TEXT: Today there are tribes in the Amazon rainforest that have not interacted with the modern world.

SCOTT WALLACE (AUTHOR, THE UNCONQUERED): Within Brazils indigenous affairs agency, there is a special unit charged with going out into the field and verifying the reports that come in from eyewitnesses or from aerial, you know, intelligence recon flights of a fleeting group of indigenous people.

TEXT: Today, there are about 100 of these tribes. One hundred years ago, there were many more.

TEXT: In 1914, when U.S. president Theodore Roosevelt traveled to an uncharted river, his party encountered some of these tribes.

SCOTT WALLACE: The forest back then was still unexplored and populations unknown. There was probably a count of somewhere around 350, 400 tribes. But nobody was really keeping count at that point.

TEXT: Over the years, contact with outsiders was often perilous for the Indians.

SCOTT WALLACE: In the 19th century, early 20th century, during the rubber boom, tappers, went deep into the Amazon forest, rounding up indigenous villages and press ganging them into tapping rubber and basically to serve as slaves.They were just completely wiped out, often maybe it was violence to begin with, massacres, but what massacres or extreme violence didnt do, epidemic diseases did.

TEXT: Todays isolated tribes are still under threat as development spreads.

SCOTT WALLACE: Generally speaking, the advance of civilization into these areas, are illegal loggers, illegal gold prospectors, illegal animal hunters. These are the kinds of elements who are prone to violence, to shoot first and ask questions later. So, the face of civilization thats presented to these groups is not a welcoming one.

TEXT: To avoid contact, they have been pushed into smaller and smaller regions, raising the question of how long they can remain isolated.

SCOTT WALLACE: A number of people have suggested and even argued that its really no longer a humane thing to keep these groups isolated, that they should enjoy the benefits of modern civilization. The problem is that often these groups end up in the lowest rungs of society. We say, Oh, theyll benefit from our education and our modern medicine, but so often they dont get those benefits, and so they end up often living in squalor and destitution.

TEXT:As their world shrinks, what will that mean for their future and ours?

SCOTT WALLACE: These groups cannot survive without intact, pristine rainforests. They need water thats unpolluted, they need the trees, they need to be free from persecution by outsiders coming into poach their animals or cut their trees or dig up their land. If these tribes, all of them, disappear, it will be a tragedy for humanity.