You have to have all four techs researched and it's surprisingly easy to forget about one of them. I know there was a game I was running the dev version and after waiting ~30min for my Eradica, I decided it "must" be a bug and just spawned one via the dev commands. A couple hours later, I realized I still didn't have the techs and felt more like an idiot from this game than I have in a long time.
