Pre-modern humans may have picked up genes from Homo erectus
Ars Technica » Scientific Method 2013-12-18
It's a busy time in our attempts to study our species' pre-modern history. Just two weeks ago, researchers reported the sequence of the oldest bones to yield human DNA. Now, the same research group is back with an entire genome, obtained from a bone found in Siberia's Denisova cave. This genome comes from a Neanderthal, but all the data reveals a lot about all the interconnections among the pre-modern human groups that were wandering around Eurasia tens of thousands of years ago. The analysis came with a tantalizing hint that one of those groups had interbred with a species separated from modern humans by over a million years—perhaps Homo erectus.
The Denisova cave is famous for having yielded the bones that helped us identify the Denisovans, a group of archaic humans that inhabited Asia at the same time as the Neanderthals. Although we haven't found enough bones to know much about what the Denisovans looked like, DNA analysis has revealed that they are most closely related to Neanderthals and that they interbred with modern humans that went on to populate East Asia, the Americas, and the Pacific.
The new results spring from a toe bone found in the same cave, this one from a layer that is estimated to be tens of thousands of years earlier. DNA sequencing revealed the bone to be from a Neanderthal, a different group of pre-modern humans that is most closely related to the Denisovans. The DNA was in excellent condition and had a minimal (about one percent) contamination with sequences from modern humans. The team generated a high-quality genome using samples from this bone.