Researchers mapped out one of the oldest-known baby booms in North American history.
The "growth blip" occurred among southwestern Native Americans between 500 and 1300 A.D. A crash in the baby boom is believed to have followed soon after, Washington State University reported.
To make their findings the researchers looked at data on thousands of remains from hundreds of sites across the U.S. The team assembled a detailed Neolithic Demographic Transition in which the area's stone tools reflect a cultural transition from cutting meat to pounding grain.
"It's the first step towards all the trappings of civilization that we currently see," Tim Kohler, WSU Regents professor of anthropology, said.
Maize is believed to have been grown in the region as early as the year 2000 B.C., by 400 B.C. the crop is believed to have made up 80 percent of the peoples' calories. At this time birth rates were on the rise, and continued to climb until 500 A.D.
Around 900 A.D. populations remained high but birth rates started to fluctuate. One of the largest-known droughts occurred in the Southwest occurred in the mid-1100s. Even in this time of conflict birth rates remained high.
"They didn't slow down -- birth rates were expanding right up to the depopulation," Kohler said. "Why not limit growth? Maybe groups needed to be big to protect their villages and fields."
"It was a trap," he said. "A Malthusian trap but also a violence trap."
The northern southwest contained about 40,000 people mid-1200s, but only 30 years later it was mysteriously empty. The population may have been too large to feed itself as the climate changed, causing the society to collapse. As people began to leave it would have been difficult maintain the social unity required for the population to defend themselves and obtain new infrastructure.
"Population growth has its consequences," the researcher said.
