Board Thread:Speculation House/@comment-14138255-20141017020106/@comment-30764484-20141017074757

^ Yes, but that's actually exactly what Grimm do: they evolve in the Pokemon sense of the term. An Ursa Major is an Ursa Minor that survived long enough to become one. Just as people noted from the cave drawings, that Deathstalker grew while it was inside the cave. The Giant Nevermore was once the same size as those Blake killed in Glenn, as were all Giant Nevermores. They all start somewhere, then Pokemon-evolve into better (and fairly clearly defined) "stages".