25/05/2017 04:34 BST | Updated 25/05/2017 05:32 BST

Uncontacted Tribes Are Not Only The Most Vulnerable Peoples On Earth - They're Also Vital To Its Future

Only through a global outcry and sustained pressure on governments, multinationals, and international bodies like the UN will the most vulnerable peoples on the planet stand any chance of surviving. I've added my voice to this call, and urge others to do the same.

For as long as I can remember I have considered it a very significant and moving fact that there are people in the world who don't live as we do. It is very common in industrialized society to assume that our ways are simply the norm, and that if they haven't already taken over in any other culture or part of the world, they soon will. Most people consider the spread of industry, technology, capital and a materialist outlook on life to be not only normal, but good, a sort of "progress" which we should actively support.

That simply isn't my view. More importantly, it isn't the view of many indigenous people around the world, who have been battling for centuries against colonial efforts to steal their land and resources and force them into the mainstream. This battle isn't only about culture and diversity, but about people's right to live as they choose, and define "progress" and "development" in terms which they see as suitable to them.

This is truer of uncontacted tribes than it is any of any other societies on Earth. These groups - some small, some fairly numerous - have no peaceful contact with industrialized society, and are the most vulnerable peoples on the planet. We know very little about them. But we do know that there are more than 100 such tribes around the world, most of them in the Amazon, but also in the Paraguayan Chaco, the Andaman Islands, and West Papua. And we know whole populations are being wiped out by genocidal violence from outsiders who steal their land and resources, and by diseases like flu and measles to which they have no resistance.

We also know that they have expressed a clear desire to remain uncontacted. There are signs which no outsider could possibly mistake: spears crossed in the forest, or arrows pointed at passing planes. The Sentinelese people in the Indian Ocean - who miraculously survived the 2004 tsunami - make their wishes plain with gestures of understandable aggression towards outsiders approaching their island. Their counterparts in the world's great rainforests aren't able to demarcate their own territory quite as clearly, but they make similar gestures when provoked.

Besides justified hostility, there are other signs we can get from looking at photos or footage of uncontacted people. In general, we see healthy human beings, including children and older people - well-fed and not showing any outward signs of illness. Some have large dwellings, and well-maintained gardens full of crops such as manioc and maize. We even see traded goods from outside: the occasional metal pot or knife obtained via complex networks of exchange.

This clear evidence undermines the suggestion that it is our duty to forcibly contact these people. As far as we can tell, they neither need nor want our intervention in their lives. They are aware that outsiders exist but they have chosen to remain apart from mainstream society. These people are not backward and primitive relics of a remote past. They are our contemporaries and a vitally important part of humankind's diversity. They're not crying out for "progress," but rather, for the freedom to determine their own futures.

Uncontacted tribes' knowledge is irreplaceable and has been developed over thousands of years. Their languages, mythologies, and views of the cosmos are a unique heritage which outsiders have no right to steal or destroy. They are also the best guardians of their environment. And evidence proves that tribal territories are the best barrier to deforestation. Any satellite image of the Amazon will clearly show protected indigenous territories - still a shamefully small part of the rainforest - as islands of green surrounded by deforestation, cattle ranches and plantations.

There are plenty of people who would like to see these territories reduced in size, or even abolished altogether. Brazil for example, which is home to more uncontacted tribes than any other country, also hosts a powerful agribusiness lobby - the ruralistas - who would gladly see all indigenous people wiped out so that they can profit from exploiting their land. An urgent and horrific humanitarian crisis is already unfolding in the country, as a pro-agribusiness government moves to cut all remaining protection and change the law in favour of the ranchers.

Some anthropologists say that we have a responsibility to undertake so-called "controlled contact" expeditions, forcibly bringing uncontacted people into the mainstream. But this ignores a wealth of historical evidence that contact is always fatal. Initiating contact must be uncontacted peoples' choice alone. Those who enter uncontacted tribes' territories deny them that choice. People like the Zo'é, the Kawahiva, and the Akuntsu have been decimated in the recent past, and further efforts at "controlled contact" will only lead to further genocide.

My passion for indigenous rights took me to Survival International - the global movement for tribal peoples' rights. Since 1969, Survival has been leading the global fight for uncontacted peoples' right to land, life, and a secure future. Only through a global outcry and sustained pressure on governments, multinationals, and international bodies like the UN will the most vulnerable peoples on the planet stand any chance of surviving. I've added my voice to this call, and urge others to do the same.

With energetic support from around the world, I believe uncontacted tribes can thrive. I encourage people to watch and share this short film which I was proud to feature in alongside Gillian Anderson, and to get involved in the movement.

Sir Mark Rylance is an actor, director, activist and ambassador for Survival International