Dec. 4 (UPI) -- The oldest known human DNA, from a 400,000-year-old femur found at the Sima de los Huesos, or "Pit of Bones" cave site in Spain, has been sequenced, and raises a lot of questions concerning human evolution.
The DNA was retrieved from an ancient hominin fossil dating back 400,000 years, far older than the 100,000-year-old previous record-holder. Initially believed to be from an ancestor of the Neanderthal, the fossil was found to belong to a lineage of humans known as Denisovans after genetic testing.
Scientists knew of Denisovans because of an 80,000-year-old fossil found in Siberia, and the connection is forcing them to rethink human evolution.
“Right now, we’ve basically generated a big question mark,” Matthias Meyer, geneticist at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany and co-author of the new study, told The New York Times.
Experts now believe there might be other extinct human populations about which we know little. Scientists hope further research will help clarify this mismatch in lineage, assuming these ancient humans must have interbred and swapped DNA.
Based on the anatomy of the fossil, researchers assumed it was from an ancestor of Neanderthals that lived around 200,000 to 30,000 years ago. But after sequencing the mitochondrial genome, researchers found that it did not match the DNA of Neanderthals, instead matching Denisovans.
“Everybody had a hard time believing it at first,” Dr. Meyer said. “So we generated more and more data to nail it down.”
Meyer and his team were the first to discover the Denisovan lineage of humans in 2010. The new finding, published in Nature, has confirmed Denisovans' spot in the human family tree. Denisovans, previously thought to be limited to East Asia, may have been more widely prevalent given their likeness to Neanderthals.
Researchers are now trying to rework the lineage of humans based on this DNA, and hope to find more specimens at the Spanish site.
[The New York Times]