It was an attempt to explain a real observation — the genuine morphological difference between early and later American skeletal material — using the tools and frameworks available.

And it made specific predictions that could in principle be tested: if there had been two distinct founding populations, those populations should show genetic differences, and ancient DNA from early American individuals should reveal the expected genetic signals.

What the ancient DNA eventually showed was more complicated than either a simple confirmation or a simple refutation of the two-population model.

Before the genomic evidence arrived, however, the morphological debate generated significant heat and some light.