An analysis of fossil teeth pushes the human-Neanderthal divide to about 1 million years ago.Specifically, the new study published in the journalScience Advances, exposes that modern humans and Neanderthals separated from a common ancestor more than 800,000 years ago, much earlier than many researchers have previously thought.
That conclusion is derived from an analysis of the first fossilized Neanderthal teeth found at the famous Spanish site known as the ‘Sima de los Huesos’ (an avenue in the Sierra de Atapuerca that contains a 430,000-year-old site).During hominin evolution, dental crowns changed in size and shape at a constant rate,comments Aida Gómez-Robles, a paleoanthropologist at University College London (England). Neanderthal teeth, which date to approximately 430,000 years ago,their distinctive forms could have evolved at a rate typical of other hominins only if Neanderthals originated between 800,000 and 1.2 million years ago, according to the researcher.
The current study indicates that, if there was a common ancestor of today’s humans and Neanderthals about 1 million years ago, “there was not enough timeso that Neanderthal teeth would change at the rate they do in other parts of the human family tree “, explains paleoanthropologist Bernard Wood, from George Washington University in Washington DC (USA).
Many experts presume that a species nicknamedHomo heidelbergensis, which originated about 700,000 years ago, inhabited Africa and Europe, and gave rise to an ancestor of both Neanderthals and Homo sapiens about 400,000 years ago. Genetic evidence that the Sima de los Huesos fossils came from Neanderthals raised suspicions that a common ancestor with Homo sapiens existed much earlier.Recent Neanderthal DNA studies place that common ancestor between 550,000 and 765,000 years old.But those results are based on controversial estimates of the speed and consistency of cumulative genetic changes over time.
With that molecular debate in mind, the leader of the work, Gómez-Robles,calculated the rate at which eight ancient hominin species evolved in terms of the shape of their teeth.That allowed him to calculate how long it took for the remains of the Sima de los Huesos to evolve after the Neanderthals split from a common ancestor with Homo sapiens.
The expert used two possible evolutionary trees in the eight hominid species to estimate the rates of dental evolution. Aside from Spanish Neanderthals and Stone Age H. sapiens, the teeth in his study came from African hominins dating back 3.2 million years. Total,examined 931 teeth belonging to 122 individuals found at the Sima de los Huesos siteof Burgos.
The hominins of the Sima de los Huesos have very small posterior teeth (premolars and molars) that show multiple similarities with those of classic Neanderthals.
According to the paleoanthropologist Aurélien Mounier, from the Musée de l’Homme in Paris (France), it seems reasonable to go back the date of an evolutionary division between Neanderthals and H. sapiens. However, the timing of that division could change, if further research modifies the age of the Spanish fossils, he clarifies.
Other Spanish hominid teeth dating back nearly 800,000 years show some Neanderthal features, which support the new study’s findings, says New York University paleoanthropologist Shara Bailey. But it’s unclear whether Gomez-Robles’s claim that hominin teeth evolved steadily will remain the definitive answer.
And it is that this conclusion implies that any more recent human species of 800,000 years cannot be the common ancestor of Neanderthals and modern humans because it would be after the divergence of both groups.
Referencia: A. Gómez-Robles. Dental evolutionary rates and its implications for the Neanderthal-modern human divergence. Science Advances. Published online May 15, 2019. doi:10.1126/sciadv.aaw1268.
