In the "Fiat Lux" section, Thon Tadeo mentions evidence that the humans then-living were not the original humans, but a created servant race who had rebelled. It seems clear from the context that he had misinterpreted a piece of fiction.
Was Miller referring to a specific work? Was it Frankenstein, perhaps, or is there another more obvious reference I'm overlooking?
The most natural candidate would seem to be Karel Capek's play R.U.R., from which we famously get the word "robot." The Rossum's Universal Robots in the story are biological and human-like, which fits. It's also one of the relatively few stories with the right kind of plot that predates A Canticle For Liebowitz.
I agree that it's probably R.U.R. by Karel Capek.
This is from the scheme when Thon Tadeo is arguing with the monks over the Book of Genesis. Tadeo cites a fragment of a reference he found in the Memorabilia. He wonders if a "'pre-Deluge race, which called itself Man, succeeded in creating life," and whether that life might actually be them.
Dom Paulo cuts that argument down by pointing out that the fragment is part of a play. This is likely R.U.R., given the real-life relative chronology of Canticle and R.U.R.
I was thinking of Wells' Time Machine. In the future the Morlocks had the Eloi who were a sub-species of human that were servants who rebeled.
