AranaszarSzuur
Vassal

Recently realised something mind-blowing about Eldar from the first age of Rogue Trader (up to WD97 and Book of Astronomican).
Remember the half-Eldar librarian in the Index Astartes: Ultra-marines?
So, yeah, Eldar and humans usually could interbreed…
Which means that Eldar are basically humans, more specifically abhumans.
They also happen to use human technology, in that age of Rogue Trader but the very advanced type…
Hmm… It’s almost like the Eldar are an advanced human civilization that survived the Age of Strife…
But the Imperial propaganda would never admit it, so the imperials believe it’s about a “common ancestor”.
I would assume they are some sort of genetically enhanced human aristocracy - hence the early Eldar being obsessed with aristocratic titles.
At the time Ultra-Marines article was written, Horus Heresy was still in embryonal phase and original Ultra-Marines were actually a treacher legion whose name and number was given to a new chapter. So I assume that the fall of Eldar and existence of Eldar as a separate alien species was also a later concept.