Tooth evidence shows Neanderthals and modern humans differed from common ancestors around 800,000 years ago – hundreds of thousands of years earlier than standard estimates. The findings could finally reveal the origin of our ancestors, but some experts say the new evidence is inconclusive.
Archaeological evidence and genetics show that Neanderthals roamed around Eurasia about 400,000 years ago, and that modern humans, Homo sapiens, appeared in Africa around 300,000 years ago. These two groups of hominins – both human types – were descended from unknown ancestors. The time and geographical location of their important evolutionary cleavages is unknown, but studies of skulls and DNA show it happened around 500,000 to 600,000 years ago.
The new study, published this week in Science Advances, shows the difference between Neanderthals and modern humans from our common ancestor (LCA) that occurred no earlier than 800,000 years ago. The only author of the new study, anthropologist Aida Gómez-Robles of University College London, reached this conclusion after analyzing Neanderthal teeth dated 430,000 years ago. However, experts we spoke to said more evidence was needed to support this claim.
The Neanderthal teeth used in this study were previously found at Sima de los Huesos, a Spanish cave that housed hominins during the Middle Pleistocene. The remains of nearly 30 individuals have been found in Sima, and they show anatomical features that are very similar to Neanderthals. In fact, they are very like Neanderthals so scientists think that these bones and teeth might have originated in the early versions of Neanderthals.
The layer where the remains were found previously dated 430,000 years ago. That means Neanderthals, with their different features, must deviate from our LCA long before that. Evolution moves very slowly. But as new research shows, features seen in teeth require more than a few hundred thousand years to appear.
"Any time difference between Neanderthals and modern humans younger than 800,000 years ago would require the evolution of unexpected rapid teeth in the early Neanderthal of Sima de los Huesos," Gómez-Robles said in a UCL statement. "There are various factors that have the potential to explain these results, including a strong selection to change these hominin teeth or their isolation from other Neanderthals found on mainland Europe. However, the simplest explanation is that the difference between Neanderthals and modern humans is more than 800,000 years old. This would make the rate of early Neanderthal evolution from Sima de los Huesos roughly comparable to that found in other species. "
Hominins at the Sima site have very small premolars and molars, which are consistent with Neanderthals. This small tooth picture probably evolved from a tooth larger than the LCA that has not been identified. For this study, Gomez-Robles analyzed the teeth of different hominin species and used quantitative data to determine the basic level of tooth evolution among hominins.
"The Sima people's teeth are very different from what we hoped would be found in their last common ancestral species with modern humans, suggesting that they evolved separately over a long period of time to develop very striking differences," said Gómez-Robles.
LCA with us with Neanderthals is still unknown, but these findings suggest that mystery species should not be much younger than 800,000 years. Hominin species Homo heidelbergensis, who lived from around 800,000 to 300,000 years ago, are now unlikely candidates, according to new research.
Katerina Douka, an archaeologist at the University of Oxford who is not affiliated with the new study, said the statistical analysis and modeling carried out in this study were "very interesting," but the conclusion was based on a single basic assumption: That absolute dates are set for individuals Sima de los Huesos actually right.
"However, we know that Sima's age is not bulletproof and if actual age is younger, as young as 250,000 years for example, the level of difference calculated in this study will be compatible with average evolutionary levels, and not at all controversial," Douka explained to Gizmodo by email.
Sharon Browning, a biostatistics expert from the University of Washington, feels that new papers are too dependent on extrapolations made from one data point, which is the observed dental divergence. The paper, he told Gizmodo in an e-mail, was not enough to consider all the other data, especially DNA differences.
"The authors argue that uncertainty in mutation rates, for example, can influence the results of DNA divergence. This is true, to a certain extent, "Browning said. "However, even using lower reasonable mutation rates," previous studies from 2012 "found the time of the human-Neanderthal split was not more than 600,000 years ago," he said.
Also, the DNA data available for Sima individuals is not very complete, so even though their DNA may have similarities to Neanderthals, it is possible that this group mated with several other unknown hominins, producing observed tooth differences, according to Browning. . "It is only one possibility to reconcile dental data with a range defined for the time of a Neanderthal-human split," he added.
Indeed, while new research provides interesting food to think about, it is clear that more evidence will be needed to support the conclusions reached by Gomez-Robles. Until then, the last common ancestor of Neanderthals and modern humans must remain an eternal mystery.