It's integral to the setting. Basically humanity was all humans until a virus, combined with the reawakening of magic across the world caused a % of humans to mutate into either Dwarves, Orcs, Trolls, or Elves.
The history of the setting goes on to mention that occasionally two parents one race will give birth to a child of a completely different race due to latent genes. (referred to as "spike babies.")
There's also a small % of people that undergo mutation during puberty from human to a different race because of the same latent genes.
I'll see about working a brief "as you know Watson" explanation into the back story for readers unfamiliar with the setting, thanks for the suggestion.
I like her. Like Siren said, she's pretty standard fare, but the back-story was a well-written and enjoyable read. The main issue I have with this piece is probably inherent in the setting, but . . . how can a pair of elves produce a human child? That really messes with my suspension of disbelief. Was she really switched at birth? Adopted, but her parents didn't want to admit it later? Some explanation there would be helpful.