What Can We Learn From Ancient Southwest’s Baby Boom?

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Aeial view of Pueblo Bonito, Chaco Canyon, Not licensed for use in commercial settings
Sites like Pueblo Bonito in northern New Mexico reached their maximum size in the early A.D. 1100s, just before a major drought began to decrease birth rates throughout the Southwest. Photo: Scott Haefner, scotthaefner.com

Researchers at Washington State University have detailed one of the greatest baby booms in North American history – a centuries-long “growth blip” among southwestern Native Americans between 500 to 1300 A.D.

It is suspected that the advancements made in farming and food storage at the time had likely progressed the population to a point where birth rates “exceeded the highest in the world today”, the researchers write in the Proceedings of the National Academy of Sciences.

However, after the steady rise in population, “a crash followed”, said Tim Kohler, WSU Regents professor of anthropology, offering a warning sign to the modern world about the dangers of overpopulation.

“We can learn lessons from these people,” said Kohler, who coauthored the paper with graduate student Kelsey Reese.

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. While many of the remains 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.

From 400 B.C. to A.D. 500, maize (corn) had provided about 80% of the region’s calories. The birth rates at this time varied across the region. People in the Sonoran Desert and Tonto Basin, in what is today Arizona, could be considered 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.

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, with continued population growth and limited resources similar to what Thomas Malthus predicted for the industrial world in 1798.

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.

The northern Southwest had as many as 40,000 people in the mid-1200s, but within 30 years it was empty, leaving a mystery that has consumed several archaeological careers, including Kohler’s. Perhaps the population got too large to feed itself as climates deteriorated, but as people began to leave, it would have been hard to maintain the social unity needed for defense and new infrastructure, said Kohler.

Whatever the reason, he said, the ancient Puebloans point up that, “population growth has its consequences.”

Read More: Ancient baby boom holds a lesson in over-population

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