JMA-PSOS

At the end of the last ice age, around 13,000 years ago, retreating glaciers created an inland corridor connecting Siberia to the Americas. People from northeast Asia crossed the Bering Strait land bridge and entered a new world. [...] But, according to the University of Kansas anthropological geneticist Jennifer Raff, that’s not quite how it happened.

In her new book, “Origin: A Genetic History of the Americas,” Raff beautifully integrates new data from different sciences (archaeology, genetics, linguistics) and different ways of knowing, including Indigenous oral traditions, in a masterly retelling of the story of how, and when, people reached the Americas. While admittedly not an archaeologist herself, Raff skillfully reveals how well-dated archaeological sites, including recently announced 22,000-year-old human footprints from White Sands, N.M., are at odds with the Clovis first hypothesis. She builds a persuasive case with both archaeological and genetic evidence that the path to the Americas was coastal (the Kelp Highway hypothesis) rather than inland, and that Beringia was not a bridge but a homeland — twice the size of Texas — inhabited for millenniums by the ancestors of the First Peoples of the Americas. 

About 17,000 years ago, on the western coast of present-day Alaska, the ice sheets began to melt, and the First Peoples expanded southward. This expansion left very clear imprints in the genomes of their descendants. Mitochondrial DNA lineages show us that after the LGM, people were suddenly and rapidly spreading out. Their populations were growing enormously—about 60-fold between about 16,000 and 13,000 years ago.

This population explosion is exactly what we expect to see in the genetic record when people move into new territories, where resources are far less limited, there is no competition from other people, and the game animals have no natural fear of humans, having never seen them before.