The discovery of teeth frozen in Arctic soil have helped scientists make sense of the waves of human settlement in the Americas.
One discovery, making scientists forever grateful to some ancient tooth fairy, was of two milk teeth from distantly related boys buried near the Yana River in north-eastern Siberia. The site has been excavated for almost 20 years, bringing to light thousands of animal bones, ivory, and stone tools. None of that has been as scientifically valuable, however, as the DNA trapped in the teeth for 31,000 years because of the icy conditions.
The boys were from an ethnic group called the Ancient North Siberians who, despite their location, were twice as closely related to Europeans as east Asians.
Professor Eske Willerslev of Cambridge University said in a statement: "These people were a significant part of human history, they diversified almost at the same time as the ancestors of modern day Asians and Europeans and it's likely that at one point they occupied large regions of the northern hemisphere."
To survive a winter in Siberia today is a challenge. To do it in the middle of the last ice age demonstrates these people's remarkable resilience. Native Americans have DNA that is a mix of that seen in these Ancient North Siberians and East Asians, so the latest discovery provides a missing link in explaining Native American genetic heritage, although a sample of DNA found closer to Mongolia is more closely related to modern Native Americans.
The teeth were the highlight, but Willerslev and co-authors also explored in Nature the ancient genomes from 34 people dating back almost 32,000 to 600 years ago. They revealed that the Ancient North Siberians showed no signs of being inbred, despite what must have been very low local population density. Somehow, they found ways to expand their breeding pool, even if it required immense migrations. In contrast, the last Neanderthals were, around the same time, suffering from severe inbreeding, raising the intriguing possibility that modern humans' greater propensity for finding unrelated mates was what allowed us to outcompete our nearest relatives.
Another paper in the same edition reports on a related study of the genetics of those who have inhabited the Arctic over the last 5,000 years. It compares the genomes of 48 ancient people from the far north and 93 modern individuals living in similar areas. The study confirms that modern populations in eastern Siberia, Alaska, northern Canada, and the Aleutian Islands are descended from a group known as the Paleo-Eskimos, who arrived in North America around 5,000 years ago.
For whatever reason, the ancestors of modern Inuit and Yup'ik people, having initially crossed the Bering Strait with the Paleo-Eskimo arrival, went back to eastern Siberia for around 1,000 years before returning to Alaska.
On returning to Alaska, some members of this group apparently decided they didn't like the cold so much after all, and their genetic heritage can be found among speakers of the Na-Dene languages along the US west coast and the American south-west.