Five years after vacating the White House, Teddy Roosevelt took an expedition down the River of Doubt—an uncharted waterway in Brazil’s Amazon rain forest that was home to less-than-friendly tribes and a swarm of deadly diseases. The man who led his troops up Cuba’s Kettle Hill in the Spanish-American War managed to fend off the region’s natives, but he wasn’t a rough-enough rapids rider to cope with the indigenous afflictions: The jungle fever he contracted on that 1914 trip eventually proved fatal. Since then, the ex-president’s family has hired three expeditions to chart the Rio Roosevelt, as it came to be known, although without success (one even disappeared without a trace). Last year, however, TR’s great-grandson, Tweed Roosevelt, managed to successfully follow in the footsteps of the first Bull Moose. The investment-adviser-turned-explorer recounts the exploits of his team’s travails in a slide-illustrated lecture at 8 p.m. at the Museum of Natural History’s Baird Auditorium, 10th & Constitution Ave. NW. $11. (202) 357-2700. (Alan Green)