The Surprising Story of 400,000 Year Old Human DNA

Researchers have just announced a major advance in their quest to recover DNA from ancient humans.  400,000 year old bones contain badly damaged DNA sequences, but experts in Leipzig, Germany, have developed new techniques to extract and piece together tiny fragments until they can read at least a small portion of the genes carried by ancient humans who once lived in northern Spain.

Caption: The Sima de los Huesos hominins lived approximately 400,000 years ago during the Middle Pleistocene. Credit: Javier Trueba, Madrid Scientific Films.Usage Restrictions: None

A team led by Matthias Meyer at the Max Planck Institute for Evolutionary Anthropology in Leipzig worked together with a Spanish team of paleontologists led by Juan-Luis Arsuaga to extract tiny amounts of bone from fossil remains found at Sima de los Huesos, northern Spain’s famous “bone pit.”  This site has been excavated for more than two decades.  It has yielded at least 28 skeletons, usually classified as Homo heidelbergensis, a form of humans seen as the ancestors of the Neandertals.

 

But here is where this study broke new ground.  It turns out that the Sima de los Huesos humans were more closely related to the recently discovered Denisovans than to the Neandertals.  "The fact that the mtDNA of the Sima de los Huesos hominin shares a common ancestor with Denisovan rather than Neandertal mtDNAs is unexpected since its skeletal remains carry Neandertal-derived features," Meyer said in a press release provided by the journal Nature, which carries the report in its 4 December 2013 issue. 

What makes this finding all the more intriguing is that the Denisovans were completely unknown to us until 2010, when the Leipzig team “discovered” them by reconstructing their DNA and comparing it to Neandertals and today’s humans.  Through a spectacular technological achievement, Leipzig researchers discovered that these Denisovans lived as a distinct population some tens of thousands of years ago, when they interbred with other humans. 

"This unexpected result points to a complex pattern of evolution in the origin of Neandertals and modern humans. I hope that more research will help clarify the genetic relationships of the hominins from Sima de los Huesos to Neandertals and Denisovans" says Arsuaga. 

Caption: This is a skeleton of a Homo heidelbergensis from Sima de los Huesos, a unique cave site in Northern Spain.  Credit: Javier Trueba, Madrid Scientific Films.  Usage Restrictions: None

 

According to the most recent discovery, the Sima de los Huesos hominins seem to have shared a common ancestor with the Denisovans some 700,000 years ago.  The idea that they are more closely related to Denisovans than to Neandertals suggests that these mysterious Denisovans, totally unknown just four years ago, may have played a far bigger role in the story of human origins than ever imagined. 

It is important to point out that so far, researchers have only reconstructed the DNA of the mitochondrial.  And even there, the work is not complete.  Whether they succeed in reconstructing the DNA of the far more daunting heidelbergensis genome remains to be seen.  But if past experience is any predictor, we might look for advances not just here but in other human remains from hundreds of thousands of years ago.  Each technical achievement may fill in a page in our past, maybe even re-writing whole chapters.  When it comes to human origins, we should expect more surprises. 

Putting this most recent news in a larger context, Svante Pääbo, the director of the Leipzig research, said this in the Nature press release: "Our results show that we can now study DNA from human ancestors that are hundreds of thousands of years old. This opens prospects to study the genes of the ancestors of Neandertals and Denisovans. It is tremendously exciting."

The article, “A mitochondrial genome sequence of a hominin from Sima de los Huesos,” appears in the 4 December 2013 issue of the journal Nature.