December 21, 2015
University of Wyoming students excavate a prehistoric rock shelter in the Big Horn
Mountains of northern Wyoming during the summer of 2015. Hearths excavated at sites
such as this provided many of the radiocarbon dates for new research showing that
hunter-gatherers in the region that is now Wyoming and Colorado grew at the same rate
as farming societies in Europe. (UW Photo)
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. The research is reported this week
in the Proceedings of the National Academy of Sciences (PNAS), a major scientific
journal.
“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 PNAS paper. “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 paper’s lead author 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 in the research.
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 -- around 0.04 percent -- 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.
While concluding that population growth held steady overall at about 0.04 percent
annually for thousands of years, the paper acknowledges that there were short-term
fluctuations in human growth rates in certain regions lasting from a few hundred to
1,000 years. The authors suggest further statistical analysis of radiocarbon dates
of human remains to study the mechanisms regulating population growth.
