Fridge Brilliance: There's a passing mention in Hogfather that pencils in Discworld aren't manufactured, but grown as stems of a type of bush native to Sumtri. Considering how many other utensils started sprouting from the Mono Island vegetation, it's quite possible that this is where that bush's ancestors came from.
More Fridge Brilliance: Ponder's and Ridcully's discussion of how stepping on an ant might change the future takes on new depths of irony when you realize that they're only having the conversation because of a single ant. Specifically, the one that the Lady arranged to divert from its course through Hex's tubing, at the end of Interesting Times, thus causing Rincewind to be teleported to Fourecks rather than back to UU. If not for that one ant, the faculty wouldn't have had any reason to visit the office where the portal to Mono Island could be found, in the first place.
Fridge Brilliance meets Continuity Nod: When fleeing from the police in Bugarup, Rincewind is dismayed and amazed by how the pursuing officers stay on his tail. Aside from a very brief sojourn in Interesting Times, Rincewind hasn't been in Ankh-Morpork since the events of Sourcery, so has completely missed the rebirth of his home city's Watch in the wake of Guards Guards!. He only remembers how lazy and fearful the Watch used to be, and is probably quite astonished to see what's become of them once he gets home at last.
Possibly just a coincidence, but waaaaaay back in Equal Rites, Granny Weatherwax told Mrs. Whitlow's fortune via tea leaves, and predicted (i.e. made up) a future in which several young men would vie for her ample favors. Even though she was just telling the customer what she thought Mrs. Whitlow wanted to hear, it seems the only thing she got wrong was the would-be paramours' age!
Fridge Logic: The god of evolution mentions having had believers at some point, as well as experimenting on a cow he wanted to make more inflammable. If so, how does he not recognise the wizards as humans or, indeed, not know the most popular way of producing new generations, or even about different sexes? What sort of believers (or cows) did he have?
Fridge Brilliance hits again when you realize that his lack of believers may have affected his memory. As demonstrated in Small Gods, gods without belief tend to regress mentally and, amongst other things, tend to lose memory.
It's established that the Fate of Discworld came there from another eventuality, so it's also possible that the God of Evolution is likewise an immigrant to the region. In which case, the followers (and cows) in question might not have been humans, or even organic life forms for that matter: for all we know, they and their "cows" really did reproduce by binary fission.
Alternately, everyone back then was also far too embarrassed to explain.