The rule could be anything, as funny or as serious as you want. The universe will progress in a similar way that it has up until this point, unless your changed rule prevented it from doing so.
Some examples might be:
- The invention of currency is not allowed.
- Iron is slightly less stable.
- The Ancient Greeks are able to cultivate Silphium, which does not go extinct now.
Any public service over $1m revenue needs to offer a childfree version.
I don’t understand, my wife and I are childfree but I don’t get you or the other commenter are getting at
A necessary requirement for higher intelligence is proper, functioning empathy. If you lack this, you’re just… Incapable of intelligent thought beyond that of a particularly stupid dog
Colonization never occurs
Karma is real.