Sometime between 30,000 and 40,000 years ago, the Neanderthals abruptly disappeared after a run of perhaps 200 millennia in the Near East, west Asia and, most notably, in the ice age caves of Europe. On that score, there is no dispute.

How this happened, and why, is another matter. For years, paleontologists have argued about whether anatomically modern humans invading from the east either wiped out the Neanderthals or out-innovated them; or, alternatively, whether Neanderthals and the invaders simply interbred to create today's Homo sapiens.

This debate has taken on new virulence amid an accumulation of new, but still inconclusive, evidence.

DNA analysis to date suggests that Neanderthals and modern humans are quite probably unrelated -- that Neanderthals were a distinct species altogether.

However, archaeologists have shown in the past few years that modern human remains thought to be associated with human-made artifacts from the late Neanderthal era actually date from much more recent times. No one has found modern human remains buried with artifacts older than perhaps 32,000 years.

The argument now is about whether Neanderthals were comic book characters -- not-quite-bright, club-carrying, knuckle-draggers who couldn't keep up with the invaders -- or, instead, simply a different people who somehow got sideswiped into extinction for some other reason.

This mystery, central to the study of human culture during the Stone Age, is nowhere near resolution. "A lot of this discussion is about how we see our own relationship to these creatures," said Princeton University anthropologist Alan E. Mann. "I worry these discussions are becoming much less about science."

Early this month, researchers poured more gasoline on the fire, reporting in the journal Nature on the results of new studies of a famous Neanderthal site at Chatelperron, in France. They said the new analysis of materials from old excavations showed that Neanderthals and modern humans coexisted in western Europe during the Neanderthals' waning days, and thus had "potential demographic and cultural interactions."

Co-author Paul A. Mellars, a University of Cambridge archaeologist and leading proponent of the view that modern humans shoved aside the Neanderthals and eventually replaced them, said in a telephone interview that he knew "there would be screaming" after publication of the Nature paper.

And there was. "It's hogwash," said Erik Trinkaus, an anthropologist at Washington University in St. Louis who is an advocate both of Neanderthal-modern human interbreeding and Neanderthals' ability to adapt and "modernize." The evidence is not convincing, Trinkaus said, and Mellars "is grasping at straws."

The cave at Chatelperron, in central France, was first discovered in the 1840s during railroad construction, and it was excavated periodically through the rest of the 19th century. Today it has become archaeology's prototype late Neanderthal site.

In the early 1950s, the famous French archaeologist Henri Delporte revisited the site and meticulously documented five levels of Neanderthal-era occupation. The most recent top three layers and the bottom-most layer had distinctively Neanderthal artifacts.

But the fourth layer had modern human, or "Aurignacian," material -- including the "split-based point" of a weapon made from an antler and two ornaments crafted from perforated animal teeth -- typical of the artifacts attributed to early modern humans who spread across Europe perhaps a little more than 40,000 years ago.

Mellars said this "interstratification" provided solid evidence that Neanderthals and modern humans had co-existed in Europe. Delporte, now dead, published two obscure papers on the findings, "but didn't make as much of it as he should have," Mellars said. "There was a deep-rooted conviction" that overlap between Neanderthals and modern humans had not occurred.

Mellars joined Cambridge graduate student Brad Gravina, lead author of the Nature article, in reexamining the Chatelperron materials after Gravina found among the Delporte artifacts animal bones that could be dated by modern methods.

Radiocarbon analysis of the bones showed the bottom Neanderthal level to be between 42,000 and 43,000 years old. The overlying Aurignacian level was between 41,000 and 42,000 years old, while the Neanderthal level on top of that was between 40,000 and 41,000 years old.

Mellars suggested that the back-and-forth shift may have occurred because modern humans were better prepared to cope with a western European cold snap about 41,500 years ago. "When it got cold, the Neanderthals moved out and the modern humans moved in," Mellars said.

"Anatomically Neanderthals were cold-adapted," he added, acknowledging that Neanderthals survived most of Europe's ice age, but modern humans probably had "better clothing and shelter, better fire control and better technological adaptation."

Trinkaus, speaking in a telephone interview, disputed both the integrity of the site and the accuracy of the interpretation. He said Chatelperron was a "heavily damaged, classic site" that had been picked over for 150 years.

He also noted that the Gravina-Mellars team had not dated the ornamental teeth or the antler, and "a butchered animal bone doesn't tell you anything." More important, he added, Chatelperron, like other contemporary European sites, had no modern human skeletal remains with the artifacts.

"You cannot argue that these things were made by modern humans just because modern humans made that type of tool," Trinkaus said. "The implication is that Neanderthals were too stupid to do it themselves."

Mellars noted Delporte's undisputed credentials as an excavator. Also, he said, "I have been looking at these stone tools for 45 years," and they have always been associated with modern humans. The teeth and antler point were not dated because they would have been damaged in the process.

However, he acknowledged Trinkaus made "a fair point" about the lack of modern human skeletal remains at Chatelperron. Indeed, this has been the Achilles' heel of those who propound the contact-and-replacement theory.

There are sites in Europe about 35,000 years old that do have bones of modern humans but no artifacts with them, and there are several sites, such as Chatelperron, that have artifacts purportedly made by modern humans -- but no bones. All the sites thought to have both have turned out to have remains of much more recent humans, almost certainly the result of later burials that were dug into older archaeological deposits.

Either the oldest of Europe's modern humans didn't bury their dead, or archaeologists haven't yet found the bones. Or maybe modern humans weren't there, after all, and the early modern human artifacts were made by Neanderthals.

A cave discovered in the 1840s at Chatelperron, in France, and excavated during the 19th century has become the prototype late Neanderthal site.

In the cave at Chatelperron, excavation produced modern human, or "Aurignacian," artifacts, including the "split-based point," left, of a weapon made from an antler, a typical blade, center, and two ornaments crafted from perforated animal teeth. Above and below the layer where modern human tools were found, researchers excavated typical Neanderthal artifacts: a burin, left, a scraper, center, and a blade.