Two hundred years ago this May, Meriwether Lewis and William Clark, together with the three dozen army volunteers and hired hunter-interpreters who made up the Corps of Discovery, departed their winter camp at the mouth of the Missouri River, north of St. Louis, Missouri, and set out to make history. President Thomas Jefferson had charged them with the monumental task of exploring the unknown lands of the Louisiana Territory, purchased from France the year before, and trying to find a navigable route to the Pacific Ocean via the Missouri River. The explorers were also asked to make extensive geological, geographic, anthropological, and biological observations. Their biological duties included the collection of both plant and animal materia...