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Bacho Kiro Cave

Early evidence of modern humans
H. sapiens replace Neanderthals

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Photo of cliffs surrounding Bacho Kiro Cave, one of the first sites in Europe to be occupied by modern humans
Bacho Kiro Cave in the valley of the Andaka and Dryanovo River, Bulgaria. Image by Izvora. (Public Domain).

Modern Humans at Bacho Kiro

Early evidence of modern humans in Europe has been found at Bacho Kiro Cave in Bulgaria.

Human fossils, directly dated to 43,000 BC or earlier, were found alongside stone tools, animal remains from hunting activities, bone tools, and personal ornaments.

These findings push back the timeline for the earliest known Upper Paleolithic H. sapiens in Europe by about 5,000 years. They also shed light on the transition from Neanderthal culture to the more advanced H. sapiens culture.

Furthermore, the stone tools found at the site establish a connection between Bacho Kiro Cave and discoveries across Eurasia, as far east as Mongolia.

[Note: the latest evidence from Mandrin Cave near Montélimar, in France, has pushed back the date for the first arrival of modern humans in Europe, to 54,000 BC.]

For more about early humans, see our articles on Homo Erectus (2m - 120,000 BC), Homo Ergaster (2m - 600,000 BC), Homo Heidelbergensis (600-300,000 BC) and the Denisovans (up to 30,000 BC).

Location and Excavation

Bacho Kiro Cave - named after the Bulgarian revolutionary leader Kiro Petrov Zanev - is located roughly 6 kilometres southwest of Dryanovo, in central Bulgaria, some 70 kilometers south of the Danube River.

The cave is a cavity eroded from limestone rock, at an elevation of 335 metres. The cave stretches for roughly three and a half kilometres, and its entrance is only a few hundred metres from the Dryanovo Monastery of Archangel Michael.

It was partially investigated in the 1930s and again in the 1970s, but fossils recovered from these earlier excavations were lost, and the site's stratigraphic layers were disrupted, leaving the dating of the site unresolved.

In 2015, an international team based at the Max Planck Institute for Evolutionary Anthropology set out to clarify the chronology of Bacho Kiro by digging two new trenches adjacent to the previous excavation.

This time, the archaeologists found thousands of animal bones (with marks of butchering), stone and bone tools, beads, pendants, and traces of five human fossils.

Jean-Jacques Hublin, the director at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, explains:

"The Bacho Kiro Cave site provides evidence for the first dispersal of H. sapiens across the mid-latitudes of Eurasia. Pioneer groups brought new behaviors to Europe and interacted with local Neanderthals. This early wave predates the one that ultimately led to the extinction of Neanderthals in western Europe 8,000 years later."

Fossil ID From Protein Analysis

Due to the fragmented nature of the human fossils, it was too difficult to identify them visually. Instead, their protein sequences were analyzed for recognition.

Frido Welker, a Postdoctoral Research Fellow at the University of Copenhagen and a research associate at the MPI-EVA, explains:

"Most Pleistocene bones are so fragmented that it is impossible to determine the animal species they belong to by sight. However, the proteins exhibit slight variations in their amino acid sequences across different species. By utilizing protein mass spectrometry, we can quickly identify these bone specimens that otherwise would be unrecognizable as human bones."

To determine the age of the fossils and the deposits in Bacho Kiro Cave, the team used an accelerator mass spectrometer to obtain highly precise age estimates and directly date the human bones.

The results indicated that occupation of the cave by modern humans - known as Cro-Magnons - occurred between 43,820 and 41,650 BC, and possibly as early as 45,000 years ago.

The radiocarbon dates from Bacho Kiro Cave represent not only the largest dataset ever collected from a single paleolithic cave but also provide the most precise error ranges.

Neanderthals or H. sapiens?

In order to determine which group of humans occupied Bacho Kiro Cave, researchers conducted archaeogenetics tests on the fragmented fossil bones.

