Re-read Malifaux Chronicles issue 1. The second paragraph in the meet the Neverborn chapter implicitly states that the Neverborn are the side effect of the original inhabitants of Malifaux using dark and horrible magic.
I like to think of the Neverborn as Americans. They came, they committed genocide, they settled in, now they think they own the joint. Now other people are showing up with the same idea. This makes everyone evil... except The Plague and Seamus, they want to kill all life and since everyone deserves it, they can't really be all bad can they? They are doing both worlds a huge favor be getting rid of their pesky infestations.
On a side note, further along in the article it refers to humans repopulating Malifaux in reference to the original Breach of the Great Barrier, which means that the original denizens of Malifaux were human. Which also implies that the Tyrant-Entities were human at some point.