"Today [December 4, 2013], researchers announced they have obtained DNA sequences from the earliest human skeletal remains yet, a Spanish fossil from a site known as Sima de los Huesos, or pit of bones. Although the study is undoubtedly a triumph of technology and technique, the results themselves have researchers scratching their heads, since the most closely related DNA has only been found on the opposite side of Eurasia.
The sequencing of DNA from fossil humans has already shaken up our view of the past. The completion of the genome of Neanderthals indicated that they had interbred with modern humans enough to introduce a small bit of their DNA into genomes of any population that left Africa. But sequencing other bones revealed that there was a second group of pre-modern humans in Siberia that also interbred with our ancestors. This group, called the Denisovans, also contributed DNA to our ancestors, but it only appears in groups that migrated into the Pacific.
To confuse matters further, although we have many Neanderthal skeletal remains and a good idea of how they differed from modern humans, so far, all we have of the Denisovans is a couple of teeth. These tell us that their teeth were very large, but little else. Still, the only real question seemed to be how the Denisovans, whom we only know from Siberian remains, ended up getting their DNA carried out into the Pacific."