From the plane we catch glimpses of the Urubamba River, below Machu Picchu, plunging thousands of feet, then snaking through an ocean of trees that spreads east until it is lost in haze—the Amazon, the world’s largest and most diverse rainforest. We land in the humid furnace of Puerto Maldonado, the fourth-largest city in the wooded eastern half of Peru, known as the selva (the jungle). The airport is full of foreign tourists, mostly European and American, in jungle safari garb, and the parking lot is packed with kitschy jungle safari buses with thatched roofs, waiting tochauffeur them to boats on the Tambopata River, 15 minutes from here. One or two planeloads of tourists a day are shuffled in and out of 15ecolodges with capacities of 16 to 60, or more. My 11-year-old son, Zachary, and I are embarking on a more unusual adventure. We’re on our way to the Amazon Rainforest Conservation Center (ARCC), an ecolodge and research center located eight hours up the Rio de las...