Population size greatly affects the human condition but is difficult for archaeologists to estimate. For the Neolithic North American Southwest, we use indirect methods to estimate birth rate and life expectancy, two major factors determining population size. The population boom usually accompanying the introduction of cultivated plants and animals, the “Neolithic Demographic Transition,” was slow to emerge here and was marked by considerable subregional variability in birth rate. This variability is likely related to differing morbidities and availability of agricultural lands in various subregions. In common with many Neolithic peoples, pre-Hispanic Puebloans experienced very high birth rates, especially between A.D. 500 and 1300 when they possibly exceeded the highest in the world today, and quite low life expectancy at birth. 
 
 Abstract 
 
 In many places of the world, a Neolithic Demographic Transition (NDT) is visible as a several-hundred-year period of increased birth rates coupled with stable mortality rates, resulting in dramatic population growth that is eventually curtailed by increased mortality. Similar processes can be reconstructed in particular detail for the North American Southwest, revealing an anomalously long and spatially variable NDT. Irrigation-dependent societies experienced relatively low birth rates but were quick to achieve a high degree of sociopolitical complexity, whereas societies dependent on dry or rainfed farming experienced higher birth rates but less initial sociopolitical complexity. Low birth rates after A.D. 1200 mark the beginning of the decline of the Hohokam. Overall in the Southwest, birth rates increased slowly from 1100 B.C. to A.D. 500, and remained at high levels with some fluctuation until decreasing rapidly beginning A.D. 1300. Life expectancy at 15 increased slowly from 900 B.C. to A.D. 700, and then increased rapidly for 200 y before fluctuating and then declining after A.D. 1400. Life expectancy at birth, on the other hand, generally declined from 1100 B.C. to A.D. 1100/1200, before rebounding. Farmers took two millennia (∼1100 B.C. to ∼A.D. 1000) to reach the carrying capacity of the agricultural niche in the Southwest. 

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– A baby boom among Native Americans that started some 1,500 years ago was so massive that birth rates likely surpassed the highest found anywhere in the world today, according to researchers scouring data tied to thousands of human remains found at hundreds of sites across the region where Arizona, New Mexico, Colorado, and Utah meet. It was a centuries-long rise followed by a sudden and dramatic fall, one that should serve as a warning sign about the dangers of overpopulation, the anthropologists conclude. "We can learn lessons from these people," one of the paper's authors says in a news release. As early as 2000 BC, corn was grown in the region, though it wasn't until 400 BC that consumption of it jumped. It become the dominant calorie source, and propelled birth rates to peak levels around 500 AD, by which time Discover reports the people were utilizing "two hallmarks of civilization: settled agriculture and food storage." Per the study published in the Proceedings of the National Academy of Sciences, that birth rate then "remained at high levels with some fluctuation" for centuries. But by the mid-1100s, a terrible drought hit hard, and conflicts arose; still the birth rate stayed high right until 1280, by which time farmers seem to have had enough and fled. Within 30 years the area of 40,000 people was empty. The population may have simply grown too large to feed itself, researchers surmise, leaving behind a lesson: Overpopulation is not sustainable.