An international group of researchers has sequenced the genomes of Late Upper Paleolithic (13,300 years old) and Mesolithic (9,700 years old) males from western Georgia in the Caucasus and a Late Upper Paleolithic (13,700 years old) male from Switzerland. In doing so, they have revealed a previously unknown fourth strand of ancient European ancestry.
Hunter-gatherers. Image credit: T.P.S. Dave.
The newly discovered lineage stems from populations of hunter-gatherers that split from western hunter-gatherers shortly after the out of Africa expansion some 45,000 years ago and went on to settle in the Caucasus region.
Here these hunter-gatherers largely remained for several thousands of years, becoming isolated as the Ice Age culminated in the last Glacial Maximum around 25,000 years ago, which they weathered in the shelter of the Caucasus mountains until eventual thawing allowed movement and brought them into contact with other populations, likely from further east.
This led to a genetic mixture that resulted in the so-called Yamnaya culture: Steppe herders that swept into Western Europe approximately 5,000 years ago, heralding the start of the Bronze Age and bringing with them metallurgy and animal herding skills, along with the Caucasus hunter-gatherer strand of ancestral DNA – now present in almost all populations from the European continent.
“This new lineage diverged from western European hunter-gatherers around the time of the first migrations of early modern humans into Europe about 45,000 years ago and from the ancestors of early farmers around the time of the glacial maximum, 25,000 years ago,” said Dr Andrea Manica of the University of Cambridge, UK, co-author of a paper published in the journal Nature Communications.
“This is a major new piece in the human ancestry jigsaw, the influence of which is now present within almost all populations from the European continent and many beyond,” added co-author Prof. Daniel Bradley, of Trinity College Dublin in Ireland.
“Previously, ancient Eurasian genomes had revealed three ancestral populations that contributed to contemporary Europeans in varying degrees,” Dr Manica said.
DNA from ancient samples is notoriously difficult to work with as it degrades over time and has often vanished before scientists are able to analyze it.
The cool, dry environments found in caves can be excellent for DNA preservation and, by targeting cave sites, the team was able to recover the genomes of two males who lived in Georgia in the Caucasus 13,300 and 9,700 years ago.
The scientists also sequenced the genome of a male who lived in what is now Switzerland 13,700 years ago.
“DNA was extracted from three samples – two from Georgia (Kotias Klde cave and Satsurblia cave) and one from Switzerland (Grotte du Bichon),” the researchers said.
“This is the first sequence from Georgia – I am sure soon we will get more paleogenetic information from our rich collections of fossils,” said co-author Dr David Lordkipanidze of the Georgian National Museum.
“The sequencing of genomes from this key region will have a major impact on the fields of paleogeneomics and human evolution in Eurasia, as it bridges a major geographic gap in our knowledge,” added co-author Prof. Ron Pinhasi of University College Dublin.
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Eppie R. Jones et al. 2015. Upper Palaeolithic genomes reveal deep roots of modern Eurasians. Nature Communications 6, article number: 8912; doi: 10.1038/ncomms9912
