In the July issue of the journal Geology, a team of researchers has suggested that the climate phenomenon known as El Nino has been a contributing factor in the rise and fall of ancient civilizations in Peru. Using archeological evidence from sites along the Peruvian coast, scientists from the University of Maine, Yale University, University of Pittsburgh and University of Miami suggest that the fate of organized Peruvian societies may be related to environmental changes caused by flood cycles starting about 5,000 years ago.
Daniel Sandweiss of the UMaine Department of Anthropology and Institute for Quaternary and Climate Studies (IQCS), is lead author of the article which describes changes in mollusk assemblages in midden heaps. Co-authors are Kirk Maasch of the UMaine Dept. of Geological Sciences and IQCS, Richard L. Burger of Yale University, James B. Richardson III and Harold B. Rollins of the University of Pittsburgh and Amy Clement of the University of Miami.
“We found that there was a change in the frequency of El Nino events about 3,000 years ago and that this correlates in time with cultural change,” says Sandweiss.
Other researchers have reported similar evidence from Central and North America, Greenland and the Middle East that suggests a relationship between climate and culture. “We don't argue that climate is the driving force behind cultural development, but the evidence points to a strong contributory role,” says Sandweiss.
Mollusks are good environmental indicators, Sandweiss adds, because they are sensitive to rising temperatures. Since 1982, one species, Mesodesma donacium, has been driven further south, likely as a result of El Nino events. Researchers have shown that another species that lives further south along the Chilean coast, Choromytilus chorus, dies at an increasing rate when faced with water temperatures similar to those brought on by El Nino.
In ancient Peruvian sites, these two species were common in middens between 9 and 7 degrees south latitude but had disappeared by about 2,800 years ago. “The rapid disappearance of these species from northern Peruvian archaeological sites probably reflects an increase in the frequency of strong El Nino events to within the modern range of variability,” the Geology paper states.
Early cultural development in coastal Peru has been dated to just after the apparent onset of El Nino about 5,800 years ago. It is marked by large temple complexes and elaborate public art. These systems had collapsed by the period between 2,900 and 2,800 years ago. The longest lasting of the temple complexes is also the only one in which evidence of flood mitigation has been found.
“By doing something proactive about El Niño, the leaders of this site (Manchay Bajo) appear to have been making an appropriate response to changes in their environment. Whether or not it really worked for the most serious effects of El Niño we can't say, but if it did, that could have given them more long-lasting control,” Sandweiss suggests.
“The close temporal correlation between these changes in El Nino frequency and the construction and abandonment of monumental temples in this region suggests that climate and culture are here linked in a complex causal network,” the authors wrote.
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