We like to think that we invented everything, and more-or-less recently, but the fact of the matter is that there are no new ideas. Everything we think is nifty is either a rip-off, spin-off or direct product of something that came before. And the shared universes we’re seeing nowadays - like the Marvel Cinematic Universe, the DC Extended Universe, the Arrowverse and beyond - are no exception. Sure, those examples all sprang from shared universe comic books, but the idea of connected worlds isn’t even all that novel on television.