Oldest premonitory DNA baffles researchers

400, 000-year-old genetic material from Spain is related to Siberian friars

The DNA was isolated from this 400, 000-year-old thigh bone found in the Sima de los Huesos Cave. © Javier Trueba / MADRID SCIENTIFIC FILMS
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Researchers have sequenced the oldest genetic material of a primitive man. The genetic material was extracted from 400, 000-year-old bones of early humans, which were found in a cave in northern Spain. The strange thing about it is that the DNA of the Primal Spaniard is most similar to that of Denisova's humans - a human species previously known only from Siberia. How it came to this Europe-spanning connection is still unclear, as the scientists report in the journal "Nature".

The Sima de los Huesos Cave in northern Spain is considered one of the richest deposits of early Pleistocene early-human fossils - the height of the Ice Age. At the bottom of a 13-meter-deep shaft, 500 meters from the nearest cave entrance, scientists have dug up the bones of at least 28 human individuals and some cave bears (Ursus deningeri) in recent years. Dates of the finds gave an age of far more than 300, 000 years.

Part Neanderthal, partly Homo heidelbergensis

The human fossils have numerous features of the Neanderthals, including their teeth, jaws and also their facial skulls. In other properties, however, they are very similar to the Homo heidelbergensis. This is usually considered the ancestor of the European Neanderthals and as a link between these and the much older Homo erectus. Due to the ambiguous characteristics of the assignment of fossils from Sima de los Huesos, however, was controversial.

So the people of Sima de los Huesos could have looked 400, 000 years ago. © Javier Trueba / MADRID SCIENTIFIC FILMS

Matthias Meyer from the Max Planck Institute for Evolutionary Anthropology in Leipzig and his colleagues have therefore tried to come closer to a genetic answer. However: "So far, DNA preservation has been documented for hundreds of thousands of years only under permafrost conditions, " explain the researchers. However, they tried it anyway, because the conditions in the cave are particularly favorable: the humidity is very high, the temperature is constant at around 10 degrees Celsius and the fossils have been spared from their deposits of disturbances.

Reconstructed mitochondrial genome

For their DNA analysis, the scientists extracted just under two grams of material from the femur of one of the fossil skeletons. After the isolation and duplication of the contained gene residues, the hardest part began: the analysis. Because the genome has largely decomposed or disintegrated into small fragments after such a long time, it has to be put together like in a puzzle. This is most promising with mitochondrial DNA, the genetic material that is not stored in the cell nucleus but in the cell's power plants, the mitochondria. display

In fact, the researchers were able to reconstruct a good 15, 000 bases of primeval DNA - and thus about 98 percent of the mitochondrial genome. The sequence thus obtained was compared by Meyer and his colleagues with that of modern humans, the Neanderthal, the Denisova man and the chimpanzee.

Ridiculous connection to Siberia

Because of the location in Western Europe and the age of the bones, the researchers expected that the ancestors of the Sima de los Huesos cave would be most closely related to the Neanderthals and possibly their direct ancestors zhlten. But to their surprise, that was not the case.

Instead, the Spanish Friihmenschen proved to be a sister group of the Denisova people, a type of human, of which so far only one finger bone was found in Siberia. "Mitochondrial DNA demonstrates an unexpected link between Denisova humans and Western European fossil finds, " the researchers report. This relationship is closer than with the Neanderthals or modern humans.

Skeleton of a 400, 000-year-old peasant from Sima de los Huesos Javier Trueba / MADRID SCIENTIFIC FILMS

Sprinkled ancestors?

But how did this relationship come about? "Several evolutionary scenarios would be conceivable, " explain the researchers. Theoretically, the Spanish friars could be related to the ancestors of the Denisova people. They would then have lived in Western Europe before evolving into Siberia. But Meyer and his colleagues think that this is unlikely. Because that would mean that the ancestors of Neanderthals and Denisova lived at the same time and in the same area in Europe, without merging genetically. Another scenario would be that the Spanish friars belonged to the ancestors of both the Neanderthals and the Denisova. That could explain the Neanderthal-like features of the Sima de los Huesos relics.

Or immigrants?

However, it would also be possible for a hitherto unknown group of people to immigrate to both Spain and Siberia, leaving traces in the DNA of the local early human beings. That, too, would lead to genetic similarities between the two types of human beings. For this variant, it speaks that there are some fossils in Europe and Asia that are about as old as the Spanish, but still have no clear Neanderthal characteristics. Even a few hundred meters from the cave Sima de los Huesos away such fossils have been discovered.

In any case, the result of DNA analysis raises new questions about the history of the early humans in Europe. There may have been more different types of people living in this region than previously thought. Clarity could create more samples of early human DNA from other sites in Europe. "But that will be a big challenge, " say the researchers. In order to be able to reconstruct such old genetic material, one not only needs the most modern technical aids, but also plenty of luck with regard to the preservation of the relics. (Nature, 2013; doi: 10.1038 / nature12788)

(Nature, 05.12.2013 - NPO)