The results of a DNA test of a 400,000 year old human thighbone reveals human evolution was even more confusing than thought. The fossil, a thigh bone found in Spain, had previously seemed to many experts to belong to a forerunner of Neanderthals, but its signature(DNA) is most similar to that of a different ancient human population from Siberia, known as the Denisovans. Denisovans were known only from DNA retreived from 80,000 year old remains in Siberia.

Presently, modern humans are the sole surviving successors of the human species while the predecessors are now extinct. Neanderthals and the newly found Denisovans being among them, bore a striking resemblance to the modern humans.

Matthias Meyer, who is a molecular biologist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany said, “This is the oldest human genetic material that has been sequenced so far,".

The thighbone was found during an investigation in the Sima de los Huesos, also known as'Pit Of Bone' which is an underground cave in Spain which is 30 meters below the surface. Thousands of fossils of atleast 28 individuals have been found from the Pit of Bones and Denisovans is one of them.

Researchers have come up with a few assumptions and explanations: 1) It is unlikely that the fossil belongs to ancestors of Denisovans. This is because, the territory of Denisovans and Neanderthal ancestors seem to imbricate which makes one think how are they genetically diversified then. 2) It may also be possible that Sima de los Huesos humans are connected to ancestors of Denisovans and Neanderthals. 3) They differ from the Neandarthals and Denisovans yet there are certain similarities – the mitochondrial DNA with Denisovans and skeletal features with Neanderthals.

"The story of human evolution is not as simple as we would have liked to think," Meyer said. "This result is a big question mark. In some sense, we know less about the origins of Neanderthals and Denisovans than we knew before."

This discovery challenges the abiding theories about human evolution that will bring to light how early species of human spread across different continents.