Ecology and Easter Island
Moai in Rano Raraku. Photo (cc) GliderKing.
Easter Island is one of the places I’d most like to visit. It’s history is a tragedy, one of eventual destruction at the hands of the modern world. From an engineering perspective the work that has gone into the creation and erection of the moai, the enigmatic statues, that seem to litter the island is stunning. Also, from looking at the pictures on Flickr, it looks like the entire island is a neatly mowed lawn and you’re never more than a few
metres yards from a frowning face — which makes it a very English idyll. It’s the lawn, or rather the deforestation, which is the subject of vigorous debate at the moment, as reported recently in the Independent.
The traditional story is that the island was settled around the middle of the first millennium AD. The population grew, built moai and chopped down forests to support growing population and the engineering work. Sometime in the 2nd millennium the island ran out of trees and the population collapsed with the culture falling into savagery. In 1722 when Dutchman Jacob Roggeveen found the island and isolated visits from Europeans occurred till 1862 when the Spanish, looking for workers to die their silver mines, made the population an offer it couldn’t refuse. The population fell from from two or three thousand at discovery to just one hundred and eleven by 1877.
The big question is: Were the people that Roggeveen found the typical population of the island, or were these people the survivors of a collapse that had occurred a century or two before?
One of the problems in archaeology is that you already know how the story ends. It’s what comes before that matters which makes it a bit like reading a novel backwards. One of the dangers of this is that interpretation of earlier periods is then often interpreted in a telelogical fashion. The past had to occur a certain way so that we end up here. To an extent this makes sense. A history of the Roman Empire that doesn’t conclude with its fall is going to difficult to reconcile with the divided Europe of today. But equally people living today don’t see their future as inevitable so that we end up wherever we are a century from now. That dynamic might well be clear to historians a thousand years in the future, but it’s not how we live our lives. So explanations of Easter Island’s history that are written in order that the ecology collapses may ignore the element of free will that islanders thought they had. In his article Rethinking the Fall of Easter Island Terry Hunt explores this problem.
The first question is over the colonisation date. Originally it was thought to be around AD 400 based on a radiocarbon date, but radiocarbon is a probability rather than a precise date. When people say something is carbon dated to AD 400, what they usually mean is there’s a 95% chance that the sample dates from AD 400 +/- around a century. That means one time in twenty the sample is misleading. Additionally there can be problems with contamination of carbon samples in the natural environment, so usually one date is not usually enough. In the case of Easter Island linguistic evidence suggested that divergence from other Polynesian languages occurred around AD 800, so this has been the more recent accepted date. This has been correlated by some radiocarbon samples, so it appears that more than one line of evidence points to this date.
Terry Hunt points out one of the features that makes Easter Island so interesting when he looks at the linguistic evidence. Usually in archaeology is makes no sense to identify a ‘culture’ with a biological group of people. People marry in or out of society. Equally ideas flow between cultures which means that what it means to be American or Chinese or Indian is constantly changing. Easter Island is isolated. The nearest inhabitable island is over 2000km away. This means the interaction with other peoples did not occur till 1722. With this lack of interaction with other Polynesian societies would the usual rules of linguistic dating apply? One of the features of interaction with other societies would be that norms would be exchanged so that some idiosyncratic changes in language would be subsumed by the wider network. Easter Island did not have this. Could the linguistic difference therefore be a matter of isolation? Instead he’s worked to see what other evidence for colonisation there is. He’s worked with Carl Lipo to re-examine the radiocarbon dates.
Radiocarbon dating is still being improved. Past processes generating carbon-14 in the atmosphere still aren’t fully understood. In the early days some periods like the Neolithic were moved wildly in chronology back and forth by a thousand years as evidence of changing background levels of carbon-14 in various periods was found. This information meant that some of the previously accepted radiocarbon dates were suspect. To their surprise they found that if modern models and sampling methods were applied to the island then the earliest colonisation dates would be in AD 1200. This would be around the time that deforestation occurred on the island. The accepted explanation of colonisation was that from AD 800 to AD 1200 the colonists had little ecological impact on the island and after AD 1200 something dramatic changed in Easter Island’s society. Hunt and Lipo argue that the big change was that this was when society on Easter Island started.
There’s some findings from elsewhere in the Pacific which would tie in nicely with these findings. The island of Rapa (also known as Rapa Iti to avoid confusing it with Rapa Nui — another name for Easter Island), over two thousand miles to the west, also appears to have been colonised around AD 1200. The argument is based on dates recovered from the Tangarutu Rock Shelter, which seems to have the oldest settlement remains. Douglas Kennett, leading the research at Rapa, suggests that the colonisation of the eastern Polynesia was in a late burst of activity.
What makes this particularly interesting from an outsider’s point of view is that passion is very close to the surface of the debate. The basic question is are the samples which yield carbon-dates earlier than AD 1200 from uncontaminated contexts? Instead the argument seems to be about modern attitudes to colonisation and ecology. The Independent quotes Bahn and Massey’s rebuttal of the re-dating in their recent article from the Rapa Nui Journal. Talking about those who argue for the late colonisation they say:
“They view the island through rose-coloured spectacles, choosing to believe that the community was thriving up to 1722 and that it was the Europeans who destroyed them.
“It is undeniable that many calamities befell the island thanks to European visits… but the Europhobic model ignores the mass of archaeological, oral, botanical and sedimentological evidence which documents the prehistoric transformation of the island by humans from pristine subtropical rainforest to a virtually treeless landscape.”
I’ll be interested to see how this develops. I’m inclined to agree with Bahn and Massey about prehistoric deforestation. Studies from other colonisations show that when humans arrive somewhere it dramatically alters the local ecosystem and the change can be catastrophic for the bits of ecosystem that taste nice when barbequed. At the same time It does seem that Hunt and Lipo have a reasonable argument that there may have been late colonisation of Easter Island and the late colonisation of Rapa is consistent with this.
This may change our understanding of the island’s history, but even a late colonisation combined with indigenous deforestation would leave Easter Island as a warning of ecological carelessness. The work on Rapa would also suggest it’s not an isloated tale. Douglas Kennett described Rapa as:
“…a compelling story. To me, this is an example of what’s happening on the planet today in terms of expanding populations, environmental degradation and increasing warfare. Rapa is a little microcosm of our planet. There are lessons about the consequences of population growth to be learned there.”
Eurekalert has a press release on Kennett’s work at Rapa.
The Independent article may or may not be behind a paywall as the server sees fit.
In related research Chris Turney has a blog entry about the recent Polynesian Chicken Flap.