Where does the magic come from?

[Ittoni 538]

I think is a resource you can channel or create with the aid of years of evolution. Like uh... Like the sun? Plants use the sun to photosynthesize so it's part of their whole system of life, but others only use it to raise body temperature or transform proteins. Or maybe like electricity, were everyone possess it to be able to function and transmit instructions and reactions between cells and the body's components, but some animals have evolved to store and discharge a powerful amount of electricity to stunt their food or an enemy. 

So magic in that sense could be something everyone possess in equestria, some more some less depending on the attributes of an individual in their respective race and how they utilize that "energy", but there some species that have evolved to channel it to attack and for other convenient things. In my opinion is more like a type of energy.