Scientists have long used tree rings to examine the climatic history of the locations tree have grown. A new analysis shows how tree rings might also shed light on the social and demographic movements of humans. 

The study, just published in Science Advances, identifies patterns of “exploration” and “exploitation” in pre-Hispanic peoples (A.D. 500-1400) through analysis of tree-ring data from more than 1,000 archeological sites in the American Southwest. Four periods of high investment in construction stand out, when well-known structures such as those in Chaco Canyon and Mesa Verde were built. Each of these peaks—termed periods of “exploitation”—is eventually terminated by a downturn in maize production. Human populations then have dispersed across the landscape and experiment with new locations and new organizational structures. (The exploration and exploitation dichotomy is a concept developed by complexity pioneer John Holland.)

“These are periods of exploration,” says SFI External Professor Tim Kohler, one of the study's co-authors. Eventually in each case, populations discover new productive locations and rebuild societies in them on slightly different terms, a process that can be thought of as cultural niche construction. 

Though the analysis draws from data collected in the American Southwest, the authors suggest that these patterns probably apply to Neolithic societies in other areas of the world, which likely faced similar problems of “how to coordinate ever-larger groups and how to avoid degrading local environments.” 

“For archaeologists, [this] method of data analysis and its conclusions are big steps forward,” says Kohler. “We are working on temporal resolutions of one year instead of decades, as is the norm for the Southwest, or a century or more, as for portions of the world relying on 14C dating.” 

Read the paper in Science Advances (April 1, 2016)