I’ll start by saying that I think what Dogen told us about how he got to the island the same way Jack did is true for all characters. Every single one of them, including people like Jacob and MIB, got to the island via seemingly random events e.g. a place crash, a shipwreck etc.
On the island, there has always been a ‘higher power’, but the person playing that role changes. One side of the higher power is a god-like entity (Jacob, in our timeline of events through the eyes of the 815ers) and one side is the evil-like entity (the MIB/Monster). I’m also counting the ‘advisor’ role as being one of the ‘higher power’ people, which, of course, is Richard.
Everyone comes to the island as nothing more than a human - a survivor - and from there they end up falling in to their places. (Backed up by the conversation between MIB and Sawyer in Substitute where MIB said he used to be a man, just like Sawyer was.) At a certain point in the islands history, there is a struggle in the ‘higher power’ which causes new people to take over the roles of the island. We have seen the list of candidates, there was people on there from as far back as ’55 (Jones - the army guy who’s uniform we saw 17 year old Charles Widmore wearing back in S5). This is because the current ‘higher power’ have to collect people on to the island, as many as they can, before the struggle happens - forcing them to start picking from their list, as if these people are baseball trading cards.
So, when this struggle occurs, the choices of who replaces who are made. The god-like entity uses a list of candidates - the very best of the best who could replace him - to work out who the best choice would be. He monitors them and slowly crosses them out as he finds they aren’t what is needed. The evil-like entity uses a different method - claiming those who are dead. This cycle repeats endlessly until someone can finally get the right people in to the right roles and make their side become strong enough to stop the other side from being able to bring a new player to the equation. This fits the line by Jacob to the MIB in The Incident, ‘It only ends once. Anything that happens before that is just progress’.
Jacob was a man chosen from a list of people on the island by the previous light entity and the MIB was a man ‘claimed’ by the previous dark entity. This doesn’t necessarily mean that the light entity is the good guy and the dark entity is the bad guy, it is merely a way of separating two contrasting view points on how the island should be handled.
Where does this translate in to what we’re seeing now? Well, we’ve just seen the power struggle in the ‘higher power’ which resulted in Ben stabbing Jacob. This started the change over of new people filling the roles. By this point, I think that we’ll see Jack fill out the light entity’s role, while Sayid (who was ‘claimed’) will fill out the dark entity’s role when the current MIB is destroyed. There’s a reason I specified that I count the advisor as part of the ‘higher power’ and it ties in to the list of candidates. I believe Kate will take over that role when Richard is finally killed/removed of his ageless power. A popular theory right now is that it’s only guys who are still on the list of candidates but from the list we saw, Austin was never on that list. I believe she wasn’t on there (despite the fact other female character’s last names were) because she was never seen as being capable enough to be the full leader but she was seen as the! perfect person to be the advisor of the light entity. This is backed up by the way that, ever since S1 of Lost, we have seen Jack constantly asking Kate of her opinion and if she has his back.
Everyone who isn’t part of the ‘higher power’ are left to choose who to follow. In the end, one side will get the right people in the right places and will finally break the cycle. Until then, this rotation will carry on happening.