Any clues to why it is called Second Son?

So I've played this game once and am now on my evil playthrough, but I still haven't found any relation to the title. I've looked around the web as well and have really only seen speculation, but I have to think they named it Second Son for some reason other than to just highlight that it is a new story arc.

I'm wondering if maybe the Cole DLC campaign really is about this underground group that is finding conduits, i.e. the First Sons, and this is just the new group. If so though, you would think that there would be a little bit more about that story tied into the game.

Maybe there will be DLC down the line that highlights this, but just wondering if anyone else has picked something up from the gameplay.