Board Thread:Warhammer 40k General Discussion/@comment-7699236-20150618150629/@comment-26436507-20150621234834

Why - I don't know, that might never be revealed or maybe later.

Sources - At least one book of the original three books in the Horus series has Horus speaking with some agent of chaos who mentions it. In 'Vengeful Spirit' Horus travels through a portal to directly speak/interact with the chaos gods directly. He fought wars and became a demi god there, much as what the Emperor did. This is insofar as he gained significant powers here. The exact involvement is unknown at the moment but we will know doubt learn more later in the series. Hence my use of 'in one way or another'. Maybe it was an attempt to unbalance the chaos gods or the Emperor might have nicked some power. Can't say.

It's tricky to misunderstand 'you can't make a female space marine'...If the Emperor has a few on ice under the Imperial palace, just awaiting them been brought out in a book sometime then people are going to look silly. That been said, might actually be right and it is impossible.