David Livingstone, the famous nineteenth-century missionary and explorer, was eager to travel into the uncharted lands of Central Africa to preach the gospel. On one occasion he arrived at the edge of a large territory that was ruled by a tribal chieftain. He was instructed to stop at the perimeter and wait. According to tradition, the chief would come out to meet him there. Livingstone could go forward only after an exchange was made. The chief would choose any item of Livingstone's personal property that caught his fancy and keep it for himself, while giving the missionary something of…