LARAMIE, WYOMING—Science Magazine reports that Robert Kelly of the University of Wyoming and his colleagues compiled more than 60,000 radiocarbon dates for artifacts from the United States and Canada. Then, assuming that the amount of radiocarbon data collected from a given region reflects its population at that time, the researchers made comparisons between the possible size of the populations over time and between regions. The study suggests that North American populations grew for about 2,000 years and peaked around A.D. 1150, then the size of the population decreased by at least 30 percent by 1500. Yet populations grew and declined in different regions at different times, likely reflecting regional climate shifts, disease, and warfare. “The entire continent is not in lockstep,” Kelly said. For example, the population of Cahokia, which is situated near the confluence of the Mississippi and Missouri rivers, had an estimated population of more than 10,000 by A.D. 1100. Droughts are thought to have brought about a reduction in crops, population collapse, and migration to other regions, leading to the abandonment of Cahokia by 1350. Overall, the population of North America began to rebound around 1450, the researchers suggest, but was then decimated by disease, violence, and loss of territory following the arrival of Europeans. For more on Kelly's efforts to compile radiocarbon dates for material excavated across North America, go to "Save the Dates."
