Board Thread:General Grimm Discussion/@comment-5301811-20160430205203/@comment-29704672-20160820204212

While I've only watched casually until recently, this makes PERFECT sense to me. Recall in Season 4, Episode 2 or 3, Nick sees on Opthamologist because of his inability to see Juliette right in front of him, and instead had a vision of Adalind's dungeon.

The specialist reported that rather than the normal human 3 types of cones, red, blue, and green, Nick possessed 4 or 5 types of cones in his eyes. Those additional types would be what enabled him to perceive Wesen. Wesen would need the same to perceive each other. Seems pretty clear that's a genetic trait. Of course, that children don't become Grimm until their forebears die is kinda wonky, but that could be an evolutionary adaptation to provide young time to reach maturity safely, hidden from other Wesen.

In the real world, only species that have diverged within the last 500,000-600,000 years can interbreed and produce viable young that are also fertile (unlike horses and donkeys, which produce sterile mules). So if the creators maintain any real world foundation, all 3 species (if there are 3), human, Grimm, and Wesen, are relatively closely related genetically.