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 But these hunter-gatherers proceeded to behave like an "invasive
species," with their population surging then crashing as they
relentlessly depleted natural resources. Only much later did people
muster exponential population growth after forming fixed settlements
with domesticated crops and animals.
Those are the findings of research published on Wednesday in the
journal Nature that provides the most comprehensive look to date of
the peopling of South America, the last habitable continent
colonized by humankind.
The researchers identified two distinct colonization phases: the
first unfolding about 14,000 to 5,500 years ago, with the human
population hitting around 300,000; the second occurring about 5,500
to 2,000 years ago, with the population reaching about a million.
 "Humans are just like any other invasive species," Stanford
University biology professor Elizabeth Hadly said. "If we use up our
resources, we will decline. It is stating the obvious, but our study
shows that even over vast geographic areas such as continents,
humans can consume too much, too fast."
The researchers reconstructed the history of human population growth
in South America using radiocarbon-dating data from 1,147
archaeological sites.
Our species first appeared in Africa about 200,000 years ago, then
spread to Europe and Asia and eventually crossed into the Americas
roughly 15,000 to 20,000 years ago using a land bridge that once
connected Siberia and Alaska.
The first phase of colonization in South America coincided with the
extinction of many large animals including elephant relatives,
saber-toothed cats, big ground sloths, armadillos and huge
flightless birds.
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During this period, human populations underwent "boom-and-bust
cycles" as people exhausted local plant and animal resources,
Stanford anthropologist Amy Goldberg said.
Some people, particularly in certain Andes regions, began
domesticating animals and growing crops including squash and
peppers. But most remained nomadic.
About 5,000 years ago, people settled into stable societies,
launching 3,000 years of exponential growth when the continent's
population roughly tripled, Goldberg said.
"We find that it is the large settlements, not merely stable food
sources, that allow humans to 'conquer' their environment and grow
unbounded," Goldberg said.
"Most lived in modern Peru, Ecuador, and northern Chile, as well as
a smaller but substantial population of hunter-gatherers in
Patagonia."
(Reporting by Will Dunham; Editing by Sandra Maler)
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