Humans have wandered over the planet for nearly the past two million years. In a rapid global expansion, ancient humans migrated from the valleys of eastern Africa to the Middle East, Asia, and Europe, and crossed the Bering Sea land bridge and the Pacific and Atlantic Oceans. Anthropologists (scientists who study the origin, behavior, and development of humans) believe that growing populations, which increased competition for food and space, may have been a factor in this spread. They believe that these ancient humans may have been motivated as well by a basic human impulse: curiosity.

The desire to explore the landscape ahead and the sky above has been a part of human nature since before recorded history. Over the last few thousand years, many cultures and civilizations have undertaken major explorations, seeking out new land and adventures. The experiences gained through these journeys often...