I was talking to a friend the other day and he brought up something I hadn't thought about before.
He said that suppose the entire world was wiped out except for say 100 people. Humans have made huge advances being industrialized, but in this scenario, things as they are now could not be maintained. Life would revolve around survival and these people would revert back to hunter/gatherers and stay that way for a long, long time, even with the knowledge we have now. Just surviving would take all their time.
I believe it was Carl Sagan that thought this scenario has played out many times in the history of the earth. If a major disaster, like the Yellowstone caldera exploding or a huge meteorite hitting, life as we know it would be changed. If the disaster was bad enough man would go backwords just trying to survive.