I don't think you understand what I mean by public social graph. What I mean is that anybody could publish or withdraw statements of two forms:

- "I, owner of account A, certify that owner of account B is human."

- "I, owner of account C, have a reason to trust/distrust the certification of account A about account B."

The collection of these statements would be the public social graph.

The social graph would then be used to establish provenance of facts, which are statements of the form:

- "I, owner of account B, certify account A being witness to event X."

Now whether to believe this or not depends on whether A certified B to be a human, and how much you transitively believe that statement.

So there is a kind of reversal - your statement about your uncle being human helps him to certify what you say, and vice versa.