Technological breakthroughs have allowed scientists to sequence human DNA from an astonishing 400,000 years ago—but analysis of an ancient leg bone has raised more questions than answers, the BBC reports. Researchers were surprised to find that the early human whose remains were unearthed in Spain's "Pit of Bones" site had a much closer genetic link to an early species of human found thousands of miles away in Siberia's Denisova Cave than to the Neanderthals who inhabited the region until around 30,000 years ago. The Pit of Bones people are believed to have shared a common ancestor with the Denisovans around 700,000 years ago.
Scientists suspect mitochondrial DNA could have been passed down from a population related to both the Denisovans and the Neanderthals—or been introduced by interbreeding with another early species of human. More tests are expected to provide answers to piece together the puzzles of human evolution. "We need all the data we can get to build the whole story of human evolution," a researcher says. "We can't just build it from stone tools, we can't just build it from the fossils. Having the DNA gives us a whole new way of looking at it." (Read more Neanderthals stories.)