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A new theory of Easter Island's collapse: rats and STDs

The previous best theory of Easter Island's demise was that thoughtless deforestation ruined them. New evidence suggests stowaway rats were responsible for the deforestation and for keeping the islanders very well fed. It wasn't until explorers found them and boned them and gave them sexually transmitted diseases that things really fell apart.

What Happened On Easter Island — A New (Even Scarier) Scenario : Krulwich Wonders... : NPR

Here's their argument: Professors Hunt and Lipo say fossil hunters and paleobotanists have found no hard evidence that the first Polynesian settlers set fire to the forest to clear land — what's called "large scale prehistoric farming." The trees did die, no question. But instead of fire, Hunt and Lipo blame rats.

Polynesian rats (Rattus exulans) stowed away on those canoes, Hunt and Lipo say, and once they landed, with no enemies and lots of palm roots to eat, they went on a binge, eating and destroying tree after tree, and multiplying at a furious rate. As a reviewer in The Wall Street Journal ,

In laboratory settings, Polynesian rat populations can double in 47 days. Throw a breeding pair into an island with no predators and abundant food and arithmetic suggests the result ... If the animals multiplied as they did in Hawaii, the authors calculate, [Easter Island] would quickly have housed between two and three million. Among the favorite food sources of R. exulans are tree seeds and tree sprouts. Humans surely cleared some of the forest, but the real damage would have come from the rats that prevented new growth.

As the trees went, so did 20 other forest plants, six land birds and several sea birds. So there was definitely less choice in food, a much narrower diet, and yet people continued to live on Easter Island, and food, it seems, was not their big problem.