After watching an episode of Channel 4's Pioneer House, it struck me that you'd have to be pretty optimistic to have been an early migrant to the New World. Even if news of the appalling survival statistics didn't make it back to the motherland, the migration would be a step into the complete unknown, starting with a terrifying ocean voyage. Even later migrations, whilst frequently fleeing abject poverty, would be based purely on the hope of a better life. That seems a pretty good definition of optimism to me.
So I wondered if this meant that the population of the US was seeded by overwhelmingly optimistic people, and this has led to a genetic bias in favour of optimism in the US ?