Board Thread:Warhammer 40k General Discussion/@comment-7699236-20150618150629/@comment-25177957-20150621051055

Possible or not, it would take too much work for the Imperium at present. Making a very slight modification to the Astartes gene seed results in catastrophic results and genetic failures for thousands of Astartes. Not to mention that it certainly wouldn't add anything new to the lore, Space Marines were meant to be masculine warrior-hero types, like I said emulating famous warriors and armies from human history, and there's already plenty of strong women-warriors in 40k, another thing I've noted before. We've already got the Sisters of Battle, female Space Marines would be the same thing with some lore-breaking and Wardian-esque codex writting.

Infering that the Emperor of Mankind didn't create female Astartes because he didn't see women as warriors would be incorrect, especially for one such as the Emperor. The Sisters of Silence were an all female order of psychic blanks used to kill psykers who were threats to the Great Crusade and the stability of the Imperium. These women were among the Emperor's most favored servants. Had it not been for them and the custodes, daemons would have overtaken Terra long ago.