User blog comment:Khalael/Perpetuals/@comment-27657986-20160220065132

Apprently they are not all made, some are born naturally evem of we have the pysker Alivia. I would have to guess though this is is like winning over a thousand lotteries in a row, but she was born as a natural prepetual apprenetly

If Anval Thawn is still a canon perpetual grey knight. He would be a post heresy one, as he has died a couple times and come back. If he is than he would be the second know natural.

So it seems that They have to be psykers to be perpetuals. I wonder though if this is a requirement to become one or just concednece. It makes sences that the Cabal would choose psykers as they would be more useful and if it was not for our two naturals I would say it was etheir from selection or the processes makes them such, but the naturals change up the options. The pyschic power has to exist first (and that brings in the question of if power matters and than how strong) or they just all very luck and rolled 20s in life.

I do like the idea of them though as they have given us adamentium balls  Perrson   and Vulken

I also love the horus heresy, as it solidifyed me as a warhammer fan.