Clues to Collapse

Multiple theories for the decline of Easter Island's civilization may be complementary. 

Valenti Rull

As they stand near the Pacific Ocean from the easternmost point of the Polynesian Triangle, the stone-face moai of Easter Island (Rapa Nui) offer no clue to scientists and historians as to what happened and when to the civilization that was capable of carving and erecting these monoliths. Differing theories have relied on limited evidence from sedimentary records and archaeological findings.

Now, paleoecologist Valentí Rull, at the Institute of Earth Sciences Jaume Almera in Barcelona, Spain, and colleagues argue that the apparently conflicting views of Easter Island’s history may in fact be complementary. By analyzing evidence from a variety of approaches, including the record of droughts and wet seasons from sedimentary samples, as well as radiocarbon dating and DNA analysis of artifacts and human remains, researchers may be able to construct a more complete picture of what happened to the island’s forests and people.

The dominant theory to date, supported by certain archaeological and anthropological findings, has been that Easter Island was first colonized by Polynesians between 800 and 1200 CE. These settlers are presumed to have overexploited the island’s resources, bringing about an ecological catastrophe and in turn a cultural collapse. However, a more recent analysis of pollen in the sedimentary record indicates the presence of a human-dispersed weed from South America, as well as a deforestation event in 450 BCE, suggesting early colonization by people from that continent. This idea was further supported by the discovery of sweet potato, Ipomoea batatas, a plant of American origin, in dental remains of early skeletons.

As for the decline of the Rapa Nui society, Rull and his co-authors argue that multiple explanations are possible and are not necessarily contradictory. One idea suggests that mass deforestation across the island led to ecological collapse and civil war over the remaining natural resources. New evidence shows that the timing of deforestation varied at different sites on the island, and could have been caused by drought, intentional burning, or human-introduced rats eating tree seeds and preventing new growth. Environmental and human factors both seem to have contributed to Easter Island’s ecological and cultural demise. (Frontiers in Ecology and Evolution)