When Brazil established the Xingu Indigenous Park in 1961, the reserve was far from modern civilization, nestled deep in the southern reaches of the vast Amazon forest. When I first went to live with the Kuikuro, one of the reserve’s principal indigenous groups, in 1992, the park’s boundaries were still largely hidden in thick forest, little more than lines on a map. Today the park is surrounded by a patchwork of farmland, its borders often marked by a wall of trees. For many outsiders, this towering green threshold is a portal, like the massive gates of Jurassic Park, between the present—the dynamic modern world of soy fields, irrigation systems and 18-wheelers—and the past, a timeless world of primordial nature and society.