A single pod of brazil nuts can just about fit in a man's hand. But whenever a good-sized pod, like the ones in the National Museum of Natural History's South American exhibition, tumbles from its perch some eight stories above the forest floor, people take notice. "You sometimes see animals staggering around with large welts" where they've been struck, says Enrique Ortiz, a biologist at NMNH who has been studying Brazil nuts in Peru for more than eight years. The four- to six-pound pods hit the ground with a force that can — and does — kill a man. At times they literally plant themselves on impact.

A falling harvest is just one of the mortal dangers braved by castañeros, as people who live by collecting the nuts are known in Spanish-speaking South America. The nuts themselves are known as castañas (or castanhas in Brazil). Trying to gather Brazil nuts on a regular basis puts the castañeros in contact with vipers and jaguars, diseases like malaria and leishmaniasis, tyrannical bosses and traders, not to mention death from drowning and armed skirmishes over the possession of trees.

Brazil nuts add some $44 million annually to South American economies. Americans gobble up nearly $17 million of the nuts a year. Alone among the foods in the world economy, these nuts come almost exclusively from remote natural forests rather than more convenient plantations.

Ortiz and his colleague Adrian Forsyth describe their research goal as "getting Brazil nut forests protected based on the ecologic, economic and social viability" of collecting Brazil nuts from natural forests. They think they may be able to show that, danger of serious or fatal injury aside, castañeros can make a better living gathering nuts from a living forest year after year than from any one-shot timber harvest.

Ortiz and his team have gone to elaborate lengths with these goals in mind. Their research site is the Madre de Dios region of Peru in the Amazon's lush, upland rain forests where Peru, Brazil and Bolivia meet. This is one of the most productive areas of Brazil nut country. From Lima, it's a one-hour plane ride plus seven hours by boat. In Madre de Dios, Ortiz and a team of eight researchers keep 1,000 or so trees under surveillance, counting every pod that falls and locating the most productive areas so that castañeros can gather the nuts more efficiently. Each pod holds 10 to 25 Brazil nuts, which are technically seeds, arranged inside a pod like sections inside an orange.

Brazil nut trees flower at the start of the rainy season; each flower lasts just one day. Blossoms that open before dawn one morning fall by late afternoon. Gradually the forest floor becomes strewn with the cream-colored, marble-to-golf-ball-size flowers, which attract brocket deer and large nocturnal rodents called pacas. The mature pods fall in the rainy season.

Castañeros have to time things just right. If they come too early they waste valuable time waiting for the pods to fall. Too late and they'll lose the harvest to agoutis, cat-size brown rodents that gather up all the Brazil nut pods they can find and then bury the nuts individually, just as squirrels bury acorns for future food.

The agouti turns out to be a major player in the history of the Brazil nut. By burying the Brazil nuts, agoutis hold the key to the tree's survival in remote areas. The agouti is virtually the only animal that has teeth strong enough to open the thick husk and liberate the seeds so they can sprout. Ortiz was the first to fully understand the agouti's crucial role. To learn how many pods each agouti collected and how far it carried them, Ortiz and his team carefully opened pods that fell from 12 trees in Madre de Dios, painstakingly glued a tiny magnetic strip and a number to each seed, then glued all 120 pods back together like Russian egg puzzles.

The agoutis were completely taken in and busily began eating, or burying the doctored nuts. Ortiz's team later spent more than six months searching the forest with a magnetic locator and waiting for the seeds to sprout, a cycle that takes up to a year. Their patience is yielding a precise picture of how the Brazil nut population replenishes itself and what conditions are most favorable to its regeneration. Further research may reveal other ways in which the castañeros' harvesting could be more efficient and profitable. At present, more than 30 percent of harvested nuts spoil before they get to market.

For centuries the trees have been acquiring more and more human travel agents, those local people who found the nuts and pods useful. Many tribes, like the Yanomami, ate the nuts raw, grated and mixed into a manioc porridge. (The nuts also contain varying levels of selenium — perhaps 250 times more than most foods — depending on the soil where they're grown. Selenium may deter ovarian cancer by helping activate a powerful antioxidant, but too much can be toxic and cause balding.) Today the nuts are dried and graded, and some are shelled, before being packed in vacuum-sealed bags for shipment. They are eaten raw as well as roasted and salted. Brazil nuts contain about 14 percent protein, 11 percent carbohydrates, and 67 percent fat or oil, as well as potassium, phosphorus, calcium and Vitamin B.

People consume the Brazil nut not just as a protein-rich food, but in a special tea for stomachaches and ultimately as an ingredient in Ben & Jerry's Wavy Gravy ice cream. Its oil has been used for cooking, and in lamps and soaps and, more recently, hair conditioners. The husk can be burned for fuel, set smoking to repel mosquitoes and blackflies, or carved into ashtrays and trinket cases.

