The oldest human or proto-human DNA ever sequenced is dated at 400,000 years old and the fossil used to arrive at this date was found in Spain. At first anthropologists thought the fossil bones belonged to a Neandertal from Europe but after analysis it was revealed that this was NOT the case at all. Results showed that the remains were closer to the Denisovans found in Siberia than anything else!
The remains found in the cave in Spain are now considered the oldest human DNA ever sequenced thus far and not only that but these remains add one more tangle to our picture of human evolution. They also challenge conventional theory about Neandertals and the Denisovans. Up until this DNA was decoded it was thought that these two species of early humans lived in prehistoric Europe and then spread out to Siberia and elsewhere. But as it turns out that may not be so at all.
The remains from the Sima de los Huesos Cave in Spain consist of a thighbone that is fossilized and mtDNA was used to arrive at the 400Kya date. This type of DNA is derived from the mother’s side only. The mtDNA sequence shows a sequence highly similar to the Denisovans found in Siberia and these results are irritating some researchers who thought they had human evolution all figured out.
What this discovery strongly suggests is that the history of the Denisovans and Neandertals is very much more complicated than originally thought and there is a good possibility that both species intermixed regularly.
We know, or think we know, that Neanderthals and Denisovans arose hundreds of thousands of years ago before modern humans migrated out of Africa between 100.000 and 60,000 years ago. About 2% of modern human, Homo sapien, DNA is Neandertal DNA and Denisovan DNA is found in modern people from Indonesia and southeast Asia. So we know early H. sapiens were interbreeding with Neanderthals and Denisovans and we also know Neanderthals were interbreeding with Denisovans as well. Were Neanderthals over-sexed or what??? It seems they were interbreeding with everything and anything!
Previous to this DNA decoding of 400K years old the oldest human DNA decoded were dated at less than 120,000 years old. So what were Denisovans doing in Spain with the Neanderthals? Previously, it was thought that the remains were from another species of proto-human known as Homo heidelbergensis, Heidelberg Man, who was the common ancestor of H. sapiens, Neanderthals, and Denisovans. But that has tuned out NOT to be so!
Of course the million dollar question is this…….
HOW DOES A SPANISH EARLY HUMAN SPECIES END UP WITH SIBERIAN DNA?
In fact, there are many possibilities as to how this could happen. For one thing the “Sima hominins” could be only close relatives of the Denisovans but not really Denisovans. But, then again, that would mean they lived alongside Neanderthals in Europe and that they didn’t have close ties to them. The Sima Hominins could also be a newly discovered and different species of proto-humans that mixed with Denisovans at some time and interbred with them. But, then again, that would make it difficult to explain why the Sima Hominins have some very Neanderthal-like features and morphology!
Chris Stringer who heads the London Natural History Museum suggested another possibility. Stringer suggested that mtDNA reached the Denisovan people via interspecies sexual adventures that took place among early humans (proto-humans) and the result was the introduction of DNA from and to both the Sima Hominins and Denisovans. That’s a possibility but I prefer some other explanations.
My first thought is that the Sima Hominins may be an entirely new species of early humans that we didn’t know about before and who were living alongside and even interbreeding with Neanderthals. But, what about the Siberian Denisovan mtDNA in them? Perhaps early human migration and intermixing was far more common and widespread than we think! Consider this. Man has a strong instinct within him to be an adventurer and explorer. Man is a curious species who isn’t satisfied with not knowing what’s over the next hill. Might not our early ancestors have had the same thirst for adventure and exploration as we have today?
My second thought is that the Sima Hominins are, in fact, fossil remains of Heidelberg Man who was a common ancestor, as near as we can tell, of H. sapiens, Denisovans, and Neanderthals. Denisovans could have well began as a species in Spain and maybe even elsewhere in Europe and at some point they, along with some Neanderthal pals, migrated into Siberia. That’s yet another possibility. Of course that would mean Denisovans aren’t Siberians at all but Europeans and, maybe, specifically Spanish!
Bottomline is that these Sima Hominins are a mystery for now as we don’t really know how Siberian Denisovan mtDNA ended up in them. A lot of additional work is needed to solve this mystery and, sadly, right now the current mtDNA data in regards to our ancestors is very limited. DNA breaks down over time and very little if any is found in earlier ancient human ancestor fossils and what is found is typically not enough to even be decoded.
