Re: There must be a second Earth...
i think there are two offshoots of humanity..... ie.if the neandrathals also evolved parallel to us. but in this case its the earth humans (more similar in DNA, etc. to the skin job cylons) and the 12 colony humans.
at somepoint the "toaster" cylons grab some sort of technology from the earth humans (maybe alluded to by ellen tigh's words at the end of 4.11) and then use this technology to make the skinjob model cylons.
The greatest man to come out of Canada since William Shatner
"my daughter will grow up believing that her father is a traitor....but she will grow up"
- Admiral Jarok, the defector.