Czech cave skull may contain oldest modern human genome


The Zlatý kůň skull.

The Zlatý kůň skull.
Image: Martin Frouz

A sequenced genome from a modern human skull is approximately 45,000 years old, making it the oldest such discovery. It is a significant archaeological discovery, but the use of an unconventional dating method leaves the result in doubt. In a related study, scientists also show that Neanderthal-human mixing occurred more frequently than we thought.

Modern humans, also known as Homo sapiens, emerged about 300,000 years ago in Africa. There are skeletal remains of our distant ancestors, but the fossil record is poor. Even poorer is the genetic evidence, the oldest of which is the genome of a 45,000-year-old Ust’-Ishim person from western Siberia. described in 2014.

But like new investigate published today in Nature Ecology & Evolution reveals, scientists may have stumbled upon an even older genome. A team co-led by Kay Prüfer of the Max Planck Institute for the Science of Human History in Germany has discovered what may very well be the oldest reconstructed modern human genome in the fossil record. That is, if the dating method used can be considered reliable. The genome, extracted from a skull found in the Czech Republic, appears to be at least 45,000 years old and possibly even older.

A related paper, also published today in Nature Ecology & Evolution, describes the remains of the first modern humans found in a Bulgarian cave. The DNA of these people, dating back to roughly the same time period, suggests that interbreeding with Neanderthals was probably more common than previously assumed.

The skull described in Prüfer’s article was removed from the Koněprusy cave in 1950 and was found along with other skeletal remains. This cave is located in Zlatý kůň, which means “golden horse” in Czech, and is a short drive of 40 km (25 miles) from Prague.

Front view of the skull of Zlatý kůň.

Front view of the skull of Zlatý kůň.
Image: Zlatý kůň

Genetic analysis of the mostly intact skull, which belonged to a human female, shows that she was between 2% and 3% Neanderthal ancestry, which basically matches the numbers found in non-African people living today. That said, no human living today is directly descended from the Zlatý k as woman, as she belonged to a population that did not transmit any DNA to subsequent European or Asian populations of early modern humans.

“As far as we know, the population he belonged to was not contributing to current populations,” Prüfer explained in an email. “We speculate that its people became extinct along with Neanderthals, who were living in Europe at the time, and that a large volcanic eruption in Italy that occurred approximately 39,000 years ago may have contributed to their demise.”

Prüfer refers to the Ignimbrite volcanic eruption from Campania, which severely altered the climate in the Northern Hemisphere, making life difficult for both modern humans and Neanderthals during the last European ice age.

This is all good and (reasonably) uncontroversial – it’s when we get to dating the skull that problems arise.

Initial radiocarbon dating of the skull yielded a date close to 15,000 years. Prüfer and his colleagues did not believe this to be true (the anatomy of the skull suggested an older date), resulting in a date closer to 27,000 years ago. After some cleansing treatments, a third radiocarbon date was determined, suggesting that the woman lived about 19,000 years ago. It was at this point that the scientists realized they were dealing with a highly contaminated specimen.

“We found evidence of contamination with cow DNA in the analyzed bone, suggesting that a bovine-based glue used in the past to [fix] the skull was returning radiocarbon dates younger than the actual age of the fossil, ”Cosimo Posth, co-lead author of the study and professor of paleogenetics at the University of Tübingen, explained in a statement. Posth had previously worked as a research group leader at the Max Planck Institute.

With radiocarbon dating ruled out as a useful tool for this specimen, the team turned to a technique in which the length of DNA segments can be used to infer a person’s age. Specifically, the scientists measured the length of the Neanderthal segments, as these segments get shorter with each successive generation.

This analysis suggests that the Zlatý kůň woman lived at least 2,000 years after the last interbreeding event involving her modern Neanderthal and human ancestors (approximately 63 to 78 generations). The “lengths of the Neanderthal segments are longer than those observed in the currently oldest modern human genome of the ~ 45,000-year-old individual Ust’-Ishim from Siberia, suggesting that this individual from Zlatý kůň is one of the first inhabitants of Eurasia following expansion out of Africa, ”the authors wrote in their study. The Ust’-Ishim person was separated from Neanderthals for around 84 to 94 generations, according to the newspaper.

Working under the assumption of a single interbreeding event, the new results mean that Zlatý kůň is basically the same age as the Ust’-Ishim specimen of approximately 45,000 years, or possibly “up to a few hundred years older,” depending on the paper. . But if a second Neanderthal interbreeding event occurred along the Ust’-Ishim lineage after this intermingling common Neanderthal, then “Zlatý kůň could be even several thousand years older than Ust’-Ishim,” the authors wrote, adding they have not. found support for a second Neanderthal mix.

This is all very intriguing, but you obviously need to set a firmer date, hopefully by using other methods.

The authors “really don’t know how old the skull is, and the range given is wide,” Israel Hershkovitz, an archaeologist at Tel Aviv University and an expert on early modern humans, said in an email. That said, Hershkovitz said that the data used to determine the age of the skull – the mitochondrial DNA and the pattern of the Neanderthal gene segments – are “interesting,” but he’s not entirely sure of their efficacy as a dating technique.

However, if these results are accurate, the Zlatý kůň specimen now represents the oldest modern human genome in the fossil record. Additionally, the new article offers a rare glimpse into the genetic makeup of early modern European humans dating back to this time period.

The group to which the Zlatý kůň woman belonged did not survive, which is also interesting. It suggests multiple waves of migrations to Europe from Africa and / or some complex population replacement scenarios, in which some groups survived and others did not. That this specimen belonged to “a population prior to the split between European and Asian populations” is significant, Hershkovitz said, provided his first claim, “that the skull is very old, is correct.”

That modern humans were living in Europe so long ago is not a major exaggeration. Evidence from 2020 suggests that modern humans present in southeastern Europe between 47,000 and 43,000 years ago, while 2019 evidence suggests that some modern humans had reached Europe, specifically Greece, 210,000 years ago.

The second article, led by Mateja Hajdinjak of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, describes the remains of early modern humans found in the Bacho Kiro cave in Bulgaria. These remains were initially described in the aforementioned 2020 paper, but the new analysis dives into their DNA.

Neanderthals and humans interbred sometime between 55,000 and 60,000 years ago. However, until now, archaeologists only had one person, a 40,000-year-old Oase1 fossil from Romania, which exhibited recent Neanderthal ancestry, in a finding that suggests modern humans and Neanderthals were bred multiple times.

“However, we could not exclude that this was just a chance finding,” Hajdinjak explained in an email. “Now in this study, we have the three approximately 45,000-year-old individuals from the Bacho Kiro cave with very close Neanderthal ancestry in their family history, just like Oase1,” he said, which means that “the mixture was more common than we previously thought. “

In fact, the three oldest individuals found at Bacho Kiro carried between 3% and 3.8% Neanderthal DNA, which is slightly more than current populations. Incredibly, these people had Neanderthal ancestors as little as six, or even fewer, generations ago, in what is a truly astonishing find.

“Unlike what might be expected of ancient individuals in Europe, Bacho Kiro individuals are more closely related to human groups that contributed their genetic material to East Asians than to West Eurasians,” Hajdinjak said. “Fundamentally, all of the older individuals from the Bacho Kiro cave have very closely Neanderthal ancestry in their family trees, suggesting that mixing between these early humans in Europe and Neanderthals was common.”

Palaeogenetics is revealing some remarkable things about our past, especially when working in conjunction with skeletal and archaeological artifacts. Our story becomes more and more focused and the view becomes more intriguing.

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