A new study that analyzed dental evolutionary rates in early Neanderthals from Sima de los Huesos, a cave site in Atapuerca Mountains, Spain, found that the teeth of these Middle Pleistocene hominins diverged from the modern human lineage approximately 800,000 years ago, which is much earlier than previously thought.
Sima de los Huesos hominins lived in what is now Spain about 400,000 years ago. Image credit: © Kennis & Kennis / Madrid Scientific Films.
Modern humans share a common ancestor with Neanderthals, the extinct species that were our closest prehistoric relatives.
However, the details on when and how they diverged are a matter of intense debate within the anthropological community.
Ancient DNA analyses have generally indicated that both lineages diverged around 300,000 to 500,000 years ago, which has strongly influenced the interpretation of the hominin fossil record.
This divergence time, however, is not compatible with the anatomical and genetic Neanderthal similarities observed in the Sima de los Huesos hominins.
“Sima de los Huesos hominins are characterized by very small posterior teeth (premolars and molars) that show multiple similarities with classic Neanderthals,” said study author Dr. Aida Gomez-Robles, a researcher at University College London and the Natural History Museum, London.
“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.”
Dental shape has evolved at very similar rates across all hominin species, including those with very expanded and very reduced teeth.
Dr. Gomez-Robles examined the time at which Neanderthals and modern humans should have diverged to make the evolutionary rate of the early Neanderthals from Sima de los Huesos similar to those observed in other hominins.
The scientist used quantitative data to measure the evolution of dental shape across hominin species assuming different divergent times between Neanderthals and modern humans, and accounting for the uncertainty about the evolutionary relationships between different hominin species.
“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.”
The study was published in the journal Science Advances.
_____
Aida Gómez-Robles. 2019. Dental evolutionary rates and its implications for the Neanderthal–modern human divergence. Science Advances 5 (5): eaaw1268; doi: 10.1126/sciadv.aaw1268
