What’s the story behind the mystery of Easter Island? It’s not set in stone

Most people have heard of the decimation of the population of Easter Island (also called Rapa Nui) and have seen pictures of the massive stone statues (moai) that line the coastline. The conventional explanation of population decline is that the islanders cut down all the island’s trees, precipitating an ecological reaction that killed off most of the population.

But this is no longer accepted as an accurate description of what happened. Anthropologist Terry Hunt, who carried out extensive archaeological field research on Easter Island, tells the story in The Folio Book of Historical Mysteries (The Folio Society, 2008).

Easter Island, 24km long by 16km wide, was named by Dutch navigator Jacob Roggeveen, who landed there on Easter Sunday 1722. Located in the South Pacific, it is one of the most isolated inhabited islands in the world – the nearest inhabited land is Pitcairn Island (colonised by the Bounty mutineers) 2,015km away. Chile is more than 3,000km away.

Easter Island’s native Polynesian inhabitants arrived from other islands around 1200 and established a thriving culture, as evidenced by over 800 moai carved between 1400 and 1650, each weighing several tons and some over 9m high. They commemorate ancestral high chieftains. The initial population increased rapidly, reaching a peak of 3,000 to 4,000 around 1350 and remaining fairly stable until the Europeans arrived. But by 1877 the population had decreased to 111. What caused such a dramatic decline?

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The moai were carved in inland quarries and moved to the coast, often kilometres away. There are several proposals to explain how the moai were moved. The most popular involve wooden logs – the statues were either moved along on rolling logs or pulled on wooden sleds by ropes. Another ingenious proposal is that the statues “walked” from the quarries to their coastal destinations, being rocked from side to side by islanders pulling on ropes attached to the statues’ heads, rather like moving an upright fridge.

Palm trees

Easter Island was covered with palm trees for over 30,000 years, but is treeless today. There is good evidence that the trees largely disappeared between 1200 and 1650. Assuming that wood was used to move statues, a popular proposal was formulated that the islanders, besotted with their moai, cut down all the palm trees in order to move statues.

Almost all palm seed shells found on the island show evidence of having been gnawed on by rats, which would seriously affect the trees' ability to reproduce

When the trees went the whole ecosystem deteriorated: soil eroded quickly; most birds vanished having no place to nest; many plants vanished; wood wasn’t available for building canoes or houses; people starved and the population crashed. With our present preoccupation with climate change, this story served as a parable illustrating how human interference with the natural world has disastrous consequences. However, as Hunt explains, the truth is more complicated. Rats play a prominent part in the story.

Rats can cause rapid and widespread environmental degradation. For example, deforestation took place on the Hawaiian island of Oahu between 900 and 1100, but there is no evidence of human presence there until 1250. However there is evidence the Polynesian rat (Rattus exulans) was present from 900 and it seems clear that these rats caused widespread deforestation.

Stowaways

Rats accompanied the original settlers to Easter Island either as a source of food or as stowaways. The island is an ideal environment for rats: unlimited food, including palm tree nuts, and no natural predators except humans. Under these conditions rat populations can double every six weeks. Almost all palm seed shells found on the island show evidence of having been gnawed on by rats, which would seriously affect the trees’ ability to reproduce.

But, apart from the role played by the rats in deforestation, the people of Easter Island themselves were also very likely profligate in their use of the palm forests. They practiced “slash and burn” agriculture and may well have cut down trees to move statues. Diseases such as TB and smallpox, introduced by Europeans and others, killed large numbers of islanders and in the 1800s Peruvian slavers kidnapped and removed 1,500 islanders, about half the population.

The relative contributions to the woes of Easter Island made by the islanders cutting down trees, the contribution of rats to deforestation and the ravages of disease and slavery have yet to be calculated. But, as Hunt demonstrates, the popular parable of moving the statues doesn’t explain everything.

William Reville is an emeritus professor of biochemistry at UCC