The gray-bearded, balding man sips coffee in the kitchen of his apartment in Brasília, Brazil. With a blank stare, he ponders the future of the three things to which he has dedicated his life: "Everything dies at its own time. The forest dies, with it die the Indians, with them die the sertanistas." But at 67, Sydney Ferreira Possuelo acknowledges that the sertanistas, men who make a living out of protecting the isolated indigenous peoples in the Brazilian jungles, may be the first to go.

Counting Possuelo, only five members remain. They travel to the remotest corners of the Amazon rain forest to track down isolated tribes and contact them before miners, cattle ranchers, loggers and others do, usually at gunpoint. Their job is to divert development around those tribes, so as to keep them from sharing the usual bleak fate of indigenous Brazilians. But it has been 20 years since the last sertanista was hired. And most of the old school--that is, people who have actual contact experience--have either died or retired.

Possuelo has done neither, although he was fired from his position with Brazil's National Foundation for Indigenous Peoples (FUNAI) last year after publicly criticizing the remarks of its president, who stated that there might be too much land already in the hands of native Brazilians. Today he coordinates efforts through the Instituto Indigenista Interamericano, a nongovernmental organization that is part of a multinational alliance dedicated to the protection of isolated tribes.

Possuelo had helped initiate a sea change in federal policy toward indigenous tribes by persuading the government that the natives should be left alone, to live exactly as they have since prehistoric times. The decision to make contact should be left to them. The prevailing wisdom throughout much of the 20th century and before had been "integration" into society. "The idea was that we should go fetch those peoples and share with them the benefits of civilization, since civilization is a good of all humankind that belongs to non-Indians and Indians alike," Possuelo says.

But such a bright positivist view conflicted with reality. After contact, many natives lost their lives to influenza and other diseases to which they had no natural defense. Not a few were expelled from their traditional territories to make room for highways, dams and cattle ranches. Many were murdered, in some cases with approval of government officials. But perhaps worst of all was the cultural dislocation.

When meeting a new group, Possuelo recounts, "you must keep an eye on the folks who are there. The guys fight you with bows and arrows, they kill you, they speak up to you, they assault you." Contact, however, changes all that: "One year later they are slack, emaciated, bowing their heads and begging for food and money by the roadside." A case in point: the Arara people, who had been called the scourge of the Trans?amazônica Highway for their attacks on work crews but today live as poor peasants fully dependent on federal aid. "You break down their health, their mythical universe, their work and their education system. They become outcasts, and many of them have been outcasts for 500 years," Possuelo says.

The veteran sertanista's career began in 1959, as a disciple of Orlando and Cláudio Villas Bôas, two of the three brothers credited with saving 15 tribes by creating the Xingu Indigenous Park, Brazil's first megareservation. With them, he journeyed into the Amazon for the first time in the early 1960s. In the 1970s he joined FUNAI and made his first solo contact with an isolated group, the Awá-Guajá of Maranhão.

By 1987 Possuelo decided to take the Villas Bôas strategy further, because even peaceful contact with such groups often destroyed their native culture and self-sufficiency. His idea: to avoid contact altogether. He convinced the government that it was more practical to demarcate indigenous lands and to guard the borders with armed agents than to provide for them indefinitely. "We do it for threatened animal species, why can't we do it for a unique ethnic group that has been there for thousands of years?" he asks. "That's good for the Indians, who will see their land and their tribal traditions respected, and good for the state, who will no longer be charged with genocide." As an added bonus, a study found that legally recognized indigenous lands in the Amazon had lower average deforestation rates (1.14 percent) than federal conservation units (1.47 percent).

Executing Possuelo's plan, however, means identifying the indigenous groups before miners, loggers and others find them--encounters that could lead to long-lasting, deadly skirmishes, as in the case of the Korubo people of the Javari Valley, which lies near the Peruvian border. First contacted in 1972, they violently resisted intruders and over the decades had clubbed to death many who ventured into their territories. In 1996 Possuelo managed to establish peaceful encounters with one Korubo clan, in part by singing aloud (enemies come in silence) and by offering gifts. Despite having known the clan for many years now, Possuelo still considers them unpredictable; he has kept anthropologists away, he has said, for their own safety. He himself will not bother to contact a larger Korubo group deeper in the jungle, feeling that they are remote enough that they will not meet outsiders.

The noninterference strategy has gained worldwide approval. The United Nations Declaration on the Rights of Indigenous Peoples, adopted in 2006, incorporates the right to nonassimilation. Despite that, the policy faces critics in Brazil, who see such protection as an additional burden to taxpayers that only postpones inevitable integration. "Of course, you're buying time," says Márcio Santilli, head of Brasília's Socio-Environmental Institute and a former president of FUNAI. "But buying time is central to mitigating the impacts of contact."

And time is running out for those Indians. Brazil has demarcated less than a dozen lands with isolated peoples. Possuelo and his colleagues have identified 22 isolated groups in the Amazon, although FUNAI believes that the true number might be closer to 68, based on aerial surveys and witness accounts. Some live in previously protected indigenous lands, some in areas that are right in the range of agricultural expansion.

In the other six South American countries with isolated peoples--Ecuador, Peru, Bolivia, Paraguay, Colombia and Venezuela--the prospect is even bleaker. "The issue is all but unknown to them," Possuelo states. "And it is no use to undertake protection policies here if indigenous peoples are not protected across the border and get killed on the other side."

In 2005, before leaving FUNAI, Possuelo organized a meeting in the Amazon city of Belém that gave birth to an alliance for the protection of isolated peoples in the seven countries. The alliance, consisting of state attorneys, environmental defense groups, anthropologists and indigenous organizations, called on their governments to identify and protect their indigenous charges. "The idea here is to raise public consciousness in the first place," he says. "Then we'll be able to talk about public policy." The alliance has been facing an unexpected challenge, though--from indigenous peoples themselves. "In Ecuador last year, contacted Indians killed 20 isolated Indians," says Marcelo dos Santos, who took over Possuelo's old FUNAI post.

Possuelo agrees that the isolated groups may not last much longer. But pointing at several figurines of Don Quixote that he keeps in his living room, he says he has not given up. "The fate of those peoples will depend ultimately on our choices," he argues. "Those peoples are the last Americans. We are indebted to them."