Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past

by David Reich

How could humans have gotten south of the ice sheets before the ice-free corridor was open? During the peak of the ice age, glaciers projected right into the sea, creating a barrier more than a thousand kilometers in length along the western seaboard of Canada. But in the 1990s, geologists and archaeologists, reconstructing the timing of the ice retreat, realized that portions of the coast were ice-free after sixteen thousand years ago. There are no known archaeological sites along the coast from this period, as sea levels have risen more than a hundred meters since the ice age, submerging any archaeological sites that might have once hugged the shoreline. The absence of archaeological evidence for human occupation along the coast in this period is therefore not evidence that there was no such occupation in the past. If the coastal route hypothesis is right, humans could have walked at that time or later (but still in time to reach Monte Verde) along ice-free stretches of the coastline, possibly bypassing ice-covered sections with boats or rafts, and arriving south of the ice millennia before the interior ice-free corridor opened.

Failure of imagination