Doorknobs Weren't Actually Around Until ...
1878. Check this out:
187-freakin'-8 is when the doorknob was patented. That is, a knob that actually turned and made a little metal thing retract and allow the door to open, the way they do now.
Before knobs, doors were opened and closed through latches like this. It wasn't until 1878 that inventor Osbourn Dorsey filed a patent for the doorknob mechanism we know and love, and along with it the first internal door-latching mechanism.
And shortly thereafter, the fish-door.
But then it took a long time for the doorknob to become a common fixture around the world -- we can only guess because it took a few generations to master that difficult simultaneous turning and pulling motion you have to make to get it to work. Watch a dog try to do it -- it's hilarious.