There's a theory, that at some point during human history, earth was visited by "aliens", who intervened at certain points, and helped us out a little bit as far as technology, and general advancement goes. A History Channel documentary was covering the topic, and I've been watching the episodes online. Very interesting stuff - especially when you listen to some of the old accounts of people coming down in various "flying machines". This is the first episode - think they go up to season six!? http://www.youtube.com/watch?v=DIOpEFvmal8