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Study tracks early Native American ‘baby boom’

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Mesa Verde was a center of southwestern civilization. Photo courtesy National Park Service.

Native American population history may offer lesson for modern society, as climate change may have caused subsequent crash

Staff Report

FRISCO — Everybody knows about the post-WWII baby boom, but there was another era when North America’s population swelled, as Native Americans in the Southwest shifted from hunting and gathering to agriculture.

The “growth blip” between about 500 and 1300 A.D. is probably linked with emerging early features of civilization — including farming and food storage — and birth rates may have “exceeded the highest in the world today,” according to research published in the journal Proceedings of the National Academy of Sciences.

But like so often in human history, the boom was followed by a crash, offering a warning sign to modern societies about the potential risks of overpopulation, according to Tim Kohler, an anthropologist at Washington State University, who co-authored the paper with WSU researcher Kelsey Reese.

“We can learn lessons from these people,” Kohler said, estimating that, at the peak of the population boom in the mid-1200s, the northern part of the southwestern region, encompassing the San Juan Basin and northern San Juan regions of what are now northwest New Mexico and southwestern Colorado, there were as many as 40,000 people living in the region.

But 30 years later, the area was nearly depopulated, leading to speculation that the population had grown too large to feed itself as the climate deteriorated.

The study looks at a century’s worth of data on thousands of human remains found at hundreds of sites across the Four Corners region of the Southwest.

“This research reconstructed the complexity of human population birth rate change and demographic variability linked with the introduction of agriculture in the Southwest U.S.,” says Alan Tessier, acting deputy division director in the National Science Foundation’s (NSF) Directorate for Biological Sciences, which supported the research through NSF’s Dynamics of Coupled Natural and Human Systems (CNH) Program.

“It illustrates the coupling and feedbacks between human societies and their environment.”

While many of the remains studied have been repatriated, the data let Kohler assemble a detailed chronology of the region’s Neolithic Demographic Transition, in which stone tools reflect an agricultural transition from cutting meat to pounding grain.

“It’s the first step toward all the trappings of civilization that we currently see,” says Kohler.

Maize, which we know as corn, was grown in the region as early as 2000 B.C.

At first, populations were slow to respond, probably because of low productivity, says Kohler. But by 400 B.C., he says, the crop provided 80 percent of the region’s calories.

Crude birth rates–the number of newborns per 1,000 people per year–were by then on the rise, mounting steadily until about 500 A.D.

The growth varied across the region.

People in the Sonoran Desert and Tonto Basin, in what is today Arizona, were more culturally advanced, with irrigation, ball courts, and eventually elevated platform mounds and compounds housing elite families.

Yet birth rates were higher among people to the North and East, in the San Juan Basin and northern San Juan regions of Northwest New Mexico and Southwest Colorado.

Kohler said that the Sonoran and Tonto people eventually would have had difficulty finding new farming opportunities for many children, since corn farming required irrigation. Water from canals also may have carried harmful protozoa, bacteria and viruses.

But groups to the Northeast would have been able to expand maize production into new areas as their populations grew.

Around 900 A.D., populations remained high but birth rates began to fluctuate.

The mid-1100s saw one of the largest known droughts in the Southwest. The region likely hit its carrying capacity.

From the mid-1000s to 1280, by which time all the farmers had left, conflicts raged across the northern Southwest but birth rates remained high.

“They didn’t slow down,” said Kohler. “Birth rates were expanding right up to the depopulation. Why not limit growth? Maybe groups needed to be big to protect their villages and fields.’

Whatever the reason, he concluded, the story of the ancient Puebloans show that population growth has clear consequences.

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