To help solve this mystery not only is mtDNA going to have to be further decoded but also nuclear DNA so we get a complete map of who and what the Sima Hominins are and where they come from. Up until recently we thought Denisovans only existed in Siberia but the Sima Hominin discovery dispel that notion completely! Obviously, the Denisovans were also in Spain!
One thing that is becoming very evident is that interbreeding between modern humans (H. sapiens), Neanderthals, and Denisovans was more common than we once thought. In terms of the Denisovans, fossils from them were only discovered in 2010 and those fossils found in Siberia consist of only a finger bone and a tooth found in 30K–50K rock layers in Siberia’s Denisova Cave. We, therefore, do NOT have anywhere near a complete skeleton of a Denisovan. DNA from those two Siberian fossils revealed that the Denisovans were a distinct species of hominin from modern humans and Neanderthals, yet, they apparently interbred with both.
The mtDNA from the Sima Hominins indicates they shared a common ancestor with Siberian Denisovans although the Sima Hominins have some very Neanderthal morphology!
Professor and Paleoanthropologist Dr John Hawks of the University of Wisconsin-Madison was NOT part of the study but he thinks the results are nothing surprising at all. He notes that mtDNA from many other species such as ancient bison, cave bears, mammoths, etc does NOT resemble that of more recent species. Further, he is cautious about concluding that the Sima Hominin bones are closely related to Denisovans in Siberia. He says that the difference between Denisovan and Sima gene sequences is about the same as the difference between Neanderthal and modern humans today. Neanderthal DNA is about 97% the same as modern human DNA. Hawks says it is unfair to assume Denisovan and Sima Hominins represent a single population.
One thing that MUST BE KEPT IN MIND REGARDING MTDNA is this:
We need to use caution when it comes to mtDNA results as they are NOT full proof! Results from mtDNA have in past pointed us in erroneous directions at times. For instance, early studies using mtDNA suggested that modern humans and Neanderthals did not share a common ancestry but we know today that that is NOT TRUE as we share a common ancestor which we know as Homo heidelbergensis or Heidelberg Man. Further, mtDNA is only a small portion of the human genome that comes from the female line to offspring and not from the male line. To have a complete picture we must know not only the female line but also the male line of descent. Early interbreeding events may NOT come out in mtDNA even though we know mtDNA can be transferred between species when there is interbreeding between species. Additionally, we know that in some interspecies breeding that mtDNA has gotten mixed up and, thus, the mtDNA results are not accurate. We have found this to be the case with some decoding of DNA from polar bears and brown bears in the past.
The Sima Cave where these bones were found is in Spain in the Atapuerca Mountains. It is a very famous archaeological site. Some of the oldest human remains ever found have been found in this area of northern Spain. Sima de los Huesos is the most famous cave in the area. It has been excavated since 1997 and more than 6K ancient bone fossils have been found there since then. Those 6K bones belong to 28 ancient humans as near as we can tell. And they lived around 400K years ago. HOWEVER, this pile of bones in the cave have origins that remain UNCLEAR!
Some sort of natural cataclysm could have taken place at some point in time or carnivore activity (a kill site for carnivores eating humans) could explain the bones in the cave. This possibility has been suggested by the lead excavator at the site, Dr Juan Luis Arsuaga who has led the excavations at Sima for the past 30 years. He also suggests that the bones may be the result of early hominins who gathered the corpses of their dead relatives and friends and buried them or disposed of them inside the Sima cave and that would make it a burial site not a cave in which ancient human ancestors actually lived.
In terms of the Sima Hominins having Neanderthal features these features include the fact that the Sima Hominins have thick brow ridges like Neanderthals and they also have features found in Heidelberg Man specimens. Homo heidelbergensis lived about 600K years ago. As I said earlier, Heidelberg Man is thought to be the common ancestor of modern humans, Neanderthals, and Denisovans presently.
The Sima Hominins continue to be a mystery. If the mtDNA results are correct then there are some very big questions that need to be answered and reconsidered in terms of human evolution. I’ll hold out until nuclear DNA is decoded on these finds but right now I’m thinking either the Sima Hominins are a new species of human ancestor OR they are remains of Heidelberg Man as first thought. BUT, one thing that is fairly certain is that the remains are presently the oldest human DNA decoded and that in itself is exciting!!