The mystery of the Easter Island
Speculators believe the giant statues were sculpted by aliens stranded on earth. Now my own curiosity can rest: Jared Diamond explains in a review essay for the New York Review of Books that the statues were actually made by real people paying homage to their chiefs. Diamond points out that Easter Island was once a rainforest, where the long ropes used to haul the statues came from.

The island suffered massive deforestation sometime in the sixteenth century as the different clans one-upped each other in building the more garish and bigger statues. Because of the deforestation and the concomitant decline in the animal species in the island, islanders practiced cannibalism for lack of food.

No tree remains on Easter Island today:

The overall picture for Easter is the most extreme example of forest destruction in the Pacific, and among the most extreme in the world: the whole forest gone, and all of its tree species extinct. Immediate consequences for the islanders were losses of raw materials, losses of wild-caught foods, and decreased crop yields.

Diamond also writes how the Easter Island crisis serves as a caveat for the rest of us of how a society can be torn apart by environmental degradation:

The Easter Islanders' isolation probably also explains why their collapse, more, perhaps, than the collapse of any other pre-industrial society, haunts readers and visitors today. The parallels between Easter Island and the modern world are chillingly obvious. Thanks to globalization, international trade, jet planes, and the Internet, all countries on Earth today share resources and affect each other, just as did Easter's eleven clans. Polynesian Easter Island was as isolated in the Pacific Ocean as the Earth is today in space. When the Easter Islanders got into difficulties, there was nowhere to which they could flee, or to which they could turn for help; nor shall we modern Earthlings have recourse elsewhere if our troubles increase. Those are the reasons why people see the collapse of Easter Island society as a metaphor, a worst-case scenario, for what may lie ahead of us in our own future.