An international team that includes Spanish researchers has sequenced the mitochondrial genome (special DNA passed on exclusively by mothers) of bears who lived about 400,000 years ago in Atapuerca, near Burgos in northern Spain. This brings scientists closer to sequencing the entire genome of pre-Neanderthal humans who lived at the same time, and who hold clues about the evolution of our species.
The small mtDNA fragments were found inside samples of bear bones that were mixed in with hominid fossils at Sima de los Huesos (Pit of the Bones) at the Atapuerca site, which contains the world's largest collection of human remains from the Middle Pleistocene. Until now, the oldest samples of DNA recovered in temperate areas - not frozen at high altitudes - were between 100,000 and 120,000 years old.
The breakthrough could have significant implications for human paleontology.
"Let us hope that the methodology that we are presenting here will help recover ancient DNA sequences from other organisms of the Middle Pleistocene. The fossils of Sima de los Huesos are the target of these efforts," write Jesse Dabney and his colleagues in Proceedings of the National Academy of Sciences (PNAS), which this week publishes the entire mitochondrial genome of those early cave inhabitants.
"Yes, of course I am optimistic about the possibility of obtaining DNA from human fossils at the pit; if it is there in the bear bones, it can be there in the human bones, which are contemporary to the latter," says Juan Luis Arsuaga, co-director of the Atapuerca site and one of the authors of the new study.