This skull, from a Romanian cave, shows signs of both Neanderthal and modern man.

The idea that Neanderthals and early humans living in Europe may have interbred has been strengthened by a re-analysis of bones unearthed in a Romanian cave more than 50 years ago.

The bones show a mixture of modern human and Neanderthal features, leading researchers to suggest that the two groups could have intermixed and produced offspring.

The fossils include parts of a skull and jaw, and a shoulder blade. Although they mainly resembled modern humans, with a narrow nose and small brow bones, for example, the remains also showed other features normally associated with Neanderthals - a pronounced bump on the back of the skull, and a distinctive lower jaw bone.

"Modern humans met, intermixed with, and interbred with Neanderthals across Europe," says Erik Trinkaus of Washington University in St Loius, Missouri, whose team reports the findings this week in the Proceedings of the National Academy of Sciences¹. "The evidence from the fossils is one more piece in this puzzle."

Previous hybrids (or possible hybrids) have similarly been found by Trinkaus in Portugal and the Czech Republic^2,3. The more such samples that are discovered, he notes, the more solid the idea that the species intermixed.

Messy history

Recent finds have hammered home the fact that Neanderthals and modern man lived in many pockets of shared habitat for thousands of years. Before 50,000 years ago, Neanderthals were alone on the European continent. But 20,000 years later, most European inhabitants were modern humans. The interim is an "absolute mess", says Clive Finlayson of the Gibraltar Museum, who studies this time in history (see 'Neanderthal's last stand').

There remains debate about whether the two warred, lived peacefully side-by-side, or even mated. It is also not clear whether their offspring would have been fertile, or sterile like a mule. Trinkaus, however, is convinced that the two were producing fully functioning offspring.

One thorn in this theory's side is the burgeoning amount of evidence from Neanderthal DNA. The sequences analysed so far suggest that no genetic mixing between Neanderthal and modern-human populations went on - lending weight to the idea that Neanderthals were replaced by modern humans as they swept through Europe, giving them no opportunity to swap genes.

Another unsolved puzzle is that virtually no European fossils older than 30,000 years resemble pure modern humans. "If we've got Neanderthals and modern people and they're hybridizing, why is it that all we find are Neanderthals and hybrids?" asks Finlayson. "Where are the other guys?"

Trinkaus and his colleagues characterized the bones, which were discovered in the Pestera Muierii cave of southern Romania, and radiocarbon dated them to pinpoint their age. They found them to be 30,000 years old. This slots in nicely with the theory that hybrids were formed while both Neanderthals and modern man shared European territory.

"The most important part is that it shows that when these people met, they saw each other as physically and socially appropriate mates," says Trinkaus. "And they got it together."

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• References

  1. TrinkausE., et al. PNAS, doi:10.1073/pnas.0608443103 (2006).
  2. Duarte C., et al. PNAS, 96 . 7604 - 7609 (1999).
  3. Wild, M. E., et al. Nature, 435 . 332 - 335 (2005) doi: 10.1038/nature03585. | Article |