Rats, Not Recklessness, May Have Done Easter Islanders In

By Valerie Ross | September 19, 2011 5:45 pm


Enormous stone statues, called moai, on Easter Island

What’s the News: Easter Island is often held up as an example of what can happen when human profligacy and population outpace ecology: Wanton deforestation led to soil erosion and famine, the story goes, and the islanders’ society declined into chaos and cannibalism. But through their research on Easter Island, paleoecologists Terry Hunt and Carl Lipo have unearthed evidence that contradicts this version of events. The Polynesian settlers of Easter Island prospered through careful use of the scant available resources, they argue in their new book The Statues That Walked; the island’s forests were done in not by greedy humans, but by hungry rats.

What’s the Context:

  • The usual tale of Easter Island’s demise, originated by scientists in the 1990s and popularized in Jared Diamond’s book Collapse, suggests that the island’s residents cut down trees to clear farmland and to use in the transport of the enormous stone statues for which the island is famous. This deforestation threw the island’s ecological systems out of whack—which led the populace to make more statues in an effort to placate the gods, leading to more deforestation, and so on.
  • Effectively stranded 1,500 miles from the nearest populated island, this version of events says, the Easter Islanders starved—they resorted to cannibalism for lack of other food, some scientists suggest—and the population crashed. When the first European ship arrived in 1772, nearly no trees and perhaps three thousand people remained.
  • Hunt and Lipo came to the Easter Island—now called by its original name, Rapa Nui—to glean more knowledge about the island’s archaeology, not to rewrite its history. When they carbon dated samples from the island’s oldest settlement, however, the researchers dug up surprising evidence, detailed in a 2006 paper in Science: The samples suggested Polynesian settlers didn’t arrive there until around 1200 AD, 800 years later than earlier studies estimated.
  • This revised date posed another problem: It suggested that the deforestation of Rapa Nui started not centuries after the settlers arrived, but decades—meaning that deforestation was fairly immediate, not the eventual result of a heedless, ever-expanding populace. So the scientists kept digging, and their continued work forms the basis of their new theory.

What’s the Theory:

  • The island’s statues, which weigh as much as 80 tons, weren’t rolled into place on tree trunks, Hunt and Lipo argue. Instead, the inhabitants, called the Rapanui, “walked” the statues into place, with what essentially amounts to a gigantic version of the rocking, shuffling way one might move a refrigerator across the kitchen. (The scientists did some experiments to test out the idea, and from those results estimate that it would have taken perhaps 20 people to walk the statues.)
  • The Rapanui undoubtedly cut down some trees, the scientists write, but the deforestation was likely due instead to the Polynesian rat, which stowed away on their ships when they left Polynesia and whose bones have been found on the island. At the rate rats reproduce, their population would have quickly reached a few million. These hungry rodents would then have eaten the palm seeds, preventing the forest from regenerating. This series of events—stow-away rats find a predator-free island home, their multitudinous offspring eat seeds and tree sprouts, local forests shrink drastically—played out on Hawai’i and other Pacific islands, so seems likely that it happened on this island as well.
  • In fact, the researchers contend, the Rapanui cleverly made use of the sparse natural resources available, such as using rocks to fertilize poor soil and building wind breaks to keep their farm plots from drying out.

What’s the Verdict:

  • As Hunt told Smithsonian magazine, the collapse of Rapa Nui’s civilization and ecology “was a synergy of impacts,” with no one factor explaining the decline in its entirety. Hunt and Lipo’s tale is sound and compelling—but more evidence will ultimately tell whether one version of events, or elements of both, account for the island’s demise.
Image courtesy of Drozdp / Wikimedia Commons
CATEGORIZED UNDER: Environment, Human Origins, Top Posts
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