The cell-surface receptor, SIRP-alpha, initiates the innate immune response in hosts.
The stone statues of Easter Island Credit: Courtesy of Terry Hunt Related: Slideshow: Solving the Easter Island mysteries On one side of a quarry roughly two-thirds the size of a football field is "El Gigante,"
August 1, 2007|
On one side of a quarry roughly two-thirds the size of a football field is "El Gigante," a half-finished stone statue seven stories tall, and weighing almost 300 tons. Prehistoric tools lie scattered nearby. Whoever made these head-and-torso statues, known as moai, seemed to have decided one day to drop their tools and disappear into history, leaving behind a harsh, barren landscape. It's one of the mysteries of Easter Island, which budding scientists have flown halfway across the world to solve.
During an excavation project last summer, Jeffrey Boutain, who graduated from the University of Michigan, Dearborn, in May, routinely woke up at 7:00 a.m. and rode a jeep 10 miles to reach an excavation site at Anakena beach. The team was digging for signs of the prehistoric civilization, such as animal bones, charcoal, and cooking implements. Boutain also used GPS to help survey the island's archaeologic features, including ancient roads and buried fireplaces, and helped catalogue all 800-plus moai on the island - the most comprehensive attempt to date.
Last summer, Boutain was one of 26 college students who flew to a South Pacific island no bigger than three Manhattans to do summer fieldwork. Although all 20 enrollees this summer are new to field science, they've helped turn some theories about Easter Island upside down.
The traditional view about Easter Island, popularized by Jared Diamond in his 2005 book, Collapse , is that the people who settled on Easter Island destroyed the island's once-lush tropical forests; it is one of the supposedly clearest examples of humans wreaking havoc on their environment. Some of the data that the summer students gathered helped two researchers - Carl Lipo at California State University in Long Beach and Terry Hunt, director of the program and an anthropologist at University of Hawaii at Manoa - propose another controversial theory on what leveled the landscape.
Based partly on charcoal records found at Anakena beach, Hunt and Lipo suggested in a Science paper last year (311:1603-6, 2006) that the early Easter Island settlers colonized the island around 1200 AD, at least 400 years later than previously thought, and around the time the forests began disappearing. It would be hard for humans to systematically destroy vegetation that quickly, they reason, suggesting there may be another culprit to blame, at least partially - rats.
Ancient rat bone DNA evidence from the beach suggests that a few rats stowed away with the first settlers, then exploded into a population of two to three million, and quickly devoured the palm seeds. Without seedlings to replenish the aging stock, the palm forests eventually withered away.
This summer, Hunt's group worked on excavations, sifting through sites for rat-gnawed seeds and nuts to bolster his new theory. He has already found evidence, in the form of hundreds of rat bones deep in the sands at Anakena beach and half-eaten palm seeds scattered across the island, suggesting that the rat population grew much more rapidly than did the human population. Hunt hopes to find signs in pollen embedded in the sediment from the lake near the quarry, showing that the forest started declining before humans began any widespread clearing. "Diamond blames the natives for destroying the island," says Lipo, who also helps run the field school. "But maybe they weren't crazy, and it is us who have lessons to learn on how to coexist with nature."
Well-known in archaeologic circles, the Easter Island field school of the University of Hawaii at Manoa couldn't be more remote. Located 2,300 miles from any sizable land mass (South America), temperatures on the island, known as Rapa Nui by locals, hover at around 65° F (18° C) - on a good day. Sudden rainstorms aren't uncommon. Flights from the United States can take as long as 24 hours, not including delays.
It's worth the trip, says Boutain, who is about to enroll in UH-Manoa's botany program for his master's degree. "I would do it again in a heartbeat." Last year's surveying efforts, including photos and descriptions of 650 moai, can be accessed at www.rapanuidatabase.org, the public database for the mapping project.
"There are field schools all over the world, but to be this isolated in such a spectacular little place is pretty unusual," says Hunt. "It's one of the last places on earth you really have a sense of being remote."
August 23, 2007
September 6, 2007