In a way, these earnest expeditions say much about how the very idea of adventure has changed. Once naturalists like Darwin made sense of a wild world. Explorers like Lewis and Clark sought to map what seemed limitless wilderness. Adventurers like Livingstone and Scott sought to conquer the earth's natural challenges and sometimes died trying.

Over the past half-century, backpackers and other adventurers beat new paths across Asia, South America and other locales - only to discover years later that some paths had been clear-cut into highways fit for Holiday Inns.