Post by UKarchaeology on Apr 2, 2016 20:48:28 GMT
The earliest Americans have long been shrouded in mystery. For decades, scientists have debated what route they traveled into North America and how long it took for them to spread to every nook and cranny of the New World. Now, a new genetic study traces those ancient populations from their first foray all the way through European contact, which may have been even more cataclysmic for indigenous populations than researchers thought.
“[The study] is confirming a picture that has been emerging” about how and when the first people arrived in the Americas, says Jon Erlandson, an archaeologist at the University of Oregon in Eugene who wasn’t involved in the research. “It challenges archaeologists to catch up with the genomics people, because they’re creating models for us that need to be tested.”
At the heart of the new research is a unique dataset: 92 skeletons and mummies, mostly from the western part of South America. These individuals lived between 8600 to 500 years ago in regions ranging from Mexico to Chile. A team of researchers sequenced each sample’s mitochondrial genome, or the genes found in the power plants of a person’s cells. Mitochondrial genes are passed down directly from mother to offspring, so the sequences open a window onto the matrilineal heritage of indigenous Americans extending all the way back to their roots in Siberia.
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. At that point in time, “the route can only be along the Pacific coast,” says Alan Cooper, an evolutionary biologist at the University of Adelaide in Australia who helped lead the study. “The ice sheets are still so thick at that point that there’s no way through [farther inland].”
Full story: www.sciencemag.org/news/2016/04/mummy-genomes-reveal-just-how-catastrophic-european-contact-was-new-world