Sima de los Huesos remains, Neanderthals, Denisovans and their nuclear and mtDNA

A very interesting paper published in Nature (Matthias Meyer et al.) has confirmed that the Sima de los Huesos remains, that are 430 ky old, have mtDNA that resembles that of Denisovans more closely than that of the Neanderthals. But, their nuclear DNA is more similar to that of Neanderthals than to Denisovan nuclear DNA.

Since the Sima de los Huesos hominins are supposed to be the ancestors of Neanderthals it is reasonable that their nuclear DNA is similar to that of Neanderthals and different from Denisovans. But why is the relationship regarding mtDNA exactly the opposite?

The paper offers three explanations:

1. The Sima de los Huesos people had two very diverging mtDNA types, one leading to Neanderthals the other to Denisovans, and these samples are of the first kind.
2. Some "other" hominin contributed its mtDNA to both Denisovans and Sima de los Huesos people
3. The original proto Neanderthal mtDNA was inherited by their Neanderthal descent but was completely diluted by later inflow of Neanderthal mtDNA from Africa, which we find in more recent Neanderthals.

In science, the breakthroughs come from finding the correct answer to discrepancies like these. So it is very exciting and who knows what will eventually be learned from this!.

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