Origin: A Genetic History of the Americas

archaeologist Ruth Simpson turned up artifacts that she believed were much
older—in geological layers that might have been deposited anywhere
between 200,000 and 50,000 years ago. She brought in the famous
paleontologist Louis Leakey to help her study the site. Leakey, an expert on
early hominins and their stone tool industries, confirmed that many of the
broken stones at the site were deliberately manufactured tools based on
their resemblance to what he was seeing in Olduvai Gorge. However,
Simpson and Leakey’s claims did not stand up to scrutiny. The rocks were
found in the middle of a geological deposit produced by a fast-moving
river; their breaks could easily have been caused by the actions of water.
Without any human skeletons or more positive evidence of human activity,
the Calico Early Man Site’s earliest dates are rejected most archaeologists
(34).
Such has been the fate of all American Paleolithic sites proposed thus
far. And yet, new claims continue to be made for very early sites. In 2017, a
group of researchers led by Steven Holen published a paper in the
prestigious journal Nature claiming that a site in Southern California
provides evidence of humans in the Americas 130,000 years ago (35).
A peopling of the Americas this early would have occurred before the
major migration of anatomically modern humans—people like us—out of
Africa about 100,000 years ago. Different kinds of humans had been living
throughout Eurasia before then. Homo erectus, humans with smaller brains
and very differently shaped skull from ours (probably reflecting differences
in their diets), had evolved in Africa around 1.9 million years ago and were
dispersing throughout Eurasia by around 1.8 million years ago.
Neanderthals, humans with larger brains and sturdier bodies than us,
evolved from H. erectus populations in Europe around 140,000 years ago
and spread throughout Eurasia. Denisovans, whose physical features are
currently unknown to us because most of our information about them comes
from their genomes, evolved from a common ancestor shared with
Neanderthals around 450,000 years ago (probably H. erectus) and also lived
throughout Eurasia.
Anatomically modern humans start showing up in Africa’s fossil record
as early as 300,000 to 270,000 years ago. They evolved gradually and also
moved around a bit before their major migration out of Africa; some have
been found in China dating to as old as 120,000 years ago, in Israel between