Due to the exceptional preservation of DNA in the molar and the hominin fragments identified through protein mass spectrometry, researchers were able to reconstruct complete mitochondrial genomes from six out of seven specimens.

The recovered mitochondrial DNA sequences from all seven specimens belong to modern humans.

Interestingly, when comparing these mtDNAs with those of ancient and modern humans, the mtDNA sequences from Bacho Kiro closely align with the base of three major macrohaplogroups found in present-day populations outside of Sub-Saharan Africa.

What's more, the DNA dates fitted almost perfectly with the radiocarbon dates.

The findings show that Homo sapiens entered Europe and started interacting with Neanderthals around 45,000 years ago, and possibly even earlier.

They brought high-quality flint into Bacho Kiro Cave from sources located up to 180 kilometres away, which they used to craft tools like pointed blades, potentially for hunting and most likely for butchering the animal remains found at the site.

Bone Tools and Other Artifacts

According to palaeontologist Rosen Spasov from the New Bulgarian University, "the animal remains discovered at Bacho Kiro consist of a mix of species adapted to both cold and warm environments, with bison and red deer being the most common."

But the most interesting aspect of the faunal assemblage is the extensive collection of bone tools and personal ornaments.

Curiously, teeth from cave bears were fashioned into pendants, some of which bear a striking resemblance to later artifacts made by Neanderthals in western Europe. Were moderns learning from Neanderthals?

For more Neanderthal decorative art, see: Krapina White Eagle claw jewellery (130,000 BC) and Los Aviones Cave shell jewellery (115,000 BC). The best known example of Neanderthal mobiliary art is the Divje Babe Flute from Slovenia, now ESR dated to between 60,000 and 50,000 BC.

Homo sapiens Takes Over

The age of the human remains at Bacho Kiro corresponds to a critical period of the late Stone Age, when populations of Neanderthals were shrinking after inhabiting the continent for almost 400,000 years.

Archaeologists have long debated how Neanderthals came to be extinct. Possible theories include conquest at the hands of newly arriving bands of modern humans, competition with the newcomers for resources, and reproductive weaknesses caused by Neanderthals living in small, widely scattered groups.

In any event, Bacho Kiro is well placed, both geographically and chronologically, to provide clues.

For example, Bacho Kiro Cave illustrates a new approach to stone tool production and a set of behaviours, including the creation of personal ornaments, that differ from what we know of Neanderthals during this time.

Overall, the sediments at Bacho Kiro Cave provide evidence of the period in Europe when Upper Paleolithic Homo sapiens began to replace Middle Paleolithic Neanderthals.

The assemblages of the first Homo sapiens at the site are considered to belong to the Initial Upper Paleolithic, a term used by archaeologists to describe the very earliest signs of modern humans in Europe.

Until now, the Aurignacian culture was regarded as the beginning of the era of Upper Paleolithic art in Europe. It was seen as the the most advanced type of Stone Age culture - embracing social, technological and artistic customs - which replaced the more limited 'vision' of Neanderthals.

Previously believed to start around 40,000 BC, the Initial Upper Paleolithic at Bacho Kiro Cave, along with other sites in western Eurasia, like Mandrin Cave - and possibly even others in SE Asia - pushes that date back to 43,000 BC in SE Europe and 54,000 BC in Western Europe.

Among other things, this means that many examples of cave art - hitherto assigned to Neanderthals - may have been created by H. sapiens, not H. neanderthalensis.

References

(1) Fewlass, Helen; et al (11 May 2020). "A 14C chronology for the Middle to Upper Palaeolithic transition at Bacho Kiro Cave, Bulgaria". Nature Ecology & Evolution. 4 (6): 794–801.
(2) Hublin, Jean-Jacques; et al (21 May 2020). "Initial Upper Palaeolithic Homo sapiens from Bacho Kiro Cave, Bulgaria" (PDF). Nature. 581 (7808): 299–302.

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