Humans' body structures and genetics are much different than the red eyed races. This is the reason that humans can't interbreed with the red-eyed races or use the same type of magic.
Long ago, humans were ruled by a species with red eyes, who bred fear with overwhelming power and drank human blood to survive. But their reign didn't last long. At some point, the rulers disappeared from the human world.
The people with red eyes were feared and called monsters by the other villagers.
It is said because of a contract the vampires and humans made long ago the humans and vampires can't produce offspring. But because of Lark born with red eyes Bathony goes to the Naverus library to do research on it and finds out that a human escaped the 'contract' what this means is not yet known yet.