( progression which are found principally...)40,000-year-old skull shows both modern human and Neandertal traits

Professor Zilhao said: "Such differences raise important questions about the evolutionary history of modern humans. They could be the result of evolutionary reversal or reflect incomplete palaeontological sampling of Middle Paleolithic human diversity.

"They could also reflect admixture with Neandertal populations as modern humans spread through western Eurasia. This mixture would have resulted in both archaic traits retained from the Neandertals and unique combinations of traits resulting from the blending of previously divergent gene pools.

"The ultimate resolution of these issues must await considerations of larger samples of European early modern humans and chronologically intervening specimens. But this fossil is a major addition to the growing body of fossil, genetic and archaeological evidence indicating significant levels of biological and cultural interaction between modern humans and the anatomically archaic populations (including the Neandertals) they met along the way as they spread from Africa into Eurasia."

It is apparent that the Oase 2 cranium indicates there was significant modern human morphological evolution since the early Upper Paleolithic, the researchers conclude. Oase 2 is 'modern' in its abundance of derived modern human features, but it remains 'nonmodern' in its complex constellation of archaic and modern features.