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The analysis of the teeth suggests that Neanderthals and modern humans separate far earlier than thought

In the new study, samples of some hominine teeth were analyzed.
Image: Aida Gomez-Robles

Dental data show that Neanderthals and modern humans have deviated from a common ancestor about 800,000 years ago – hundreds of thousands of years earlier than standard estimates. The finding may finally reveal the origin of our shared ancestry, but some experts argue that new evidence is inconclusive.

Archaeological and genetic evidence suggests that the Neanderthals had traveled around Eurasia about 400,000 years ago, and that modern humans, Homo sapiens, which originated in Africa about 300,000 years ago. These two groups of hominids – both of them – originate from an unknown common ancestor. The time and geographic location of their significant evolutionary split are not known, but skull and DNA studies suggest that this happened about 500,000 to 600,000 years ago.

The new study, published this week in Science Advances, suggests that the difference between Neanderthals and modern humans from our last common ancestor (LCA) occurred not earlier than 800,000 years ago. The lone author of the new study, anthropologist Aida Gomez-Robles of University College London, came to this conclusion after analyzing the teeth of Neanderthals 430,000 years ago. However, the experts we talked with said that more evidence is needed to support this claim.

The neanderthal teeth used in the study were previously found in the Sima de los Huesos, a Spanish cave, which hosted the holmines during the Middle Pleistocene. In Sima, remains of nearly 30 individuals have been found and they exhibit anatomical features that are very Neanderthal characteristic. In fact, they are so Neanderthal that scientists believe that these bones and teeth probably come from an early version of Neanderthals.

The layer in which the remains were found was dated 430,000 years ago. This means that Neanderthals, with their different characteristics, must deviate from our LCA long before. Evolution moves very slowly. But as stated in the new study, the characteristics of teeth require more than several hundred thousand years.

"Any mismatch between Neanderthals and modern humans 800,000 years ago would lead to an unexpectedly rapid evolution of teeth in the early Neanderthals of Sima de los Huesos," said Gomez-Robles in a statement by UCL. There are various factors that could potentially explain these results, including a strong selection for tooth replacement of these hominids or their isolation from other Neanderthals found in continental Europe. The simplest explanation is that the differences between Neanderthals and modern humans were over 800,000 years old. This will make the evolutionary levels of the early Neanderthals of the Sima de los Huesos roughly comparable to those found in other species. "

Simina's hominins had very small premollars and molars, which is consistent with Neanderthals. These small tooth features may have evolved from the larger teeth of the not yet identified LCA. For the study, Gómez-Robles analyzed the teeth of different types of chimpanzees and used the quantitative data obtained to establish the baseline level of dental evolution among the Hominins.

"The teeth of the people in Sima are very different from those we would expect to find in their last general pedigree with modern people, suggesting that they have evolved separately over a long period of time to develop such obvious differences "says Gomez-Robles.

Our joint LCA with Neanderthals is not yet known, but this finding suggests that the mysterious species can not be much younger than 800,000 years. Types of hominin Homo heidelbergensis, which has lived from about 800,000 to 300,000 years, is now unlikely candidate, according to the new study.

Catherine Duca, an Oxford University archaeologist not related to the new study, said the statistical and modeling analyzes carried out in the study were "very interesting," but the conclusions are based on one basic assumption: that the absolute date set for the Sima de los Huesos individuals are actually correct.

"However, we know that Sima's age is not armored and if the real age is younger, at the age of 250,000 years, for example, the divergence coefficients calculated in this study would be compatible with the average evolutionary rates rather than totally contradictory, Duca explained to Gizmodo in an email.

Sheron Browning, a biostatist at the University of Washington, believes that the new book is based too much on extrapolation made from a single point of data, which is the observed divergence of teeth. The document, reported by Gizmodo in an email, did not take enough of all other data, especially the DNA divergence.

"The author argues that uncertainty in mutation rates, for example, may affect the results of DNA divergence. That's definitely true, "Browning said. "However, even when using the lower end of plausible levels of mutations, previous studies from 2012" they found time for the Neanderthals-human division no more than 600,000 years ago, "she said.

Also, the DNA data available to Sima individuals are not very complete, so although their DNA may be similar to Neanderthals, it is likely that this group has shrunk with some other unknown hominins, leading to observed dental differences , according to Browning, "This is only an opportunity to reconcile dental data with the established boundaries for the time of the Neanderthal-human division," she added.

Indeed, while the new study offers interesting food for thought, it is clear that further evidence will be needed to strengthen the conclusion reached by Gomez-Robbles. Until then, the last common ancestor of Neanderthals and modern humans will have to remain a lasting mystery.

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