The ancestry of “modern humans” is becoming increasingly complex … with each new publication of DNA sequencing from some small bone chip or other fossil from long ago.
When modern humans spread out of Africa and the Near East (about 75,000–50,000 years ago), at least two archaic hominin groups, Neanderthals and Denisovans, inhabited Eurasia. Whereas Neanderthals are known from an abundant fossil record in Europe, and in western and central Asia, Denisovan remains had been currently only known from the Altai Mountains in southern Siberia. However, Denisovan ancestry has been detected in present-day human populations from Oceania, mainland Asia, and in Native Americans, suggesting that Denisovians were once more widespread.
The article below describes the unique findings of 28 hominins––found in Sima de los Huesos in the Sierra de Atapuerca (Spain) ––which had been dated to ~430,000 years ago. The question the authors now posed is: how are these Middle Pleistocene hominins related to those who lived in the Late Pleistocene epoch (in particular to Neanderthals in western Eurasia, and to Denisovans in southern Siberia).
While the Sima de los Huesos hominins were reported to share some derived morphological features with Neanderthals, the mitochondrial genome (mtDNA) retrieved from one individual from Sima de los Huesos was found to be more closely related to mtDNA of Denisovans than to that of Neanderthals. However, because mtDNA does not reveal the full picture of relationships among populations, the authors investigated genomic DNA (gDNA) sequences in several individuals found at Sima de los Huesos.
In the attached report, they describe gDNA sequences from two specimens that show that the Sima de los Huesos hominins were related to Neanderthals rather than to Denisovans––indicating that population divergence between Neanderthals and Denisovans must predate ~430,000 years ago. One individual’s mtDNA shares the previously described relationship to Denisovan mtDNAs, suggesting, among other possibilities, that the mtDNA gene pool of Neanderthals changed considerably, later in their history.
Nature 2016; 501: 504–508