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Hundreds of monumental skulls are located on the coast of a remote Pacific island, Rapa Nui, or Easter Island. Settled by a small group of Polynesian hunters about 900 years ago, it’s a fascinating place that has been the subject of fierce debate about how complex societies can sometimes fail catastrophically.
Some experts, such as geographer Jared Diamond in his 2005 book, “Collapse,” have used Easter Island as a cautionary example of how the exploitation of limited resources can lead to catastrophic population decline, ecological devastation and cultural destruction.
Other researchers suggest the opposite – that Easter Island is a story of how isolated people created a sustainable system, allowing a small but stable population to thrive for centuries until the first contact with early European colonial powers. in the 18th century.
Now, research using remote sensing data and machine learning to map evidence of island farming offers a new clue that could help solve the mysterious disappearance of the island’s original civilization. The new finding suggests that the island was not densely populated, making ecological collapse less likely.
“All these pieces of evidence that have been collected over the last 15 or 20 years have kind of started to throw a wrench” in the story of the disaster, said Dr. Dylan Davis, lead author of the study published Friday in the journal Science Advances.
“And this is what this paper builds on.”
The inhabitants of Easter Island used rock gardens
Rapa Nui, part of present-day Chile, is more than 2,000 kilometers (1,242 miles) from the nearest inhabited island of Pitcairn and about 3,700 kilometers (2,300 miles) from the South American mainland, according to the study.
Davis, a postdoctoral research fellow at the Columbia School of Climate’s Lamont-Doherty Earth Observatory, and his team focused on farming practices to understand how much the island’s population could support. At 163 square kilometers (63 square miles), it is slightly smaller than Washington, DC.
The rock gardens covered up to 21.1 square kilometers (8.1 sq mi) and could have housed up to 17,000 people, previous research suggested. The February 2013 finding added to the idea that humans drained Rapa Nui’s limited resources.
Archaeologists have identified remains of rock gardens where the islanders would have grown sweet potatoes and other crops. The scattered and crushed rocks make the land more productive by adding and sealing in nutrients and moisture and protecting young plants from wind – an ancient farming technique also known as rock mulching.
However, in the new study, Davis and his colleagues found that the maximum number of people on Rapa Nui was nearly 4,000, less than a quarter of that higher estimate.
The team determined the much smaller population by using a machine learning model trained to recognize rock gardens from high-resolution infrared and near-infrared data collected by satellite.
“What we use in this paper is short-wave infrared imagery,” Davis said, “and it’s good for identifying very subtle differences in moisture content and mineral changes in the soil.”
The researchers found that rock gardens, identifiable by vegetation patterns and soil composition, covered about three-quarters of 1 square kilometer (0.4 square miles), and rock garden cultivation supported only about 2,000 people. When combined with estimates of the availability of fisheries and other seafood, the team believes that Rapa Nui could have a population of 3,901 people.
Davis said the team verified the model by hand, which was 83% accurate. “This is good right now because of the data available,” he said. “If there were any obvious errors, we removed them.”
Another limitation of the approach was the possibility that rock garden features could be destroyed over centuries.
What really happened on Easter Island?
Thegn Ladefoged, a professor of archeology at the University of Auckland in New Zealand who conducted the similar study published in February 2013 that led to the higher population estimate, said the latest research “provides new insights into Rapa Nui’s transport capacity ancient and possible population. estimates.”
“Their analysis of high-resolution infrared remote sensing data found that the total area of the rock garden was 5 to 20 times lower than previous estimates,” Ladefoged said via email. “This decision led to the integration of new remotely sensed data, data that was not available when we did our original study.” He was not involved in the new research.
“I agree with the authors that there was no pre-colonial extinction on Rapa Nui, and that the population did not collapse.”
However, Christopher Stevenson, professor of anthropology at the School of Global Studies at Virginia Commonwealth University, said the machine learning methodology was “far from clear and not well evaluated.”
“The authors try to say how their approach is vastly superior to past work without actually showing how they handle the complexities of the data set,” Stevenson said via email.
The belief that the island was once home to a population of thousands of people stems from the assumption that it would take more than 800 to build and move the large number of giant stone statues or moai that were built around the island.
However, a study in January 2022 suggested that it may not require as much muscle power as previously thought. Additionally, while it was initially thought that the islanders partially cut down trees to move the carved heads, a study in January 2017 suggested that the native palm vegetation was burned to make the soil more fertile.
“Ultimately, we have no evidence that thousands and thousands lived there. In fact, when the Europeans first make contact with the Rapa Nui people, they only report seeing maybe 3,000 or 4,000 people and they report that people were in good spirits,” said Davis.
“And then the real population collapse happens, which is probably due to exposure to disease.”
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