We take for granted that popular entertainers can and should advocate for causes they believe in. But until Harry Belafonte pioneered that kind of activism in the middle of the last century, stars largely kept their political leanings private. In the lead-up to last year’s Many Rivers to Cross festival, which Belafonte helped dream up, the New Yorker staff writer Jelani Cobb paid a visit to the actor, musician, and civil-rights icon. Belafonte turned ninety this year and is looking to pass the torch, but he’s worried about the state of the civil-rights movement and what he sees as a lack of organized response: we have a struggle, he says, but not a movement. Cobb, who covers many civil-rights and other political issues for the magazine, teases out what Belafonte means.   Plus, the Mashco Piro tribe is one of the last remaining groups to survive only by hunting and gathering with tools that its members make themselves. Residing deep in the Amazon rain forest, they are extremely isolated and, for nearly a century, have rarely been seen by outsiders. Recently, however, there have been encounters with the outside world—and members of the Mashco Piro have killed two people. In this segment, the New Yorker staff writer Jon Lee Anderson journeys up the Madre de Dios River to a remote contact point where government anthropologists are trying to establish relations with the Mashco Piro. They are charged with protecting the tribe from potentially fatal contact with drug traffickers, loggers, and epidemic diseases, and with preventing further violence.   This episode originally aired on September 30, 2016