A Comparative Analysis of Population Growth Rates in North America

Primary Author: Darcy Bird

Faculty Sponsor: Timothy Kohler


Primary College/Unit: Arts and Sciences

Category: Physical and Social Sciences

Campus: Pullman



Principal topic

When the climate improved at the start of the Holocene (ca. 11,650 years ago), human populations increased dramatically. Many researchers argue that the adoption of agriculture increased fertility to cause the Agricultural Demographic Transition (ADT), which would consequently lead to increased population growth. Zahid et al. 2016, however, found that Wyoming hunter-gatherers had a population growth rate of about 0.04% annually, which is comparable to agriculturalist growth rates. The goal of this research is to use the same methodology to calculate and compare hunter-gatherer and agriculturalist population growth rates.



I used radiocarbon summed probability distributions (SPDs) to represent population. My dataset includes all freely available radiocarbon dates in North America between 6,000 and 300 cal BP.  I used a linear regression and linear mixed effects model to calculate population growth rates. I directly compared the SPD growth rates between early agricultural adopters (before 2000 cal BP), late agricultural adopters (between 2000 and 500 cal BP), and non-agricultural societies. I also subdivided the agricultural sequences to include hunter-gatherer, horticulture, and agriculture phases, as applicable, to see if growth rate changes dramatically within each sequence between each phase.



I found that early agriculture sequences have a higher mean exponential growth rate than non-agricultural societies, while late agricultural adopters have a mean growth rate in between. These results contradict Zahid et al.’s conclusion that hunter-gatherer and agriculturalist societies have comparable growth rates. They also support the conclusion that the ADT prompted a dramatic population increase during the Holocene.