The first movement of people into the Americas, whatever its precise timing and route, involved people moving from the Beringian region into what is now Alaska.

Alaska is therefore the geographic source region for the entire hemisphere’s Indigenous population — the place where the founding population was first present in the Americas in the sense that we understand that term.

Finding an ancient individual in Alaska whose genome is basal to all other sampled Native American populations is exactly what we would predict if we had successfully sampled the founding population close to the source.

USR1’s position in the family tree of Native Americans reflects her geographic location as well as her temporal one: she was in the right place, at the right time, to represent a branch of the founding population that had not yet been diluted by the demographic processes of the southward expansion.