In what may hold lessons for modern society, scientists have sketched out one of the greatest baby booms in North American history, a centuries-long "growth blip" among south-western Native Americans between 500 and 1300 A.D.
It was a time when the early features of civilization, including farming and food storage, had matured to a level where birth rates likely exceeded the highest in the world today, said the researchers.
"Then a crash followed, offering a warning sign to the modern world about the dangers of overpopulation," said Tim Kohler, an anthropologist at Washington State University (WSU) in the US.
"We can learn lessons from these people," he said.
Maize, which we know as corn, was grown in the region as early as 2000 B.C.
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At first, populations were slow to respond, probably because of low productivity, said Kohler, but by 400 B.C. the crop provided 80 percent of the region's calories.
Crude birth rates were by then on the rise, mounting steadily until about 500 A.D.
Around 900 A.D., populations remained high but birth rates began to fluctuate.
The mid-1100s A.D. saw one of the largest known droughts in the southwest. The region likely hit its carrying capacity.
"They didn't slow down. 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," said Kohler.
It was a trap, however.
The northern southwest had as many as 40,000 people in the mid-1200s, but within 30 years it was empty, leaving a mystery.
"Whatever the reason, the ancient Puebloans show that population growth has clear consequences," Kohler noted.
The findings appeared in the journal Proceedings of the National Academy of Sciences.
