User blog comment:Maki Kuronami/Lesson 25: Knowledge is the most powerful weapon/@comment-10390252-20141003140235

Okay, theory time: We know that Dust reacts to aura, which is an energy created by the soul. However, the soul can be light but it can also be dark. Whilst light soul energy generates things like shielding and healing, it's very clear that dark soul energy attracts Grimm... Or does it?

Given that Grimm are believed not to have 'souls' in their own right and very clearly start to dissolve when they are killed, I'm wondering if they do not have any independent existence at all! What if they are solely and completely the manifestation of darkened aura through raw Dust in some way? In that case, then the old theory that the rise of the number of Grimm would be associated with a social and moral breakdown in human/faunus society is suddenly back in play. When the times grow darker and the lights of civilisation flicker and fade in the face of greed, envy, hate and selfishness, that is when the Creatures grow in number and get stronger.

A dark turn of civilisation leads to the creation of large numbers of new Grimm. So, once again, the possibilty of Grimm being some kind of antibody reaction on the part of Remnant to human/faunus evil comes into play.