Neanderthals and modern humans diverged earlier than previously thought, according to a new survey of ancient teeth.

Using the 430,000-year-old teeth of hominins recovered from Sima de los Huesos, a cave in Spain, researchers were able to quantify the rate of dental evolution among early humans, ancestors of Neanderthals. The rates suggest Neanderthals and modern humans diverged at least 800,000 years ago.

Rates of evolutionary change among the dental shapes of hominins are consistent across several species and lineages. As such, scientists were able to use the rate of dental evolution among Sima de los Huesos teeth to deduce when Neanderthals first split.

"The Sima people's teeth are very different from those that we would expect to find in their last common ancestral species with modern humans, suggesting that they evolved separately over a long period of time to develop such stark differences," Aida Gomez-Robles, an anthropologist at University College London, said in a news release.

Using quantitative analysis, scientists determined the rate of change was too great for Neanderthals and modern humans to have diverged more recently than 800,000 years ago.

"There are different factors that could potentially explain these results, including strong selection to change the teeth of these hominins or their isolation from other Neanderthals found in mainland Europe," Gomez-Robles said. "However, the simplest explanation is that the divergence between Neanderthals and modern humans was older than 800,000 years. This would make the evolutionary rates of the early Neanderthals from Sima de los Huesos roughly comparable to those found in other species."

Previous DNA analysis suggests Neanderthals and modern humans diverged between 300,000 and 500,000 years ago, but the anatomical and genetic analysis of the hominin remains recovered from Sima de los Huesos, located in the Atapuerca Mountains, suggest otherwise.

Previous studies suggest Neanderthals and humans share a common ancestor, but the details of their evolutionary split remain murky and fiercely contested. The latest research suggests Sima de los Huesos were close relatives of Neanderthals.

"Sima de los Huesos hominins are characterized by very small posterior teeth (premolars and molars) that show multiple similarities with classic Neanderthals," Gomez-Robles said. "It is likely that the small and Neanderthal-looking teeth of these hominins evolved from the larger and more primitive teeth present in the last common ancestor of Neanderthals and modern humans."

Gomez-Robles and her colleagues shared their analysis of Sima de los Huesos teeth this week in the journal Science Advances.

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