Origin: A Genetic History of the Americas

een open in time for an initial peopling via that route. This perspective is
bolstered by several independent lines of genetic evidence, discussed below.
Importantly, there has never been any archaeological evidence
whatsoever showing that anyone moved from Beringia through the interior
corridor to the Plains or Great Lakes area. We don’t see the kinds of tools—
microblades and a kind of spear point called a Chindadn point—that people
were making at the northernmost end of the corridor at sites within the
corridor or below the ice wall. x The only archaeological evidence in the
corridor is of people moving northward: from the Northern Plains to
Alaska/Yukon several millennia after Clovis (23).
A research team extracted and analyzed microfossils and pollen from
sediment cores taken from two lakes—Charlie Lake and Spring Lake—
which are the remnants of glacial Lake Peace, a massive lake that formed in
the middle of the corridor as the ice sheets melted. By sequencing all the
DNA from each layer in the sediment core, the researchers generated an
overall picture of what kinds of animals and plants (and microorganisms)
were living at different periods in that region’s past. This molecular time
capsule showed them that even if the entirety of the ice-free corridor was
open by 13,000 years ago, it wouldn’t have had vegetation until about
12,600 years ago and animals living within it until about 12,500 years ago.
The corridor’s “viability” date would have constrained the movement of
people through it, as they would have needed things to eat during their trek
through the 2,000-kilometer corridor (24). In addition, as paleoecologist
Scott Elias notes, the melting of the enormous ice sheets would have littered
the corridor with huge amounts of rock, mud debris, chunks of ice, and
water everywhere as the billions of gallons of frozen water were released.
“As a human migration route, it would have been absolutely awful,” he told
me.
The genomes of Native Americans also argue against the ice-free
corridor route. We will talk about this more in later chapters, but complete
genomes from ancient and contemporary Indigenous peoples show that
major population splitting events were almost certainly associated with the
initial peopling of the continents. These population splits occurred
extremely rapidly—so rapidly that they have been described as “leapfrogging”
southward across large tracts of the American landscape. This is
not a pattern consistent with slower, overland diffusion of hunter-gatherer