Clarifying the evolution of Homo sapiens
Scientists have found traces of another species of ancient humans in the DNA of Neanderthals
Geneticists have recovered part of the DNA of the oldest Neanderthals in Europe and found traces of another population of ancient people, relatives of the ancestors of Cro-Magnons who penetrated into Europe at least 220 thousand years ago, according to an article published in the journal Nature Communications (Posth et al., Deeply divergent archaic mitochondrial genome provides lower time boundary for African gene flow into Neanderthals).
"Such a scenario allows us to reconcile the differences between the evolution trees of ancient and modern humans, built on the basis of nuclear and mitochondrial DNA, and also clarify the picture of when the ancestors of Homo sapiens and Neanderthals separated, about which there has also been a debate for a long time," says Johannes Krause from the University of Tubingen (Germany).
The fourth extra
Despite the external similarity, modern humans and Neanderthals developed in completely different ways. The ancestors of modern humans and Neanderthals, as scientists believed today, separated about 700-650 thousand years ago, and the former remained in Africa and gradually colonized it, while the latter migrated north and settled Europe and Asia.
For a long time it was believed that humans and Neanderthals have nothing in common, but in 2009, scientists restored the genome of the first "aborigines" of Europe and found that the DNA of most modern people, in addition to the inhabitants of Africa, contains about 2-3% of Neanderthal genes. This fact, as well as the presence of typically "human" genes in the genome of Homo neanderthalensis, distinguishing them from "Denisovans" and other hominids, made scientists wonder how contacts between the ancestors of humans and Neanderthals could have proceeded.
Krause and his colleagues found some of the answers to these questions, and found out that the history of the settlement and life of Neanderthals in Europe was much more complicated than we imagine, studying the remains of an ancient man who lived in the Holenstein-Stadel cave in the southwest of modern Germany about 120 thousand years ago.
According to paleontologists, the femur of this proto-man was found by archaeologists during the Nazi era, in 1937, and since then it has been repeatedly studied by paleontologists and anthropologists, trying to understand who it could belong to. The bone was partially gnawed by a predator, which, coupled with the poor conditions inside the cave itself, made the search for DNA in it extremely unpromising.
Nevertheless, Krause's team still managed to solve this problem and extract fragments of mitochondrial DNA from the remains – a small segment of the genome contained in the "power stations" of the cell, mitochondria. This DNA is transmitted along with mitochondria from the mother to her children, which allows establishing kinship relationships between human populations and using mtDNA to study the history of their migrations, as well as building a single "family tree" of humanity.
Secrets of the Stone Age Genealogy
The "resurrection" of this DNA automatically made it the oldest sample of the genome of humans and their relatives that scientists could obtain, and allowed Krause and his colleagues to fill in some of the gaps in the history of the evolution of Neanderthals and, as it unexpectedly turned out, Cro-Magnons.
The fact is that the mtDNA of the Neanderthal from Holenstein-Stadel was radically different from how the mitochondrial genomes of other Neanderthals, whose genomes have been restored in recent years, were arranged. In its structure, it was much closer to a similar part of the genome of the "Denisovans", another species of ancient humans, than to the mtDNA of Neanderthals and modern Homo sapiens.
Counting the number of small mutations in the mtDNA of the cave dweller and other Neanderthals, scientists came to the conclusion that their ancestors split unexpectedly long ago, about 270-220 thousand years ago, when another group of ancient people from Africa penetrated into Europe, who were close relatives of the progenitors of mankind, and not Neanderthals or "Denisovans".
Diagram from the Max Planck Institute for the Science of Human History press release
DNA of early Neanderthal gives timeline for new modern
human-related dispersal from Africa – VM.
The number of these "aliens" from whose women more modern Neanderthals inherited their mtDNA was relatively small, their contribution to the genome of Homo neanderthalensis was almost imperceptible. Nevertheless, they were able to achieve extremely great success in procreation, since most of the restored genomes of Neanderthals contain almost human mitochondrial DNA, and not the "Denisovan" version of it.
How this could have happened and why it happened, scientists do not yet know – to answer this question, nuclear DNA of a Neanderthal from Holenstein-Stadel is needed. Its restoration is extremely unlikely, but Krause and his colleagues do not lose hope and at the same time try to find the remains of the equally ancient "aborigines of Europe" preserved in a slightly better form.
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05.07.2017