Lecture 36: Comparing the World Zones
extinctions and the widespread use of ¿ restick farming demonstrate that even
where agriculture did not appear, humans could have a signi¿ cant impact on
their environments.The American world zone formed just 3 million years ago, when a large
fragment of the supercontinent of Laurasia (North America) touched a large
fragment of Gondwanaland (South America) at the isthmus of Panama. As
a result, this zone (uniquely) stretches from the Antarctic to the Arctic and
spans all major ecological and climatic
zones. As Jared Diamond has pointed out,
this north-south orientation means that
when humans arrived they found that most
migrations led them into new and unfamiliar
environments, in contrast to Afro-Eurasia,
where it was possible to migrate huge
distances east or west while remaining
in regions of roughly similar climate and
ecology. Did the north-south orientation
of the Americas slow the pace of change
here? Humans entered the Americas from
East Siberia, certainly by 13,000 years ago and maybe several millennia
earlier. As in Sahul, the sudden entry of humans into unfamiliar territory may
help explain the massive megafaunal extinctions. The removal of so many
large species of mammal may have had a signi¿ cant impact on American
history because it meant that there could be no American equivalent of the
“secondary products revolution.”The Paci¿ c world zone formed a huge island archipelago whose communities
were separated by hundreds or thousands of miles of open sea. Each island
had distinctive features and therefore a distinctive history. But all (except
New Zealand) were small. (As Jared Diamond has pointed out, the diverse
ecologies of different Paci¿ c islands set up a wonderful series of natural
experiments in the impact of environment on human history.) The Paci¿ c
world zone was not occupied until the later Agrarian era. It was settled by
migrants who brought knowledge of farming and superb navigational skills.
It used to be assumed (for example, by Norwegian scholar and adventurer
Thor Heyerdahl) that the Polynesians came from the Americas. However,Estimates of the
population of the
Americas 500 years ago
range widely from about
40 million to as high as
about 100 million.