Board Thread:Warhammer 40k Novels/@comment-27376167-20151210113237/@comment-24091837-20160416002949

And by the way Silberstich, have checked the Tau section on the Psyker page recently? The Ethereals may well have some psyker-like power in the form of pheromone control/manipulation.

So while my words may not be quite precise, my theory is still plausible, even though it may not be what GW originally intended.

The reason I would like to think that one of the lost Primarchs ran away to join up with the Eldar, while the other ran off to watch over/guide the Tau, is cause those are the only intelligent Xeno races that a Primarch logically would sympathise with. Especially considering the original tactic the Imperium used when encountering intelligent Xenos was destruction of the Xenos' planet. So two of the Primarchs perhaps had empathy for intelligent Xenos which would make for a logical case of falling out with their brothers, their father, and led to a war among family.

The Emperor might be so moved to anger that he destroyed their statues, and regretted the act later. His regret was great enough for him to decide that if ever any of his other sons turned from his teachings, he would rather choose to veil their likenesses rather than destroy them, so he could always see his lost sons, & tell them what he wished he could have said to them when he still had the chance.