The invention of agriculture changed humans and the environment forever, and over thousands of years, the practice originated independently in at least a dozen different places. But why did agriculture begin in those places, at those particular times in human history?
Using a new methodological approach, Colorado State University and Washington University in St. Louis researchers have uncovered evidence that underscores one long-debated theory: that agriculture arose out of moments of surplus, when environmental conditions were improving and populations lived in greater densities.
The first-of-its-kind study, “Hindcasting global population densities reveals forces enabling the origin of agriculture,” published in the June 4 issue of Nature Human Behaviour, lends support to existing ideas about the origins of human agriculture.
Bruno Vilela, postdoctoral researcher in biology in Arts & Sciences at Washington University in St. Louis, is a first author on this study. Other Washington University co-authors include Carlos Botero, assistant professor of biology, and postdoctoral researcher Ty Tuff.
Predicting into the past
Studying the depths of human history is challenging, as little data are available when looking back tens of thousands of years. Scientists typically rely on archeological evidence, but getting a broad picture is difficult because archeological digs cover relatively small areas.
To overcome these limitations, the researchers modeled correlations between the environment, cultural traits and population densities of relatively recent foraging societies, which used hunting, fishing and gathering to obtain food.
Among the factors they considered as possible predictors of population density: environmental productivity; environmental stability; the average distance traveled when people in a community moved to a new location; whether people owned land or other resources; and distance to the nearest coast.
This model, the team found, did a remarkably good job at predicting recent population densities, which led the researchers to pair the model with data on past climate. In doing so, they could hindcast — or predict into the past — the potential population density of the entire globe dating back thousands of years.
This study was the first to produce maps of potential population densities dating back as far as 21,000 years. The researchers used these maps to examine conditions that existed in each of the 12 centers of origin, at the point in time that agricultural practices began.
Although the centers of origin varied in time by thousands of years and ranged from the New Guinea Highlands to Central America and the Middle East, they all had one thing in common: improving environmental conditions and the potential for higher population densities.
Researchers believe that improving environmental conditions may have allowed people the luxury of tinkering with new ideas and that having more people living in one place would allow ideas to be shared and honed, with sparks of innovation following.
The research team is now exploring other applications for the maps they produced.
This story is adapted from a news release by Colorado State University.