Study Pegs Divergence of Neanderthals and Humans at 800,000 Years Ago

(CN) – Teeth can weather a lot, even 800 millennia in a cave. A batch of them – along with prehistoric fossils found in a cave system – have led scientists to a stunning new conclusion: Modern humans likely began breaking away from our Neanderthal relatives 800,000 years ago, much earlier than previously thought.

The study, published Wednesday in the journal Science Advances, was based on an analysis of the traits of fossilized teeth.

While the search for modern human’s last common ancestor with Neanderthals continues, the study suggests future researchers should rule out any fossils younger than 800,000 years old.

Neanderthals are modern human’s closest ancient relatives and lived until 40,000 years ago. Among anthropologists there is speculation about how and when the two groups diverged, but DNA-based estimates previously led scientists to believe the lineages split between 300,000 and 500,000 years ago. This foundation has played a key role in how hominin fossil records have been studied.

The new study suggests a much earlier break.

Enter Sima de los Huesos (Pit of Bones), a cave site at Sierra Atapuerca in northern Spain. Some 5,500 skeletal remains have been excavated at the site since 1997, amounting to 28 archaic humans. Previous estimates pegged the age of the site at around 430,000 years old.

Aida Gomez-Robles from the anthropology department at the University of London says the hominins found at Sima de los Huesos have very small posterior teeth like premolars and molars. They share multiple similarities with classic Neanderthals.

Hominin teeth. (Aida Gomez-Robles)

“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,” says Gomez-Robles.

Any divergence of Neanderthals and modern humans less than 800,000 years ago would have meant an unexpectedly quick evolution of the dental characteristics of early Neanderthals from the site. The study authors say several variables could explain the results, including a strong need for a change in the type of teeth necessary for survival or the group’s isolation from other prehistoric hominins found in mainland Europe.

Gomez-Robles offers a different hypothesis.

“The simplest explanation is that the divergence between Neanderthals and modern humans was older than 800,000 years,” said Gomez-Robles. “This would make the evolutionary rates of the early Neanderthals from Sima de los Huesos roughly comparable to those found in other species.”

Fossils found at the time are considered likely Neanderthal ancestors based on their anatomical features and DNA analysis.

“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,” Gomez-Robles said.

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