Genomes of the earliest Europeans

Last year, a research team led by researchers from the National Institute of Archaeology with Museum at the Bulgarian Academy of Sciences and the Max Planck Institute for Evolutionary Anthropology, Germany, reported the discovery of modern human remains found in direct association with the Initial Upper Palaeolithic stone tools at the site of Bacho Kiro Cave in Bulgaria. The oldest individuals found in the cave were directly radiocarbon dated to between 43,000 and 46,000 years ago. They are thus the earliest known dispersal of modern humans across the mid-latitudes of Eurasia.

Mateja Hajdinjak and colleagues have now sequenced the genomes of five individuals found at the Bacho Kiro Cave. Four individuals are between 43,000 to 46,000-years-old and were found together with stone tools belonging to the Initial Upper Palaeolithic, the earliest culture associated with modern humans in Eurasia. An additional individual found in the cave is around 35,000-years-old and found with stone tools of a later type. It was previously thought that bearers of the Initial Upper Palaeolithic died out without contributing genetically to modern humans arriving later. However, the researchers now show that the oldest Bacho Kiro Cave individuals, or groups closely related to them, contributed genes to present-day people. Surprisingly, this contribution is found particularly in East Asia and the Americas rather than in Europe where the Bacho Kiro Cave people lived. These genetic links to Asia mirror the links seen between the Initial Upper Palaeolithic stone tools and personal ornaments found in Bacho Kiro Cave and tools and ancient jewelry found across Eurasia to Mongolia.

Genetic differences between individuals

Importantly, the later 35,000-year-old individual found in Bacho Kiro Cave belonged to a group that was genetically distinct from the earlier inhabitants of the cave. This shows that the earliest history of modern humans in Europe may have been tumultuous and involved population replacements.

The earliest people at Bacho Kiro Cave lived at a time when Neanderthals were still around. The researchers therefore scanned their genomes for fragments of Neanderthal DNA. "We found that the Bacho Kiro Cave individuals had higher levels of Neanderthal ancestry than nearly all other early humans, with the exception of a 40,000-year-old individual from Romania. Crucially, most of this Neanderthal DNA comes in extremely long stretches. This shows that these individuals had Neanderthal ancestors some five to seven generations back in their family trees" says Mateja Hajdinjak.

Although only a handful of genomes from modern humans who lived at the same time in Eurasia as some of the last Neanderthals have been recovered, nearly all of them have recent Neanderthal ancestors. "The results suggest that the first modern humans that arrived in Eurasia mixed frequently with Neanderthals. They may even have become absorbed into resident Neanderthal populations. Only later on did larger modern human groups arrive and replace the Neanderthals" says Svante Pääbo, who coordinated the genetic research.