Ancient Southwest baby boomers offer lesson in overpopulation

TAOS, N.C., July 1 (UPI) -- In the 5th century, the native population of America's Southwest began expanding exponentially -- an ancient baby boom.

By studying a large collection of ancient human remains, researchers at Washington State University were able plot out the story of the Neolithic Demographic Transition, a time period when native populations began eating more grain and less meat.

Buoyed by their newfound diet of maize, which accounted for 80 percent of their diet, the Pueblo people of the modern day Four Corners region -- where Arizona, New Mexico, Colorado and Utah converge -- began having more and more children.

Thanks to agriculture and food storage, population growth continued for eight centuries. But by the year 1300, the once fertile agriculture lands of the Puebloans was lonely and abandoned. The once rapidly expanding Pueblo population -- still kicking as late as 1280 -- dissipated quickly and mysteriously.

"They didn't slow down -- birth rates were expanding right up to the depopulation," explained Washington State anthropology professor Tim Kohler. "Why not limit growth? Maybe groups needed to be big to protect their villages and fields."

Kohler, along with graduate student Kelsey Reese, authored the study the Puebloans boom and bust featured this week in the journal Proceedings of the National Academy of Sciences.

Although it's not entirely clear why the Puebloans vanished so quickly, Kohler argues that a changing climate likely prevented the land from sustaining a population that had grown too large. As natives abandoned the declining and now unstable population, the Puebloans were likely more and more vulnerable to attacks from the outside.

"It was a trap," Kohler said. "A Malthusian trap but also a violence trap" -- referring to Thomas Robert Malthus, a clergyman and economist of late 18th century who argued populations tend to outpace their means of subsistence until war, famine and epidemic help them hit the brakes.

"We can learn lessons from these people," Kohler added.

There's an alternative, too, Kohler says. The Sonoran and Tonto people to the south had less stable water supplies. Because they recognized the inability of the land and climate to support more people, argues Kohler, they refrained from population expansion and avoided catastrophe.