Wednesday, January 28, 2015

Ancient skull from Galilee cave offers clues to the first modern Europeans

The discovery of a 55,000-year-old partial skull in Northern Israel provides new insights into the migration of modern humans out of Africa. The rare find is reported in the journal Nature this week by an international team of Israeli, North American and European researchers.

A key event in human evolution was the expansion of modern humans of African origin across Eurasia, replacing all other forms of hominin (humans and their predecessors), around 40,000-60,000 years ago. However, due to the scarcity of human fossils from this period, these ancestors of all present-day non-African modern populations have largely remained a mystery.

Now, researchers describe a partial skull that dates to around 55,000, which was found at Manot Cave in Israel's Western Galilee. The skull has a distinctive "bun"-shaped occipital region at the back. In this way its shape resembles modern African and European skulls, but differs from other anatomically modern humans from the Levant. This suggests that the Manot people could be closely related to the first modern humans that later colonized Europe.

The specimen also provides evidence that both modern humans and Neanderthals inhabited the southern Levant during the late Pleistocene, close in time to the likely interbreeding event between modern humans and Neanderthals.

This finding represents the first fossil evidence from the critical period when genetic and archaeological models predict that African modern humans successfully migrated out of Africa and colonized Eurasia. It also represents the first fossil evidence that during the late Middle Paleolithic, the Levant was occupied not only by Neanderthals but also by modern humans.

The researchers suggest that the population from which this skull is derived had recently migrated out of Africa and established itself in the Levantine corridor during a time span that was favorable for human migration, due to warmer and wetter climatic events over the Northern Sahara and the Mediterranean.

Manot Cave 

Manot is a karstic cave in the North of Israel, very close to the Lebanese border. The first excavations began in 2010 and are continued up to day. Countless archaeological objects were discovered which document the peopling of the cave since more than 100,000 years. Around 30,000 years ago, the roof of the cave collapsed and sealed the archaeological layers until the 21st century. Beside stone tools and animal bones, some few human remains were preserved. The most spectacular finding was made on an elevated shelf within a small chamber of the cave: a very well preserved "calotte", hence the upper part of a braincase. The facial bones which contain a lot of diagnostic traits for paleoanthropologists, were, however, missing.

"Virtual Anthropology" allows identification

The traditional methods of anthropology permit to draw only a coarse picture with regard to classification if it comes to a partial braincase which features mainly smooth curvatures. By means of methods that were developed at the University of Vienna in the last 15 years it is now possible to come to much stronger statements. This "Virtual Anthropology" uses sophisticated mathematical-statistical procedures to analyse 3D data from objects. Professor Gerhard Weber from the Department of Anthropology at the University of Vienna was thus invited by the Israeli colleagues to participate. Together with his former Ph.D. student Dr. Philipp Gunz, who now works at the Max Planck Institute Leipzig, they examined carefully computer-tomographic images of the calotte. In doing so, numerous measuring points in a dense array were located on the virtual representation of Manot and on several hundreds of other braincases to capture differences and similarities. Weber states: "The shape analysis shows very clearly that Manot was a modern human. It is interesting that the most similar skulls in our sample come from recent Africans on the one hand, and on the other hand from those modern humans that lived in Europe between 20-30,000 years ago as, for instance, Mlade? 1 or P?edmostí 4 from the Czech Republic".

Absolute dating proves old age

The morphological results alone would be, however, not enough for a sensation. The Manot people could have been modern humans that later re-migrated from Europe back into the Levant. Luckily, the conditions in the flowstone-cave lead to the accumulation of several thin layers of calcite on the inner and outer surface of the skull fragment. These can be reliably dated with the uranium-thorium method. The Israeli colleagues documented an age of approximately 55,000 years. Manot is thus 10,000 years older than any modern human found in Europe, and about 5-10,000 years younger than the point when geneticists predict the appearance of our direct ancestors in Africa.

The Levant as crossing point of migration

One of the logical migration routes from Africa to Europe leads through the Levantine corridor. The age and the morphology of Manot suggest that the first modern humans took this route. At the same time, they had opportunity to meet Neandertals which occupied the Levant in this time but could never expand further south. Genetic results indicate that recent humans carry between 1-4% of Neandertal genes in their genome. So far it was speculated that admixture could have happened in Europe. Manot is changing this picture. It is likely that interbreeding happened already earlier on the way of the first modern humans through the Levant.

Manot connects

"This skull remain at Manot", Weber summarises "is exactly what we anthropologists have looked for since decades. It connects perfectly in space and time those separated parts of human history that we have known". But Manot is not only a fluke for our knowledge about human evolution. It also lead to a very successful scientific collaboration between Israeli and Austrian, respectively German, institutions. Further projects and increased exchange of know-how are on the way.

No comments: