It may be genetics.
Researchers have claimed that our urge to explore the world is at least partially rooted in a genetic mutation known as DRD4-7R, aka the explorer's or adventurer's gene. In 1999, an extensive study by the University of California found this genetic mutation more common in nomadic, migratory populations. A follow-up study looked at 18 indigenous populations living along the ancient African migratory routes, and found that the DRD4-7R gene, along with its cousin 2R, is indeed more common in the people who have traveled the farthest from their ancestral homes.
Some farther than others.
And you might have it too! The explorer's gene is thought to be in 20 percent of the population, and it's probably the reason you're shifting in your chair right now, yearning to explore strange new frontiers and bone exotic green women.