Recent advances in ancient DNA research have significantly enhanced our understanding of human history, revealing fascinating insights into the interactions between early modern humans and Neanderthals. Studies have shown that these two groups likely interbred in the Near East around 50,000 years ago, soon after modern humans began migrating out of Africa. This interbreeding has left a lasting genetic legacy: all people outside of Africa carry between 2% and 3% Neanderthal DNA in their genomes. Interestingly, over time, the Neanderthal DNA segments in modern human genomes have become progressively shorter, with their length now serving as a tool to estimate when particular individuals lived.
In a groundbreaking study published in Nature Ecology & Evolution, an international team of researchers has shed light on what is likely the oldest reconstructed modern human genome to date. The fossil in question, known as Zlatý kůň, was discovered in Czechia and represents a crucial piece of the puzzle in understanding early human migrations and interactions with Neanderthals. The genome of Zlatý kůň was found to have longer stretches of Neanderthal DNA compared to previous ancient human genomes, such as the 45,000-year-old Ust’-Ishim individual from Siberia. This discovery provides key insights into the genetic makeup of early human populations that predate the formation of the ancestral groups that gave rise to modern-day Europeans and Asians.
The study’s findings are based on a combination of fossil analysis and cutting-edge genetic techniques. Zlatý kůň’s skull shape has shown distinct similarities to human populations that lived in Europe before the Last Glacial Maximum, roughly 30,000 years ago. However, previous attempts to radiocarbon date the fossil had yielded inconsistent results, with some dating as recent as 15,000 years ago, which initially caused confusion regarding its true age. It wasn’t until the collaboration between archaeologists from the Faculty of Science in Prague and the genetics laboratories at the Max Planck Institute for the Science of Human History that a clearer picture began to emerge.
Cosimo Posth, co-lead author of the study, explained that contamination from bovine DNA, likely from glue used in past restoration attempts, was responsible for the misleading radiocarbon dates. The glue had affected the accuracy of the dating, leading to younger than expected results. Once the researchers corrected for this contamination, they were able to more accurately estimate the fossil’s age.
What truly sets Zlatý kůň apart, however, is the amount and nature of the Neanderthal DNA found in her genome. While she carried roughly the same amount of Neanderthal DNA as other modern humans outside Africa, the key difference lies in the length of these genetic segments. Neanderthal DNA fragments in Zlatý kůň’s genome were significantly longer, suggesting that she lived closer in time to the admixture event between Neanderthals and early modern humans. This finding allowed the team to estimate that Zlatý kůň lived approximately 2,000 years after the last known Neanderthal admixture event, providing new insights into the timeline of human-Neanderthal interactions.
Kay Prüfer, another co-lead author of the study, highlighted the importance of this discovery, noting that the extended Neanderthal DNA segments in Zlatý kůň’s genome offer a direct link to the era when modern humans were still closely interacting with Neanderthals. This discovery is a significant contribution to our understanding of human evolutionary history, as it suggests that Zlatý kůň represents one of the earliest human genomes ever recovered, roughly 45,000 years old, and possibly a few hundred years older than the famous Ust’-Ishim individual.
The study also brings attention to the fact that these early modern humans, including Zlatý kůň, did not leave any direct genetic legacy in present-day Europeans. Despite their advanced genetic and cultural traits, the populations that existed in Europe around 40,000 years ago did not survive or contribute to the gene pool of later populations. As Johannes Krause, senior author of the study and director at the Max Planck Institute for Evolutionary Anthropology, pointed out, there is no genetic continuity between the earliest modern humans in Europe and later populations, which raises questions about why these early groups ultimately disappeared.
One possible explanation for this genetic discontinuity lies in the dramatic climatic events of the Ice Age, particularly the Campanian Ignimbrite volcanic eruption, which occurred around 39,000 years ago. This massive eruption triggered severe climate changes that likely disrupted ecosystems across the northern hemisphere. These environmental changes may have contributed to the extinction of Neanderthals and early modern humans in many parts of Europe. The resulting collapse of ecosystems would have significantly reduced the survival chances of these early populations, paving the way for the eventual dominance of later human groups.
The study of Zlatý kůň’s genome adds a critical piece to the growing body of evidence regarding the complex history of human migration, interbreeding, and survival during the Ice Age. As more ancient genomes are sequenced and analyzed, the story of humanity’s earliest expansion out of Africa becomes clearer. The interactions between early modern humans and Neanderthals, the environments they inhabited, and the factors that shaped their survival and eventual extinction are slowly being uncovered.
Future research will undoubtedly continue to refine our understanding of these early human populations. As genetic techniques improve and more fossils are discovered, scientists hope to uncover even more details about the genetic relationships between different human groups that coexisted in prehistoric Europe and Asia. This will further illuminate the fascinating story of our species’ journey from Africa to the far reaches of the Eurasian continent and the complex genetic legacy we carry with us today.
More information: A genome sequence from a modern human skull over 45,000 years old from Zlatý kůň in Czechia, Nature Ecology & Evolution (2021). DOI: 10.1038/s41559-021-01443-x