When
did humans complete their expansion around the
world? I'm convinced, but can't yet prove, that
humans first reached the continents of North America,
South America, and Australia only very recently,
at or near the end of the last Ice Age. Specifically,
I'm convinced that they reached North America
around 14,000 years ago, South America around
13,500 years ago, and Australia and New Guinea
around 46, 000 years ago; and that humans were
then responsible for the extinctions of most of
the big animals of those continents within a few
centuries of those dates; and that scientists
will accept this conclusion sooner and less reluctantly
for Australia and New Guinea than for North and
South America.
Background to my conjecture is that there are
now hundreds of thousands of sites with undisputed
evidence of human presence dating back to millions
of years ago in Africa, Europe, and Asia, but
none with even disputed evidence of human presence
over 100,000 years ago in the Americas and Australia.
In the Americas, undisputed evidence suddenly
appears in all the lower 48 U.S. states around
14,000 years ago, at numerous South American sites
soon thereafter, and at hundreds of Australian
sites between 46,000 and 14,000 years ago. Evidence
of most of the former big mammals of those continents—e.g.,
elephants and lions and giant ground sloths in
the Americas, giant kangaroos and one-ton Komodo
dragons in Australia—disappears within a
few centuries of those dates. The transparent
conclusion: people arrived then, quickly filled
up those continents, and easily killed off their
big animals that had never seen humans and that
let humans walk up to them, as Galapagos and Antarctica
animals still do today.
But some Australian archaeologists, and many American
archaeologists, resist this obvious conclusion,
for several reasons. Archaeologists try hard to
find convincing earlier sites, because it would
be a dramatic discovery. Every year, discoveries
of many purportedly older sites are announced,
then to be forgotten. As the supporting evidence
dissolves or remains disputed, we're now in a
steady state of new claims and vanishing old claims,
like a hydra constantly sprouting new heads. There
are still a few sites known for the Americas with
evidence of human butchering of the extinct big
animals, and none known for Australia and New
Guinea—but one expects to find very few
sites anyway, among all the sites of natural deaths
for hundreds of thousands of years, if the hunting
was all finished locally (because the prey became
extinct) within a few decades. American archaeologists
are especially persistent in their quest for pre-14,000
sites—perhaps because secured dating requires
use of multiple dating techniques (not just radiocarbon),
but American archaeologists distrust alternatives
to radiocarbon (discovered by U.S. scientists)
because the alternative dating techniques were
discovered by Australian scientists.
Every year, beginning graduate students in archaeology
and paleontology, working in Africa or Europe
or Asia, go out and discover undisputed new sites
with ancient human presence. Every year, new such
discoveries are announced to the other three continents,
but none has ever met the requirements of evidence
accepted for Africa, Europe, or Asia. The big
animals of the latter three continents survive,
because they had millions of years to learn fear
of human hunters with very slowly evolving skills;
most big animals of the former three continents
didn't survive, because they had the misfortune
that their first encounter with humans was a sudden
one, with fully modern skilled hunters.
To me, the case is already proved. How many more
decades of unconvincing claims will it take to
convince the holdouts among my colleagues? I don't
know. It makes better newspaper headlines to report
"Wow!! New discovery overturns the established
paradigm of American archaeology!!" than to report,
"Ho hum, yet another reportedly paradigm-overturning
discovery fails to hold up."