Some prior migration, by some route, had to be invoked.

The alternative route that Monte Verde and other pre-Clovis evidence pointed toward was the coast.

If people had moved south along the Pacific coast of North America, following marine resources, they would have been able to move quickly — marine resources are relatively uniform along a coastline, reducing the need for adaptation to dramatically new environments.

They would also have left evidence that is now largely invisible: the coastline of 14,000 to 15,000 years ago is now drowned under the risen sea that followed the end of the Ice Age.

The archaeological sites of the first coastal migrants, if any existed, are on the seafloor.