A single tooth and a few bone fragments found in a cave in Bulgaria prove that modern humans reached Europe more than 45,000 years ago, some 5,000 years earlier than previously thought.
The finds from Bacho Kiro Cave, a prehistoric site on the slopes of the Balkan mountain range, show that Homo sapiens coexisted for thousands of years with Europe’s autochthonous hominins, the Neanderthals. The early modern humans likely had a strong influence on Neanderthal culture, an international team of researchers reports in a paper published Monday in Nature.
While the study is unlikely to dispel the mystery surrounding the Neanderthals’ disappearance, it does suggest that the story of how modern humans expanded into Eurasia and replaced our evolutionary kin is much longer and more complex than we believed.
The debate on the extinction of the Neanderthals, and whether our direct ancestors played any nefarious role in it, has often been linked to the question of when modern Homo sapiens first encroached on their territory. Until now, the earliest undisputed modern human remains in Europe came from Oase Cave in Romania and were dated to around 41,000 ago (some specimens found at sites in Italy and Britain are said to be slightly older, but their age is controversial because the finds could not be directly dated).
Since Neanderthals were all but gone by 39,000 years ago, this chronology suggested their decline was rapid and happened suspiciously close – relatively speaking – to the arrival of the first humans in Europe. But the new finds from Bacho Kiro Cave challenge that picture, says lead researcher Jean-Jacques Hublin, head of the Department of Human Evolution at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
“Pioneer groups brought new behaviors into Europe and interacted with local Neanderthals,” Hublin says. “This early wave largely predates that which led to their final extinction in western Europe 8,000 years later.”
As with many recent discoveries in paleontology, the archaeologists who have been digging at Bacho Kiro since 2015 didn’t come up with well-preserved skeletons or similarly spectacular fossils, but applied advanced scientific techniques to minute finds that may have been easily overlooked or dismissed until recently. At the Bulgarian site, they uncovered a single human tooth and six bone fragments belonging to hominins. The bits of bone were so small they could not be identified by their appearance, but were studied using a new technique that analyzes protein sequences in animal remains and can assign them to one species or another.
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The morphology of the single tooth, a second lower molar, matched that of modern humans, the study reports. Additionally, DNA was extracted from the remains and compared to the genetic material of sapiens, Neanderthals as well as Denisovans, a hominin that lived in Asia at the time. The results confirmed that the inhabitants of the cave had been modern humans.
While the bones from Bacho Kiro were carbon-dated to around 45,000 years ago, the tools and animal remains associated with them stretch back 47,000 years ago, suggesting that humans may have inhabited the place already then, some 8,000 years before the final disappearance of Neanderthals.
Who copied who?
The team also uncovered thousands of animal bones, stone and bone tools, beads and ornaments, especially pendants made out of cave bear teeth. These assemblages are known to archaeologists as “Initial Upper Paleolithic,” or IUP, and represent “a new way of making stone tools and new sets of behavior including manufacturing personal ornaments that are a departure from what we know of Neanderthals up to this time,” says Tsenka Tsanova, a researcher from the Max Planck Institute for Evolutionary Anthropology.
The IUP lithic industry first appears around 50,000 years ago in what is today Israel, at an open-air site in the Negev called Boker Tachtit. It then spreads to Lebanon, Turkey and across Eurasia, as far as Mongolia. While the march of this tool style seems to proceed in keeping with the dispersal of modern humans out of Africa through the Levant and then onwards to the rest of Eurasia, researchers had until now been unable to securely link this industry to Homo sapiens, due to the lack of human remains at these sites.
“So far is was impossible to prove that these tools were made by modern humans, but here we have a clear genetic identification of the inhabitants of the cave as modern Homo sapiens,” Hublin concludes.
Interestingly enough, similar bone tools and pendants to the ones unearthed in Bacho Kiro have been found at later Neanderthal sites in western Europe, leading archaeologist to debate which hominin was the first to introduce these more advanced cultural markers.
“Some believe the Neanderthals invented by themselves what we call the Upper Paleolithic, while others like me claimed it was the result of the arrival of modern humans,” Hublin says. Because of their earlier date, the finds at Bacho Kiro are further evidence that it was modern humans that introduced these new behaviors and techniques to Europe, influencing the local Neanderthals to follow suit.
“You have modern humans arriving between 47,000 and 45,000 years ago in Eastern Europe and, bingo, at 44,000 the Neanderthals start to do things they never did before,” Hublin notes.
As to how much ‘intimate’ contact there may have been between the two groups, Hublin says that a separate study on the presence of Neanderthal DNA in the genome of the Bacho Kiro humans is still in the works and will be published soon.
We do already know that most human populations today carry a small, varying percentage of Neanderthal DNA, but whatever miscegenation was going on at Bacho Kiro and other contemporary sites, it is unlikely to have had an influence on our own genome. That’s because another key find of the newly published study is that the DNA of the humans that populated the Balkans so long ago did not contribute to the genome of today’s Europeans, Hublin says. In other words, these early Europeans were largely replaced by later waves of newcomers also arriving from the Levant and Africa.
“The peopling of Europe is more complex than just a wave of modern humans sort of invading the territory of the Neanderthals,” Hublin tells Haaretz in an interview. “It was a long process that included at least two distinct waves.”
The first, “pioneering” groups reached only eastern Europe and did not completely replace the Neanderthals, but coexisted with them in the continent for several millennia. This wave of humans likely vanished, possibly due to worsening climate that may have affected Neanderthal populations as well.
A second wave of modern humans better equipped to deal with the hardships of Ice Age Europe then reached the region around 42,000 years ago, populating the entire continent and fully replacing the Neanderthals. The last known pocket of Neanderthals, on Gibraltar, are now believed to have died out about 40,000 years ago (a theory that an isolated population survived in Siberia until about 31,000 years ago is not widely accepted).
Not our first rodeo in Europe
To be clear, the migrations of the Upper Paleolithic are not the first case in which Homo sapiens is known to have ventured beyond its evolutionary cradle in East Africa and mingled with other hominins that lived in Eurasia.
Hublin himself is best known for identifying a 300,000-year-old skull found at Jebel Irhoud, in Morocco, as the oldest sapiens remains found to date. Bones identified as belonging to early humans have since cropped up in Israel, dated to 190,000 years ago; 100,000-year-old sapiens teeth have been unearthed in China and there are some researchers that believe these first out-of-Africa migrants reached as far as Greece, though that discovery is still questioned by other experts.
Be that as it may, it is clear there were multiple pulses of migration out of Africa, probably every time the climate allowed hominins to live in and cross what today are the Sahara and Arabian deserts, Hublin says. However, we need to distinguish clearly between early sapiens and the people who started the last great migration out of Africa and across Eurasia, making us the only hominin to populate the entire planet.
“These early sapiens are on our lineage, but they are not fully modern,” Hublin explains. “Only for the last 100,000 years of evolution, at most, we can talk about modern humans in terms of anatomy and maybe only for the last 50,000 years in terms of behavior.”