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.
I was hoping we’d go for more of a wholistic biotech thing, like domesticating animals came with hunting, not agriculture. Agriculture just let us domesticate cattle and deer and goats.
Before then we had wolves and dogs and chickens and pigs, and I imagine 5k years of selective breeding coupled with modern degrees of research but in a different direction that by then we custom grow organisms from a caul for whatever our needs.