Unless you studied anthropology in college, you may not know the name of the Yanomami Indians who dwell in the Orinoco river basin of Brazil and Venezuela. But you’ll immediately recognize the disc-lipped tribe in this subtle, disturbing documentary about the scientists who began to study the “virgin soil population” in the ’60s. National Geographic stories and TV specials followed, along with many books by the various experts in Secrets of the Tribe. Yet they, the anthropologists, are the tribe being studied by director José Padilha (Bus 174, Elite Squad). Sexual conquest and murder are among the theories attempting to explain why the Yanomami regularly interrupt their eco-idyllic existence—endorsed by Sting!—with bloody raids. As it turns out, however, rival academics are just as hostile and sexually rapacious, if not more so. Retired UCSB prof Napoleon Chagnon is here accused of genocide, but he seems an entirely calm and peaceful fellow. Until the name of rival researchers Kenneth Good is raised, whom Chagnon calls a pedophile for marrying one of the Yanomami. This back-and-forth is largely based on Patrick Tierney’s 2000 book Darkness in El Dorado, and he’s a source here, too. Then there’s the matter of Jacques Lizot, a protégée of Claude Lévi-Strauss, whose behavior is revealed to be even more horrifying. Those supposedly rational men observing the Yanomami all seem to have gone slightly mad, like Brando in Apocalypse Now. And their madness, like measles, is shown to be pathogen we imported. (SIFF Cinema: 4 p.m. Weds., June 2; and Harvard Exit, 9:15 p.m. Mon., June 7.)