I went with "from other primitives" --
They prove it everyday by referencing other DU threads when another primitive wants a link to whatever 'fact' was posted by the OP.
In many ways the Primitives put into practice an age-old demonstration on the importance of good communication skills - where you form a line of a dozen people and read a message to the first person, who then whispers the message in the second persons ear and so on until the final person repeats what he heard - which has very little to do with the original message.
A primitive reads an actual article some place, posts it- and through wilful, wishful, or ignorant interpretation spin the original article - and other primitives do the same until the information they accept as fact has nothing to do with reality.
Such as "Bush Invaded Iraq because of Saddam's connections to 9/11" - this was never the case, but at DU, its accepted fact.