“By tallying up the random mutations that accumulate in populations that have been separated, geneticists can count backwards and figure out when two groups last had a common ancestor. When the researchers applied that technique to the 92 mummies and skeletons, they found that their ancestors had last been in contact with Siberian populations about 23,000 years ago. After that, a group with about 2000 child-bearing females (perhaps about 10,000 people total) spent 6000 years or so genetically cut off from other groups of humans. That supports the idea that the ancestors of the earliest Americans spent a few millennia stranded in Beringia, the now submerged landmass that once stretched from Siberia to Alaska, before the ice sheets started to melt and open up passages to the New World.

Then, 16,000 years ago, the population boomed, with many different lineages suddenly branching off from one another. The researchers believe that represents the moment at which people were first able to move out of Beringia and into the Americas, where a host of new land and resources allowed the population to grow and spread out rapidly…

That structure stayed in place until the cataclysm that was European contact. The researchers didn’t have to do any fancy modeling to understand just how severe the population collapse was. None of the 84 lineages they found are even traceable past contact because not a single living person who belongs to any of them has been found. “When Europeans arrived, some of those populations were wiped out completely,” says Bastien Llamas, a geneticist also at the University of Adelaide and first author of the new study.”