Origin: A Genetic History of the Americas

194,000 and 177,000 years ago, and in Greece as early as 210,000 years ago
(36).
At this point in reading this book, you have probably already figured out
that it can be difficult to reconcile different lines of evidence in
understanding past events. This is true of human origins as well. On the one
hand, we have fossil evidence, combined with genetic evidence in
Neanderthal genomes of African H. sapiens populations reproducing with
European Neanderthals sometime prior to 200,000 years ago. This seems to
clearly point to a very early human movement out of Africa. But on the
other hand, when you look at genomes from all ancient and contemporary
H. sapiens populations, you see clear evidence of their migration out of
Africa much more recently: only 100,000 to 60,000 years ago (37). There
are several possible explanations (perhaps the Greek fossils were actually
Neanderthals?), but one of them, as geneticist Aylwyn Scally notes, “is
multiple or semi-continuous migration(s) of humans out of Africa” (38).
So could one of these possible early human dispersals have occurred in
the direction of Siberia, across the Bering Land Bridge, and down through
North America, all the way to California? Or could another kind of human,
like a Neanderthal, H. erectus, or Denisovan, have gotten to the Americas?
Most archaeologists and geneticists are very skeptical of either possibility.
From an archaeological perspective, no skeletal remains that look even
remotely like an early human have been found in the Americas, and we
have none dating from anywhere near that age. We also don’t see any
unambiguous stone tools known to have been made by these earlier
peoples: no Acheulian handaxes made by H. erectus, or Mousterian knives
and scrapers made by Neanderthals, or Aurignacian blades made by Upper
Paleolithic modern humans and Neanderthals.
What is found at the very early sites in the Americas tends to be either
less direct evidence of a human presence or stones that some archaeologists
suggest were flaked by humans. During much of early human history, many
kinds of stone tools were created by flaking pieces off of a stone called a
core; both the flakes and the core were used as tools. But how do you tell
the difference between a flake removed from a larger stone by human hands
(an artifact) and one that broke off naturally (a geofact)? Every professional
archaeologist I’ve ever met has had to deal with countless numbers of
people bringing them random rocks that they insist are tools. xi Humans are