At the end of the 15th century, unbeknownst to the Amazonians, Spain and Portugal divided up South America. The Portuguese got Brazil and started sending back tantalizing samples of the New World in ships laden with gold and jaguars. Meanwhile, the Spanish infiltrated from the west coast. On a reconnaissance mission in 1569, Spanish officer Juan Alvarez Maldonado and his exhausted troops flopped down to rest in the middle of some Brazil nut groves near the Madre de Dios River. The Cayanpuxes Indians told Maldonado about the nuts, and he ordered that thousands be collected for rations. The Spanish called them "almendras de los Andes" — "almonds of the Andes."

But it wasn't until 1633, when the trade-savvy Dutch sent some of the nuts home, that Brazil nuts gained a truly world market. The German botanist-explorer Alexander von Humboldt and French colleague Aimé Bonpland ventured to South America in 1799. During a five-year expedition, they collected 60,000 plants, as well as other specimens, and data on wildlife, climate and geology. Humboldt was the first European to observe how the poison curare was made. He scrambled most of the way up the Andean volcano Chimborazo, more than 20,000 feet tall, setting a world altitude record that stood for 30 years. On their return to Paris, they were treated like homecoming astronauts. It was they who named the Brazil nut tree Bertholletia excelsa, after Humboldt's friend the chemist and salon host Claude Louis Berthollet.

By the second half of the 19th century, the celebration of Christmas in England had snowballed into a lavish affair, and the holiday brought bowlfuls of the raw, bitter-tasting nuts to households throughout the country. "I'm Charley's aunt from Brazil — where the nuts come from," was a boffo line in various versions of the farce Charley's Aunt, which opened in London in 1892 and had many lives, including a movie with Jack Benny.

Along the way a remarkable thing happened. Brazil nuts got hooked up with that other Amazonian wonder, rubber, in a symbiotic relationship. The enormous demand for rubber that started in the mid-19th century brought waves of settlers from the coast into the forest, where they tapped the gooey white latex from May to November. Many collected raw rubber in Brazil nut husks. In the rainy winter, Brazil nut harvesting kept them working in the forest from December to March. When the rubber market soared, Brazil nut sales followed. From 1847 to 1897, rubber exports grew by more than 2,000 percent. But in the 1870s colonists in Southeast Asia found they could grow Brazilian rubber trees free from the parasites prevalent in South America. From 1910 on, Brazilians watched rubber's price plummet. Those stranded in the forest with no sure income turned to the Brazil nut. Today's castañeros live a lot like they did a hundred years ago. They make huts in the forest and wait for the nuts to fall. Most collecting is done in the morning, when the wind is still and there's less chance of being beaned by a falling pod. On a good day, an experienced collector can find upwards of a thousand pods, chop them open with a machete and haul the nuts, in sacks of up to 140 pounds, to the nearest river or road.

The Brazilian port of Belém still exports about half the world's Brazil nuts, but the supply pyramid is steep: many thousands of collectors feed only a few exporters; several of Brazil's largest export firms are held by one family. In the backcountry the nuts remain a kind of currency, and occasionally violence erupts. In Macapa, Brazil, in 1985, six collectors were killed and 12 wounded in a fight over Brazil nuts. Dealers cruise the waterways in boats loaded with food and manufactured goods, looking to barter for nuts. Castañeros squirrel away Brazil nuts as insurance against emergencies. Ortiz tells of one family crisis when a collector had to rush his son, who was running a high fever, to a clinic. With no money on hand, the man threw several sacks of shelled nuts into the canoe. At the village, he quickly sold the nuts and bought the boy's medicine.

There have been changes. Parts of the Amazonian forests have given way to dams, cattle ranching and slash-and-burn farming. Last year fires consumed thousands of square miles of forest. Ortiz and Forsyth know it won't be biology alone that makes the Brazil nut business healthier for the castañeros and the trees. A sharp drop in the market price can transform some castañeros into chain-saw-wielding outlaws.

Though felling Brazil nut trees is illegal, a black market exists for the trees' durable wood. But understanding biology can help. "Think about the connections," says Ortiz. "Bees pollinate and affect fruit production, which determines the harvest size, and ultimately this justifies land-use policies, which determine the forest's fate." Likewise, "changes in the agouti population may affect seed losses, regeneration of the trees, forest health and collectors' incomes," says Ortiz. "This needs to be known." The agoutis aren't talking, however. One stands poised in the NMNH display, just a few feet from the Brazil nuts, forever awaiting its snack.

By David Taylor