The results now show that the Sima de los Huesos hominins were indeed early Neanderthals. (Representational Image)
Nearly 400,000-year-old fossils from Spain have provided clinching earliest genetic evidence of the Neanderthals, suggesting that they may have acquired different genomes later perhaps as the result of gene flow from Africa.
Till date, it has been unclear how the 28 fossils of individuals found at the Sima de los Huesos ("pit of bones") site in northern Spain were related to Neanderthals and Denisovans who lived until about 40,000 years ago.
A previous report based on analyses of mitochondrial DNA from one of the specimens suggested a distant relationship to Denisovans, extinct relatives of Neanderthals in Asia.
This was unexpected since their skeletal remains carry Neanderthal-derived features.
Researchers from the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, have since worked on sequencing nuclear DNA from fossils from the cave, a challenging task as the extremely old DNA is degraded to very short fragments.
The results now show that the Sima de los Huesos hominins were indeed early Neanderthals.
"Sima de los Huesos is currently the only non-permafrost site that allows us to study DNA sequences from the Middle Pleistocene, the time period preceding 125,000 years ago", said lead researcher Matthias Meyer in a paper published in the journal Nature.
The nuclear DNA sequences recovered from two specimens secured show that they belong to the Neanderthal evolutionary lineage and are more closely related to Neanderthals than to Denisovans.
This finding indicates that the population divergence between Denisovans and Neanderthals had already occurred 430,000 years ago when the Sima de los Huesos hominins lived.
"These results provide important anchor points in the timeline of human evolution. They are consistent with a rather early divergence of 550,000 to 750,000 years ago of the modern human lineage from archaic humans," noted Svante Paabo from the Max Planck Institute for Evolutionary Anthropology.