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Tooth Study Has Modern Humans Splitting From Neanderthals 400,000 Years Earlier Than Thought

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Neanderthals and modern humans diverged at least 800,000 years ago, substantially earlier than indicated by most DNA-based estimates, according to new research by a UCL academic.

The research, published in Science Advances , analyzed dental evolutionary rates across different hominin species , focusing on early Neanderthals. It shows that the teeth of hominins from Sima de los Huesos, Spain - ancestors of the Neanderthals - diverged from the modern human lineage earlier than previously assumed.

The Discovery of the Neanderthal Teeth

Sima de los Huesos is a cave site in Atapuerca Mountains, Spain, where archaeologists have recovered fossils of almost 30 people. Previous studies date the site to around 430,000 years ago (Middle Pleistocene), making it one of the oldest and largest collections of human remains discovered to date.

Excavation site where the Neanderthal teeth were discovered

Excavation site where the Neanderthal teeth were discovered. (Mario modesto / Public Domain )

Dr Aida Gomez-Robles (UCL Anthropology), said: "Any divergence time between Neanderthals and modern humans younger than 800,000 years ago would have entailed an unexpectedly fast dental evolution in the early Neanderthals from Sima de los Huesos."

"There are different factors that could potentially explain these results, including strong selection to change the teeth of these hominins or their isolation from other Neanderthals found in mainland Europe. However, the simplest explanation is that the divergence between Neanderthals and modern humans was older than 800,000 years. This would make the evolutionary rates of the early Neanderthals from Sima de los Huesos roughly comparable to those found in other species."

Modern Human verses Neanderthal Teeth

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 analysis has 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 hominins from Sima de los Huesos. The Sima fossils are considered likely Neanderthal ancestors based on both anatomical features and DNA analysis .

Fossil of Neanderthal teeth found in the Sima de los Hueso cave system.

Fossil of Neanderthal teeth found in the Sima de los Hueso cave system. (UtaUtaNapishtim / CC BY-SA 4.0 )

Dr Gomez-Robles said: "Sima de los Huesos hominins are characterized by very small posterior teeth (premolars and molars) that show multiple similarities with classic Neanderthals. 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. This new study 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.

Upper and lower postcanine dentition of one representative SH individual - upper dentition is represented on top

Upper and lower postcanine dentition of one representative SH individual - upper dentition is represented on top. (A. Muela / Fair Use )

The Study’s Findings

The research 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.

Anatomical comparison of skulls of Homo sapiens, left and Homo neanderthalensis, right

Anatomical comparison of skulls of Homo sapiens, left and Homo neanderthalensis, right. (Honza.havlicek / CC BY-SA 2.0 )

The study has significant implications for the identification of Homo sapiens last common ancestral species with Neanderthals, as it allows ruling out all the groups postdating 800,000 years ago.

Top image: Neanderthal verses human skull. Source: Bruder / Adobe.

The article ‘ Neanderthals and modern humans diverged at least 800,000 years ago, research on teeth shows ’ was originally published on Science Daily.

Source: University College London. " Neanderthals and modern humans diverged at least 800,000 years ago, research on teeth shows ." ScienceDaily. ScienceDaily, 15 May 2019.

References

Gómez-Robles, A. 2019. Dental evolutionary rates and its implications for the Neanderthal–modern human divergence . Science Advances. [Online] Available at: https://advances.sciencemag.org/content/5/5/eaaw1268

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