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.
All sentient beings have photographic memories and, through DNA, they can store and recall all of their previous ancestors’ memories. All the way back to their oldest sentient ancestor.
Basically Assassin’s Creed
is born
immediate ptsd from the memory of my parents plowing passionately which ended with my creation
crawls to the roof and jumps
It wouldn’t be weird if you just always knew
You don’t want to know others memories; including those of your ancestors. Not photographically at least.
Or they upload to the resurrection ship