Hominin bones that were found at an excavation site in Spain known as Sima de los Huesos, or "pit of bones" in 2013 offer the earliest genetic evidence of Neanderthals.
The fossils, which come from remains found inside what anthropologists believe is a 400,000 year old burial site, contain DNA, which an earlier mitochondrial analysis suggested belonged to distant relatives of the Denisovans.
Findings of a new study, however, suggest that the specimens appear to be more closely related to Neanderthal ancestors than those of Denisovans.
Matthias Meyer at the Max Planck Institute for Evolutionary Anthropology and colleagues sequenced the nuclear DNA from the bones and found that the specimens belong to early Neanderthals.
The findings suggest that the Neanderthals and the Denisovans may have diverged about 430,000 years ago, which is much earlier than what geneticists previously thought.
"The Sima de los Huesos hominins were related to Neanderthals rather than to Denisovans, indicating that the population divergence between Neanderthals and Denisovans predates 430,000 years ago," the researchers wrote in their study, which was published in the journal Nature on March 14.
"A mitochondrial DNA recovered from one of the specimens shares the previously described relationship to Denisovan mitochondrial DNAs, suggesting, among other possibilities, that the mitochondrial DNA gene pool of Neanderthals turned over later in their history."
It is known that the Denisovans and the Neanderthals have a common ancestor that had split from the lineage of modern human. The new nuclear DNA evidence suggests that the split may have occurred as early as 765,000 years ago, which is far earlier than what previous DNA studies suggest that the split happened between 315,000 and 540,000 years ago.
If this ancient split is correct, it would mean that modern humans may not have evolved from the Homo heidelbergensis hominin, which did not evolve until 700,000 years ago, or after modern humans and the Denisovans and Neanderthals had split.
It could mean that another species known as Homo antecessor could be our common ancestor. The species first emerged more than a million years ago and is characterized by a face that is very similar to that of modern humans.
"These results provide important anchor points in the timeline of human evolution," study author Svante Paabo said. "They are consistent with a rather early divergence of 550,000 to 750,000 years ago of the modern human lineage from archaic humans."