Baby tooth found in Siberian cave reveals secrets of ancient humans from 200,000 years ago

A new Denisovan fossil found inside a cave in the Altai Mountains in Siberia could offer new clues about this mysterious human species. This is the fourth fossil of its kind and it's about 200,000 years old.

Denisovans formed a sister group of Neanderthals, discovered by scientists thanks to DNA analyses of ancient human remains unearthed from Siberia's Denisova cave. The ancestors of both groups split about 190,000 to 470,000 years ago.

Up to now, only three fossils - one finger bone and two molars - had been recovered and analysed, greatly limiting what researchers could say about this ancient human species.

There was a stark contrast between this sparse fossil record and the rich archaeological and paleontological data supporting the presence of Neanderthals in Europe and West Asia before the arrival of Homo Sapiens.

But this situation now appears to be changing. In a study published in the journal Science Advances, researchers describe the fourth fossil unearthed from a deep rock layer inside the cave – a lower second molar belonging to a young Denisovan female.

This fossil sheds a new light on the Denisovans' history and suggests these ancient humans lived in and around the Altai Mountains for much longer than previously thought.

Retracing Denisovans' history

Past genetic analyses have indicated that Neanderthals and Denosivans may have interacted and interbred, but more research was needed to confirm this. Denisovans are also thought to have contributed genetically to present-day populations in South-east Asian islands and Oceania.

Scientists want to learn more about the history of Denisovans and their relationships with Neanderthals to shed light on all these issues. Here, they managed to retrieve some of the DNA from the 'baby tooth' described in this research, which allowed them to establish that it had belonged to a 10 to 12-year-old Denisovan girl.

This molar was found in a deep sediment layer, suggesting that it is much older than all the other Denisovan fossils that had previously been studied. Indeed, this deep layer has been dated to between 128,000 to 227,000 years old.

This age makes the tooth one of the oldest human fossils discovered in the region to date, and about 50,000 to 100,000 years older than the other Denisovan fossils.

The findings thus reveal that Denisovans were present in the Altai region for a very long time, increasing the probability that they interbred with Neanderthals.

Furthermore, the scientists say that their DNA analyses, combined with previous investigations of the other fossils, suggest that there was low levels of genetic diversity among the Denisovans. This low level of genetic diversity is comparable to the lower range of modern human genetic diversity seen among small isolated populations today.