In this photo released by Brazil's indigenous peoples' agency Funai, 'uncontacted' tribesmen react to an overflight by agency officials. Funai warns that illegal logging and mining are putting such communities at risk of disease and cultural annihilation. (Gleison Miranda, Funai/Associated Press)

In May 2008, Brazilian officials released photographs of what's believed to be one of the last groups of indigenous peoples in the world who haven't had face-to-face contact with outsiders.

A Sentinelese man fires arrows at a passing helicopter passing over his island in the days after the 2004 tsunami. (Indian Coast Guard/Survival International)

Indeed, there are more than 100 such tribes worldwide today, according to Survival International, an advocacy group for indigenous peoples.

Most of these groups have had some contact — indeed, some are engaged in conflict — with outsiders, but are considered "uncontacted" because there is no ongoing peaceful communication.

They remain isolated sometimes due to rugged terrain, such as the rainforest of the Amazon. Often times, though, these tribes have fled violent encounters with the outside world in the past and now choose to live apart from it.

Some uncontacted tribes have numbers in the tens … or fewer. One Brazilian tribe consists of only a solitary Indian called The Man of the Hole. He is believed to be the last known survivor of his people and survives in a shelter dug out from the ground, away from outside contact.

The Amazon regions in Peru and Brazil are home to most of the world's uncontacted peoples. But several uncontacted tribes live in a number of other places around the world, such as West Papua and the Andaman Islands of India.

Threat of extinction

Throughout history contact with outsiders has ended, most often, in disaster.

Apart from the possibility of violence, first encounters can often be fatal because the indigenous people lack the antibodies to fight off viruses —colds and flus — common to the outside society.

Today, the existence of remote tribes is threatened in some areas by logging and oil and gas interests that have encroached on their lands. This has placed the tribes in potential conflict with other indigenous and uncontacted groups.

In some cases, roads built through indigenous lands have increased contact with outsiders, including loggers, ranchers, missionaries and sometimes tourists.

As Jose Carlos Meirelles of Brazil's National Indian Foundation told the Associated Press after the release of the May 2008 pictures: "We put the photos out because if things continue the way they are going, these people are going to disappear."