Easter Island
Ecocide hypothesis

In his book Collapse: How Societies Choose to Fail or Succeed, Jared Diamond suggested that cannibalism took place on Easter Island after the construction of the moai contributed to environmental degradation when extreme deforestation (ecocide) destabilized an already precarious ecosystem. Archeological record shows that at the time of the initial settlement the island was home to many species of trees, including at least three species which grew up to 15 metres (49 ft) or more: Paschalococos (possibly the largest palm trees in the world at the time), Alphitonia zizyphoides, and Elaeocarpus rarotongensis. At least six species of land birds were known to live on the island. A major factor that contributed to the extinction of multiple plant species was the introduction of the Polynesian rat. Studies by paleobotanists have shown rats can dramatically affect the reproduction of vegetation in an ecosystem. In the case of Rapa Nui, recovered plant seed shells showed markings of being gnawed on by rats. This version of the history speculates a high former population to the island that had already declined before Europeans arrived. Barbara A. West wrote, "Sometime before the arrival of Europeans on Easter Island, the Rapanui experienced a tremendous upheaval in their social system brought about by a change in their island's ecology... By the time of European arrival in 1722, the island's population had dropped to 2,000–3,000 from a high of approximately 15,000 just a century earlier."

By that time, 21 species of trees and all species of land birds became extinct through some combination of over-harvesting, over-hunting, rat predation, and climate change. The island was largely deforested, and it did not have any trees taller than 3 m (9.8 ft). Loss of large trees meant that residents were no longer able to build seaworthy vessels, significantly diminishing their fishing abilities. According to this version of the history, the trees were used as rollers to move the statues to their place of erection from the quarry at Rano Raraku. Deforestation also caused erosion which caused a sharp decline in agricultural production. This was exacerbated by the loss of land birds and the collapse in seabird populations as a source of food. By the 18th century, islanders were largely sustained by farming, with domestic chickens as the primary source of protein.

As the island became overpopulated and resources diminished, warriors known as matatoa gained more power and the Ancestor Cult ended, making way for the Bird Man Cult. Beverly Haun wrote, "The concept of mana (power) invested in hereditary leaders was recast into the person of the birdman, apparently beginning circa 1540, and coinciding with the final vestiges of the moai period." This cult maintained that, although the ancestors still provided for their descendants, the medium through which the living could contact the dead was no longer statues but human beings chosen through a competition. The god responsible for creating humans, Makemake, played an important role in this process. Katherine Routledge, who systematically collected the island's traditions in her 1919 expedition, showed that the competitions for Bird Man (Rapa Nui: tangata manu) started around 1760, after the arrival of the first Europeans, and ended in 1878, with the construction of the first church by Roman Catholic missionaries who formally arrived in 1864. Petroglyphs representing Bird Men on Easter Island are the same as some in Hawaii, indicating that this concept was probably brought by the original settlers; only the competition itself was unique to Easter Island. According to Diamond and Heyerdahl's version of the island's history, the huri mo'ai – "statue-toppling" – continued into the 1830s as a part of fierce internal wars. By 1838, the only standing moai were on the slopes of Rano Raraku, in Hoa Hakananai'a in Orongo, and Ariki Paro in Ahu Te Pito Kura.
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