Ancient fire use flickers inside cave.

China's Zhoukoudian cave in Beijing contains a set of deposits that accumulated from 500,000 to 200,000 years ago. As well as yielding the famous Peking Man fossils, this site has also provided the oldest broadly accepted evidence for controlled fire use by members of the human lineage.

However, a new analysis of artifact-bearing sediment at the Chinese cave raises doubts about whether prehistoric folks indeed built fires there.

A number of burned animal bones lie in the same Zhoukoudian soil layers as stone tools, perhaps reflecting intentional fire use, reports a team led by biologist Steve Weiner of the Weizmann Institute of Science in Rehovot, israel. But despite an intensive investigation, Weiner's group failed to uncover remnants of ash, charcoal, or hearths in this sediment, any of which would solidify the evidence for ancient campfires.

"Although indirect evidence for burning is present [at Zhoukoudian], there is no direct evidence for ... controlled use of fire by humans," the scientists write in the July 10 Science.

More than 60 years ago, the first investigators of the cave also reported finding burned bones, as well as antlers and pieces of wood, in sediment that contains stone implements. Soil associated with the cave's artifacts exhibited signs of having been heated or baked, they maintained.

After preparing the site in 1996 and 1997 for renewed investigations, Weiner and his coworkers collected new soil samples and animal bones from two sediment layers that contain stone artifacts. Evidence of burning appeared on a small proportion of the unearthed bones. Some of these burned bones were turquoise colored, an indication that only after fossilization were they exposed to fire, probably naturally ignited, the scientists hold.

Chemical analyses of the Zhoukoudian soil uncovered no signs of wood ash or its byproducts, even though several earlier descriptions of the site had assumed that artifacts lay in ash-saturated sediment.

Several alleged hearths contain no charcoal but display a mix of silt, clay, and organic matter that probably accumulated in a pond of water at a time when the Zhoukoudian cave was more open to the elements, say Weiner and his colleagues.

"This is a valuable new analysis that puts a big question mark over what was thought to be the best evidence for ancient fire use," remarks anthropologist Christopher B. Stringer of the British Museum in London.

More than a decade ago, Stringer directed a preliminary investigation of Zhoukoudian soil samples that also failed to find any signs of ash.

A few locations in Europe bear convincing evidence of ancient fire use that occurred at least 100,000 years ago and perhaps as early as 300,000 years ago, Stringer says.

Several sites dating to around 1 million years ago in southern and eastern Africa contain pieces of burned bone or wood. These materials do not represent "cast-iron evidence" of fire use by human ancestors, asserts anthropologist Bernard Wood of George Washington University in Washington, D.C.