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How a misunderstanding over diet created an ecocide

For years the tale of how the inhabitants of Easter Island depleted their soils and destroyed their ecosystem has been a cautionary tale for western civilisation. There's just one problem with this as a historical warning - it seems that it never happened.

To some extent, it must be fun at parties to say you study the archaeology of Easter Island. It’s an iconic site in archaeology, but it’s also been a misunderstood site, and that misunderstanding has become very popular.

Moai on Rapa Nui
Witnesses to ecocide? Moai on Rapa Nui. Photo: Terry Hunt – University of Oregon

What happened is fairly simple. Polynesian settlers arrived on the island, which they called Rapa Nui, some time in the past. If you want to know how far in the past you can radiocarbon date their bones and the earliest date that pops out is some time in the 1st millennium AD. Sometime between AD 900 and 1200 the islanders started building megalithic platforms, and eventually the large stone heads that watch out to sea. As they did that they destroyed the local trees. Without trees, they couldn’t make canoes and, with no canoes, they could no longer fish so they ate chickens, rats and agricultural crops.

However, Rapa Nui is not a tropical paradise with fertile soils so crop productivity decreased. The result was they drove themselves to cannibalism and ended up in effectively post-apocalyptic conditions.

It’s a powerful story, and it has supporting evidence, such as pollen cores from bogs, which seem to support some burning of the forest.

There’s new research that can test this idea, to an extent by looking at what people ate, through isotope analysis. Jarman et al. have published their results in the American Journal of Physical Anthropology and have found something odd.

The research team analysed archaeological material dating from 1400AD to the historic period from the Kon Tiki Museum in Oslo, Norway. These included some material from excavations lead by the famous Norwegian explorer and anthropologist Thor Heyerdahl in the 1950s and 1980s. Other samples were provided by Terry Hunt at the University of Oregon and Carl Lipo professor of anthropology at Binghampton University that were collected as part of University of Hawai‘i archaeological field schools.

In Professor Brian Popp’s laboratory at the University of Hawai’i at Mānoa School of Ocean and Earth Science and Technology (SOEST) and in the Leibniz Laboratory for Radiometric Dating and Stable Isotope Research at the Christian-Albrechts University of Kiel, Germany, the team analysed the stable isotope ratios of carbon and nitrogen in archaeological soils, human and animal bone and plant remains from around 1400 AD, and modern soil and plant samples from the island.

Professor Popp said: “Human and animal bone retain isotopic ratios that reflect a consumer’s diet in life. By studying these isotope ratios, particularly in individual amino acids, we estimated the relative proportions of different food sources in each individual’s diet.”

Christian-Albrechts from the University of Kiel Thomas Larsen, added: “We used three independent lines of isotopic evidence to determine what the ancient Rapa Nui people ate. Although we cannot say that no rats were eaten, all our results indicate that seafood was an important part of the Rapa Nui diet.”

The paper concludes “Our results of carbon and nitrogen isotopic analysis of individual amino acids show that in our samples, seafood made up about half of the protein in human diets, which is considerably higher than previous estimates based on bulk data with similar isotopic compositions.”

That is only part of the diet, there was also a surprise in the agriculture and it can from the same place as the marine isotopic analysis δ15N. δ15N is a measure of the ratio of the two stable isotopes of nitrogen, 15N:14N. Botanists will recognise it because you can use it to trace fertilisers.

Catrine Jarman, the lead author of the study and PhD student at the University of Bristol’s Department of Anthropology and Archaeology, said: “We also discovered that agricultural crops consumed must have been planted in soils that were deliberately managed and manipulated to provide better yields.

A rock mulch garden on Rapa Nui with taro (Colocasia esculenta) growing.
A rock mulch garden on Rapa Nui with taro (Colocasia esculenta) growing. Taro has long been a staple food of the natives of Polynesian Islands. Photo: Terry Hunt – University of Oregon.

“Previous work has shown that plants of Rapa Nui were grown in rock mulch gardens and planting enclosures known as manavai. These had been carefully constructed and deliberately managed, and our study showed that the islanders may have added fertilisers.”

The large marine component of the diet indicates that the ecosystem did not immediately collapse to prevent fishing. The marine element also means that radiocarbon dates will appear older than reality, as 14C takes time to transition to the submarine environment. The δ15N from the crops, however, shows that inhabitants were adapting to the changes in the environment their (and rats) arrival were making to the island. The paper concludes: “Our results point to concerted efforts to manipulate agricultural soils, and suggest the prehistoric Rapa Nui population had extensive knowledge of how to overcome poor soil fertility, improve environmental conditions, and create a sustainable food supply. These activities demonstrate considerable adaptation and resilience to environmental challenges – a finding that is inconsistent with an “ecocide” narrative.”

It’s this failure to recognise Polynesian farming techniques that has created the ecocide narrative according to Prof Carl Lipo of Binghampton University. “The Rapa Nui people were, not surprisingly, smart about how they used their resources,” he said. “And all the misunderstanding comes from our preconceptions about what subsistence should look like, basically European farmers thinking, ‘Well, what should a farm look like?’ And it didn’t look like what they thought, so they assumed something bad had happened, when in fact it was a perfectly smart thing to do. It continues to support the new narrative that we’ve been finding for the past ten years.”

You can pick up Diet of the prehistoric population of Rapa Nui (Easter Island, Chile) shows environmental adaptation and resilience as an Open Access paper from the American Journal of Physical Anthropology.

Source material: AlphaGalileo, Newswise.

Reference

Jarman, C. L., Larsen, T., Hunt, T., Lipo, C., Solsvik, R., Wallsgrove, N., … Popp, B. N. (2017). Diet of the prehistoric population of Rapa Nui (Easter Island, Chile) shows environmental adaptation and resilience. American Journal of Physical Anthropology. https://doi.org/10.1002/ajpa.23273

About the author

Alun Salt

When he's not the web developer for AoB Blog, Alun Salt researches something that could be mistaken for the archaeology of science. His current research is about whether there's such a thing as scientific heritage and if there is how would you recognise it?

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  • My example of “ecocide” is the Burren on the west coast of Ireland. Now it is regarded as a major protected landscape and a national park, actually the upland limestone pavement should be covered with trees growing over peaty soils. From Neolithic times onwards through the Bronze age (4000 to 1000 BC), overgrazing and burning stripped the vegetation and then soil cover, leading to the limestone rocky surface of today.