The rats of Easter Island

3 minute read

A new article in Science is claiming that the Easter Island population did not have a long duration on the island, and probably did not cause its own population crash.

There is a LiveScience news account by Ker Than, with some great quotes:

Lipo thinks the story of Easter Island's civilization being responsible for its own demise might better reflect the psychological baggage of our own society than the archeological evidence.
"It fits our 20th-century view of us as ecological monsters," Lipo said. "There's no doubt that we do terrible things ecologically, but we're passing that on to the past, which may not have actually been the case. To stick our plight onto them is unfair."

Ann Gibbons' Science news article on the paper is also pretty helpful.

[Terry] Hunt and co-author Carl Lipo of California State University, Long Beach, took eight samples of wood charcoal from the bottom of the oldest known archaeological site on the island, called Anakena. When they got radiocarbon dates that clustered at about 1200 C.E., Hunt at first assumed the dates were wrong and put them aside. But later he and Lipo decided to scrutinize all earlier dates from Anakena, to make sure they did not contain carbon from marine organisms or old wood, which can skew dates too old. After discarding what they considered unreliable dates, the pair found a high probability (50%) for the first human settlement starting just after 1200 C.E. The evidence does not rule out an occupation at 1000 C.E., but the probability is very low, says Hunt. The new dates are a "significant improvement" over the old ones, says radiocarbon-dating expert Tim Higham of Oxford University, U.K.
Although several researchers welcome the rigorous analysis of dates, not everyone agrees with the criteria the team used. "Some of his criteria are fair; others are not," says zoologist David Steadman of the Florida Museum of Natural History in Gainesville, whose 1000 C.E. dates for Anakena were left in the pair's analysis.
The new results are in keeping with a trend in the past decade toward later dates for colonization of some of the outermost Pacific islands. "This is an important paper, because it is part of a revision on the chronology of the Pacific that shows there is a big gap between settling west Polynesia [e.g., Samoa] and the marginal areas of south and east Polynesia," such as New Zealand, says archaeologist Atholl Anderson of the Australian National University in Canberra.

And then there were the rats. From LiveScience:

"The collapse was really a function of European disease being introduced," Lipo said. "The story that's been told about these populations going crazy and creating their own demise may just be simply an artifact of [Christian] missionaries telling stories."
At a scientific meeting last year, Hunt presented evidence that the island's rat population spiked to 20 million from the years 1200 to 1300. Rats had no predators on the island other than humans, and they would have made quick work of the island's palm seeds. After the trees were gone, the island's rat population dropped off to a mere 1 million.

Of course, the reason why this is a story is that it cuts against the Diamond collapse explanation.

Thinking about it, islands just aren't very good analogies for most human societies. A group of people get to an island; there's no disease that they didn't bring with them; there are plenty of animals and plants with no natural resistance to human predation. Humans can have a pretty high intrinsic growth rate under those circumstances -- 3 kids per women can take your group from 20 to 60,000 in 400 years.

Now what do you do? Malthusian dynamics are not our fault, especially when the rats get there first.


Gibbons A. 2006. Dates revise Easter Island history. Science 311:1360. DOI link

Hunt TL, Lipo CP. 2006. Late colonization of Easter Island. Science (published online) Abstract