Ecology and Easter Island

Easter Island Moai
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.

Rapa Rock Shelter
Tangarutu Rock Shelter, Rapa. Photo by Douglas Kennett.

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.”

You can read Terry Hunt’s art­icle in American Scientist and down­load the paper co-written with Carl Lipo as a PDF.

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.

…and via DSLRBLOG I found this page of Easter Island pho­tos which look dif­fer­ent from the usual images you see.


When he's not tired, fixing his car or caught in train delays, Alun Salt works part-time for the Annals of Botany weblog. His PhD was in ancient science at the University of Leicester, but he doesn't know Richard III.

1 Response

  1. Carl Lipo says:

    I think you will be inter­ested to read the upcom­ing issue of the Rapa Nui Journal in which Hunt and I respond to Bahn and Flenley’s art­icle. There, we detail the assump­tions that are made and demon­strate how little empir­ical evid­ence there is to sup­port “early” occu­pa­tion, col­lapse and the rest of the story. Once one does a bit of exam­in­a­tion of the basis for most of the pop­u­lar claims, it is really sur­pris­ing to find that there is almost noth­ing empir­ical to sup­port them. As it turns out much of what we know about Easter Island may actu­ally be the product of a mod­ern myth. In con­trast to the claims by Bahn and Flenley, though, this find­ing doesn’t imply that we (i.e., indus­trial soci­et­ies) don’t have any­thing to worry about — it just means our own his­tor­ical lin­eage has res­ul­ted in our cur­rent situ­ation and that Easter Island pre­his­tory isn’t neces­sar­ily a good ana­logy for our own history.