No one knows for sure. At a rough guess, there are probably more than 100 around the world, mostly in Amazonia and New Guinea, says Rebecca Spooner of Survival International, a London-based organization that advocates for the rights of indigenous peoples. Brazil’s count is likely to be the most accurate. The government there has identified 77 uncontacted tribes through aerial surveys and by talking to more Westernized indigenous groups about their neighbors.

There are thought to be around 15 uncontacted tribes in Peru, a handful in other Amazonian countries, a few dozen in the Indonesian part of the island of New Guinea and two tribes in the Andaman Islands off the coast of India. There may also be some in Malaysia and central Africa.