Neanderthals and modern humans diverged at least 800,000 years ago, significantly earlier than currently thought, according to new study based on analyzing how the teeth of ancient fossils evolved instead of relying on genetic techniques.
The proposed new timeline is around 300,000 years earlier than current estimates, and would in turn mean that Homo heidelbergensis, another extinct human species, cannot be the last common ancestor between our species and our Neanderthal cousins, as many anthropologists presently believe.
In recent years, scientists seeking to unlock the mysteries of our species' evolution have used DNA analyses to provide a "molecular clock" to date fossils, based on assumptions about the rate of genetic change per generation.
The new research by Aida Gomez-Robles at the University College London instead examined dental evolutionary rates across extinct human species, finding that tooth crowns changed in size and shape at a steady rate.
Her study then focused on the molars and pre-molars of around 30 fossils from the Sima de los Huesos site, which earlier research has reliably dated to 430,000 years ago -- close to the previously assumed date when sapiens and Neanderthals split.
But she found strong similarities between the Sima hominins' teeth and those of Neanderthals, which meant they could only have existed after the long-held date of divergence.
Statistical analysis was used to extrapolate the new date of divergence to 800,000 years ago.
"Any divergence time between Neanderthals and modern humans younger than 800,000 years ago would have entailed an unexpectedly fast dental evolution in the early Neanderthals from Sima de los Huesos," she said.
"The major implication is Homo heidelbergensis cannot be the last common ancestor between modern humans and Neanderthals," she told AFP.
Gomez-Robles' work was praised by Mirjana Roksandic, a biological anthropologist at the University of Winnipeg.
"She is pinpointing a time when Neanderthals must have moved their own way and that is a very very significant result," said Roksandic.
But it received pushback from Susan Cachel, a professor in human evolution at Rutgers University.
"If the ancestors of anatomically modern humans and Neanderthals do not come from the taxon Homo heidelbergensis, then where do they come from? Some unknown, shadowy ancestor?"