Confirm the existence of a new human species, “sister” of Neanderthals

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The researcher Svante Pääbo has succeeded in sequencing the genome of the Denisova hominin, the mysterious species found in Siberia in 2010 and has survived only a fragment of a child and two finger teeth.

In March 2010, an odd fossil first came to light. Found two years ago in the remote Siberian cave Denisova , in the Altai mountains, it was a fragment of the little finger of a child (or a child) about seven years of age who lived in this region for over 50,000 years . In the same place were also several artifacts and tools and, somewhat later, two teeth.

The remains were too few to determine, by their morphology, the human species to which they belonged. So ended in Leipzig (Germany), owned by Svante Pääbo , director of the Max Planck Institute for Evolutionary Anthropology and one of the world’s leading experts in fossil DNA .

Pääbo, the researcher was able to sequence the Neanderthal genome , managed to extract the finger bone samples several mitochondrial DNA , genetic material not found in the nucleus of cells, but distributed in various organelles (mitochondria) from the cytoplasm cell and only passed from mother to daughter. So the fossil dubbed as “Woman X” .

A new group of people

The results of genetic analysis of the Denisova hominin assumed a major surprise to the researchers. In fact, their mitochondrial DNA did not match that of Neanderthals , as assumed in the beginning, and not with that of modern humans, our own species. By contrast, the genetic differences were deep enough to think of a whole new group .

Immediately, Pääbo and his team began to work for, and sequencing,nuclear DNA of the child little finger . An essential item to confirm (or deny) the “message” suggested by the fossil mitochondrial DNA. Today, in an article published by the journal Science , the mystery is revealed at last. And it confirms what scientists have long suspected: the “X-woman” belonged to a species hitherto unknown human . A species that has its roots in the mists of time and that is closely related to Neanderthals, with which it shares a common ancestor. “Genetic sequencing shows that Neanderthals and Denisovans are sister groups , which were separated from a common ancestral population after split of modern humans, “said David Reich, one of the scientists involved in the research.

To obtain the DNA from the nucleus of cells, Pääbo used based method that allowed sequencing the Neanderthal genome . Researchers got so a gene sequence that is very detailed andcomparable to what is available for the study of modern human genome . “This was the first time that has been discovered and defined a new group of humans extinct by evidence drawn from DNA sequencing, and studying the morphology of the bones,” Pääbo said. He also said that “with few exceptions there is no technical difference between what we can learn from the genetic analysis of a modern person or 50,000 years ago, whenever we have enough well-preserved bones.”

Contribution to the genome in Melanesia

The next step of the research was precisely to compare the Denisova hominin genome with different modern populations in many different areas of the planet. And the result was that theDenisovans contributed to modern human genome , although this contribution varies from one population to another. “While Neanderthals contributed to the DNA of all living humans out of Africa, the Denisovans only provided to people of Papua New Guinea, Fiji, Australia and elsewhere in Melanesia,” Pääbo said.

In addition, some alleles Denisovans (each of the variants may have a gene) were found in both populations of Asia and South America and Europe, although Pääbo think coming over hybridization between modern humans and Neanderthals than directly from the Denisovans .

But the study provides further information surprising. Such as the girl (or boy) whose genome was sequenced alleles carried in modern humans are related to a skin and dark hair and brown eyes . “It is very probable that they were dark-skinned. It’s really all we can say about her appearance. The truth is that the study of the genome can be deducted only features of what it was like in appearance, “Pääbo said.

The researchers also developed a list of changes in the human genome since its separation from the Denisovans. That is, changes that occurred only in the modern human genome. They found that the initial population of Denisovans must have been very small , but very quickly grew and spread to much of the world. “The genetic diversity of the Denisovans was apparently much lower than that of modern humans,” said Matthias Meyer, who developed the technique of genetic sequencing has allowed to carry out the study.

The finding, finally, suggests a new model of human evolution, based not in one but in many successive outputs of Africa , which implies a much more complex than previously thought.

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