Feeling as if the Tyrol subplot on Friday's Battlestar Galactica was a little... retconnish? In the latest commentary podcast, series showrunner and episode writer Ronald Moore comes clean about how the idea came up. Spoilers!
Explaining the out-of-nowhere revelation that Tyrol and Callie's son Nicky wasn't actually Tyrol and Callie's son, Moore admitted:
This whole little subplot about Nicky's real father being discovered was something we, you know, decided in the writers' room... Once we had decided that Tyrol was a cylon, that automatically meant that Nicky was another Cylon hybrid. And we had said, very clearly, on the show... that Hera was the only hybrid between human and Cylon. And I didn't want to change that, Hera's role in the firmament of the show is very firmly established in my mind and I had a specific place where I wanted it to go, and then suddenly we had this additional problem if Tyrol was a Cylon. So we did have some conversations at the end of season 3, when we decided to make Tyrol a Cylon. And the long and the short of it is, somebody said, "Well, what if he's not the father?" and we all kind of laughed, and then we said, "Actually, that makes sense."
So there you have it; Callie's good name, besmirched as the easiest solution to a plot problem. Official.
Battlestar Galactica Episode Commentaries [Scifi.com]