The evolution took the form of degeneration.
"English Literature and Society in the Eighteenth Century"
Leslie Stephen
Finally he takes to drinking and becomes a picture of degeneration.
"If Any Man Sin"
H. A. Cody
Of course, the tale of the still and the threatened raid was of a piece with all of Jim Bartleton's hatred; of a piece, too, with his seeming degeneration.
"The Tempering"
Charles Neville Buck