User blog comment:Khalael/Perpetuals/@comment-3110123-20160220130744

Interestingly, I think the first "perpetuals" were the Shamans of ancient Terra (Earth). They were all Psykers and had the ability to reincarnate into a new form. I think perpetuals are simply special Psykers who have the ability to do just this but somehow they can avoid the turbulence of the Warp and the malicious intent of its denizens. Basically they're the kind of Psykers who can reincarnate except they have some access to a detour that permits them to avoid all the cocaine-fueled Daemonic blood-orgies.

Just my 2 cents.