[Theodore] Roosevelt lived during the last days of the golden age of exploration, a time when men and women of science roamed the world, uncovering its geographical secrets at a breathtaking pace and giving rise to bitter international competitions. The year he was born, the earnest young explorer John Hanning Speke, traveling with the famed Orientalist Richard Burton, discovered the source of the White Nile. In 1909, the year that Roosevelt left the White House, Americans Robert Peary and Matthew Henson won the race to reach the North Pole ... Just two years later, in late December 1911, Norwegian explorer Roald Amundsen became the first man to reach the South Pole. Robert Scott, a renowned explorer and British hero, made it to the pole a month later, only to find the Norwegian colors flapping in the polar wind where he had planned to plant the British flag. Shocked and dispirited, Scott and his men froze to death on their long, bitter journey back to their ship. Sir Ernest Shackleton and his men, in a legendary attempt to cross Antarctica, narrowly escaped the same fate two years later, the same year that Roosevelt would set off down the River of Doubt.SOURCE: The River of Doubt: Theodore Roosevelt's Darkest Journey, by Candice Millard (Doubleday, 2005), pp. 61-62
To [Henry Fairfield] Osborn, Roosevelt's decision to descend this river seemed insane if not suicidal, and he ordered [Frank] Chapman to tell the former president that the American Museum of Natural History expected him to adhere to his original plan. However, when Chapman's letter, with all the weight of the museum behind it, reached Brazil, it had less effect than a leaf falling in the rain forest. Having found the challenge he had been yearning for, Roosevelt was beyond the reach of Osborn's persuasion. In a letter to Chapman, Roosevelt wrote, "Tell Osborn I have already lived and enjoyed as much of life as any nine other men I know; I have had my full share, and if it is necessary for me to leave my bones in South America, I am quite ready to do so."