The recent killing of an American missionary by members of an isolated tribe on a small island in the Indian Ocean has reignited questions about the fate of the last few groups of people living off the grid.

In an era when people across the globe are hyper-connected by technology and increasingly interlocked economies, the survival of a few dozen groups of hunter-gatherers living in complete isolation may seem extraordinary. But experts say they may not survive undisturbed for much longer.

Because most of these groups are small and highly vulnerable, anthropologists and indigenous activists have been debating whether it makes more sense to leave them alone — or try to establish contact with them to offer basic medical care, such as vaccines. Here are some basic facts about the world’s remaining isolated tribes.

How many are there, and where?

Anthropologists and activists who study the issue say it’s hard to know for certain. But based on satellite images and field research, experts believe there are more than 100 communities living in isolation.