Solved riddles of Sima early humans?

430, 000-year-old fossils from Spain are early Neanderthals

So the Sima mesnc could have looked around 430, 000 years ago. © Kennis & Kennis Madrid Scientific Films
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Strange mixture: researchers have for the first time decoded the genetic material of the enigmatic Sima early humans. These hominins living in Spain around 430, 000 years ago are probably early Neanderthals, as the scientists report in the journal "Nature". Although previously doubted because the mitochondrial DNA of these early humans has a striking match with the Denisova people of Siberia.

28 early-human skeletons from the Sima de los Huesos cave in northern Spain have long been a mystery. For the approximately 430, 000 years old fossils are similar in some traits to the Neanderthals, in other properties, however, they seem primitive. Given their age and location, it was therefore reasonable to classify the Sima people as early Neanderthals or their predecessors.

Riddles about Denisova's "Connection"

In 2013, however, came the surprise. Analysis of the mitochondrial DNA of a bone from the Sima cave revealed that this genome, which was only transmitted through the maternal line, did not originate from a Neanderthal man. Instead, it showed similarities to the Denisova humans, a mysterious human type of whom so far only one finger bone was found in the Siberian Altai Mountains.

From this canine of a skeleton from the Sima cave, the DNA was extracted and analyzed. © MPI for Evolutionary Anthropology

But how was this strange remote connection from Siberia to early humans explained in Spain? To get more information about this, Matthias Meyer from the Max Planck Institute for Evolutionary Anthropology in Leipzig and his colleagues have now for the first time also analyzed the DNA from the nucleus of Sima humans. The sequences then compared them with the DNA of the Denisova humans, the Neanderthals and an early Homo sapiens.

They were Neanderthals

The result: The genetic material of the Sima people agrees with clearly less than ten percent of the letters in the code with the Denisova people. Between 31 and 53 percent on the other hand fit to gene sequences of the Neanderthal, as the researchers report. "This suggests that the Sima hominins are more akin to the ancestors of Neanderthals than to the Denisova humans, " say Meyer and his colleagues. display

According to the anthropologists, the Sima people were therefore probably already early Neanderthals or very closely related to the ancestors of these Ice Age people. The hypotheses that the Sima people were scattered ancestors of the Denisova people or the result of crossing with a still completely unknown group of people are thus very unlikely, as the researchers explain.

Skeleton of a Friulian from the Sima de los Huesos Cave in Northern Spain Javier Trueba, Madrid Scientific Films

Where does the mitochondrial DNA come from?

However, it remains puzzling why the Sima people in their mitochondria carried the genetic material of the Denisova people and did not resemble the later living Neanderthals. For Neanderthals and Denisova people were at that time, about 430, 000 years ago, long two separate lines.

Meyer and his colleagues suggest that the solution to this riddle lies not with the Denisova people, but with the Neanderthals themselves. The reference for the typical mitochondrial Neanderthal DNA comes from fossil skeletons, the Hundreds of thousands of years are younger than the Sima people.

"Perhaps the late Ice Age Neanderthals did not receive their mt DNA until later, for example through a subsequent gene entry from Africa, " the researchers speculate. Should this be confirmed, then the puzzling mt DNA of the Sima people would have been quite normal for former early Neanderthals and a relic of the common ancestors of Denisova- Humans and Neanderthals. (Nature, 2016; doi: 10.1038 / nature17405)

(Nature, 15.03.2016 - NPO)