Climatic issues alone were not enough to end the periods of development of the ancient Pueblo in the southwestern United States.
Drought is often blamed on the periodic disturbances of these Pueblo societies, but in a study with potential implications for the modern world, archaeologists found evidence that the slow build-up of social tensions likely played a substantial role in three upheavals. dramatic in the development of Pueblo.
The results, detailed in an article in Proceedings of the National Academy of Sciences, showed that farmers in Pueblo often persevere during droughts, but when social tensions increase, even modest droughts can spell the end of an era of development.
“Societies that are cohesive can often find ways to overcome climate challenges,” said Tim Kohler, archaeologist at Washington State University and corresponding author of the study. “But societies that are torn apart by internal social dynamics of all kinds – which could be differences in wealth, racial disparities or other divisions – are fragile because of these factors. So climate challenges can easily become very serious. . “
Archaeologists have long speculated on the causes of occasional upheaval in pre-Spanish societies created by the ancestors of contemporary Pueblo peoples. These ancestral communities of Pueblo once occupied the Four Corners region of the United States from 500 to 1300 where today Colorado borders Utah, Arizona and New Mexico.
Although these communities were often stable for many decades, they experienced several disruptive social transformations before leaving the region in the late 1200s. When more precise measurements indicated that droughts coincided with these transformations, many archaeologists decided that these climate challenges were their main cause.
In this study, Kohler collaborated with complexity scientists at Wageningen University in the Netherlands, led by Marten Scheffer, who showed that loss of resilience in a system approaching a tipping point can be detected by subtle changes in fluctuation patterns.
“These red flags turn out to be surprisingly universal,” said Scheffer, the study’s lead author. “They are based on the fact that slower recovery after small disturbances signals a loss of resilience.”
Other research has found signs of such a “critical slowdown” in systems as diverse as the human brain, tropical rainforests and ice caps as they approach critical transitions.
“When we saw the incredibly detailed data put together by the Kohler team, we thought it would be the ideal case to see if our metrics could detect when companies are getting unstable – which is quite relevant in the social context. current, “Scheffer said.
The research used ring analyzes of timber beams used for construction, which provided a time series of estimated logging activity over several centuries.
“This record is like a social thermometer,” said Kohler, who is also affiliated with the Crow Canyon Archaeological Center in Colorado and the Santa Fe Institute in New Mexico. “Cutting down and building trees is a vital part of these societies. Any deviation from the normal tells you that something is going on.”
They found that a weakened recovery from disruptions in construction activity preceded three major transformations of Pueblo companies. These slowdowns were different from other interruptions, which showed a rapid return to normal in the following years. Archaeologists also noted an increase in signs of violence at the same time, confirming that tension had likely increased and societies were on the verge of a tipping point.
This happened at the end of the period known as Vannier III, around AD 700, as well as at the end of the periods known as Pueblo I and Pueblo II, around 900 and 1140 respectively. Towards the end of each period there were also signs of drought. The results indicate that it is the two factors together – social fragility and drought – that have caused problems for these societies.
Social fragility was not at stake, however, at the end of the Pueblo III period in the late 1200s, when Pueblo farmers left the Four Corners, most moving far south. This study supports the theory that it was a combination of drought and conflict with outside groups that caused the Pueblo people to leave.
Kohler said we can still learn from what happens when climate challenges and social issues coincide.
“Today we face multiple social issues, including increasing wealth inequalities as well as deep political and racial divisions, just as climate change is no longer theoretical,” Kohler said. “If we are not ready to face the challenges of climate change as a cohesive society, there will be real problems.