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Neandertals, Modern Humans May Have Interbred, Skull Study Suggests

John Roach
for National Geographic News
January 16, 2007
 
Modern humans continued to evolve after they reached Europe 40,000 years ago and may have interbred with Neandertals, according to new research.

The findings are based on an analysis of the oldest modern human skull yet found in Europe.

Neandertals (often spelled Neanderthals) were heavy browed, big boned early humans that lived in Europe and parts of Asia for about 200,000 years.

Neandertals disappeared from the fossil record 28,000 years ago, about 12,000 years after modern humans began to spread across Europe. (Related: "Neandertals' Last Stand Was in Gibraltar, Study Suggests" [September 13, 2006].)

Scientists have long debated the relationship between modern humans and Neandertals.

This past fall a genetic study suggested that the two species split 400,000 years ago. But days later a bone study suggested that they mated much more recently than that.

The newly analyzed skull, reported online this week in the journal Proceedings of the National Academy of Sciences, adds to the heated discussion.

Modern and Archaic

The skull was discovered in a cave in southwestern Romania and is at least 29,000 years old. A jawbone found nearby with similar morphological traits is dated to 40,500 years ago. The researchers conclude both specimens are about 40,000 years old.

Comparisons to other skulls suggest the Romanian skull clearly belongs to a modern human, said paper co-author Erik Trinkaus, an anthropologist at Washington University in St. Louis, Missouri.

"But some characteristics are extremely unusual and rather archaic," he said.

For example, the forehead is "extremely long and flat" when compared to modern humans from western Europe and Africa, Trinkaus said. And the molars are the largest ever documented for modern humans.

These differences suggest that "modern human evolution did not stop when people we call moderns appeared," he said. "There have been significant changes in human anatomy since the time we have the first modern humans."

Moreover, Trinkaus said, the unusual features suggest intermixing between modern humans and Neandertals.

The archaic features had been lost in early modern humans in Africa, he said.

Therefore, the features' reappearance in the Romanian skull either requires a reversal of evolution once modern humans reached Europe or some degree of intermixing with Neandertals, according to the study.

"It's much more likely the latter that happened," Trinkaus said.

Interpretation Questioned

Eric Delson is an anthropologist at Lehman College and the American Museum of Natural History, both in New York.

The Romanian skull is definitely a modern human's with some unusual characteristics, he agreed—but the interpretation is questionable.

"It's not very clear that the features they've located indicate interaction with Neandertals as opposed to a holdover from the more archaic past or local population differences," he said.

According to Delson, analysis of the skull with a more statistically advanced technique that looks at the entire skull shape instead of individual features might help resolve some of these issues.

Richard Potts, director of the Human Origins program at the Smithsonian Institution in Washington, D.C, said the skull shows "there is continuing evolution for the modern human skull even after humans got to Europe and other places in the world."

But, he said, as the authors point out, the skull lacks uniquely Neandertal traits and thus does not prove interbreeding. In fact, he said, similar archaic traits are found in modern human remains found in a cave in China.

Nevertheless, he added, evidence for interbreeding between modern humans and Neandertals would not be a surprise.

"Evolution has involved sloppiness of boundaries between lineages," he said. "But if [interbreeding] occurred, it is extremely rare. Otherwise, we'd find much more of a mixing."

Trinkaus has long argued that Neandertals interbred with modern humans as they spread across Europe.

The Romanian skull supports the notion that the two "got it together," he said. "For some reason, many people find that very difficult to accept."

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