Human is the only playable race, and spell casting is allowed. In the IC I was going to elaborate that mana granted to humans is a permanent thing; you either have mana to cast magic with or you don't, and how strong a caster you are depends on how much of it you can precisely control. For example, a weak magician might consistently access 50% of their mana and only be able to fine-tune a portion of that, whereas an adept magician can access over 75% and use almost all of it precisely. Mana would also have been in your family tree, so your ancestors or any children you have might have mana too. The "conservation of mana" aspect is mostly people trying to make the most use of the mana-wielders left since they are dying off little by little.