June 19, 2012 at 9:43 PM ET
Did Easter Island's famous statues rock, or roll? After doing a little rocking out themselves, researchers say they're sure the natives raised the monumental figures upright, and then rocked them back and forth to "walk" them to their positions.
Their findings mesh with a scenario that casts the Polynesian island's natives in the roles of resourceful engineers working with the little that they had on hand, rather than the victims of a self-inflicted environmental catastrophe.
"A lot of what people think they know about the island turns out to be not true," Carl Lipo, an archaeologist at California State University at Long Beach, told me today.
Lipo and University of Hawaii anthropologist Terry Hunt lay out their case in a book titled "The Statues That Walked" as well as July's issue of National Geographic magazine. Their story serves as a counterpoint to a darker Easter Island saga, detailed in "Collapse: How Societies Choose to Fail or Succeed," a better-known book by UCLA scientist-author Jared Diamond.
In Diamond's scenario, Easter Island's society is portrayed as one that chose to fail through overpopulation, conflict and deforestation. Polynesians colonized the island as far back as 1,600 years ago, and cut down forests of palm trees as part of a slash-and-burn strategy that led to intensive farming, soil degradation, conflict, cannibalism and massive depopulation. By the time the Europeans arrived in the 18th century, Easter Island's society was on the ropes.
The island's statues, known as moai, play a significant part in this scenario. Diamond relies on the findings of other researchers who say the monoliths, weighing as much as 90 tons, were dragged into place by hundreds of islanders, using downed trees as sleds, rollers and levers. Rival chieftains recruited whole tribes to erect monuments to their glory. The broken statues found along the island's path were a testament to the stone-carving society's final failure.
Hunt and Lipo take a different view: The way they see it, Easter Island was never that great a place to live. "It was never verdant, and there were never very many people on the island," Lipo said.
In this scenario, the Polynesians settled on the island about 800 years ago — and brought rats along with them. The settlers ate the rats, but because the rodents were an invasive species with no other natural predators, they took over the island and feasted on palm nuts, hastening the pace of deforestation. The population remained relatively stable for centuries, but when the Europeans arrived, the islanders who were there fell victim to diseases that their immune systems couldn't fight.
Hunt acknowledged that, "from a biodiversity standpoint, it was a catastrophe." But he said the farming methods used by the ancient islanders were designed to make the best of a bad situation. Rocks were piled up to create circular garden plots known as "manavai," and crops were planted within the circles. Nutrients would quickly leach out of the soil, but fresh rock was pulverized and added to the soil as a mulch.
"They were able to engineer their lives in a way that was really stable and sustainable," Lipo said.
The statues play a different role in the two scientists' alternate scenario. They said it wouldn't take all that many people to move the statues if they were raised up vertically and then rocked down the road. Taking on the task would have helped blow off steam, and might have served as a kind of social glue, Hunt said.
"You're actually putting a lot of your effort into the process of moving a statue rather than fighting," he told me. "Moving the moai was a little bit like playing a football game."
Trial by transport
After "The Statues That Walked" came out, Diamond sharply disputed the conclusions reached by Hunt and Lipo, declaring on climate expert Mark Lynas' blog that they were "considered transparently wrong by essentially all other archaeologists with active programs on Easter Island." Diamond addressed the debate in detail, including the idea that the statues could have been moved vertically.
"This seems an implausible recipe for disaster," Diamond wrote. "Imagine it yourself: If you were told to transport a 90-ton statue 33 feet high over a dirt road, why would you risk tipping and breaking it by transporting it vertically with all its weight concentrated on its small base, rather than avoiding the risk of tipping by laying it flat and distributing its weight over its entire length?"
Lipo and Hunt had their own counter-rebuttal published on Lynas' blog as well, and the debate over the historical record depends on sophisticated interpretation of radiocarbon dating tests, pollen analysis and tooth marks on palm nut shells. But the part about the horizontal vs. vertical transport? That could easily be tested.
UCLA's Jo Anne Van Tilburg had previously shown that the horizontal method was workable, as long as you had lots of laborers and logs. Lipo and Hunt set up their own experiment: They built a 5-ton moai replica, with the weight distributed as it was in a real statue. Then they tied ropes around it, raised it up using a crane, and got ready to let it stand free.
They could immediately see that the statue would fall forward if the crane relaxed the tension on the line. Hunt said he and Lipo were just about to walk away in disgust when the crane operator slipped a 2-by-4 under the front edge of the statue and had it standing. "As soon as we saw this, Carl and I said, 'Of course! This makes perfect sense!"
The researchers found that the statue's fat belly produced a forward-falling center of gravity that facilitated vertical transport. A crew of as few as 18 people could use ropes to rock the statue back and forth, and forward. (In comparison, Van Tilburg's team used 60 pullers.) The vertical-transport trick worked with four rope-pullers on each side, plus 10 people to pull on the statue from behind, as if they were holding back a dog that was straining forward on a walk.
"It's really unnerving and beautiful, all at the same time," Hunt said.
Of course, a 90-ton statue is bigger than a 5-ton statue, but Hunt found that the technique was scalable. "With the physics of the taller statue, you have greater leverage," he told me. "It almost gets to the point where you would have to do it that way."
'We're not failures'
The statue-walking experiment alone doesn't prove that the entire scenario put forward by Hunt and Lipo is true, but it's consistent with the claims in the islanders' oral tradition that the statues "walked" down the road in ancient times. It also provides an alternate explanation for the ruined statues that littered the roads: When you lose control of the ropes, that's what happens, and you don't have any good way to move the broken pieces.
So did the statues rock, or roll? The debate over the two scenarios surrounding Easter Island's past could well continue for generations. But it's clear which scenario is preferred by the islanders themselves.
"The young people ... they're celebrating. I don't think there's any other word for it," Hunt said. "One came up to me and said, 'It's so important for my generation to know we're not failures.' That brought tears to my eyes."
More about Polynesia:
Hunt and Lipo are scheduled to discuss "The Statues That Walked" at the National Geographic Society's headquarters complex in Washington on Thursday. The presentation is sold out.
"The Mystery of Easter Island," a Nova-National Geographic special focusing on the research conducted by Hunt and Lipo, is scheduled to air on PBS on Nov. 7.
Alan Boyle is msnbc.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. You can also check out "The Case for Pluto," my book about the controversial dwarf planet and the search for new worlds.