They had mixed with the East Asian-ancestry populations that were also part of the founding mix.

The resulting admixed population — carrying both East Asian and Ancient North Eurasian ancestry — had eventually crossed into the Americas, either via Beringia or some other route, and had given rise to the diverse Indigenous peoples who inhabited the Western Hemisphere by the time European contact began.

This is what researchers mean when they talk about the “hidden source” of Native American ancestry.

The East Asian connection had long been recognized — it was visible in the physical features and the genetic profiles of Native American populations and had been confirmed by multiple earlier genetic studies.