I also feel that I should mention, because there seems to be some mild confusion, that magus isn't something you're gifted with. In theory [i]anybody[/i] can be an Arcanist, you're not born as an Arcanist or else magically infertile. If they're clever and you do well in school, or they've got parents who'll educate you themselves, then they can learn to use Magus. Arcanist isn't an inherent race or title, it's more or less Luxas' equivalent of having PhD in your name. The only thing that restricts your studies is what magus manifests when you know the basics. If you learn the fundamentals of magus and it turns out you're an opacamancer, that's the point at which studying auroramancy ceases to become feasible. 

Furthermore, magus is not an energy inherent in anybody, either. An Arcanist doesn't pulsate with it in their veins, or anything. They draw it from other places. From the Duskthorough, from the Dawnstream and The Nocturne. Or even from the planet itself. The reason Arcanists are hard to come by is because it takes a lot of work to become one, not because they've got some sort of low magical birth rate.