When the explorers Lewis and Clark asked the Shoshone woman Sacagawea and her husband, French trapper Toussaint Charbonneau, to act as interpreters for their expedition, the couple brought along their two-month-old son, Jean Baptiste. Over the course of the two-year journey, baby Baptiste won the hearts of the rough men of the corps. Captain Clark called him "my little dancing boy." But the rest of the story of this intriguing young figure has been...