One of the most fascinating studies I have read was conducted by a group of biologists who compared the randon mutations of rat mitochondria (the little fuel processing organelles in each of our cells that have their own, much simpler DNA) during episodes of widespread plague and during normal periods. They found that mitochondrial DNA mutations occurred 3 times faster in the presence of virulent pathogens (during plagues) that during normal times.
I think this is precisely the system property that makes the US economy more robust and adaptable than most other major economies. As American business owners and managers can tell you, in the US competitors try to kill your business every day, forcing adaptation, cost cutting, rationalizing, restructuring, soul-searching and, ultimately, growth. Without the relentless attacks of pathogens (your competitors) none of this would happen.
UPDATE: Commander Cornflake provides helpful perspective in the comments.