See, the lack of any real female representation in the game is a well known issue, but whenever someone tries to bring up that maybe the largest and most pervasive army in the setting should maybe stop being a No Girls Allowed club, everyone will immediately inform them that Space Marines can’t be girls. Trust me, I know. This has happened to me. Repeatedly.  Maybe that's because this guy's friends fundamentally understand what 'fiction' is and he doesn't. This is one of the most annoying and stupid tactics I see used to debate Sci-Fi or Fantasy logistics.  "If it ain't real I can say whatever I want about it" is only true so long as you are the author of the work.  After its said, its locked in.  This is fandom basics.  If we can make up our own bullshit then we stop having a thing in common. Head-canon bullshit is fine for you and your friends, but it doesn't make Lin  ffa  k a girl, Samus a tuck, or Poison anything at all.  Framing the issue as "the author said they can only be male for reasons, but that's sexist" is a non-starter argument.  The author could say "they can only be male for NO reason, suck it" and that would also be NOT SEXIST.  The author is only denying the possibility of a fictional outcome in a fictional universe...  that he owns. Also, holding the 'face' of a franchise to a higher standard than everything else, is stupid and typical of SJW whiners.  "I want my thing that I like to not be embarrassing to me when my feminist friends see the cover of the box, waaa waaa" is all I'm hearing. Random afterthought, maybe someone here knows 40k well enough to clarify for me: but aren't Marines all genetic copies (with some permutation) of the original set of guys that served the "Emp'rah" ?  Do we really need a detailed explanation involving chromosomes that explain that they're all dudes since the first guys were?  In before someone tries to argue that that doesn't stop them from flipping the chromosomes on the clones intentionally sometimes.  And someone else pointing out that we don't want boinking in the barracks distracting us from all the Heresy out there.