The most effective way.
"Illegal immigration" from other sentient worlds.
Just because people may look human and be born here, doesn't mean they really "are" human.
They would be able to try to introduce new ideas. Who knows - maybe sci-fi was invented by folks who weren't even really human. And it's quite possible they didn't even know they weren't human, which is the most effective way to bring change. Someone who knew it would hold back, but someone who actually thinks they are human wouldn't and wouldn't hesitate to write AMAZING stories or PLANET stories.
