In the 1860s, medical missionary David Livingstone was an international celebrity—famous most of all for disappearing on an African expedition. When journalist Henry Morton Stanley found him in 1871, Stanley’s supposed greeting to him (“Dr. Livingstone, I presume?”) became the stuff of folklore. In this colorful eight-week series, four modern-day adventurers—explorer Benedict Allen, war correspondent Kevin Sites, navigator Pasquale Scaturro, and wildlife expert Mireya Mayor—retrace Stanley’s 1,000-mile journey into the interior of modern-day Tanzania, contending with thirst, disease, and poisonous snakes. Sunday, May 31, at 10 p.m., History