The non-human creatures of Altern are all born unnaturally, meaning that they are not born through human means of reproduction or by any natural means. They are, by default, creatures of magic and myth. Humans are the only ones who reproduce; obviously by means we're all familiar with.
There you go. I know, it's basic and what not, but so be it! I'll also be digging more into the magic and providing a definitive definition of it. And I'll have the five unstable substances all ironed out!
(Don't click the read more, there isn't any more after this!)