Board Thread:Warhammer 40k General Discussion/@comment-25618639-20150112024430/@comment-98.233.152.2-20171125002941

They're descended from the Thousand Sons. GW don't need to 'officially' confirm this - there're enough mentions - some of them quite direct - in the Horus Heresy series to reach this conclusion - particularly in A Thousand Sons. Another short story about a surviving fleet of Thousand Sons Rebirth, Chris Wraight) - Magnus orders an entire battlegroup of Thousand Sons away, immediately before the Wolves arrive in Prospero. The major 'give' for this fleet being the basis of the Blood Ravens is:

'...the dim red light of the angry magma fires caught on his shoulder-guard, exposing the serpentine star set about the black raven-head of his cult discipline. Then he was gone, a shadow among shadows'.

This quote is preceded by the well known Blood Ravens motto: 'knowledge is power'. The quote refers to a Marine called Arvida. His fellowship (akin to any other Legion's Company disposition' is the Corvidae (Ravens).

Another source in Thousand Sons: a human psyker is induced into a death trance, by the Thousand Sons 'cranking up' her connection to the Warp. As a result, she becomes a conduit for prophecy, specifically prophecy regarding the Thousand Sons:

'It's too late... the Wolf is at the door and it hungers for blood. Oh, Throne... no, the blood! The Ravens, I see them too. The lost sons and a Raven of blood. They cry out for salvation and knowledge, but it is denied!'

Games Workshop will never, 100%, close any story arc. In this case, though Graham McNeill has manned up and settled the matter for us. It's good enough for me.

TL/DR - The Blood Ravens gene seed is descended from The Thousand Sons, more specifically, from a fleet Magnus protected from the Wolves.