My take on the origin of Jacob and MIB by Vince Caramela

Looking at all the variables and what we've seen so far (episode 6.5 "The Lighthouse") I believe that the young blonde boy that evil Locke/MIB sees on the island is the young Jacob. This is obvious (to most Lost fans, to some degree) and I believe it will be explained as to what purpose it serves in later episodes.

Also, in episode 6.5 we are introduced to Jack Shephard's alternate universe son. This is quite a surprise and I think there is a real reason why we are being introduced to this character so late in the game.

My theory is this: Jacob and Aaron are one and the same... the young boy running through the jungle and communicating with Evil Locke is Aaron who later grows up to become Jacob and the origin of the Man in Black (MIB) we will find is Jack's alternate U. son. I think this makes sense since MIB wants so badly off the island and "exist" since he lives a normal functioning life in the real world I believe he hates his "cousin" Aaron/Jacob and the latter's acceptance of their fate when the two timelines become merged and both children are forced to assume their proper place on the island time-traveling and watching as things gets played and re-played in an almost Sisyphean struggle.

I don't know... hopefully this can stick by the time this posts since another episode will have aired.

Thanks.