This contrasts with the secretive atmosphere surrounding the digs to near Orce, in southern Spain, which has yielded tools indicating human presence that predate the finds at Atapuerca. In 2013, Arsuaga co-authored a paper which reported the finding of the oldest human DNA ever, dating back 400,000 years. The mitochondrial DNA that stemmed from a fossil found in a cave in Sima de los Huesos had similarities to mitochondrial genomes previously found in the extinct Denisovans in Siberia.[1][2]