This rapid expansion model has implications that go well beyond the Spirit Cave case.

It suggests that the people who became the first Americans were extraordinarily mobile — capable of traversing a hemisphere within a few thousand years.

It suggests that they encountered a landscape full of large animals that had never seen human hunters, and that they moved through that landscape with a speed and effectiveness that had catastrophic consequences for the megafauna.

And it raises questions about the pre-Clovis sites — like the White Sands footprints, dated to approximately 21,000 to 23,000 years ago — that suggest human presence in the Americas even earlier than the Spirit Cave Man.

If people were in New Mexico more than 20,000 years ago, what is their relationship to the founding population represented by the Spirit Cave Man?