Recently, a SF&F user asked this question, about Inhumans vs. Mutants in the Marvel Universe. With the arrival of the Inhumans in Marvel’s Agents of S.H.I.E.L.D. (and an upcoming movie), and Scarlet Witch and Quicksilver’s appearance in two separate movie universes, its a topic that has generated a bit of interest.
This post is an expanded, more in-depth version of my answer to that question. There’s a lot more to Marvel’s mutant population than just mutants and Inhumans, and things can get confusing. Unfortunately, as with most things Marvel-related, it not a simple question to answer. What constitutes a mutant? How many kinds are there? What’s the difference between them? Are they different species? Here, I’ll try to answer all of these questions and more.
One note on the cinematic universes: there are a lot of movie universes based on Marvel material, but I’m only going to discuss two of them here: Earth-199999, the Marvel Cinematic Universe, and Earth-10005, the X-Men Cinematic Universe. These are the only two large-scale cinematic universes that are still active; as far as I am aware, none of the other (now-defunct) movie universes included any type of mutated human. This includes the two Spider-Man universes, the two Fantastic Four universes, etc, all of which I’ll be ignoring from here on out.