A null hypothesis.
If you take the output of GPT for what it really is; the sum of all written human thoughts divided by several billion - resulting in a soup of banal, conformist cringe - then it's a marker.
Original human content can be graded by its deviation in some high dimensional space of semantic novelty.
There are two worrying social fallouts from this:
Firstly we will get used to our posts being graded, not by each
other, but by algorithms.
Second, this creates an incentive to post more extreme and unhinged
content.