Researchers have uncovered a new clue about human origins after discovering the oldest known human DNA in a legendary Spanish archeological site called Sima de los Huesos, or the “Pit of Bones.”
It came from a fossilised leg bone of an early human who died about 400,000 years ago in what is now northern Spain. The genetic sequence indicated that this early European was more closely related to a much earlier species of human living in Siberia, Denisovans, about 700,000 years ago than to the later Neanderthals of Europe who became extinct about 30,000 years ago.
Results were presented online Wednesday in the journal Nature by Matthias Meyer and colleagues at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, with co-authors in Spain and China.
“The fact that they show a mitochondrial genome sequence similar to that of Denisovans is irritating,” says the lead author of the study, Matthias Meyer of Max Planck Institute. “Our results suggest that the evolutionary history of Neanderthals and Denisovans may be very complicated and possibly involved mixing between different archaic human groups.”
Neanderthals and Denisovans arose hundreds of thousands of years before modern-looking humans spread worldwide from Africa more than 60,000 years ago. The small traces of their genes now found in modern humans are signs of interbreeding among ancient human groups, says the National Geographic.
The Denisovans were a sister group to the Neanderthals, with distinct genetic characteristics. Identified only by DNA extracted from a tiny finger bone and tooth, they are, as some researchers have remarked, “a genome in search of a fossil” because there are no substantial remains representative of this group.
By using missing mutations in the old DNA sequences, the researchers calculated that the Pit of Bones individual shared a common ancestor with the Denisovans about 700,000 years ago.
“The fact that the Sima de los Huesos [mitochondrial DNA] shares a common ancestor with Denisovan rather than Neanderthal [mitochondrial DNA] is unexpected in light of the fact that the Sima de los Huesos fossils carry Neanderthal-derived features,” says the study.
To access the pit (called Sima de los Huesos in Spanish) scientists must crawl for hundreds of metres through narrow cave tunnels and rope down through the dark. The bodies were probably deposited there deliberately – their causes of death unknown.
The age of the bones has been hard to determine. A rough estimate from analyzing the DNA is around 400,000 years, which supports what Meyer said is the current view of the anthropologists excavating the site.
Todd Disotell, an anthropology professor at New York University, said geological techniques suggest the remains are older than 300,000 years but it’s not clear by how much. By comparison, modern humans arose only about 200,000 years ago.
More than 28 human skeletons have been excavated from Sima de los Huesos cave, along with the bones of extinct animals such as cave bears dating back about 600,000 years, making it one of the richest sources of prehistoric fossils in Europe.
Prof Paabo, the institute’s director, said: “Our results show that we can now study DNA from human ancestors that are hundreds of thousands of years old,” adding: “It is tremendously exciting.”