One of the greatest clues to solving the mystery of our species’ origin was recently revealed by Archaeologists in Spain. But, it seems the discovery might raise more questions than answers. It has been a long held belief that the Neanderthals and Denisovans, two ancient species of hominid, were in a different evolutionary branch than our genetic ancestors. But this recent discovery shakes up many of our assumptions on the origins of the human species.
Sequencing Ancient DNA
In the June 6th issue of Current Biology, a group of researchers led by Catherine Hänni of Ecole Normale Supérieur in Lyon, France published their analysis of a 100,000 year old Neanderthal genome. It was the oldest DNA that had ever been sequenced.
The finding was a breakthrough because the genetic material used predates the period when Neanderthals cohabited with modern humans.
Bear in mind that the process of working with ancient DNA is one of the most challenging for a geneticist; there are so many factors that can affect an accurate sequencing of genetic material, including modern human contamination and the fact that decomposition has occurred.
This was a huge deal!
The decomposition process begins after any organism dies. This process, by nature begins breaking down the DNA as well and usually, within 100,000 years, any recognizable DNA has been broken down into (scientifically speaking) unusable organic matter.
When Archaeologists are able to secure a small piece of bone fragment or similar fossil, the DNA that can be extracted is typically damaged or in fragments and this can result in inaccurate analysis because of protein changes in the DNA strands.
Photo Credit: Javier Trueba, Madrid Scientific Films
Now, a new analysis of genetic material from a 400,000 year old thigh bone has shaken the foundation of our beliefs about evolution and the human genome. Thanks to breakthroughs in modern technology, researchers used a new technique for the sequence, one that they say was not even possible one year ago. Instead of the typical DNA strand we imagine, researchers were able to sequence the genetic material from the Mitochondrial DNA (mtDNA), which is only passed through a lineage through the mother.
The Pit of Bones
In the 1970’s, Archaeologists in the Atapuerca Mountains of Northern Spain discovered what would come to be known as The Pit of Bones. About 43 feet below the surface in an underground cave, the bones of a new species of ancient humanoid dubbed homo heidelbergensis were discovered and they have been studied ever since. All together it was determined that the bones of at least 28 ancient hominids have been collected from that cave along with the bones of some bears.
Though it isn’t clear whether this was some sort of burial ritual or these people had simply fallen into the pit, it was clear that these bones ranged from 350,000 years old to well over a million years old.
This strange new species of hominid obviously lived long before the Neanderthal was fully evolved.
Until this point, modern scientists have accepted it was a creature called homo erectus that predated modern Neanderthals. Even though the bones appeared to have a close resemblance to Neanderthal bones, it turns out their genetic make-up is much closer to the hominids known as the Denisovans.
Denisovans
In the Altay Mountains of southern Siberia there is a cave called Denisova. In 2008, researchers in the Altay Mountains of Southern Siberia unearthed a fossilized pinky bone that altered our ideas about the DNA of human beings. Testing at the Max Planck Institute for Evolutionary Anthropology determined that the tiny chipped fingertip belonged to a young Denisovan girl between the age of five and seven years when she died.
This extinct species of hominid is said to have lived about 80,000 years ago and genetic traces are still found in some from East Asia and a native tribe in Papua New Guinea.
Researchers theorize the transocean migration of the Denisovan-blooded ancestors from Eurasia may have brought them to Papua New Guinea. This also means that the Denisovans lived in small numbers throughout the continent from Siberia to Southeast Asia at some point between 80,000 and 45,000 years ago.
Evolutionary geneticist Svante Pääbo, the man responsible for inventing the new DNA sequencing technique, said of Denisova, “It’s the one spot on Earth that we know of where Neanderthals, Denisovans, and modern humans all lived.”
A fascinating piece of the puzzle is that the bones from Denisovans do not look like Neanderthals or the new species found in the Pit of Bones, Homo Heidelbergensis.
So What Does it All Mean?
The 400,000 year old thigh bone that belongs to Homo heidelbergensis contains the same Mitochondrial DNA as a Denisovan.
To explain this, researchers are now considering two possibilities:
1. There are many more species of ancient humanoids than we previously believed, or
2. The bones in the Pit of Bones are the ancestors of both the Neanderthals and Denisovans.
Photo Credit: Jonathan Friedlaender
If it’s the second option, theorists suggest that the Mitochondrial DNA may have been bred out of the Neanderthal species over time.
What do you think? Is there a third option? And would it surprise you to know that some of the natives in Papa New Guinea, the Melenesians, have an African or Aboriginal complexion but naturally blonde hair?
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