The Upward Sun River findings, as presented in the 2018 Nature paper and as understood by the broader scientific community in the years since, represent the best current understanding of what USR1’s genome reveals about the founding of the Americas.

That understanding is not final.

Population genetics as applied to ancient DNA is a rapidly evolving field.

The methods for sequencing ancient DNA, for comparing ancient genomes to modern ones, for building demographic models, and for interpreting the patterns that emerge from those models — all of these are continuing to improve.

New computational methods, new statistical frameworks, and new ancient genomes from previously unsampled regions and time periods will all contribute to the refinement and revision of the current understanding.

The specific demographic parameters estimated in the 2018 paper — the split date of approximately 20,000 years ago, the effective population sizes, the geographic interpretation of the Ancient Beringian / proto-First American divergence — are estimates with significant uncertainty ranges.