Scientists have clarified the DNA of a hominin that died 400,000 years ago in Spain. Strangely enough, it resembles that of the much younger Denisovan from Siberia.
Thirty meters underground and half a kilometer from the nearest exit, in the Atapuerca Mountains in northern Spain, is the Sima de los Huesos cave, or 'the bone cave'. In recent years, the remains of at least 28 human ancestors have been found. Virtually all the bones of the bodies have been found. In addition, scientists have found cave bear bones in recent years. Earlier this year, the DNA of such a cave bear was read. It is estimated that the bear died 409,000 years ago.
And now it was the turn of one of the found hominids. Svante Pääbo and his international science team took a DNA sample from a femur bone. They did this by drilling tiny holes in it. In total, this yielded just under 2 grams of bone. They then purified the DNA after which they could read it. This week they write in Nature that the owner of the femur bone must have died 400,000 years ago. This has broken the record for reading prehistoric humans DNA. That stood at 44,000 years until now. Incidentally, the record for reading primal DNA is still in the name of the research group that mapped the 700,000-year-old DNA of a horse
Small, but many copies
Like the cave bear, the team took mitochondrial DNA from the mitochondria, the cell's 'energy factories'. The mitochondrial genome is 16,000 base pairs in size. That is very small compared to the genome in the cell nucleus:it has 3.2 billion base pairs. A major advantage of using mitochondrial DNA is that each cell has hundreds of copies of it. With all that material and the knowledge about how time affects DNA, it doesn't matter that much of the DNA was already broken. A reconstruction could therefore still be made.
Mitochondrial DNA is inherited from mother to child. That's because mitochondria are in the tail of the sperm, and it falls off during fertilization. The mitochondrial DNA says little about the characteristics of a person, but it does provide a lot of information about relationships with other people. As more time has passed, random changes occur in the DNA. Based on the differences, researchers can create a family tree of mitochondrial DNA.
Striking result
Until now, the found bones of the individuals from the cave were mistaken for bones of the Heidelberger Man (Homo heidelbergensis ), an ancestor of modern humans. But after Svante Pääbo's DNA research, it appears that humans are most similar to Denisovans. Only a molar and a phalanx of this human have been found in a Siberian cave, but scientists were able to map his entire DNA with this. The research team believes that the last common ancestor of these two hominins lived about 700,000 years ago, although it could be more or less three hundred thousand years.
According to the family tree, the split with the humans that later evolved Neanderthals and modern humans occurred long before that. And that is striking. The bones found in the bone cave are very similar to the bones of Neanderthals. How that is possible is speculation. The scientists write out a few scenarios in Nature. Maybe it's a new humanoid, maybe not. But the only way to find out what's going on is by reading DNA from the cell's nucleus. There is a lot more engineering involved, but there is hope because the cave is cool and dry enough to keep the DNA legible and the group has accomplished more spectacular things so far.