A 40,000-year-old skull found in a Romanian cave shows traits of both modern humans and Neanderthals and might prove the two interbred, researchers reported on Monday.
If the findings are confirmed, the skull would represent the oldest modern human remains yet found in Europe.
The study, published in the Proceedings of the National Academy of Sciences, will add to the debate over whether modern Homo sapiens simply killed off their Neanderthal cousins, or had some intimate interactions with them first.
DNA samples taken from Neanderthal bones suggest there was no mixing, or at least that any Neanderthal genetic contribution did not make it to the modern DNA pool.
The skull, probably that of a teenager, has been dated to 40,000 years ago and shows many modern traits. But it also is a little flatter than most modern Homo sapiens, and exceptionally large upper molars more associated with Neanderthals.
“Such differences raise important questions about the evolutionary history of modern humans,” said Joao Zilhao of the University of Bristol in Britain, who worked on the study.
“They could also reflect admixture with Neanderthal populations as modern humans spread through western Eurasia,” Zilhao said in a statement.
“This mixture would have resulted in both archaic traits retained from the Neanderthals and unique combinations of traits resulting from the blending of previously divergent gene pools.”
Neanderthals were also once designated Homo sapiens, although are a designated subspecies—Homan sapiens neanderthalis. But some experts now designate them as a separate species—Homo neanderthalis.