What about the gene splicing is inherently for "male" only? Because we're getting into that sexist ignorance territory pretty immediately.

If you say "there has to be a Y chromosome, that is, outrageously silly and makes very little sense. But even if so, there are plenty of men who don't have a Y chromosome and plenty of women who don't.

If you say they become a clone of the emperor's clones, it's pretty easy to have a cross sex clone. It's kind of how real life offspring take on genes from their parents and all kinds of outcomes occur, and offspring are still very much basically clones with minor mutations of their parents, with variations. Like if you said they were EXACT clones, like in Star wars, then sure. But they really aren't, to my limited knowledge.

This just really feels like there not being enough representation in the same way in the 80s how "he" was the default pronoun for a subject. But a lot of people are like NUH UHH THAT MEANS THERE WERE ONLY WHITE MEN AND NO FEMALE AUTHORITY FIGURES which is insane. Like, imagine believing skin color in the vast universe meant anything. Or like throughout the countless planets and solar systems that only XY men of scandanavian descent that lived in similar UV and dietary and other stressor ecosystems were the strongest. Like, if anything, it would be people who settled and evolved in the harshest, and most competitive environments and ecosystems, not warm weather tall people who recently migrated to become pale and unhealthy but then became well fed.

It's far more likely that to become a Space Marine, it's not limited to any specific demographic, and it's the best that whatever planet puts forth. And likely it's like some other variation of brown skin, post-human evolution, a la every earth-human demographic breeding together and then 40,000 years later looking nothing like us.

Also, the battle sisters are about as token as an all black army. It's fucked up.

It's honestly likely similar to the custodes and just... Burly massive people who probably don't even have any sort of genitals anymore because that doesn't matter. Like imagine 40,000 years of breeding humans with og-batman bane levels of steroids. Like it just doesn't matter anymore at that point.