Here's an interesting article courtesy The American Enterprise Online that examines the link between entrepreneurship and hypomania, a temperament variant genetically associated with manic-depression:
Energy, drive, cockeyed optimism, entrepreneurial and religious zeal, Yankee ingenuity, messianism, overflowing confidence—these traits have long been attributed to an “American temperament.” It is quite possible that these national characteristics have been encouraged by our rich concentration of hypomanic genes.
If a scientist wanted to design a giant petri dish with all the right nutrients to make hypomanic genius flourish, he would be hard-pressed to imagine a better natural experiment than America. A “nation of immigrants” represents a highly skewed and unusual “self-selected” population. Do men and women who risk everything to leap into a new world differ temperamentally from those who stay home? It would be surprising if they didn’t. “Immigrants are unusual people,” wrote James Jaspers in Restless Nation. Only one out of a hundred people emigrate, and they tend to be imbued “with special drive, ambition and talent.”
Could it be in the blood? Various theories abound as to what we've inherited from our risk-taking ancestors who chose to leave their homelands and sail across the Atlantic for the promise of the unknown.
On a similar note, borntoexplore.org examines "Attention Deficit Disorder", a probably-overdiagnosed "disorder" that may have actually been a useful personality trait during the days of the pioneers. In fact, this is a personality trait that has also been associated with some of the more famous and successful explorers, inventors and creative people.