Students excavate a rock shelter in the Bighorn Mountains in summer 2015. The hearths excavated at sites such as this provided many of the radiocarbon dates for a study looking at population trends for prehistoric people. (courtesy University of Wyoming)
There is a long-held belief that agriculture changed everything for human beings. Agriculture meant a stable food supply, surpluses, an ability to thrive despite natural environmental changes.
But a new study, published in December in the Proceedings of the National Academy of Sciences of the United States, challenges the idea that the start of agriculture 10,000 to 12,000 years ago is responsible for boosting the human population growth rate. Radiocarbon dating analysis shows that prehistoric hunter-gatherer human populations in what is now Wyoming and Colorado grew at the same rate as farming societies in Europe.
“It’s pretty mind blowing,” said Erick Robinson, a University of Wyoming post-doctoral researcher on the project.
Bob Kelly, professor of anthropology at the University of Wyoming, was looking at the relationship between prehistoric population sizes and climate change, using radiocarbon dating on charcoal found in prehistoric hearth sites. Scientists can use this data to estimate population growth rates for a given period of time. Previously, scientists studied population data over short time spans, like 500 years. Looking at population data is not new. What is new is the UW research team looked at growth rate across a large span of time instead of just 500 years.
When looking at the bigger picture, the two populations — hunter-gatherer societies and agriculture communities — grew at the same rate.
“It’s a brand new view,” Robinson said. “We were very, very surprised.”
Kelly said he expects there will be some disbelief as people learn about the findings. Many will want to double-check the research because they don’t believe it, and that’s fine because it’s all part of the scientific process. Robinson said right now he’s mostly heard amazement in the scientific community, but the study is so new that people are still taking it in.
Kelly looked at research from around the world and found the growth rate they saw in Wyoming kept appearing, even after the appearance of agriculture in Europe. “I said ‘That can’t be right. It doesn’t make sense.’”
Today, the world’s human population grows at an average rate of 1 percent per year. Prehistoric populations that relied on hunting and foraging grew at about .04 percent annually. Anthropologists agreed that the only major changes in human population growth rates were directly tied to the onset of agriculture then the industrial revolution. This finding, however, means that only in the 19th century did human growth rates change significantly.
Why would the growth rate remain the same all over the world, whether a society was hunter-gather or agriculture? “Quite frankly, we don’t know the answer to that,” Kelly said.
The similar overall population trajectories suggests it wasn’t agriculture that influenced growth, but something else — perhaps global climate change, or a biological mechanism found in all humans — something that puts the population into long-term equilibrium, Robinson said.
“It has to be something common to the human species that regulates these long-term growth rates,” he said.
The data sets the foundation for testing a variety of other hypotheses to determine what did regulate populations across the continents, Robinson said.
Archaeologists want to look at other states and see if the same trends occur in the data. Aside from gaining a better understanding of ancient people, the study provides a record going back 13,000 years showing how people adapted — or didn’t — to changes in their environment. That information is useful as people today adapt to a changing climate, Robinson said.
The study was funded by a National Science Foundation grant. The paper’s lead author is Jabran Zahid of the Harvard-Smithsonian Center for Astrophysics.
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