Starting about 500 CE, in what is now the Four Corners region of the American Southwest, the early features of civilization, including food cultivation and storage, began to emerge. This was quickly followed, according to researchers, by a birth rate that exceeds the highest in the world today.

The research, published this week in the journal of the Proceedings of the National Academy of Sciences, examined a century’s worth of data on remains found in the region. It indicates a “growth blip” or baby boom that lasted 800 years, from 500 to 1300 CE. It appears to have been ended by a drought, which reduced populations in some regions to zero.

“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. “It illustrates the coupling and feedbacks between human societies and their environment,” said Alan Tessier, acting deputy division director in the National Science Foundation’s (NSF) Directorate for Biological Sciences, in a statement.

While many of the remains studied have long since been repatriated, the available data allowed Tim Kohler, an anthropologist at Washington State University (WSU), to put together a timeline of the Neolithic Demographic Transition in the area. It may be the most complete picture yet of any region’s transition to agriculture.

Researchers believe that corn was the primary crop in the region, grown as early as 2000 BCE. Initially, likely due to low productivity, populations were slow to respond. However, by 400 CE birth rates were on the rise and corn, known as maize, accounted for 80 percent of the population’s calorie intake.

People in the Sonoran Desert and Tonto Basin, in what is today Arizona, were the most advanced. Evidence shows that they had irrigation, ball courts and elevated mounds housing elite families. Birth rates were the highest in the North and East, in the San Juan Basin and northern San Juan regions of Northwest New Mexico and Southwest Colorado. The Northeastern people, according to Kohler, would have had more opportunity to expand agricultural lands.

Around 900 CE birth rates throughout the area began to fluctuate and then, in about 1100 CE one of the largest droughts in history hit the area, greatly diminishing its agricultural capacity. From the mid- mid-1000s to 1280 the birth rate remained high, but the number of farmers diminished and conflicts between groups began to rise.

“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.

The northern region of the area had a population of about 40,000 by the mid-1200s but no population at all by 1300. It is still not known, exactly what caused the rapid depopulation.

“Perhaps the population had grown too large to feed itself as the climate deteriorated. Then as people began to leave, that may have made it harder to maintain the social unity needed for defense and new infrastructure,” said Kohler.

Currently the Southwest has a large population but is facing another drought which could last a very long time. It remains to be seen to what extent history will repeat itself.