Questo è un articolo interessante: esso getta nuova luce sulla linea dell'uomo di Denisova (che era strettamente imparentato con il Neanderthal ed apparve in Europa MedioOrientale, ma evidentemente si estese fino all'Europa dell'Ovest!) e mostra che - con ogni probabilità - il DNA del Neanderthal apparve ben prima di quanto prima si supponeva, in Europa, anche se la data resta approssimata e da stabilire.
Gli ominini trovati nel nord della Spagna (Sima de los Huesos, vedi articolo) si raggruppano geneticamente con i Denisova (un mtDna, quindi una donna). La figura, che illustra il nuovo albero filogenetico che ne deriva è estremamente descrittiva...
400 thousand year old
human mtDNA
from
Sima de los Huesos
A new paper in Nature reports their success, and overnight increases by an order of magnitude the time depth for which we now have human mtDNA from what is commonly designated as Homo heidelbergensis, from right in the middle of the Middle Pleistocene. Obviously, this opens new vistas for archaeogenetic research, making it possible to directly look at early pre-sapiens forms of humans, and not only on their final forms prior to their replacement, the Neandertals and Denisovans.
The most impressive aspect of the new paper is most likely the technical challenges that the researchers must've overcome to achieve this result. The cave bear DNA showed that this was possible, but human DNA adds an additional complication in the form of contamination by a closely related species, us.
But, the new evolutionary result which will interest those of us not interested in the minutiae of biomolecules will no doubt be the fact that the Sima hominin's mtDNA formed a clade with the much more recent Denisova girl.
Until now, we knew that Neandertal mtDNA grouped together and so did modern human mtDNA. The two groups shared a Middle Pleistocene common ancestor and a much more distant common ancestor (~1 million years) with the mtDNA found in Denisova. The new Sima specimen shares descent from Denisova. This is important because it shows that whatever archaic human population the Denisovan mtDNA belonged to also extended to western Europe. And, surprisingly, the Sima specimen did not group with Neandertals, as might be expected because of the incipient Neanderthaloid morphology of the Sima hominins which has been a matter of controversy as it pushes back the evolutionary lineage of H. neandertalensis deeper into the Middle Pleistocene that some researchers accept.
Before this paper, it was believed that H. heidelbergensis evolved somewhere (perhaps Near East or Africa), a subset of it evolved to H. sapiens in Africa, and a different subset evolved in Eurasia, leading up to H. neandertalensis in the west, and unknown forms in the east, of which the Denisova girl was a matrilineal descendant. The next question is: when did Neandertals and Neandertal mtDNA appear in Europe?
It can now be hoped that such questions will be answered directly. The Sima individual studied in this paper is not some frozen specimen from the Arctic, preserved by a freak accident in pristine form for hundreds of thousands of years, but a person who lived in Southwestern Europe. I am fairly sure that this won't be the last really old human we see a paper about in the coming years. Human mtDNA used to present a simple picture at the time of the discovery of African mitochondrial Eve: the deepest splits were in Africa and Eurasians belonged to a subset of African variation. But, as more and more archaic Eurasian mtDNA is sampled, it now appears that modern human mtDNA is a subset of world human mtDNA whose deepest splits are in Eurasia, and the next deepest splits are in Africa. Obviously, this may be a consequence of the fact that archaic human mtDNA has only been sampled from Eurasia, for factors relating to DNA preservation. But, it is nonetheless interesting to wonder where on the tree the mtDNA of archaic Africans would fall.
Nature (2013) doi:10.1038/nature12788
A mitochondrial genome sequence of a hominin from Sima de los Huesos
Matthias Meyer et al.
Excavations of a complex of caves in the Sierra de Atapuerca in northern Spain have unearthed hominin fossils that range in age from the early Pleistocene to the Holocene1. One of these sites, the ‘Sima de los Huesos’ (‘pit of bones’), has yielded the world’s largest assemblage of Middle Pleistocene hominin fossils, consisting of at least 28 individuals dated to over 300,000 years ago. The skeletal remains share a number of morphological features with fossils classified as Homo heidelbergensis and also display distinct Neanderthal-derived traits. Here we determine an almost complete mitochondrial genome sequence of a hominin from Sima de los Huesos and show that it is closely related to the lineage leading to mitochondrial genomes of Denisovans, an eastern Eurasian sister group to Neanderthals. Our results pave the way for DNA research on hominins from the Middle Pleistocene.
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