Milk teeth tell of a population undiscovered for over 30,000 years

‘Well, hello! There you are,’ exclaimed researchers at the Lundbeck Foundation GeoGenetics Centre at the University of Copenhagen (UCPH).

They had just been examining two milk teeth – each lost by a boy in north-eastern Siberia, near the Yana River, 31,000 years ago – and were delighted to find that the DNA told a tale long pursued by science.

The DNA held details that shed light on some of the hitherto obscure aspects of the kinship between today’s Native Americans and tribes in northern Siberia. Although these two groups are genetically very similar – and both have genetic markers from both Asia and Europe – they have no direct ancestral line in common.

‘So, we can conclude that another group of people must have had a hand in things at one time. But, up to now, we haven’t been able to say who they were, and these milk teeth are the missing piece of this puzzle. It’s extremely satisfying,’ says professor and DNA detective Eske Willerslev. Professor Willerslev is director of the Lundbeck Foundation GeoGenetics Centre and headed the study.

The two milk teeth that were found during excavation of a settlement near the Yana River have no root. However, they were well-protected by permafrost until they were discovered a few years ago, and they contain DNA which is so intact that the entire genome of both boys could be reconstructed. As Eske Willerslev says:

‘It was absolutely fantastic – and, to date, it’s some of the best human DNA science has been able to extract from early modern humans.’

The milk teeth and other archaeological DNA included in the study will also form part of another Lundbeck Foundation project headed by Eske Willerslev, Professor Thomas Werge of UCPH and the Mental Health Services, Capital Region of Denmark, and Professor Rasmus Nielsen of UCPH and UC Berkeley, USA.

Based on old bones and teeth, this project will map the DNA profiles of 5,000 people – right back to the early Stone Age – to help us understand how brain diseases and psychological disorders have evolved genetically up to the present day.

‘Until now, we thought we could only go back 10,000 years, but thanks to the milk teeth we’ve significantly extended our range,’ says Eske Willerslev.

Huts made of tusks

The story about the two teeth was recently published in the scientific journal Nature and its authors included scientists from 39 academic institutions in Denmark, Russia, Switzerland, the UK, USA, Kazakhstan, Greenland and Finland.

Professor Willerslev emphasises that, in many respects, the article in Nature – which also includes analyses of the genomes of a further 32 rare skeletons – helps deepen our understanding of early migrations:

‘These milk teeth contain DNA from a group of people who probably covered large parts of the northern hemisphere 30,000-40,000 years ago. This population died out but we’re able to identify fragments of their DNA in people living today in an area that spans from the Ural Mountains to deep into the USA – so, in Native Americans. And we now have the entire genomes of two members of this population.’

The DNA profile of the two teeth is a mix of 25% Asian and 75% European DNA. And the name ‘Ancient North Siberians’ (ANS) has been given to this lost, but recently surfaced, population.

Analyses show, among other things, that both Native Americans and tribes in northern Siberia inherited a DNA component from ancestors of the Ancient North Siberians and that they share this component with present-day Europeans.

But what else do we know about the lost ANS population?

‘Actually, we know a fair amount, and this is due to the effects found at the Yana settlement,’ says Martin Sikora, first author of the Nature article and associate professor at the Lundbeck Foundation GeoGenetics Centre:

‘They were hunters – big game hunters of the woolly mammoth and rhinoceros species that lived in northern Siberia at the time. Exquisitely made tools were found at the settlement, carved from the horn of their prey. It was also obvious that ANS used the horn and bones of animals as a sort of skeleton for building their dwellings. They were highly evolved hunters, clever craftsmen with a sophisticated sense of the aesthetic. But we’ve no idea why they died out.’

A thigh bone in the riverbank

In order to put archaeological DNA into a perspective that will give us information about migration, we need to compare – and compare again. This means examining a large number of samples to identify similarities and differences, to give an idea of how populations at that time moved around and interbred.

During this study, researchers examined the DNA of 34 people. The 31,000-year-old ANS teeth are the oldest items in the study, the most recent samples being a ‘mere’ 600 years old.

One of the reference samples comes from a different site in Siberia: Duvanny Yar by the Kolyma River. And there was yet another day of celebration when the scientists analysed the DNA of this sample at the laboratory in Copenhagen.

Eske Willerslev explains that, like the area where the Yana settlement was discovered, the climate at Duvanny Yar is bitterly cold for most of the year:

‘I actually visited the region when I was a young man: I tried my hand as an adventurer and, later, as a trapper in Siberia. Now, even in the middle of a Danish summer, thinking about winter in northern Siberia makes me shiver.’

The sample from Duvanny Yar is an approximately 10,000-year-old male thigh bone. The bone has lain tightly wedged into the bank of the Kolyma River, covered by permafrozen soil. This is now beginning to thaw, releasing myriads of prehistoric bones of animals and humans.

It is uncertain how the thigh bone ended up there, but its owner probably drowned or was thrown into the Kolyma River after he died. Professor Willerslev explains that the unique thing about this sample is that it is the closest we can get to the Asian ancestors of today’s Native Americans.

The scientific project also involves reconstructions of the climate and precipitation in northern Siberia. These tell scientists that, in all probability, the region was habitable up to 46,000-36,000 years ago.

‘So, presumably, people have lived in northern Siberia for much longer than we previously thought probable,’ says Eske Willerslev.