Scientists have retrieved an ancient human Deoxyribonucleic Acid (DNA) from a fossil dating back about 400,000 years, is raising new mysteries about human evolution.

The findings published in a paper in a journal Nature, an international science weekly made available to the Ghana News Agency says the breakthrough has broken the 100,000 years previous record on human DNA, discovered by a team of Belgian and French researchers in 2006.

The fossil, a thigh bone found in Spain- Sima de los Huesos (The Pit of Bones), was thought by many experts to belong to a precursor of Neanderthals-an extinct subspecies of human beings- but its DNA tells a different story, resembling DNA from a mysterious lineage of humans known as Denisovans.

The disparity between the anatomical and hereditary evidence surprised the scientists who are rethinking human evolution over the past few hundred thousand years.

Scientists envisioned that many more extinct human populations were yet to be discovered suspecting that they might have interbred, exchanging DNA. They believed that continued studies of extreme ancient human DNA would open the frontiers of finding answers to clarify the mystery.

?Right now, we?ve basically generated a big question mark,? said Dr Matthias Meyer, a Geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and co-author of the study.

The DNA failed to match that of a Neanderthals but agreed to that of the Denisovans that the team had discovered in Siberia in 2010.

?Everybody had a hard time believing it at first,? Dr Meyer said ?So we generated more data to nail it down.?

The new findings failed to reconcile with the picture of human evolution that has been emerging in recent years based on fossils and ancient DNA.

Based on previously discovered ancient DNA and fossil evidence, scientist generally agreed that humans? direct ancestors shared a common ancestry with Neanderthals and Denisovans that lived about half a million years ago in Africa.

Humans? ancestors, meanwhile, stayed in Africa, giving rise to Homo sapiens about 200,000 years ago. Humans then expanded from Africa into Asia and Europe about 60,000 years ago. They then interbred not only with Neanderthals but with Denisovans too, later becoming extinct.

Dr David Reich, a Geneticist at the Harvard Medical School, who was not part of the study said ?Finding such ancient human DNA was a major advance. That?s an amazing game-changing thing.?

Dr Juan Luis Arsuaga, a paleoanthropologist at Universidad Complutense de Madrid and co-author, who has found 28 nearly complete skeletons of humans during three decades of excavation, describes the Sima de los Huesos as ?Very special.?

Based on the anatomy of the fossils, he argued that they belonged to ancestors of Neanderthals, who lived in western Asia and Europe from about 200,000 to 300,000 years ago.

Dr Beth Shapiro, an expert on ancient DNA at the University of California, Santa Cruz, favours an even more radical possibility: that the humans of Sima de los Huesos belong to yet another branch of humans. They might have been a species called Homo erectus, which originated about 1.8 million years ago and became extinct within the last few hundred thousand years.

?The more we learn from the DNA extracted from these fossils, the more complicated the story becomes,? Dr. Shapiro said.

This complicated story has come to light only because of advances over the past 20 years in retrieving ancient DNA.

Dr Meyer is optimistic the team would be able to get more DNA from the Spanish fossil, as well as other fossils from the site to help solve the puzzle available to them.

?It?s extremely hard to make sense of,? he said. ?We still are a bit lost here.?

Source: GNA


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