Get a taste of what awaits you in print from this compelling excerpt.

With a gasp of brakes, the truck nears the rickety, one-lane bridge on a hot Amazon afternoon. As it slows, the cloud of dust in its wake rolls toward the truck and then washes over it, enveloping the 17 people riding on top with fine red dirt. The truck is a cisterna—a tanker—carrying a load of fuel from Cusco up over the Andes and down to the Amazon Basin, but the top of the tank is flat, with low wooden rails around it. Up here, just above the large letters that warn PELIGRO—COMBUSTIBLE on the side of the tank, the passengers close their eyes and hold their breath.

Among them are Mary Luz Guerra and her son, Alex, 14, and while Alex seems to be enjoying himself, this is not Mary's idea of a good time. The nursery school teacher and single mother had flown from her home in Puerto Maldonado, in the rain forest, to Cusco, high in the Andes, to begin her month-long vacation and pick up Alex, who had been visiting relatives. The flight, full of tourists and a handful of more prosperous locals, had taken 37 minutes. On her return, however, she discovered the fare had risen, and she could not afford seats for both herself and Alex. So the two of them were forced to come home via the service entrance, as it were—a 72-hour trip atop this truck, on a narrow dirt road that curves like an earthworm held by the tail over a 15,585-foot (4,750-meter) pass and then down, down into the humid rain forest.

It's a memorable spectacle, falling from the steep and wrinkled Andes into the endless, green, two-dimensional Amazon Basin. The truck stops for lunch in a settlement called Libertad. I join Mary, Alex, and some of the other passengers for a swim in a nearby creek; as I emerge, free of dust at last, a toucan bobs across an adjoining field and disappears into the forest canopy.

One of the two roadside restaurants is serving paca—a large rodent that is remarkably tasty fried. Mary sighs with disgust as another truck blows through town, and dust settles onto our plates. The truck belongs to a beer distributor making deliveries. When it pulls up next to us, I point out its logo to the others: Transoceanica. That word, shorthand for a proposed transcontinental highway, is all the rage here.

Mary dabs her forehead with a thin paper napkin. "I can't wait till they build that highway!" she says.

Like many in the developed world, I am enchanted by roadless places. The Earth has so few of them left, and glorious creatures like toucans depend on them. Many thoughtful people believe that the fate of the Earth itself depends on keeping nature unpaved.

But Peru is mad for new highways. Just as the north-south Pan-American Highway was the infrastructure project of the 20th century for South America, many people see an east-west Carretera Transoceanica—a road joining the Pacific to the Atlantic—as the project of the 21st.

One might assume that when people use a phrase like "transoceanic highway," they have a route in mind. But when I went to take a look at the future road, I discovered that wasn't necessarily so.

Get the whole story in the pages of National Geographic magazine.

The construction of the Transoceanica Highway has Peruvians polarized about its impact on the region. How can the benefits of a highway through Amazonia be balanced with the costs? Voice your opinion.

There are three species of true mahogany, however only one of the species (Swietenia macrophylla) is still commercially viable. The other two species (S. humilis and S. mahagoni) are both considered commercially extinct throughout much of their region. S. macrophylla, or big-leafed mahogany, occurs in South American countries, particularly Peru, Bolivia, and Brazil. Illegal logging greatly threatens the viability of these forests, raising concerns that they will not be able to sustain the mahogany trade market much longer.

The United States is the main importer of big-leafed mahogany and consumes more timber (all species) per capita than any other country in the world. The U.S furniture industry absorbs about 90 percent of the top grade mahogany lumber imported into the U.S., while lower grade mahogany goes into the production of doors, architectural millwork, and coffins. Efforts to ensure that the big-leafed mahogany supplying the international market is harvested legally and sustainably have so far been unsuccessful. Governments, nongovernmental organizations, businesses, and consumers will need to take stronger action to prevent mahogany from going extinct commercially if not overall. Consumers can support mahogany conservation by buying mahogany products that carry the Forest Stewardship Council (FSC) trademark. This certifies that the wood comes from forests managed in accordance with FSC's principles requiring ecologically and socially responsible harvesting.

—Marisa Larson