Some facts have that inevitable "duh!" quality of a truth we should have known, as with the appearance of the modern dining room.
Until the 18th century, people tended to eat where they happened to be. In medieval times family, friends, servants, traveling strangers, their dogs, and rats all often lived, ate, and slept in the single great Hall. (The kitchen might be the only other room.) Through the 1700s houses developed more rooms, but these were (to us) strangely undifferentiated in use, all rooms - even bedrooms - were used for all purposes. Chairs and "occasional" tables tended to live shoved against the walls until needed for a card game or a greasy snack.
But as expensive and easily stained upholstered furniture grew more commonplace, so did separate rooms for gravy. Living rooms grew separate from dining ones.
Just think: if clear plastic sofa covers had been invented in the 15th C, Thanksgiving turkey with gravy might be traditional sofa food.
Family dinner, public domain image messed with.
So I'm working my way through this fun grab-bag of a book...
I've escaped the terrifying chapter on fleas, bedbugs, and rat infestations (put the lid down on the toilet - take my word for it -just do it!) and am now reading about poisonous wallpaper and lead paints. Fascinating stuff!