Hajdinjak et al. 2020
DNA from the earliest Homo sapiens in Europe adds more detail to the story of the expansion of our species in Eurasia – and our complicated 5,000-year relationship with Neanderthals.
The earliest traces of our species in Eurasia are a lower molar and a few pieces of bone from the Bacho Kiro cave in Bulgaria, which is between 46,000 and 42,000 years old. A recent article describes DNA from the fossils, as well as a 42,000- to 37,000-year-old jaw from the Oasis site in Romania. The results indicate that the early waves of Homo sapiens in Eurasia, several genetically different groups were included, only some of which eventually passed on their genes to modern humans. Most of the early Eurasians mingled with Neanderthals fairly regularly.
Paleolithic and ready to mix
Neanderthals lived in Europe and Asia for at least 350,000 years (and had a complicated population history) when the first groups Homo sapiens extended northward from eastern Africa and the Levant. Today, many populations of modern humans still carry small fragments of Neanderthal DNA in our genomes as souvenirs from the blending of two hominin species 45,000 years ago. But we still do not know much about how often Neanderthals and Homo sapiens came together during the few millennia when they shared a continent.
When Max Planck Institute for Evolutionary Anthropology geneticist Mateja Hajdinjak and her colleagues DNA sequence from the Homo sapiens bones in the Bacho Kiro Cave in Bulgaria, one lower molar and a small piece of bone were left over from a man who died on the site about 45,900 years ago. But it’s enough to get genetic data for us these days. Its genome contains fragments of the Neanderthal versions of some genes, which have been divided and rearranged in a way that indicates that they have been transmitted through about six generations. In other words, one of his great-great-great-great-great-grandparents was a Neanderthal.
Two other pieces of bone at the Bacho Kiro Cave were the only remains of two men who died about 45,000 to 42,000 years ago, and both had Neanderthal ancestors seven generations back. Meanwhile, DNA from a man who died between 42,000 and 37,000 years ago revealed at the Oasis site in Romania that one of his immediate family members – a parent or grandparent – was a Neanderthal.
This is a rare glimpse into a specific, very human story: direct evidence that a Neanderthal and a Homo sapiens had sex and gave birth to a child. A tooth from the Denisova Cave in the Altai Mountains of Siberia tells a similar story about a Neanderthal, a Denisovan and their daughter 90,000 years ago. Those moments are rare in a genetic and archaeological report, which usually reveals only large, large population trends.
Although we do not have direct testimony of individual relationships – no matter what form they took, and whatever that meant to those involved – the relationships themselves were probably anything but rare.
“It is striking that all four European individuals who overlap in time with the late Neanderthals and from whom data on the entire genome were traced, had close Neanderthals in their family history,” Hajdinjak and her colleagues wrote in their newspaper. “This suggests that intermingling between Neanderthals and the first modern humans to arrive in Europe was perhaps more common than is often accepted.”
Neanderthal Desert
As Neanderthals and Homo sapiens really had sex – and a progeny – that it might sound like modern people of European and Asian descent need to carry a lot more Neanderthal DNA. But on average it is only about two percent. But the study of Hajdinjak suggests that most Neanderthal genes were eliminated very quickly by the process of natural selection. Within a few generations, the three men of the Bacho Kiro Cave had only between 3.0 and 3.8 percent Neanderthal DNA.
In modern humans, Neanderthal DNA is distributed throughout the genome, but Neanderthal versions of genes are more common in some parts of the genome than others. And in some areas, called “Neanderthal deserts”, there are no Neanderthal genes. When Hajdinjak and her colleagues examined the DNA of the three Bacho Kiro men and the one from Oasis, they found that although some Neanderthal alleles still resided in those parts of the genome, the “Neanderthal deserts” were already beginning to form. has. In other words, the Homo sapiens versions of certain genes offered such an evolutionary advantage that within a few generations they had already fought with the Neanderthal versions.
A younger bone fragment from Bacho Kiro, dating from about 35,000 years ago, comes from a person who had only 1.9 percent Neanderthal DNA, similar to the levels seen in most modern non-African people. However, Hajdjnjak and her colleagues acknowledged that “additional individuals of recent Neanderthal descent will be needed to fully address this question.”
A complicated relationship history
Prior to these few recent studies, we had DNA from just three individuals older than 45,000 years. Now we have DNA of seven, and that drastically improves our view. As always in archeology, the more data we get, the more questions we can ask.
And there are some questions we will never be able to answer. When Homo sapiens and Neanderthals had offspring, were those couples the result of illegal relationships, marriages between groups, or something more violent? It is difficult to imagine what kind of archaeological evidence can provide these details, and the genetic evidence records only the mere biological facts. But because humans have always been humans, the answer is probably “all of the above, at different times and places.”
Another recent study supports the suggestion that the story is not the same everywhere. DNA from the bones of a 45,000-year-old member of our species, from the Ust’Ishim site in Siberia, suggested that the youngest ancestor of this person was 80 to 95 generations back in the pedigree.
And when anthropologist Kay Prüfer, also of the Max Planck Institute, analyzed the DNA sequence of a woman who died in Zlatý kůň in the Czech Republic, her mitochondrial DNA (DNA outside the cell nucleus that is transmitted directly from mother to child) suggested that she was about 43,000 years old. And based on the length of the segments of Neanderthal DNA in her nuclear genome, her last ancestor of Neanderthal lived about 64 to 80 generations before her. This can mean that interactions vary as different groups of people and Neanderthals move around and may have interacted in different ways.
Who is related to whom?
The DNA from both recent studies sheds some light on how the different groups moved around and how some of them relate to groups of modern people in Central and East Asia. Both Hajdinjak and her colleagues, as well as Prüfer and her colleagues, compare DNA from their samples with genomes from other ancient and modern humans, to see how many alleles they have in common, and use computer modeling to see how they relate.
In the study of Prüfer and her colleagues, the wife of Zlatý kůň belonged to a group of people who apparently did not contribute much to the origins of later Eurasian people. And DNA from Oasis 1, the son of a Neanderthal and a Homo sapiens, suggested that its population also did not ‘contribute traceably to later populations’. In other words, he was part of a generation that was extinct.
On the other hand, the earliest known Homo sapiens remains in Europe, at the Bacho Kiro Cave, belonged to a group that shared remarkably more alleles with modern people in East and Central Asia than with the people now living in Bulgaria (or anywhere else in Europe or West -Asia) live. The Bacho Kiro population was apparently also related to another group, which included the ancestors of a 40,000-year-old person who was exhumed in Tianyuan, China.
This “proves that there was at least continuity between the earliest modern people in Europe and the later people in Eurasia,” as Hajdinjak and her colleagues put it, but it is also clear that several of the first Homo sapiens groups to reach Europe eventually disappeared without leaving much of a genetic mark.
The tooth and bone fragments at the Bacho Kiro Cave were found buried in a layer of sediment that also contains the remains of a culture known by archaeologists as the Early Upper Paleolithic. Based on a common style of stone tool making, Initial Upper Paleolithic, or IUP, artifacts have appeared in places from central and eastern Europe to Mongolia, and it is possible that some may wait to be discovered even further east. .
Archaeologists are still debating whether the IUP extends over such a wide area because one group of people has been able to spread it so far or because ideas have spread between groups. But both archaeological and genetic evidence now suggest links between the first Homo sapiens to gain a foothold in Europe and those who lived in Asia a few thousand years later.
Earth, 2021 DOI: 10.1038 / s41586-021-03335-3 (About DOIs).