And this reminds me of how some people theorize that life on Earth came from another planet.
In one way it answers the question, but also does not answer it at all.
My guess for origination online communities from scratch would be advertising and already having a small community. Well obviously content too. But I think the reddit founders early on pretended to be many more people on reddit, because no one wants to join an empty community.
The founders provided the startup community. PG's essay were the advertising. And both slashdot and the people who posted PG's essay there, where the advertising of PG's essays.
BTW, there are some YC founders that have join dates several months before us - HN was open to internal YC batches about a half-year before it went public.
Sorry, but I had to make that joke.
It's true that sorting through the low quality fics on ff.net is complicated. Though I appreciate being able to leave a positive one-liner as a review (when it's negative, I usually try to elaborate a little more).
(I was an initial user of both Hacker News and Reddit, checking both out the first day they opened. Also was an admin at FictionAlley.org, which grew from 1881 to 100,000+ users while I was there. That one was largely founded by refugees from Fanfiction.net, along with the readers of two mailing lists devoted to prominent HP fanfiction authors, Cassandra Claire and AngieJ. Same pattern: refugees from an existing community, + followers of a local Internet celebrity.)