We estimate population size around Chaco for three periods

What is it about?

We develop a technique to estimate how many people lived in the Chaco Regional System at three periods, using regularities in the relationship between population size and maize production established for another portion of the Southwest. Our approach suggests that populations were larger than previously thought, and underscores how rapidly the system grew in the mid-to-late AD 1000s. That in turn allows us to draw on other cross-cultural regularities to underscore that the famous Chacoan roads and signaling systems likely had functional import, given the large and very dispersed populations we reconstruct.

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Why is it important?

Southwestern archaeologists have been long blessed with a high-resolution tree-ring record that yields dates and allows us to reconstruct precipitation and (with somewhat lower precision) temperatures, on annual bases. Unfortunately we have attended less to the significant low-frequency trends in climate over the last few thousand years. Specifically, other recent research synthesizing pollen records suggests that cooler summers and wetter winters than today prevailed on average during Chaco's rise (and indeed during much of the first millennium AD). Such conditions—favorable for the growth of both maize and human populations—were rapidly dissipating in the 1100s. These low-frequency trends help explain the high populations we reconstruct, as well as why the Chaco Regional System began to fail in the mid-1100s.

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