User blog comment:Theory of everything/Grimm Speculations Part Two: Evolution and Transformation/@comment-1509826-20120422113539/@comment-1966944-20120422200559

This is true. Attempts to inseminate Human and/or Chimpanzee (humans closet relative gentetically) has failed. The Wesen could of evolved entirely seperately and do not have any human DNA at all but through natural selection have the ability to appear (chamelleon-like) as human. Those Wesen who were not able to "morph" died out by Genocidal extinction from the Humans, Grimm, or maybe the Verrat. Or the Wesen may have been the dominent species and the animals we have today are a sub-species. Now this is all based on what we know Genetically. As you stated, since this is a fanasy show anything could happen including some ancient "experiments" that successfully mated two different species reslulting in the Wesen we know today.