils puts them in closer
range to fossils found in open basins and plains around the cave
system that were originally dated to be much older than the
Zhoukoudian fossils. It also shows that H. erectus lived in the area
during glacial periods as well as during interglacial periods.
Many scientists thought that the species moved north with the
interglacials and south with the glacials, Ciochon said. However, this
new date shows they hung around during colder periods.
These glacial cycles didn't involve mounds of snow and ice as one
might think, rather it was "just a colder, drier period," Ciochon told
LiveScience.
The new date also sheds some light on how and when H. erectus got to
the area in the first place.
Two migrations
The Homo genus, which includes modern humans, originated in Africa
with Homo habilis about 2.5 million years ago. H. erectus likely
derived from some early version of H. habilis around 2 million years
ago, anthropologists think.
Some portion of the H. erectus population later left Africa and spread
out across the Old World (the population left behind in Africa likely
led to Homo heidelbergensis, from which the first early Homo sapiens
likely derived, Ciochon said). Other sites of H. erectus bones show
that the migration had reached Dmanisi, Georgia (in Asia), by about
1.75 million years ago and Java by about 1.6 million years ago.
"It's a species that had legs," Ciochon said, referring to the
distances traveled. "Aside from Homo sapiens, it's the most widespread
hominin species."
Some scientists had proposed that the Java population later migrated
up to present-day China, but Ciochon said that the new date for the
Zhoukoudian fossils lends credence to the idea that there could have
been more than one migration route.
"Maybe there could have been two dispersals," he said. One route could
have extended along the coast of Asia to Java, and another through the
interior of Eurasia to Zhoukoudian and the surrounding areas.
Also supporting the double-migration idea is the fact that the
Himalayas and a huge swath of primal forest unfriendly to hominin
habitation lie in the way of a direct migration from Java to China.
Cinching this argument would likely require finding more sites with H.
erectus fossils along the migration route, Ciochon said.
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