Scott Wallace

Expedition scouts examine a tapir jaw left in the cleft of a tree by uncontacted Indians in the Brazilian Amazon.

Scott Wallace

Brazilian wilderness tracker and indigenous rights activist Sydney Possuelo.

Scott Wallace

Expedition leader Sydney Possuelo (center), surrounded by Matis Indian Scouts, checks his GPS at a break in the jungle canopy.

Adapted from a pre-show interview with Scott Wallace and from his 2003 National Geographic article, "Into the Amazon."

The western rim of the Amazon follows an arch along Brazil's western border, nestled next to Peru and Bolivia. These are dense jungle areas — the most impenetrable regions of the Amazon. This is where the last uncontacted tribes in the Americas have sought refuge. This is also where, in 2002, Scott Wallace, a writer for National Geographic, went in search of the Arrow People with Sydney Possuelo, a Brazilian wilderness tracker and indigenous rights activist — and one of the few people on Earth who's made contact with isolated tribes.

"It's incredibly inhospitable to venture into these lands, and you can't reach these places even by river," says Wallace. "What's required is going as far as you can go by river, and then basically trailblazing — bushwhacking through track-less jungle. And it's because it's so inhospitable and isolated and difficult to penetrate that these Indians have been able to survive as long as they have."

For years, South American governments have refused to acknowledge the existence of these tribes. But five weeks into the expedition, Possuelo finds human tracks pointing to vast, dark virgin jungle. He knows the language of the jungle and a makeshift gate made of hacked sapling warns them to "keep out." Exploring the jungle with a team of Matis Indian Scouts, they know they are near the Arrow People, and they maintain a distance — they want to get out alive. Two Indians are seen running past them, scattering and disappearing into the rain forest. The point is not to make contact, but to protect the Arrow People.

As a community, isolated tribes have a collective memory of what making contact can do. Parallel to a world that existed hundreds of years ago, when European explorers colonized South America, some tribes that have made peaceful contact with the modern world have fallen to poverty and disease. But isolated tribes remain threatened by settlers and illegal loggers that are pushing the frontier into the Amazonian hinterlands.

In the case of the Arrow People — whose land Possuelo and his team entered — there was probably no one who entered before. Possuelo was able to go in because he had a large contingent of armed men. In the end, he finds out where they live and any hint of their lives, and then leaves.