Prehistoric human populations of hunter-gatherers in the region that is now Wyoming and Colorado grew at the same rate as farming societies in Europe, according to a new radiocarbon analysis involving University of Wyoming researchers. The findings challenge the commonly held view that the advent of agriculture 10,000-12,000 years ago accelerated human population growth.
     "Our analysis shows that transitioning farming societies experienced the same rate of growth as contemporaneous foraging societies," says Robert Kelly, UW professor of anthropology and co-author of the study. "The same rate of growth measured for populations dwelling in a range of environments, and practicing a variety of subsistence strategies, suggests that the global climate and/or other biological factors - not adaptability to local environment or subsistence practices - regulated long-term growth of the human population for most of the past 12,000 years."
     The lead author of the research is Jabran Zahid of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass. Erick Robinson, a postdoctoral researcher in UW's Department of Anthropology, also participated.
     While the world's human population currently grows at an average rate of 1 percent per year, earlier research has shown that long-term growth of the prehistoric human population beginning at the end of the Ice Age was just 0.04 percent annually. That held true until about 200 years ago, when a number of factors led to higher growth rates.
     For their research, the UW and Harvard-Smithsonian scientists analyzed radiocarbon dates from Wyoming and Colorado that were recovered predominantly from charcoal hearths, which provide a direct record of prehistoric human activity.
     For humans in the Wyoming and Colorado region between 6,000 and 13,000 years ago -- people who foraged on animals and plants to survive - the analysis showed a long-term annual growth rate of 0.041 percent, consistent with growth that took place throughout North America. During that same period, European societies were farming or transitioning to agriculture, yet the growth rate there was essentially the same. "The introduction of agriculture cannot be directly linked to an increase in the long-term annual rate of population growth," the researchers wrote.
     In general, similar rates of growth were measured for prehistoric human populations across a broad range of geographies and climates, the scientists say. "This similarity in growth rates suggests that prehistoric humans effectively adapted to their surroundings such that region-specific environmental pressure was not the primary mechanism regulating long-term population growth." Instead, the factors that controlled long-term population growth during that period likely were global in nature, such as climate change or biological factors affecting all humans, such as disease.

Edited from University of Wyoming PR (21 December 2015)