And the unexplained residual, it turned out, had a very specific address: it traced back to people like the child at Mal’ta, living in south-central Siberia during the Last Glacial Maximum.

This did not contradict the East Asian picture.

It added a new layer to it.

The founding population of the Americas, the new model suggested, was itself a mixed population — a population that had formed in Asia through the mixture of East Asian-related ancestry and Ancient North Eurasian ancestry, and that then crossed into the Americas in that mixed state.

The mixing had occurred in Asia, probably in the broad northern Asian region where the two ancestral components were geographically adjacent.