The evidence for deep human prehistory is inherently limited: we cannot run experiments, we cannot observe the past directly, and the available evidence is always incomplete.

In this context, the goal of research is not to arrive at a single certain answer quickly but to progressively narrow the range of plausible answers by accumulating evidence that eliminates some explanations while remaining consistent with others.

The Population Y debate is at this progressive-narrowing stage.

The most extreme interpretations — that Australians literally sailed to South America, that the first South Americans were not Native Americans — have been eliminated by the evidence.

The remaining competing models are all variations on a theme of ancestral complexity within the Native American founding population, differing primarily in the specific mechanism by which that complexity arose and was distributed.