John Allen Chau, 26, a Christian missionary from Vancouver, Washington, died last month while attempting to convert the Sentinelese, a remote group of skilled archers who have long repudiated contact with the outside world.

Believed to number no more than 100, the Sentinelese are the only uncontacted tribe in the world to occupy their own island. Like so many things about the Sentinelese, their origins are shrouded in mystery. They are thought to have migrated thousands of years ago from Africa to North Sentinel Island in the Indian Ocean. No one knows what the Sentinelese call themselves, nor what language they speak.

And we cannot know such things without hastening the islanders’ demise.

From Chau’s own writings in notes later recovered by Indian police, it is clear he understood his mission was both illegal and fraught with risk. But Chau did not appear to understand that his very presence posed a serious threat to the Sentinelese. As a tribe that has lived at extreme remove from the rest of the world, the Sentinelese are highly vulnerable to infectious diseases borne by outsiders, against which they have little or no immunity. The flu, measles, even the common cold could prove deadly, spreading rapidly through a close-knit community with devastating and irrevocable consequences.

There are more than 100 indigenous communities scattered across the globe still living in isolation from the outside world. The vast majority inhabit the most impenetrable redoubts of South America’s Amazon rainforests.

Brazilian authorities have confirmed the existence of 27 uncontacted tribes, but there could be as many as 70. More than two dozen groups of isolated nomads wander the forests of Peru. Neighboring Ecuador, Colombia, Bolivia, Venezuela and Guyana each host a handful of uncontacted tribes, and there is one in the scrub forests of Paraguay.

Like the Sentinelese, all these groups have managed to survive in near-complete independence from our industrial economy. No smartphones, no prepackaged food, no Nikes. They derive their sustenance solely from the forest — their food, their shelter, their clothing, their medicine. And like the Sentinelese, these groups are under mounting threat from outsiders.

Thirty years ago, Brazil made a groundbreaking decision to stop forcing contact on isolated tribes, mindful of the spasms of violence and epidemic diseases that almost always resulted. The other Amazonian countries — as well as India — have followed suit.

Sydney Possuelo was the architect of Brazil’s no-contact rule, turning the country’s policy on its ear. The government scouts who once sought to woo the tribes from the forest were deployed on a new mission: to protect the isolated nomads and the untrammeled forests they need to survive.

I trekked with Possuelo through dense primal forests 15 years ago to monitor one tribe’s well-being and possible intrusions by outsiders — while avoiding any contact with them. For Possuelo, existential threats to these populations do not come solely from disease or the barrel of a gun. Any attempt by outsiders to intrude in the lands of isolated tribes amounts to a form of coercion.

Anthropologists and human-rights activists are warning authorities not to recover Chau’s body from North Sentinel Island, and, indeed, this is the best course of action. It would be highly dangerous for everyone and could trigger a violent confrontation or, worse, the beginning of prolonged contact that would gravely imperil the tribe.

As Possuelo said in an e-mail he sent me from the Brazilian jungle this week: “Those who seek to change their culture, their gods or their beliefs are practicing a form of violence. Perhaps people will only understand this when extraterrestrials arrive here and try to evangelize us with their gods and doctrines.”

Scott Wallace teaches journalism at the University of Connecticut and is the author of “The Unconquered: In Search of the Amazon’s Last Uncontacted Tribes.”