So I started with a simple theory.

It was something that I think has been said in the forums in some way before, that the X-Men have a lot of non-mutant members and that the Avengers have very few.

So I actually went through the Team listings of both the X-Men and the Avengers and I made two lists based on the non mutant X-Men, and the Mutant Avengers.

My results were that the X-Men did have more Non-Mutants than Avengers did mutants. I just looked at the Earth-616 teams and I did use some discretion about who counted as a team member. But the X-Men did have a couple more than the Avengers did. Given that the X-men can count a few more members than the Avengers, one could argue that it is proportionally, but to get a real sense we would have to go through and take out all the non 616 members because this could be affecting the total members number.

Another possible issue is that I counted Humans that are former mutants as Non-mutants. I think that this is justified.

Another little tidbit of information that I liked was that 30% of the Mutant Avengers have been X-Men in the past 5 years. While only one of the Non-mutant X-Men was at one time an Avenger.

If I missed some characters that you think should have been on the list, let me know and I will check it out.

ms. marvel should not be counted. she refused her membership when rogue joined

neither should Deadpool

Links to the lists?

Ms Marvel is an ally of the X-Men, but never an actual X-Woman.  Deadpool is classed by the staff at Marvel as an X-Man, so there's no reason why fans shouldn't either.

@xerox_kitty: The links are in the third stanza :)

I thought while she was Binary she was considered an X-Men?

Nice blog!  
 
I think this is mainly due to racial themes of integration playing a larger role in X-Books, than in Avengers, (which still had many storylines based on) but the X-men as a whole, lacks credibility if it doesn't have non mutant characters on the team - because you will have non mutant characters who support what the mutants are fighting for, just like you have many many males, who support feminism, and many of any person willing to stand up and fight for a minority even if they are not strictly a part of that minority.  
 
As an X-Men fan, and an Avengers fan though, I do wish we could see more of each group spending a few years with the other. I think Iceman could really grow as an Avenger, Storm could be revitalized as an Avenger, and say Tigra, Blue Marvel, even someone like Lady Sif would be fun hanging out in X-Men. 

@SC: I like when the X-Men have non-mutants, but I don't know about Avengers joining their ranks. I think the X-Men have always been the underdog that the rest of the Marvel Universe scoffs at, and I know that they are trying to change this in recent years, but I dislike that trend.

If an Avenger joins, I could see them having this high and mighty idea "Well I was an Avenger" mentality that would be interesting to read, but otherwise just annoying. And if Ms Marvel wasn't ever an official X-Men (still judging this) then the X-Men would never have had an Avenger on the Team that wasn't a mutant.

I am currently reconsidering Ms Marvel and Dr Nemesis.

I don't read Avengers Books, was Squirrelgirl ever stated as an avenger officially?

I think Deadpool is justified, So unless a really good argument can be made I think he counts.

I am also debating about adding Fantomex. He isn't a mutant as far as I can tell. He is a cyborg it says. He has participated in several X-Men missions, appeared in an anthology book for the X-men and while his membership into X-Force doesn't make him an X-Men, I think he was offered it on at least one occasion

@jordama:Well from what I know, Squirrel Girl is there to act as the nanny of Jessica Jones and Luke Cage's baby. So unless I am wrong, I don't think she should count as one.

I have taken Ms Marvel and Dr Nemesis off the NonMutant X-Men List. I still think that Aliens count however.

I am still looking into several of the other characters that were brought up. And I think I will Delete Squirrel Girl.

@papad1992: I think if they were that opposed they would have left and tried to join. I think a rejection letter from the Avengers would have been hilarious. Beast also left because he was being tortured and Scott Did nothing, which is often forgotten because of the X-Force part.

I have taken Ms Marvel and Dr Nemesis off the NonMutant X-Men List. I still think that Aliens count however.

I am still looking into several of the other characters that were brought up. And I think I will Delete Squirrel Girl.

@papad1992: I think if they were that opposed they would have left and tried to join. I think a rejection letter from the Avengers would have been hilarious. Beast also left because he was being tortured and Scott Did nothing, which is often forgotten because of the X-Force part.

Have Wiccan and Speed ever been confirmed as mutants? Not to my knowledge.
Also maybe you should count the Great Lakes Avengers. Not official Avengers, but they use the name.
Daken was a Dark Avenger.
The Muir Island X-Men team had some humans.
Cerebro's X-Men were non-humans, but doubtful if they should count. They used the name X-Men though.
According to New Avengers #10 and the Avengers 1959 mini Sabretooth and Namora were Avengers

@fesak:

I thought they were.

I wasn't counting the off shoot teams like the GLA and Muir Island X-men etc..

I still think the Sabretooth thing is a little bogus, but I didn't read it. Was Namora the clone of Namor? Or is that Namorita?

I will hold off on Wiccan and Speed because of children's crusade.

The GLA was also the GLX for a while but I don't think anyone considers them Real X-men.

mutants=homo superior