Rapa Nui's early inhabitants survived despite the odds

There are hundreds of huge stone statues on Rapa Nui — the so-called Moai. No one has ever conclusively found out why they exist. But researchers have long assumed that many thousands of people must have lived on the Pacific island, also known as Easter Island, to erect the colossal figures.

Ancestors of contemporary Polynesians first settled on the then-uninhabited volcanic island around the year 1210.

No other inhabited place is so isolated in the world. Rapa Nui is 1,900 kilometers (1,180 miles) from the nearest inhabited island and almost 3,800 kilometers from the Chilean mainland.

Early theories assumed that the population grew rapidly. The inhabitants, it's been said, cut down all the trees to build the Moai, and for firewood; they killed seabirds and depleted the soil with agriculture.

Eventually, the environment was fully destroyed, and the population was said to have collapsed — that's the theory, anyway. And the island became a symbol of ecocide, a destruction of a natural habitat and environment by deliberate human action.

Books such as Jared Diamond's Collapse (2005) and Kevin Costner's feature film Rapa Nui — Rebellion in Paradise (1994) present the thesis of the islanders' demise with powerful words and images.

New studies: Rapa Nui's population remained stable

A number of studies suggest, however, the population on Easter Island or Rapa Nui never reached an unsustainable size. Instead, new arrivals found ways to get along on the island. And a small, stable population was maintained over the centuries.

But it must have been difficult to feed the people — 63 square kilometers of the island consists entirely of volcanic rock.

In contrast to lush tropical islands, such as Hawaii and Tahiti, the volcanic eruptions on Rapa Nui ceased hundreds of thousands of years ago. The minerals stirred up by the lava had long since been washed out of the soil.

Rapa Nui is also much drier than other tropical islands. And as the seabed around the island slopes very steeply, hunting for marine life would have been more difficult than in the easily accessible lagoons or reefs of other islands in Polynesia.

Rapa Nui rock gardens secured food supplies

According to researchers, the early inhabitants on Rapa Nui were successful because of their "ingenious construction of rock gardens," in which the islanders grew nutritious sweet potatoes as a staple food.

Rock gardening, or lithic mulching, involves scattering stones over low-lying areas that are at least partially protected from salt spray and wind. The stones and rocks interrupt the dry winds and create an air flow that keeps the surface temperatures reasonably constant, protecting the plants from excessive heat or cold.

Similar rock gardens are also known from the indigenous peoples of New Zealand, on the Canary Islands, and southwestern parts of the US. However, the amount of work involved is very high and the yield very low.

Disproved population collapse theory

These days, Easter Island has about 8,000 inhabitants. There are also around 100,000 tourists per year.

Most of the food is imported, but some inhabitants have gone back to growing sweet potatoes in the old rock gardens. It started as a trend during the COVID-19 pandemic, when transport routes were locked down.

According to researchers, the gardens once only provided enough land to feed a few thousand people.

"The population could never have been as large as some of the earlier estimates,” said Dylan Davis, an archaeologist at Columbia Climate School in the US, who was lead author of the latest study.

And that disproves the collapse theory, said Davis: "By changing the environment to their benefit, humans were very resilient despite limited resources."

Calculating population based potential crop yield

Researchers have tried to estimate the size of early Easter Island populations by using the size of the rock gardens and the amount of crop that people could have cultivated on that land as a guide.

For example, a 2017 study suggested that inhabitants would have required about 7,700 hectares (~19,000 acres) for sweet potato cultivation — or about 19 percent of the island. On that assumption, they calculated a population of between 17,500 and 25,000 islanders.

New study re-calculated population with artificial intelligence

The researchers in the latest study used artificial intelligence to configure satellite images in such a way that not only rocks but also places with higher soil moisture and nitrogen — both of which are characteristic of rock gardens — were highlighted.

Based on those calculations, the rock gardens are thought to have covered less than hectares (188 ha). That is less than 0.5% of the island. And if the diet was largely based on sweet potatoes, as thought, then these gardens would only have fed about 2,000 people.

Adaptation to difficult living conditions

Based on isotope (chemical) studies of bones and teeth, researchers believe the early inhabitants got 35-45% of their food from the sea and a small proportion from other, less nutritious plants, such as bananas, taro and sugar cane.

The researchers think that around 3,000 inhabitants could be fed if they succeeded in adapting to the difficult conditions on the island.

That's about the same number of people who were living on Easter Island when Europeans first arrived there in 1722.

Carl Lipo, an archaeologist at Binghamton University and co-author of the study, concluded that the idea of an ecocide on Rapa Nui cannot be proven in view of the latest findings.

Primary source:

Island-wide characterization of agricultural production challenges the demographic collapse hypothesis for Rapa Nui (Easter Island). Published by Dylan S. Davis et al. in Science Advances (June 2024) https://www.science.org/doi/10.1126/sciadv.ado1459

This article was originally published in German.