(CN) — The Ancestral Puebloans lived throughout what is now the area surrounding the Colorado Plateau, from central New Mexico on the east to southern Nevada on the west, between 500 AD and 1300 AD. Much like modern day residents, their society experienced prolonged periods of wealth inequality, racial injustice and general unrest — which didn’t bode well.
These ills chipped away at societal cohesion until finally widespread crop failure caused by a drought coupled with raiding nomads was too much to bear. Despite recovering from past droughts, that final push sent them over the edge, when a critical mass of residents eventually threw in the towel and decided their community was no longer worth saving.
Researchers from Washington State University and Wageningen University in The Netherlands collaborated to determine what exactly caused these ancient peoples to abandon their homes after overcoming such hardship in the past. They published their findings in a new study Monday in the journal PNAS.
“For me this study has two important take-aways,” explained Tim Kohler, a Washington State University archeologist and author of the study, in an email. “First, what we archaeologists see as climatic crises for past societies are probably often problems that are caused in part by internal social issues. Second, though, it seems like the end of the PIII [Pueblo III community] in the northern Southwest (late 1200s) really does have an important climate-change component, though it may be abetted by the influx of nomadic hunter-gatherers who may have found the Pueblo peoples to be easy prey.”
In the past, many researchers believed the drought itself to be the death knell for the Pueblo peoples. However, new evidence gleaned from analyzing building materials shows that these societies persevered through numerous periods of drought, and it was only when social tensions rose to an unbearable level that residents found it preferable to simply move on.
The authors assembled time-series data of building activity showing that construction in these communities slowly declined over time, pointing to a growing fragility in their social cohesion. They show that status quo stability eventually declined, leading to increasing violence and wealth inequality among residents. Researchers believe it was the cumulative effect of these mounting tensions that doomed the Pueblo society, and a major drought coupled with raiding parties was merely the final blow.
By analyzing tree-ring-dated wood beams recovered from building sites, the team was able to group construction activity into four distinct periods, separated by intervals of minimal activity. Previous work found the high-activity periods to be clustered around good maize growing seasons, but after analyzing newer datasets the authors believe these periods were no better for growing maize than the down-years, thus something else was at work.
“Radical transitions may be driven by collapse of trust in the old way of doing things, including its rituals and social and physical structures. Such distrust can be self-propagating, cascading contagiously through the society,” said the authors in their study. “One obvious stabilizing force is the vested interest of an elite who benefits from the status quo and uses her capital to maintain it. A second stabilizer is the so-called ‘sunk-cost effect.’ This is a reluctance to abandon things in which much has been invested, even if it would be rationally better to abandon them.”
The tipping point for the last Pueblo society, Pueblo III, came around the year 1200 when the Pueblo farmers finally fled the Four Corners region of the southwest United States and moved south. The authors believe a combination of drought and conflict with outside groups finally prompted them to abandon their society once and for all.
Kohler explained that the ancestors of the Pueblo people were already beginning to leave the area in the early 1200s when the climate became unfavorable for maize, many of whom moved south around the year 1220. He said a volcano erupted in the Java area, bringing on a prolonged period of cold weather, which was too much for the already weakened society to withstand.
“Lots of Pueblo people sought refuge in big, walled, canyon-head sites or cliff dwellings around then,” Kohler said in an email. “Around the same time I think that raiding of Pueblos by the ancestors of the Navajo and Apache began. They were just starting to come in from the north. When climates turned seriously bad in the mid-1270s the remaining maize farmers called it quits and sought refuge.”