: Indeed
From a practical point of view, I think one would know if one was a cyborg after a few minutes of self-examination, but if we restrict ourselves to evidence in the game, I don't think the Marine knows. In the Marathon 1 manual, the description reads "It's funny, but you've always been the colony's trouble shooter. You're bigger and stronger, and a better shot." If we assume that "it's funny" applies to the whole passage, then the Marine has no special explanation for his abilities, he thinks he's just that damn good.
Would the Marine deduce anything from his own abilities in the game, such as health recharging and being resurrected from pattern buffers? Not if he attributes them all to the battlesuit he wears. And there's nothing he does that couldn't be done by equipment that would could be used by any human.
Then there are all the places in the game where the AIs refer to the Marine (to his face) as non-human. Would this be enough to convince him? I doubt it, the AIs are pretty crazy in the first place, and it's very hard to convince a human that he is not a human after all on the strength of words alone.
I think that he would realize he is more than human in the middle of Marathon Infinity, as he begins to jump the timelines and eventually figures out that not only is he doing these jumps himself but he can control them (he ends up in the right timeline at the end, or at least a good one, which was his goal).
